Abstract:
An off-board battery cycler is used to condition an on-board battery system used in electric or hybrid electric vehicles. The battery cycler periodically discharges the vehicle&#39;s high voltage traction battery to eliminate battery “memory” that can prevent the battery from being fully charged. The cycler also recharges both the high voltage battery and an on-board low voltage battery used to power the vehicle&#39;s electrical system. High voltage AC power used in recharging the high voltage battery is switched using contactors physically isolated within the battery cycler, in order to protect operating personnel from coming onto contact with high voltage. Faults and malfunctions are recorded by the vehicle&#39;s on-board controller

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application claims the benefit of priority from Provisional Application No. 60/664,260 filed Mar. 22, 2005, the full disclosure of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   This invention generally relates to battery systems for electric and hybrid electric vehicles, and deals more particularly with an off-board battery cycler for periodically discharging the vehicle&#39;s high voltage traction battery, and for recharging both the traction battery and a low voltage battery used to power the vehicle&#39;s electrical system. 
   BACKGROUND OF THE INVENTION 
   Electric and hybrid-electric powered vehicles employ a high voltage battery pack to power electric motors that drive the vehicle. These high voltage batteries, sometimes referred to as traction batteries, must be periodically recharged. During periods of nonuse, the vehicle is connected to a source of AC power, such as 110 volt AC. A battery charger located either on-board or off-board the vehicle, converts the 110 volt AC to DC which is used to recharge the traction battery to a desired state of charge. 
   During normal operation of the vehicle, on-board systems periodically determine the state of charge of the high voltage battery, and in the case of a hybrid electric vehicle, onboard control systems switch from battery power to an alternative power source, such as a fuel cell or IC engine when the state of charge falls below a threshold value. The ability of the high voltage battery pack to hold a full electrical charge is reduced by so called battery “memory.” Battery memory is common in deep discharge batteries which are repeatedly partially discharged and recharged. The memory effect prevents drawing a full charge from a completely charged battery, and also prevents accurate state of charge calculations from being performed on-board the vehicle since a calculated state of charge of a battery suffering from memory infect does not accurately reflect the amount of charge that can be drawn from the battery. 
   In addition to the high voltage battery pack, the vehicles mentioned above employ a low voltage on-board battery, typically 12 volts, to power the low voltage electrical system on the vehicle. These low voltage batteries, sometimes referred to as SLI batteries (starting, lighting and ignition) must be periodically charged using a battery charger separate from the high voltage battery pack charger. Thus, two battery chargers are normally employed to recharge the on-board battery systems. 
   Accordingly, there is a need in the art for an improved system for charging both the high voltage and low voltage batteries on vehicles which overcomes the problems discussed above. The present invention is intended to satisfy this need. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the invention, apparatus is provided for controlling the charge on a battery system for a vehicle, wherein the battery system includes a first low voltage battery for operating electrical systems on the vehicle, and a second, high voltage traction battery. The apparatus comprises a battery cycler for charging both the low voltage battery and the high voltage battery, and a controller for controlling the operation of the battery cycler. The battery cycler is also operable for periodically discharging the high voltage battery to eliminate battery memory, and the controller is operable for controlling the battery cycler to achieve a pre-selected state of charge on the high voltage battery. The battery cycler preferably uses a constant current source for delivering constant charging current to the high voltage battery during a recharging cycle. The battery cycler is located off-board the vehicle and includes releasable electrical connections for connecting the battery cycler with the high voltage battery and the controller which is located on-board the vehicle. Faults or other malfunctions in the battery cycler are recorded by the vehicle&#39;s on-board controller. 
   According to another aspect of the invention, a battery charge control system for vehicles comprises a battery cycler for discharging and recharging a high voltage traction battery, a first controller for controlling the operation of the battery cycler, and a second controller for sensing faults in the operation of the battery cycler and the first controller. The cycler includes an AC contactor for coupling a source of alternating current with a load formed by the traction battery. The AC contactor is physically isolated within the cycler to prevent exposure of operating personal to the high voltages used for recharging the battery. The cycler includes a high voltage section coupled with an AC power source for supplying constant current to the high voltage battery, and a low voltage section that supplies low voltage for recharging a low voltage battery. 
