Patent Publication Number: US-2022227241-A1

Title: Controlling electrical access to a lithium battery on a utility vehicle

Description:
RELATED APPLICATION(S) 
     This application is a continuation of U.S. application Ser. No. 16/713,554 having a filing date of Dec. 13, 2019, and having “Controlling Electrical Access to a Lithium Battery on a Utility Vehicle” as a title, the contents and teachings of which are herein incorporated by reference in their entirety. 
     This application is related to U.S. application Ser. No. 16/407,329 having a filing date of May 9, 2019, and having “Controlling Electrical Access to a Lithium Battery on a Utility Vehicle” as a title, the contents and teachings of which are herein incorporated by reference in their entirety. 
     This application is also related to U.S. application Ser. No. 15/395,245 having a filing date of Dec. 30, 2016, and having “Controlling Electrical Access to a Lithium Battery on a Utility Vehicle” as a title, the contents and teachings of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Some conventional electric vehicles run on power from lead acid batteries. For these vehicles, operators are able to continue using the vehicles as long as there is sufficient charge available from the lead acid batteries. 
     To recharge the lead acid batteries of these vehicles, the operators simply connect the lead acid batteries to an external power source (e.g., street power). Once the lead acid batteries have been recharged, the operators are able to return to using the vehicles. 
     SUMMARY 
     It should be understood that there are deficiencies to the above-described conventional electric vehicles which run on power from lead acid batteries. Along these lines, lead acid batteries are inferior to lithium batteries from certain perspectives. For example, lead acid batteries tend to weigh more, have shorter cycle life, and provide less consistent voltage, among other things. 
     Unfortunately, it would be unsafe to simply substitute lithium batteries in place of lead acid batteries. For example, if one were to simply replace a lead acid battery with a lithium battery in an electric vehicle, it may be possible to deeply discharge and then recharge the lithium battery. However, recharging a lithium battery that has been over-discharged may make the lithium battery unstable and thus susceptible to a hazardous event. 
     Improved techniques are directed to electronically controlling electrical access to lithium batteries on utility vehicles. Such techniques provide the ability to automatically disconnect the lithium batteries from loads in response to certain situations such as fault conditions, timeouts, and sleep events. Such operation prevents the lithium batteries from discharging even due to parasitic loads while the utility vehicles are idle. As a result, such operation robustly and reliably prevents the lithium batteries from being recharged after being over-discharged and thus safeguards the lithium batteries against becoming unstable. 
     One embodiment is directed to a battery management system that controls lithium battery access on a utility vehicle. The battery management system includes a lithium battery interface configured to couple to a lithium battery, a power delivery interface configured to couple to a set of loads of the utility vehicle, and control circuitry coupled with the lithium battery interface and the power delivery interface. The control circuitry is configured to mechanically disconnect the lithium battery interface from the power delivery interface in response to a sleep event. The control circuitry is further configured to, after the lithium battery interface is mechanically disconnected from the power delivery interface, mechanically reconnect the lithium battery interface to the power delivery interface in response to a wakeup event. The control circuitry is configured to, after the lithium battery interface is mechanically reconnected to the power delivery interface, maintain connection between the lithium battery interface and the power delivery interface to convey power from the lithium battery to the set of loads of the utility vehicle through the lithium battery interface and the power delivery interface. 
     In some arrangements, the control circuitry includes a contactor having source contacts configured to couple to the lithium battery interface, target contacts configured to couple to the power delivery interface, and an electromagnetic actuator, and a wakeup circuit coupled with the electromagnetic actuator of the contactor. The wakeup circuit is configured to (i) actuate the electromagnetic actuator to a first position that connects the source contacts to the target contacts in response to the wakeup event, and (ii) release the electromagnetic actuator to a second position that disconnects the source contacts from the target contacts in response to the sleep event. The second position is different from the first position. 
     In some arrangements, the wakeup circuit is further configured to release the electromagnetic actuator to the second position that disconnects the source contacts from the target contacts in response to a low capacity event in which the lithium battery has discharged to a predefined low capacity level. 
     In some arrangements, the wakeup circuit includes a timer which the wakeup circuit is configured to start in response to the wakeup event. In these arrangements, the wakeup circuit is further configured to (i) output an actuation signal to the electromagnetic actuator of the contactor once the timer starts and before the timer expires and (ii) terminate output of the actuation signal to the electromagnetic actuator of the contactor in response to expiration of the timer, the electromagnetic actuator being spring biased from the first position toward the second position to separate the source contacts from the target contacts in response to the wakeup circuit terminating output of the actuation signal. 
     Another embodiment is directed to a utility vehicle which includes a utility vehicle body, a lithium battery supported by the utility vehicle body, a motor supported by the utility vehicle body, a motor controller coupled with the motor, and a battery management system configured to control lithium battery access on the utility vehicle. The battery management system includes: (i) a lithium battery interface that couples with the lithium battery, (ii) a power delivery interface that couples with the motor controller, and (iii) control circuitry coupled with the lithium battery interface and the power delivery interface. The control circuitry is constructed and arranged to:
         (A) mechanically disconnect the lithium battery interface from the power delivery interface in response to a sleep event,   (B) after the lithium battery interface is mechanically disconnected from the power delivery interface, mechanically reconnect the lithium battery interface to the power delivery interface in response to a wakeup event, and   (C) after the lithium battery interface is mechanically reconnected to the power delivery interface, maintain connection between the lithium battery interface and the power delivery interface to convey power from the lithium battery to the motor controller through the lithium battery interface and the power delivery interface.       

