Abstract:
An electrical system for an automotive vehicle includes a low voltage battery having a low voltage, a high voltage battery having a high voltage, and a DC-to-DC converter coupled to the low voltage battery and the high voltage battery. A controller controls a conversion of the low voltage to a high voltage through the DC-to-DC converter and controls the charging of the high voltage battery with the high voltage. The controller monitors a state of charge of the high voltage battery, compares the state of charge to a predetermined state of charge and generates an indicator when the state of charge reaches the predetermined state of charge.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to dual voltage automotive vehicles, and more specifically, to charging the batteries of the electrical systems of the vehicle. 
     Automotive vehicles with internal combustion engines are typically provided with both a starter motor and alternator. In recent years, a combined alternator and starter motor has been proposed. Such systems have a rotor mounted directly to the crankshaft of the engine and a stator sandwiched between the engine block and the bell housing of the transmission. During initial startup of the vehicle, the starter/generator functions as a starter. While functioning as a starter, the starter/generator rotates the crankshaft of the engine while the cylinders are fired. 
     After the engine is started, the starter/generator is used as a generator to charge the electrical system of the vehicle. 
     Such systems may include both a 12-volt nominal system and a 36-volt nominal system, which correspond to 14 and 42-volt operating voltages, respectively. It should be noted the dual voltage systems may also be incorporated in vehicles without starter/generators. 
     Electrical energy from the 42-volt battery of the vehicle is used to turn the starter/generator, which in turn is used to start the motor. Energy from the 12-volt system may be used to operate the vehicle lights and instrument panel. Consequently, it is important to maintain the battery so that a certain state of charge is provided to allow the battery to provide enough power to the starter/generator to start the engine. If one or both of the batteries is low, however, the vehicle may need to be jumpstarted. Typical jumpstarting is desirable, wherein jumper cables are connected between a good battery or power source and the discharged battery. Typically, if the 42-volt battery is low it may not be charged by charging the 12-volt battery. It may not be desirable to allow the operator to charge both batteries independently to prevent mixing the voltage potentials and possibly damaging the batteries or the electrical systems. 
     It would therefore be desirable to provide a method and apparatus for charging a battery to provide an indication to the vehicle operator to guide the operator through the charging process. 
     SUMMARY OF THE INVENTION 
     The present invention provides a way in which to charge the vehicle batteries so that both batteries of both voltage levels become charged. 
     In one aspect of the invention, a method of charging a high voltage battery includes electrically coupling a first low voltage source to a low voltage battery, converting the low voltage to a high voltage, charging a high voltage battery with the high voltage, monitoring a state of charge of the high voltage battery, comparing the state of charge to a predetermined state of charge, and generating an indicator when the state of charge reaches the predetermined state of charge. 
     In a further aspect of the invention, a system for an automotive vehicle includes a low voltage battery having a low voltage, a high voltage battery having a high voltage, and a DC-to-DC converter coupled to the low voltage battery and the high voltage battery. A controller controls a conversion of the low voltage to a high voltage through the DC-to-DC converter and controls the charging of the high voltage battery with the high voltage. The controller monitors a state of charge of the high voltage battery, compares the state of charge to a predetermined state of charge, and generates an indicator when the state of charge reaches the predetermined state of charge. 
     One advantage is that the indicator may provide to the vehicle operator both instructions and the state of charge of both vehicle batteries. 
     Other advantages and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic view of an automotive vehicle having a starter/generator system according to the present invention. 
     FIG. 2 is a flowchart illustrating the operation of the present invention for charging the 12-volt battery. 
     FIG. 3 is a flowchart illustrating the operation of the present invention for charging the 42-volt battery. 
     FIG. 4 is a side view of a battery terminal cover switching apparatus according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention is described with respect to a particular configuration of a starter/generator relative to a hybrid electric vehicle. However, the teachings of the present invention may be applied to various type of vehicles having dual battery powered electrical systems. 
     Referring now to FIG. 1, an automotive vehicle  10  is illustrated having an internal combustion engine  12  having cylinders  14  with pistons  16  located therein. Each cylinder  14  is coupled to a fuel pump  18  through a fuel injector (not shown) or other fuel delivery system. Each cylinder  14  also has a spark plug  20  or other ignition source coupled to a powertrain control unit. A powertrain control unit  22  controls the ignition timing and fuel pump  18  operating in a conventional manner subject to the improvements of the present invention. 
     Engine  12  is coupled to a transmission  26 . Transmission  26  may be automatic, manual or continuously variable. Transmission  26  is coupled to a differential  28  to drive an axle  30  to provide power to wheels  32 . Of course, the present invention is also applicable to four-wheel drive systems in which all of the wheels  32  are driven. 
     A starter/generator system  40  that includes a starter/generator  42  and its associated control electronics is coupled to engine  12 . In the present invention, starter/generator  42  is positioned between a housing  44  of transmission  26  and the engine  12 . Of course, those skilled in the art will recognize other positions are available including, but not limited to, belt driven types. Starter/generator  42  has a stator  46  fixedly attached to bell housing  44  and a rotor  48  coupled to a crankshaft  50  of engine  12 . A clutch  52  is used to engage and disengage engine  12  from transmission  26 . Starter/generator  42  is used as a starter during engine startup and as an alternator to supply power to recharge the batteries of the vehicle and to supply electrical loads. Clutch  52  allows starter/generator  42  to start the engine prior to engagement of the transmission. 
