Abstract:
A vehicle electrical power system includes a generator which generates power for application to loads and to chassis and batteries for storage. A starter motor for an engine is energized primarily from the battery. A contactor between the batteries has a closed state in which power can flow between the batteries and an open state which interrupts power flow between the batteries and from the generator to the cranking battery. A controller enables periodic stopping and starting of the engine is responsive to a battery state of charge for at least one of the batteries for operating the engine to maintain a minimum battery state of charge. The contactor may have a limited closed state in which power flow between the batteries is surge limited. Power flow is surge limited through the connector responsive to a voltage difference between the batteries.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The technical field relates to vehicle electrical power storage systems and related control systems. 
         [0003]    2. Description of the Problem 
         [0004]    Electrical systems for motor vehicles equipped with internal combustion engines include loads, alternators for generating electricity, a rechargeable storage battery system, distribution wiring for transmitting electrical power from the alternator to the storage batteries and loads, and an electrical starter motor drawing power from the storage battery system for cranking the internal combustion engine. A control system can be used to provide control over the loads, storage batteries, starter motor and operation of the internal combustion engine. Control functionality may be implemented using a variety of switches, contactors, direct current (DC) to alternating current (AC) inverters, DC/DC converters, connectors of various sorts such as latching relays and switches which interconnect the storage batteries and loads, and electric control elements such a microcontrollers and controller area networks (CAN). 
         [0005]    In U.S. Pat. No. 7,336,002 (Kato, et al.) it was pointed out a vehicle storage battery system may be split between applications and include batteries of more than one type. On some vehicles the storage battery system is split into two groups one of which carries most vehicle loads and the second of which is reserved for supplying power to the starter motor. In such a system the two sections of the storage battery system are sometimes called the main/primary and auxiliary batteries, or, more intuitively, the chassis (supporting a variety of system loads) and cranking batteries. Among the reasons for providing distinct chassis and cranking batteries is to isolate electrical loads from the substantial voltage variations resulting from starter motor operation. In addition, having two groups of batteries provides some system redundancy and serves to isolate the cranking battery from power drains on the chassis battery during auxiliary operation of vehicle electrical loads. This provides greater assurance of being able to start the vehicle&#39;s engine after a period of sustained electrical power demand by limiting the power drain to the chassis battery. 
         [0006]    The batteries of different groups may be of distinct types. One possible arrangement is to use lead acid batteries for the chassis battery and the lithium-ion batteries for the cranking battery. It is possible to select lead acid and lithium ion batteries which exhibit closely matched charge profile acceptance capabilities which simplifies control over recharging. However, lithium-ion batteries are more generally susceptible to damage during recharging due to environmental conditions, particularly low temperatures. 
         [0007]    Off duty electrical power demands on vehicles such as commercial trucks have tended to increase in recent years. Vehicle crew cabins may be equipped with appliances and lighting for the comfort of the off duty driver. Auxiliary operation of these devices require electrical power. In the past drivers routinely allowed vehicle engines to idle to support generation of the needed electrical power, however sustained idling was inefficient, noisy, contributed to pollution and is now largely unlawful. As a consequence extended vehicle idling is legally circumscribed and vehicles are periodically started and stopped to generate and store electricity to meet power demands when the vehicle is not in motion. Meeting these operational demands stresses batteries more than was the case when the vehicle could simply left running and can force battery recharging to occur under less than ideal conditions. 
       SUMMARY 
       [0008]    A motor vehicle electrical power supply system operates from an internal combustion engine which produces mechanical power which is coupled to a generator which generates electrical power for application to loads and to chassis and cranking batteries for storage. A starter motor for the internal combustion engine is energized primarily from the cranking battery. A multi-state contactor between the chassis battery and the cranking battery is provided which has a closed state in which electrical power can flow between the chassis battery and the cranking battery and an open state which interrupts electrical power flow between the cranking battery and the chassis battery and from the generator to the cranking battery. An idling switch is provided having active and inactive states. A controller responsive to the state of the idling switch for enabling operation of the internal combustion engine is responsive to a battery state of charge for at least one of the cranking battery and the chassis battery for periodically starting and stopping of the internal combustion engine to maintain a minimum battery state of charge. The multi-state contactor may have an additional limited closed state in which electrical power flow between the chassis battery and the cranking battery is surge limited. Power flow is surge limited through the multi-state connector responsive to a minimum voltage difference between the chassis battery and the cranking battery. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a high level schematic of a vehicle electrical power generation, storage and distribution system. 
           [0010]      FIG. 2  is a schematic diagram of a vehicle electrical power generation, storage and distribution system. 
           [0011]      FIG. 3  is a flow chart relating to control over the vehicle electrical power generation for battery recharging. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , a high level schematic of a vehicle electrical power system  10  is illustrated. The vehicle electrical power system  10  includes a chassis battery  12 , a cranking battery  13 , a generator in the form of an alternator  20  connected to supply electricity to the chassis battery  12  and to various loads  45  which represent electrical power consumers installed on a vehicle other than a starter motor, an internal combustion/thermal engine  14  connected by a mechanical couple  21  to the alternator  20  to supply mechanical power to the alternator, and a starter motor  26  for starting the internal combustion engine  14  which may be connected to the cranking battery  13  by a starter motor solenoid  24 . A variety of types of batteries may be employed. For example, chassis battery  12  usually comprises one to four lead (Pb) acid automotive batteries. Cranking battery  13  may be a type of lithium ion (Li-ion) battery. Chassis battery  12  and cranking battery  13  are selectively connected and disconnected from another by a multi-state contactor  34 . For example, if cranking battery  13  is composed of lithium-ion batteries recharging the batteries at low temperatures can shorten battery service life as compared to recharging at room temperatures. When multi-state contactor  34  is open the cranking battery  13  is electrically isolated from the vehicle charging system, loads  45  and chassis battery  12 . The open state is the default state of multi-state contactor  34  and its open status is confirmed to prevent recharging of a lithium-ion cranking battery  13  when the battery temperature is outside of low and high limits. When multi-state contactor  34  is in a closed state electrical power may flow freely (within the capacity constraints of the circuit) from chassis battery  12  to cranking battery  13  or, under some circumstances from cranking battery  13  to chassis battery  12 . This occurs to allow the cranking battery  13  to be recharged when its temperature is within the preset bounds. A third state for multi-state contactor  34  allows limited current flow between the batteries. This is used should a voltage mismatch between the chassis battery  12  and cranking battery  13  be such as a current surge would result if the free flow of power be allowed. 