     Yet another embodiment is directed to a method of controlling lithium battery access in a utility vehicle. The method includes:
         (A) mechanically disconnecting a lithium battery interface from a power delivery interface in response to a sleep event, the lithium battery interface coupling to a lithium battery supported by the utility vehicle, and the power delivery interface coupling to a set of loads of the utility vehicle;   (B) after the lithium battery interface is mechanically disconnected from the power delivery interface, mechanically reconnecting the lithium battery interface to the power delivery interface in response to a wakeup event, and   (C) after the lithium battery interface is mechanically reconnected to the power delivery interface, maintaining connection between the lithium battery interface and the power delivery interface to convey power from the lithium battery to the set of loads of the utility vehicle through the lithium battery interface and the power delivery interface.       

     Yet another embodiment is directed to a computer program product having at least one non-transitory computer readable medium, the at least one non-transitory computer readable medium having stored thereon a set of instructions to control lithium battery access on a utility vehicle. The set of instructions, when carried out by control circuitry, causes the control circuitry to perform a method of:
         (A) mechanically disconnecting a lithium battery interface from a power delivery interface in response to a sleep event, the lithium battery interface coupling to a lithium battery supported by the utility vehicle, and the power delivery interface coupling to a set of loads of the utility vehicle;   (B) after the lithium battery interface is mechanically disconnected from the power delivery interface, mechanically reconnecting the lithium battery interface to the power delivery interface in response to a wakeup event, and   (C) after the lithium battery interface is mechanically reconnected to the power delivery interface, maintaining connection between the lithium battery interface and the power delivery interface to convey power from the lithium battery to the set of loads of the utility vehicle through the lithium battery interface and the power delivery interface.       

     Other embodiments are directed to higher and lower level systems, assemblies, apparatus, processing circuits, etc. Some embodiments are directed to various processes, electronic components and circuitry which are involved in controlling electrical access to a lithium battery on a utility vehicle. 
     This Summary is provided merely for purposes of summarizing some example embodiments so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example embodiments are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other embodiments, aspects, and advantages will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, features and advantages will be apparent from the following description of particular embodiments of the present disclosure, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of various embodiments of the present disclosure. 
         FIG. 1  is a perspective view of an example utility vehicle which controls electrical access to a lithium battery. 
         FIG. 2  is a block diagram of particular systems and components of the utility vehicle of  FIG. 1  in accordance with some example embodiments. 
         FIG. 3  is a block diagram of additional details of the utility vehicle of  FIG. 1  in accordance with some example embodiments. 
         FIG. 4  is a block diagram of particular details of a wakeup circuit of a battery management system of the utility vehicle of  FIG. 1  in accordance with some example embodiments. 
         FIG. 5  is a block diagram of a first arrangement of particular user controls that provide input to the wakeup circuit of  FIG. 4  in accordance with some example embodiments. 
         FIG. 6  is a block diagram of a second arrangement of particular user controls that provide input to the wakeup circuit of  FIG. 4  in accordance with some example embodiments. 
         FIG. 7  is a block diagram of particular charging circuitry of the utility vehicle of  FIG. 1  in accordance with some example embodiments. 
         FIG. 8  is a flowchart of a procedure which is performed by the battery management system of the utility vehicle of  FIG. 1  in accordance with some example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     An improved technique is directed to controlling electrical access to a lithium battery on a utility vehicle. Such a technique provides the ability to automatically disconnect the lithium battery from loads in response to timeout (or sleep) events. Such operation prevents the lithium battery from discharging even due to a parasitic load while the utility vehicle is idle. As a result, such operation robustly and reliably prevents the lithium battery from being recharged after being over-discharged (since the lithium battery is never over-discharged) and thus protects the lithium battery against becoming unstable. 
     The various individual features of the particular arrangements, configurations, and embodiments disclosed herein can be combined in any desired manner that makes technological sense. Additionally, such features are hereby combined in this manner to form all possible combinations, variants and permutations except to the extent that such combinations, variants and/or permutations have been expressly excluded or are impractical. Support for such combinations, variants and permutations is considered to exist in this document. 
       FIG. 1  shows an example utility vehicle  20  which controls electrical access to a lithium battery. The utility vehicle  20  includes a utility vehicle body  22  (e.g., a chassis, a frame, etc.), a set of tires (or wheels)  24 , and a motion control system  26 . It should be understood that the utility vehicle  20  has the form factor of a golf car by way of example only and that other form factors are suitable for use as well such as those of personal transport vehicles, food and beverage vehicles, hospitality vehicles, all-terrain vehicles (ATVs), utility task vehicles (UTVs), motorcycles, scooters, vehicles for specialized applications, as well as other lightweight vehicles and utility vehicles. 