     A vehicle system controller  54  is coupled to starter/generator system  40 . Vehicle system controller  54  is coupled to powertrain control unit  22 , to a power inverter  56  and a battery control module  57 . Collectively, controller  54  and battery control module  57  may be referred to as a controller. In practice, the power inverter  56 , system controller  54  and battery control module  57  may be contained in a single package or interconnected using a bus system, thus making it unimportant which signals are generated at which device. The inverter  56  is used to convert DC power to AC power in the motoring mode and AC power to DC power in power generation mode as will be further described below. 
     Battery controller  57  is coupled to 42-volt battery  64  to monitor the voltage  76  and a current. By monitoring the battery voltage and current, the state of charge of the 42-volt battery  64  may be determined. 
     Power inverter  56  is coupled to an energy storage device  58  such as an ultra capacitor, a first DC-to-DC converter  60 , and a second DC-to-DC converter  62 . DC-to-DC converter  60  is coupled to a nominal 36-volt battery  64 . DC-to-DC converter  62  is coupled to a nominal 12-volt battery  66 . Of course, the actual battery voltage is dependent on the particular system to which it is attached. The present invention is particularly useful when one battery voltage is much greater than the other battery voltage. 
     It should also be noted that a contractor  68  may be electrically coupled between  36- volt battery  64  and DC-to-DC converter  60  to provide electrical isolation between the 36-volt battery and the rest of the vehicle. Battery control module  57  is coupled to contactor  68  to control the opening and closing of contactor  68 . 
     System controller  54  is also coupled to an indicator  80 . Indicator  80  may comprise an audible indicator, a visual indicator, or a combination of the two. One example of an indicator is an LCD display that can display various messages and actions for the vehicle operator to perform. Instrument panel reminder lights or chimes may also be used to generate messages. 
     A 12-volt source  65  such as a 12-volt battery from another vehicle, battery charger or generator is shown electrically coupled to 12-volt battery  66 . 
     Referring now to FIG. 2, a method for charging a 12-volt battery when the 42-volt battery is charged is illustrated. In step  100  if the 12-volt battery is not dead and the 42-volt battery is not charged the system starts again in step  100 . In step  100  if the 12-volt battery is not charged and the 42-volt battery is charged, step  102  is executed. In step  102 , the 12-volt battery is charged in a conventional manner. That is jumper cables may be connected from a 12-volt source such as another charged battery. Typically, when charging a 12-volt battery the positive terminal of the charged battery is connected to the positive terminal of the dead battery, while the negative terminal of the charged battery is coupled to chassis ground in the vehicle with the dead battery. The negative battery terminals may also be coupled together. In step  104  the charge of the 12-volt battery is monitored during the charging process. In step  106  a message indicating that the 12-volt battery charging is complete may be displayed to the driver. The message may take the form of one of the indicators described above such as audible, an indicator light, or an LCD message. 
     Referring now to FIG. 3, a method for charging the 42-volt battery whether or not the 12-volt battery is discharged is illustrated. In the case where a 12-volt battery is discharged, the 12-volt battery may be charged simultaneously with the 42-volt battery. In step  110 , if the 42-volt battery is not dead the system continues checking in step  110 . In step  110 , if the 42-volt battery is dead step  112  is executed. In step  112  a switch may be activated as will be further described below. If the switch is activated, the jumpstart process has been entered. This step is performed simultaneously with step  114 . In step  114  the jumper cables are connected to the 12-volt battery in the manner described above. During the process, messages or other indicators may be illuminated. In step  116  if the 12-volt battery voltage is greater than the voltage of the 42-voltage battery an error message is generated in step  118 . In step  116  if the 12-volt battery voltage is not greater than the 42-volt battery step  120  is executed. In step  120  the contactor  68  described above is closed. The DC-to-DC converter  60  is then used to convert the 12-volt power to 42-volt power so that 36-volt battery  64  may be charged in step  122 . In step  124  the state of charge of the 36-volt battery is monitored. In step  126 , a display message may be displayed to the vehicle operator to continue charging until otherwise notified. In step  128  the state of charge of the 42-volt battery is monitored. If the state of charge compared to a state of charge threshold indicates the 42-volt battery is not charged, steps  124  and  126  are again executed which continues displaying “continue charging.” In step  128  if the state of charge is at a level indicating the 42-volt battery is charged (above a state of charge threshold), step  130  is executed. In step  130  the display indicator may indicate “discontinue charge” so that the vehicle operator knows the 42-volt battery is fully charged. In step  132  the vehicle may be started and normally operated since both of the batteries are charged. As mentioned above, the process illustrated in FIG. 3 may be used to charge the 42-volt battery as well as the 12-volt battery, if needed. Of course, more than one of each type of battery may be provided in an automotive vehicle. That is, the 42-volt battery may be charged and fully functional prior to entering step  110  above. 
     Referring now to FIG. 4, if an LCD type display is not available, a cover  150  having an electrical switch  152  coupled to battery control module  57  may be provided. Switch  152  generates an electrical signal as to the presence or non-presence of battery terminal  154  of battery  66 . Thus, when cover  150  is opened, battery control module  157  enters a charging sequence. Thus, indications may be provided through an indicator light or an audible warning. 
     Thus, as can be seen, only a 12-volt battery source is required to charge the 42-volt battery. The DC-to-DC converter converts the 12-volt charging current to a voltage and current capable of charging the 36-volt battery. Thus, particularly during the introduction of such vehicles, commonly found 12-volt battery systems may be readily available to charge such systems in the event the 42-volt battery is discharged. 
     While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.