   According to a further aspect of the invention, a system is provided for controlling the state of charge of an onboard battery system for a vehicle, wherein the battery system includes a low voltage battery for operating electrical systems on the vehicle and a high voltage traction battery. The system comprises an off-board battery cycler for discharging and recharging the high voltage battery, and for charging the low voltage battery, and an onboard controller for controlling the operation of the battery cycler to achieving a pre-selected state of charge on each of the high and low voltage batteries. The battery cycler includes a low voltage section for charging the low voltage battery, and a high voltage section for periodically discharging and recharging the high voltage battery. The high voltage section includes a physically isolated switch for switching a source of high voltage AC into a circuit with a load that includes the high voltage battery. The high voltage section includes a constant current source used to recharge the high voltage battery. The cycler has a load bank used in discharging the high voltage battery. Faults or other malfunctions in the battery cycler are recorded by the vehicle&#39;s onboard controller. 
   One of the advantages of the invention resides in the use of a single, off-board battery cycler unit to recharge both the high voltage battery and the low voltage battery. Operating personal are protected from exposure to high voltages during the recharging process as a result of the AC contactors being contained within the cycler unit, thus physically isolating the high voltage circuits from operating personal. The battery cycler eliminates battery memory by periodically discharging the high voltage battery and recharging it using a constant current source. 
   These non-limiting features, as well as other advantages of the present invention may be better understood by considering the following details of a description of a preferred embodiment of the present invention. In the course of this description, reference will frequently be made to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a combined block and schematic diagram of a battery cycler in accordance with the preferred embodiment of the invention, shown connected to certain on-board vehicle systems. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , the present invention relates to a system for controlling the charge on storage batteries supplying power to an electric or hybrid electric powered vehicle. These batteries include a high voltage battery or battery pack  12 , and a low voltage battery  14 , both of which are located onboard the vehicle. The high voltage battery  12  provides DC current to one or more electric motors (not shown) which drive the vehicle&#39;s wheels, and is this sometimes referred to as the traction battery. The high voltage battery  12  includes a battery controller  34 , the details of which will be discussed later. The low voltage battery  14  is typically a 12 volt DC battery used power electrical systems and accessories on the vehicle, and is sometimes referred to as the SLI battery (starting, lighting and ignition). The high voltage battery  12  typically operates, for example, at between 250 and 300 volts, DC. 
   The charge control system of the present invention functions to charge and condition both the high voltage battery  12  and the low voltage battery  14 . The charge control system broadly comprises a battery cycler  10  which is located off-board the vehicle, and a controller in the form of an energy management module (EMM)  16  carried on-board the vehicle. The battery cycler  10  includes a low voltage section comprising a low voltage circuit board  26 , and a high voltage section comprising a high voltage circuit board  24 , AC contactor output switch  28  and a pair of contactor switches  60 . The high voltage section include the pair of high voltage output lines  52  which are releasably connected to the high voltage battery  12  by means of a releasable, quick disconnect electrical connector  58 . 
   The battery cycler  10  is powered by a 110 volt AC power which is delivered from a conventional AC power source via feed lines  20  to the contactor output switch  28  which is a single pole single throw 110 volt switch. The AC contactor output switch  28  is coupled by lines  54  to the high voltage circuit board  24  which includes a contactor coil (not shown) that functions to control the contactor switches  60 . When the output switch  28  is closed, the contactor coil is energized, causing the contactors  60  to close, thereby providing constant charging current to the high voltage battery  12 . However, when the contactor switch  28  remains open a signal produced by the low voltage board  26  will also energize the contactor coil, causing contactors  60  to close. With contactors  60  closed, the high voltage battery  12  is discharged through a load bank  30 , which may comprise a commercially available, air cooled load bank. 
   The low voltage board  26  receives 110 volt power from lines  20  which is stepped down to 5 and 12 volt signals used to control a variety of functions, as well as to charge the low voltage battery  14  via lines  46 . The low voltage board also controls the operation of the contactor output switch  28  as well as the contactor coil forming part of the high voltage board  24 . The low voltage board  26  includes a momentary push button switch  62  whose operation will be described later. The low voltage section of the battery cycler  10  is connected through a series of lead lines  36 - 46  to the EMM  16  and battery  14  using a quick disconnect electrical connector  56 . 
   The low voltage board  26  controls a series of LED display status lights  22 , comprising green, amber and red LEDs  22   a ,  22   b , and  22   c , respectively. The LED display  22  provides the operator with a visual indication of the operating status of the battery cycler  10 . When the push button switch  62  is initially depressed, the green LED  22   a  illuminates, indicating that the cycler  10  has been turned on. Illumination of the amber LED  22   b  indicates that the battery cycler  10  is either in the charge or discharge mode. Illumination of the red LED  22   c  indicates that a fault or other malfunction has occurred within the battery cycler  10 . Periodic flashing of the red LED  22   c  indicates that there is a fault or malfunction on-board the vehicle. 