     The motion control system  26  controls vehicle movement such as drive provided by the set of tires  24 , speed control, braking, and so on thus enabling the utility vehicle  20  to perform useful work. The motion control system  26  of the illustrated embodiments includes, among other things, a motor system  30 , a lithium battery system  32 , and additional components  34  such as a set of user controls  36  (e.g., a foot pedal, a keyed switch, a maintenance switch, etc.) and cabling  38 . As will be explained in further detail below, the utility vehicle  20  runs on power from a lithium battery and is equipped with a sleep/wakeup feature that automatically disconnects the lithium battery in response to certain timeout conditions thus preventing the lithium battery from further discharging. Further details will now be provided with reference to  FIGS. 2 and 3 . 
       FIGS. 2 and 3  show particular details of the motion control system  26  of the utility vehicle  20  ( FIG. 1 ) of some example embodiments.  FIG. 2  shows certain general components of the motion control system  26  of some embodiments and how these components are related.  FIG. 3  shows particular lower level details of the motion control system  26  in accordance with some embodiments. 
     As shown in  FIG. 2 , the motor system  30  includes a motor controller  40  and an electric motor  42 . The motor controller  40  controls delivery of stored electric power from the lithium battery system  32  to the electric motor  42  which ultimately turns at least some of the tires  24  to move the utility vehicle  20 . Additionally, the motor controller  40  of some embodiments controls delivery of regenerative power from the electric motor  42  to recharge the lithium battery system  32  (e.g., during braking, while the utility vehicle  20  coasts downhill without any pedal depression, etc.). 
     The lithium battery system  32  includes a battery management system (BMS)  50  and a lithium battery  52 . The BMS  50  controls electrical access to the lithium battery  52 . Additionally, as will be explained in further detail shortly, the BMS  50  responds to various events such as sleep events (e.g., timeouts) to prevent excessive discharging of the lithium battery  52  thus safeguarding the lithium battery  52  from becoming over discharged. The BMS  50  responds to other events as well such as wakeup events (e.g., actuation of the user controls  36 ), charging situations, fault conditions, and so on to properly and safely control charging and discharging of the lithium battery  52 . 
     It should be understood that a variety of form factors are suitable for the lithium battery  52 . For example, the lithium battery  52  may include multiple lithium battery cells, a single battery pack, combinations thereof, and so on. 
     The additional components  34  may, for example, include the set of user controls  36  (e.g., pedals, switches, etc.), the cabling  38 , a charging receptacle  60 , and perhaps other electrical components  62  (e.g., lights, a global positioning system (GPS), specialized equipment, etc.). In some arrangements, the cabling  38  includes a communications bus, such as, for example, a controller area network (CAN) bus through which the motor system  30  and the lithium battery system  32  exchange communications  70  such as electronic CAN messages in accordance with the CAN protocol. 
     As shown in  FIG. 3 , in accordance with some example embodiments, the battery management system (BMS)  50  of the lithium battery system  32  includes a power delivery interface  100 , a lithium battery interface  102 , a wakeup circuit  104 , a contactor  106 , and a charge regulation circuit  108 . These components may reside together as a single assembly or unit (e.g., within the same enclosure) or in a distributed manner among different locations on the utility vehicle body  22  (also see  FIG. 1 ). 
     The power delivery interface  100  couples with the motor system  30 . Similarly, the lithium battery interface  102  couples with the lithium battery  52 . The wakeup circuit  104  controls closing and opening of the contactor  106  to electrically connect the motor system  30  to the lithium battery  52  and disconnect the motor system  30  from the lithium battery  52 , respectively. During such operation, the charge regulation circuit  108  controls signal conditioning during discharging and charging of the lithium battery  52 . 
     As further shown in  FIG. 3 , the contactor  106  includes a set of target contacts  120  that couple with the power delivery interface  100 , a set of source contacts  122  that couple with the lithium battery interface  102 , and an electromagnetic actuator  124 . Although  FIG. 3  shows the contactor  106  controlling two signal paths between the motor system  30  and the lithium battery  52  by way of example (i.e., there are two source contacts  122  and two target contacts  120 ), other arrangements include different numbers of contacts and signal paths (e.g., one, three, four, etc.) depending on the particular application/electrical needs/etc. (e.g., DC power signals at different voltages, AC power signals in different phases, ground, etc.). 
     The wakeup circuit  104  includes control logic  130  and a timer  132  which operate to manage access to the lithium battery  52 . As will be explained in further detail shortly, such operation may be based on a variety of inputs  134  from the motor system  30 , from the user controls  36  (directly or indirectly), and so on. Along these lines, in response to a wakeup event (e.g., a user turning on the BMS  50 ), the wakeup circuit  104  outputs an actuator signal  136  that actuates the electromagnetic actuator  124  in a first direction  140  from a first position to a second position that connects respective source contacts  122  to corresponding target contacts  120  to electrically connect the motor system  30  to the lithium battery  52 . Along these lines, the electromagnetic actuator  124  may be provisioned with a solenoid or coil that closes the contactor  106  in response to the actuator signal  136 . 
     Additionally, in response to a sleep event (e.g., encountering a predefined time period of non-use while the BMS  50  is awake), the wakeup circuit  104  terminates output of the actuator signal  136  which releases the electromagnetic actuator  124 . In particular, the electromagnetic actuator  124  is spring biased in a second direction  142  which is opposite the first direction  140 . Accordingly, termination of the actuator signal  136  enables the electromagnetic actuator  124  to return back from the second position to the first position thus automatically separating the source contacts  122  from the target contacts  120  when the wakeup circuit  104  terminates output of the actuation signal  136  thus disconnecting the motor system  30  from the lithium battery  52 . As a result, there are no parasitic loads placed on the lithium battery  52  that could otherwise further discharge the lithium battery  52  to an over-depleted state. 
     In other embodiments, the wakeup circuit  104  does not need to constantly maintain the actuator signal  136 . Instead, the wakeup circuit  104  controls engagement and disengagement of the contactor  106  using discrete engagement and disengagement signals. With such use of a dedicated release signal, maintenance of a signal and termination for release is not required. 
     Wakeup/Sleep 
       FIGS. 4 through 5  provide particular details of how the battery management system (BMS)  50  responds to wakeup and sleep events in accordance with some embodiments.  FIG. 4  shows example details of wakeup circuitry  200  which is suitable for the wakeup circuit  104  (also see  FIG. 3 ) in accordance with some embodiments.  FIG. 5  shows a first arrangement of particular user controls  36  that couple with the inputs  134  and control operation of the wakeup circuit  104  ( FIG. 3 ) in accordance with some embodiments.  FIG. 6  shows a second arrangement of particular user controls  36  that couple with the inputs  134  and control operation of the wakeup circuit  104  ( FIG. 3 ) in accordance with some embodiments. 
     As shown in  FIG. 4 , the wakeup circuitry  200  controls access to the lithium battery  52  ( FIG. 3 ) in response to various events, situations, faults, etc. As shown in  FIG. 4 , the wakeup circuitry  200  includes, in an example embodiment, a communications interface  202 , memory  204 , processing circuitry  206 , and additional circuitry  208 . Such components form the control logic  130  and the timer  132  of the wakeup circuit  104  ( FIG. 3 ). 
     The communications interface  202  is constructed and arranged to connect the wakeup circuitry  200  to one or more communications media such as a controller area network (CAN) bus (also see the cabling  38  in  FIG. 1 ). Such communications may include different media such as copper-based (e.g., USB, RJ45, etc.), fiber optic communications, wireless communications (i.e., WiFi, cellular, Bluetooth, etc.), infrared, combinations thereof, and so on. 
     The memory  204  stores a variety of memory constructs  220  including an operating system  222 , specialized battery management code  224 , configuration data  226  (e.g., identification data, predefined timeout settings, charging settings, version data, model data, etc.), and other software constructs, code and data  228  (e.g., activity/event logs, utilities, tools, etc.). Although the memory  204  is illustrated as a single block in  FIG. 4 , the memory  204  is intended to represent both volatile and non-volatile storage (e.g., random access memory, flash memory, etc.), and may, in some embodiments, include a plurality of discrete physical memory units. 
     The processing circuitry  206  is configured to run in accordance with instructions of the various memory constructs  220  stored in the memory  204 . In particular, the processing circuitry  206  runs the operating system  222  to manage various computerized resources (e.g., processor cycles, memory allocation, etc.). Additionally, the processing circuitry  206  runs the specialized battery management code  224  to electronically control access to the lithium battery  52  ( FIGS. 2 and 3 ). The processing circuitry  66  may be implemented in a variety of ways including via one or more processors (or cores) running specialized software, application specific ICs (ASICs), field programmable gate arrays (FPGAs) and associated programs, microcontrollers, discrete components, analog circuits, other hardware circuitry, combinations thereof, and so on. In the context of one or more processors executing software, a computer program product  240  is capable of delivering all or portions of the software to the wakeup circuitry  200  (e.g., also see the memory constructs  220  in  FIG. 4 ). The computer program product  240  has a non-transitory (or non-volatile) computer readable medium which stores a set of instructions which controls one or more operations of the wakeup circuitry  200 . Examples of suitable computer readable storage media include tangible articles of manufacture and other apparatus which store instructions in a non-volatile manner such as flash memory, a magnetic storage medium (e.g., various disk memories such as a hard drive, floppy disk, or other magnetic storage medium), tape memory, optical disk (e.g., CD-ROM, DVD, Blu-Ray, or the like), and the like. It will be appreciated that various combinations of such computer readable storage media may be used to provide the computer readable medium of the computer program product  240  in some embodiments. 
     The additional circuitry  208  represents other circuitry of the wakeup circuitry  200 . Such circuitry may include hardware counters, signal drivers, connectors, sensors, and so on. In some arrangements, where the utility vehicle is specialized equipment (e.g., a food and beverage vehicle, an ATV, etc.) the additional circuitry  208  may represent other components such as an electronic thermostat, lighting control, and so on. 