   A CAN (controller area network) bus  48  on-board the vehicle allows information exchange between the EMM  16 , battery controller  34 , an on-board vehicle controller  64  and an off-board diagnostic interface  18  which may comprise, for example, the World Diagnostic System developed by Ford Motor Company for use with OBD2 equipped vehicles. The WDS  18  may comprise, for example, a laptop computer which can be plugged into an interface that connects a computer to a CAN bus  48 . The diagnostic interface  18  is also directly connected via lines  50  to the EMM  16  and high voltage battery  12 . Information concerning the health of the battery conditioning system is monitored by the vehicle controller  64  which is also connected to the CAN bus  48 . Faults or malfunctions in the battery cycler  10  are recorded and date stamped by the vehicle controller  64  and these faults may be accessed and diagnosed by the diagnostic interface  18 . 
   The EMM  16  monitors the charge state of batteries  12  and  14  and controls the operation of the battery cycler  10 . In operation, the user connects the battery cycler  10  to the vehicle using the quick disconnect electrical connectors  56  and  58 . The user then depresses the push button  62 , causing a 5 volt signal to be delivered from the low voltage board  26  on line  36  to the EMM  16  where it is interpreted as a request to begin conditioning of batteries  12 ,  14 . EMM  16  is responsive to this request signal to assess the current state of charge of batteries  12 ,  14  as well as determine the interval of time that has elapsed since the high voltage battery  12  was last fully discharged to eliminate battery memory. Depending upon the results of this assessment, EMM  16  sends a control signal on line  40  to the battery cycler  10  instructing it to take certain action based on the charge assessment. This control signal is a PWM (pulse width modulated) 12 volt signal whose duty cycle determines the function to be performed by the cycler  10 . For example, in one embodiment, a 50% duty cycle is interpreted by the battery cycler  10  as an instruction to begin charging the high voltage battery  12 . 
   The EMM  16  monitors the charge on the batteries  12 ,  14  and when the high voltage battery  12  is fully charged, the EMM  16  issues an 80% duty cycle signal to the cycler  10  that the charge is complete. A 30% duty cycle signal issued by the EMM  16  is interpreted by the battery cycler  10  as an instruction to switch to a standby mode. A signal with yet a different duty cycle, e.g. 20%, is issued to the battery cycler  10  in order to instruct it to begin discharging the high voltage battery  12 . When the battery cycler  10  receives a signal from the EMM  16  indicating that a charging sequence should be initiated, a signal is delivered from the low voltage board  26  to the contactor switch  28 , causing the latter to close which in turn energizes contactor coil. Powering up contactor coil closes contactors  60 , thereby connecting the high voltage battery  12  with constant charging current which may comprise a charge, for example, of 288 volts DC at 4.5 amps. Charging is continued until the state of charge of the high voltage battery  12  is 100%. 
   When the high voltage battery  12  is charged to 100%, the low voltage circuit  26  causes the contactor switch  28  to open, thereby de-energizing the contactor coil which opens contactors  60  and removes power from the battery  12 . However, in the event that the contactor switch  28  does not open as commanded, the EMM  16  closes an internal switch  32  which results in a 12 volt signal being delivered via line  44  to the low voltage circuit  26  which responds by causing the contactor switch  28  to open, in an override fashion. 
   The battery controller  34  performs a number of functions related to assessing and controlling the state of charge on the battery  12 . The battery controller  34  determines whether the battery  12  needs to be charged to reverse deactivation caused by prolonged duration of idle time at low state of charge. The battery controller  34  also determines if the battery  12  needs to be refreshed in order to reverse memory effect or whether the battery  12  needs to be rebalanced. Finally, the battery controller  34  determines whether the battery  12  needs the state of charge to be reset. 
   A variety of possible faults in the battery cycler  10  may be detected and logged by the vehicle controller. Examples of these faults include failure to charge the high voltage or low voltage buses, failure to communicate with the vehicle, failure to stop charging either the low or high voltage buses, and failures in the operation of the indicator light  22 . 
   It is to be understood that the system, which has been described is merely illustrative of one application of the principles of the invention. Numerous modifications may be made to the device of the method as described without departing from the true spirit and scope of the invention.