     With reference to  FIG. 5  and in accordance with some embodiments, a first arrangement of the user controls  36  includes a maintenance switch  260 , a keyed switch  270 , and an accelerator (or throttle) pedal  280  which are electrically connected in series to the other circuitry of the motion control system  26  (also see  FIG. 2 ). Such user controls  36  may communicate with the BMS  50  via the inputs  134  ( FIG. 3 ). Other user controls  36  may be electrically connected to the motion control system  26  as well such as a brake pedal, a forward/reverse switch, and so on. In some arrangements, one or more of the user controls  36  connect directly to the motor system  30  and input signals are sensed by the BMS  50  from the motor system  30 . 
     With reference to  FIG. 6  and in accordance with some embodiments, a second arrangement of the user controls  36  includes a keyed switch  270 , and an accelerator (or throttle) pedal  280 , and a park brake release switch  290  (e.g., a switch which energizes and releases an electric brake to enable towing) which are electrically connected in parallel to the BMS  50  (also see  FIG. 2 ). Such user controls  36  may communicate with the BMS  50  via the inputs  134  ( FIG. 3 ). Other user controls  36  may be electrically connected to the motion control system  26  as well such as a brake pedal, a forward/reverse switch, a tow switch which is different from the park brake release switch, and so on. 
     In some embodiments, the park brake release switch  290  is formed by an actual physical switching device that a user can move to different positions. In other embodiments, the park brake release switch  290  is formed by a set of jumpers (e.g., connectors, cables, etc.) that are switchable or arrangeable into different connecting configurations (e.g., a normal configuration, a tow configuration, etc.). 
     It should be understood that the control logic  130  and the timer  132  of the wakeup circuit  104  ( FIG. 3 ), which are formed by the wakeup circuitry  200  ( FIG. 4 ), operate to monitor user activity of the utility vehicle  20  as well as transition the BMS  50  from a sleeping state to an awake state and vice versa. Further details of such operation will now be provided. 
     During operation, the wakeup circuit  104  monitors operation of the user controls  36  to determine whether to electrically connect the lithium battery  52  to the motor system  30  or electrically disconnect the lithium battery  52  from the motor system  30 . For example, suppose that a human operator (or user) wishes to operate the utility vehicle  20  after an extended period of non-use such as a 24-hour period. In such a situation, the utility vehicle  20  is initially in a sleep (or unawake) mode or state in which the wakeup circuit  104  ( FIG. 3 ) is completely unpowered and the contactor  106  is open (i.e., where there is no circuit formed between the lithium battery  52  and the motor system  30 ). Accordingly, there are no electrical loads on the lithium battery  52  that could otherwise drain charge from the lithium battery  52 . 
     Further details of wakeup/sleep operation will now be provided with reference to some embodiments in connection with  FIG. 5 . Suppose that the user turns the maintenance switch  260  to an ON position (e.g., by simply transitioning the maintenance switch  260  from an OFF position to the ON position, by cycling the maintenance switch  260  from the ON position to the OFF position and back to the ON position, etc.). In such a situation, the wakeup circuit  104  of the BMS  50  turns on and responds by outputting the actuation signal  136  to close the contactor  106  ( FIG. 3 ). As a result of such a wakeup event, the contactor  106  connects the source contacts  122  to the target contacts  120  thus connecting the lithium battery  52  to the motor system  30  and waking the motor system  30 . 
     At this time and in accordance with some embodiments, both the BMS  50  and the motor system  30  perform various self-tests. For example, the BMS  50  checks the amount of charge remaining in the lithium battery  52  and, if the amount of charge is below a predefined minimum charge threshold, the BMS  50  terminates (e.g., immediately terminates) the actuation signal  136  to electrically disconnect the lithium battery  52  from the motor system  30 . Such operation prevents the lithium battery  52  from becoming over-discharged. It should be understood that, while the BMS  50  remains awake, the BMS  50  continues to monitor charge remaining in the lithium battery  52  and terminates the actuation signal  136  to disconnect the lithium battery  52  from the motor system  30  if the remaining charge reaches (or falls below) the predefined minimum charge threshold to safeguard the battery against becoming over-discharged. In particular, there is still safety margin between the predefined minimum charge threshold and an over-discharged level. 
     In some embodiments, after passing their respective self-tests, the BMS  50  and the motor system  30  communicate with each other (e.g., exchange communications  70  such as CAN messages) to verify configuration information (e.g., model numbers, versions, status, etc.). In some arrangements, the motor system  30  may be one of multiple models and the wakeup circuit  104  operates using different configuration settings depending on the particular model identified via communications with the motor system  30 . 
     Also, at this time, the control logic  130  of the wakeup circuit  104  starts the timer  132  ( FIG. 3 ) which counts or tracks time until the timer  132  reaches a predefined idle time threshold (i.e., a maximum idle time limit). In accordance with some embodiments, example values that are suitable for use for the predefined idle time threshold include time amounts within the time range of 10 hours to 14 hours (e.g., 11 hours, 12 hours, 13 hours, etc.). In accordance with other embodiments, example values that are suitable for use for the predefined idle time threshold include time amounts within the time range of 2 hours to 6 hours (e.g., 3 hours, 4 hours, 5 hours, etc.). If the timer  132  counts from an initial time value to the predefined idle time threshold (a sleep event), the timer  132  outputs a sleep event signal to the control logic  130  of the wakeup circuit  104  which directs the control logic  130  to terminate output of the actuation signal  136  thus disconnecting the lithium battery  52  from the motor system  30 . Such operation prevents the lithium battery  52  from unnecessarily succumbing to parasitic loads from the motor system  30 , from the contactor  106  (i.e., the coil maintaining the contactor  106  in the closed position), and perhaps from elsewhere in the utility vehicle  20 . 
     However, after BMS  50  has woken up, suppose that the user inserts a physical key into the keyed switch  270  and moves the keyed switch  270  from the OFF position to the ON position before the timer  132  reaches the predefined idle time threshold. In response to this sensed user activity, the control logic  130  restarts the timer  132  to the initial time value. Accordingly, the timer  132  is prevented from reaching the predefined idle time threshold and expiring. 
     Likewise, suppose that the user actuates the accelerator pedal  280  (e.g., moves the pedal  280  from its non-depressed position) before the timer  132  reaches the predefined idle time threshold. In response to this sensed user activity, the control logic  130  restarts the timer  132  to the initial time value. Again, the timer  132  is prevented from reaching the predefined idle time threshold and expiring. It should be understood that moving the accelerator pedal  280  may further signal the motor system  30  to operate the motor  42  (e.g., rotate the motor  42  in a particular direction and at a particular speed based on other factors). 
     However, if the user leaves the utility vehicle  20  unattended and the timer  132  expires by reaching the predefined idle time threshold, the timer  132  expires (a sleep event) and sends a sleep event signal to the control logic  130 . In response to the sleep event signal, the control logic  130  terminates output of the actuation signal  136  thus opening the contactor  106  to disconnect the lithium battery  52  from the motor system  30  ( FIG. 3 ) and protecting the lithium battery  52  against further discharge. 
     In accordance with some embodiments, if the BMS  50  has fallen asleep and the maintenance switch  260  ( FIG. 5 ) remains in the ON position, the user is able to wake the BMS  50  by moving the keyed switch  270  to the ON position (another wakeup event). Likewise, in accordance with some embodiments, if the BMS  50  has fallen asleep and the maintenance switch  260  and the keyed switch  270  are both in the ON position, the user is able to wake the BMS  50  by actuating the pedal  280  (yet another wakeup event). 
     In some embodiments and with reference to  FIG. 5 , the series configuration of the maintenance switch  260 , the keyed switch  270 , and the accelerator pedal  280  enables the maintenance switch  260  to disable sensing of the keyed switch  270  and the accelerator pedal  280 . In particular, when the maintenance switch  260  is in the OFF position, the keyed switch  270  and the accelerator pedal  280  are unable to provide input to the control logic  130  of the wakeup circuit  104  thus preventing the user from waking up the BMS  50  via the keyed switch  270  or the pedal  280  while the maintenance switch  260  is in the OFF position. 
     Similarly, when the keyed switch  270  is in the OFF position, the accelerator pedal  280  is unable to provide input to the control logic  130  of the wakeup circuit  104 . Accordingly, the user cannot wake up the BMS  50  simply by pushing on the accelerator pedal  280  while the keyed switch  270  is in the OFF position. 
     In some embodiments, while the maintenance switch  260  is in the ON position and the BMS  50  is awake, the motor system  30  and the BMS  50  operate to provide a walkaway protection feature that prevents the utility vehicle  20  from inadvertently rolling away at a high rate of speed. Along these lines, suppose that the user forgets to mechanically engage a brake to hold the utility vehicle  20  in place. If the utility vehicle  20  is perched on a hill and begins to roll, the motor system  30  senses that the utility vehicle  20  is moving but that the user is not pressing on the accelerator pedal  280 . Accordingly, the motor system  30  of such embodiments provides proactive speed control and regenerative power. The proactive speed control maintains motor rotation at a low speed thus enabling the user to walk up to and stop the utility vehicle  20 . Furthermore, the regenerative power recharges the lithium battery  52  thus improving efficiency. 
     Charging 
       FIG. 7  shows particular details of the charging circuitry  300  which charges the lithium battery  52  of the utility vehicle  20  (also see  FIG. 1 ), in accordance with some example embodiments. In accordance with the embodiments illustrated in  FIG. 7 , the charging circuitry  300  includes a first plug  302 , a charger (or adaptor)  304 , and a second plug  306 . The first plug  302  is constructed and arranged to connect the charger  304  to an external power source  310  such as an AC outlet. The second plug  306  is constructed and arranged to connect the charger  304  to the charging receptacle  60  of the utility vehicle  20  (also see  FIG. 2 ). The charger  304  is constructed and arranged to convert and condition a power signal from the external power source  310  for use by the utility vehicle  20 . 
     As further shown in  FIG. 7 , the charging receptacle  60  electrically couples with the motor controller  40  and the battery management system (BMS)  50 . Accordingly, when the receptacle  60  receives power from the charging circuitry  300 , the receptacle  60  provides power to the motor controller  40  and BMS  50 . In some embodiments, this initial power from the charging circuitry  300  wakes up the BMS  50  and the motor controller  40  ( FIG. 3 ). In some embodiments, the receptacle  60  also provides an interlock signal  320  to the motor controller  40  which has also woken up. In response to the interlock signal  320 , the motor controller  40  outputs a communication  330  (e.g., a CAN message) that informs the BMS  50  that the charging circuitry  300  is plugged in to the receptacle  60  and the BMS  50  then closes the contactor  106 . With the contactor  106  now closed, the BMS  50  conveys a charging signal  340  from the charging circuitry  300  to the lithium battery  52 . In some arrangements, the charge regulation circuit  108  ( FIG. 3 ) conditions the charging signal  340  to properly charge the lithium battery  52 . 
     While the lithium battery  52  charges in response to receipt of the charge signal  340  and in accordance with some embodiments, the BMS  50  monitors the lithium battery  52  to prevent overcharging. In particular, in response to sensing that the lithium battery  52  has charged to a predefined maximum charge threshold (or level), the BMS  50  deactivates the charge regulation circuit  108 , e.g., sets the duty cycle of pulse width modulation (PWM) circuitry back to 0%, where other pulse widths determine different charging rates. In some arrangements, the BMS  50  then immediately goes to sleep. In other arrangements, the BMS imposes a timeout (e.g., 30 minutes) and goes to sleep if the timeout period expires without further user activity. 
     Further Details 
       FIG. 8  is a flowchart of a procedure  400  which is performed by the battery management system (BMS)  50  of the utility vehicle  20  to control access to the lithium battery  52  in accordance with some example embodiments. 
     At  402 , the BMS  50  mechanically disconnects a lithium battery interface from a power delivery interface in response to a sleep event. The lithium battery interface couples with a lithium battery supported by the utility vehicle, and the power delivery interface couples with a set of loads of the utility vehicle. For example, a timer of the wakeup circuit may expire after a period of non-use thus indicating that the BMS  50  may disconnect the lithium battery  52  without interfering with a user of the utility vehicle  20 . Such disconnection prevents parasitic loads from further draining the lithium battery  52 . 
     At  404 , after the lithium battery interface is mechanically disconnected from the power delivery interface, the BMS  50  mechanically reconnects the lithium battery interface to the power delivery interface in response to a wakeup event. For example, in accordance with some embodiments and in response to certain conditions, the user may press an accelerator pedal or cycle a keyed switch to wakeup the BMS  50 . 
     At  406 , after the lithium battery interface is mechanically reconnected to the power delivery interface, the BMS  50  maintains connection between the lithium battery interface and the power delivery interface to convey power from the lithium battery  52  to the set of loads of the utility vehicle through the lithium battery interface and the power delivery interface. In particular, the BMS  50  may start a timer to measure a period of non-use and maintain lithium battery access as long as the timer does not expire and as long as the lithium battery does not discharge below a predefined safe level. 
     As described above, improved techniques are directed to controlling electrical access to lithium batteries  52  on utility vehicles  20 . Such techniques provide the ability to automatically disconnect the lithium batteries  52  from loads in response to timeout or sleep events. Such operation prevents the lithium batteries  52  from discharging even due to parasitic loads while the utility vehicles  20  are idle. Accordingly, the lithium batteries  52  will not discharge to unnecessarily low levels (e.g., safeguard levels). As a result, such operation robustly and reliably prevents the lithium batteries  52  from being recharged after being over-discharged and thus safeguards the lithium batteries  52  against becoming unstable. 
     While various embodiments of the present disclosure have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims. 
     In accordance with some arrangements and as disclosed above, it should be understood that the BMS  50  has the ability to disconnect the lithium battery  52  from loads if unsafe conditions are sensed. The disconnect mechanism is the contactor  106  which consumes energy when engaged. To conserve energy, the BMS  50  disconnects the lithium battery  52  after some timeout period. A wakeup signal is required to reconnect the lithium battery  52  for charging and normal use. That is, the lithium vehicle control system wakeups the BMS  50  to use the utility vehicle  20 . Such a wakeup is accomplished without additional operator input. 
     In some embodiments, the BMS  50  and motor controller  40  routinely communicate (e.g., over the CAN bus). Accordingly, the BMS  50  understands the current status of the motor controller  40  and vice versa. Additionally, as mentioned earlier, the BMS  50  monitors the status of a variety of switch inputs, e.g., a maintenance switch, a keyed switch, a pedal switch, etc. 
     During operation, the BMS  50  disconnects itself from all electrical loads on the utility vehicle  20  by opening its contactor  106 . Events that cause the BMS  50  to close its contactor  106  may be referred to as wakeup events, or simply wakeups. The BMS  50  of some embodiments includes multiple inputs for wakeup signals. Along these lines, users may expect the utility vehicle  20  to go when the key is on and the pedal is pressed—whether the utility vehicle  20  has sat for a long time or not. Accordingly, the maintenance switch, the keyed switch, and the throttle pedal switch are all capable of waking up the BMS  50  of some embodiments. 
     When the keyed switch is in the OFF position, the motor controller  40  of some embodiments provides a walkaway feature while the BMS  50  remains awake. This walkaway feature prevents the utility vehicle  20 , if unattended, from rolling down a slope rapidly. When walkaway protection is active, the motor controller  40  senses vehicle movement and causes the motor  42  to apply braking torque. This walkway protection lasts until the BMS  50  eventually times out (e.g., after 12 hours). 
     In embodiments including a maintenance switch, the maintenance switch is configured to interrupt power to the motor controller  42  to disable the walkaway feature and enable towing. For example, in some embodiments, the maintenance switch is wired in series with the keyed switch and pedal. Accordingly, the maintenance switch interrupts a wakeup signal to the BMS  50 , and interrupts power to the other wakeup switches, thereby preventing the keyed and pedal switches from waking up the BMS  50  while the utility vehicle is in tow mode. Otherwise, cycling the keyed switch wakes up a BMS  50  that was asleep with the maintenance switch closed in the ON position. Likewise, pressing the pedal wakes up a BMS  50  that was asleep with the key in the ON position. 
     In some embodiments, the same BMS  50  may support operation of different types of motor controllers  40 . To this end, the motor controller  40  of some embodiments sends a message (e.g., a CAN message) to the BMS  50  that includes controller type. Upon receipt, the BMS  50  of some embodiments stores the controller type in non-volatile memory. The BMS  50  uses the controller type to determine timeout values, and responses to wakeup signals. The first time the BMS  50  is connected to a different type motor controller  40 , the BMS  50  may not wakeup exactly as desired. To minimize the differences between wakeup protocols, wakeup signals may be re-assigned. For example, the BMS&#39; first wakeup signal may be connected to the keyed switch on for a first controller type, and the maintenance switch on a second controller type. Similarly, the second wakeup signal may be connected to the throttle pedal for the first controller type and the keyed switch for the second controller type. Furthermore, the third wakeup signal may be connected to the park brake release connectors for the first controller type and the throttle pedal switch for the second controller type. These input assignments minimize the logic differences between wakeup. The most common wakeup methods of turning on the first controller type key switch and the second controller type maintenance switch will work properly regardless of the vehicle type memorized by the BMS  50 . As long as this wakeup happens once, the BMS  50  will continue to wakeup and sleep properly until it is transferred to another utility vehicle  20  that uses the other controller type. 
     When the charger is plugged into the utility vehicle  20 , charging initiates regardless of whether the BMS  50  is asleep or awake. If the BMS  50  is awake, plugging in the charger asserts a charger interlock signal from the charge receptacle to the motor controller  40 . The motor controller  40  may be configured to send a signal to the BMS  50  informing the BMS  50  that the charger is plugged in. For example, in some embodiments, the motor controller  40  may inform the BMS  50  that the charger is plugged in via a status bit in a message, such as a CAN message. 
     The BMS  50 , in some embodiments, may be configured in response to the signal from the motor controller  40  to activate a charging mode. In these embodiments, the BMS  50  then sets a signal (e.g., a PWM signal) appropriately (when not charging, the BMS  50  sets the PWM signal to a fault mode as a failsafe). Charging can then take place. The BMS  50  stays awake until charging is complete, and goes to sleep shortly after charging is complete. 
     In some embodiments, if the charger is plugged into a utility vehicle  20  where the BMS  50  is asleep, then the charger provides power to the vehicle&#39;s electrical system. This wakes up the BMS  50  and motor controller  40 . If the BMS  50  receives a communication (e.g., a CAN message) from the motor controller  40  with the charging status bit set, then it will close its contactor  106  and set the signal (e.g., the PWM signal) appropriately. Charging then commences. 
     Additionally, it should be understood that the keyed switch was described above as being used in certain example embodiments. It will be appreciated that the keyed switch is just one example of an ignition switch that may be used in various embodiments. For example, in other example embodiments, the vehicle uses a keyless, push-button ignition rather than a keyed switch. Such ignition is enabled when an “electronic key” (e.g., an RF device) on the passenger&#39;s person is within range of a wireless sensor of the vehicle. Here, an actuation of the switch occurs through presence of the electronic key in combination with physical actuation of the button. 
     Furthermore, in some embodiments, the BMS  50  utilizes an inactivity timer that measures inactivity time based on current (also see the timer  132  in  FIG. 3 ). For example, the inactivity timer starts timing inactivity when current sensed from the lithium battery falls below a predefined current threshold (e.g., 3 amps). As long as the current remains below this predefined current threshold, the inactivity timer continues to measure time. However, if the current rises above the predefined current threshold, the inactivity timer is cleared (or reset) because this rise in current above the predefined current threshold is considered detected activity. The inactivity timer then starts counting again when current falls below the predefined current threshold. If the inactivity timer ever reaches a timeout value, the inactivity timer is considered to have expired (i.e., detected an inactivity timeout event). Such modifications and enhancements are intended to belong to various embodiments of the disclosure.