         [0013]    A control system  11  provides operational control (along dashed lines) of electrical power system  10 . Control system  11  includes elements such as an engine control module  32 , a body controller  30  and a controller area network (CAN) serial data link  40 . The serial data link  40  usually conforms to the SAE J1939 standard governing its physical and software layers and provides two-way data communications between the controllers. Body controller  30  may be used for voltage sensing or more sophisticated measures may be used to determine a battery state of charge (SOC) for chassis battery  12  or cranking battery  13 . Engine control module (ECM)  32  monitors whether internal combustion engine  14  is running and provides an engine status signal over serial datalink  40  which is read by body controller  30 . ECM  32  can shut down internal combustion engine  14  based on instructions received from body controller  30  and crank internal combustion engine  14  by applying start signal on a start signal line  22  to the starter motor solenoid  24  at the request of the body controller  30 . Body controller  30  is connected to receive the engine status signal as well as an ignition key position signal (e.g. the auxiliary position or the run position) and to monitor the position of an idling switch  50 . Idling switch  50  enables duration limited idling operation of the internal combustion engine  14  to recharge the chassis battery  12  and cranking battery  13  without concurrent driver intervention. Body controller  30  develops estimates for the state of charge of chassis battery  12  or cranking battery  13  (shown in  FIG. 2 ). The battery state of charge estimates are typically based on a proxy for state of charge such as battery terminal to terminal voltage. Body controller  30  controls the state of the multi-state contactor  34 . 
         [0014]      FIG. 2  illustrates a possible vehicle electrical power system  10  in greater detail. Vehicle electrical loads are divided into two groups categorized by operational priority as mandatory loads  46  and optional loads  48 . Latching relays  42  and  44  are provided connected between chassis battery  12  and the mandatory and optional loads  46 ,  48  enabling a vehicle controller to independently shed the optional loads  48  or to jointly shed the optional and mandatory loads  48 ,  46  as dictated by a Battery Power Management routine  78  (see  FIG. 3 ). Vehicle controller may be understood as a functional conflation of elements of control system  11  including engine control module  32  and body controller  30 . Current drawn by the mandatory and optional loads  46 ,  48  is measured by a Hall effect current sensor  38  positioned relative to power bus  16 . Limited duration idling operation of the internal combustion engine  14  for battery charging on a parked vehicle can occur within the broader context of a load management program monitoring operation of mandatory and optional loads  46 ,  48  occurring during such periods. 
         [0015]    Power bus  16  is interruptible by a contactor  58  and a precharge circuit  60 , which are positioned in the bus between a cranking battery  13 , connected to one section of the power bus  16 , and the chassis battery  12  and alternator  20 , which are connected to another section of the power bus  16 . In effect, contactor  58  in combination with precharge circuit  60  implement a multi-state contactor between chassis battery  12  and cranking battery  13  by providing states where there is no connection between the batteries, where there is current limited connection between the batteries and where there is “full” connection. Generally the precharge circuit  60  and the contactor  58  are not concurrently closed as such a state would be almost indistinguishable from simple closure of the contactor  58  alone. 
         [0016]    Vehicle controller  31  is provided with a voltage sense line  36  to the positive terminal of the chassis battery  12  and with a connection to a battery management system (BMS)  64  which is provided with the lithium-ion battery pack and which provides data relating to cranking battery  13  to the vehicle controller. BMS  64  can provide the vehicle controller with cranking battery  13  with voltage and state of charge measurements. Typically BMS  64  also provides a battery temperature reading. If such functionality is not available a thermistor  62  in contact with cranking battery  13  and communicating with vehicle controller may be added. 
         [0017]    Cranking battery  13  is located in a battery compartment  68  and battery compartment  68  may be placed in the vehicle crew cab. Locating the battery compartment  68  in the vehicle crew cabin provides an environment for the cranking battery  13  offering protection from extreme temperature transients, preventing exposure to road hazards and weather conditions and allowing the temperature around the cranking battery to be controlled. In order to reduce the chances for chassis battery  13  overheating cooled air, or air drawn from outside the vehicle, may be directed into the battery compartment  68  environment from the vehicle heating, ventilation and air conditioning (HVAC) system  72  may be routed through the battery compartment  68  by an inlet  74  from the HVAC system  72  and discharge outlet  76  to the crew cab. Additionally, the chassis battery  13  may be kept warm by directing heated air from the HVAC system  72  into battery compartment  68 . HVAC system  72  is provided with an HVAC controller in communication with the vehicle controller. Air routed through HVAC system  72  is termed “treated air”. 
         [0018]    Some vehicles may provide for connection of the electrical power system  10  to an external source of power. The manner of the connection depends upon the character of the external source. One type of power, conventionally referred to as “shore power” is household or industrial alternating current electrical power, for example: 100-120 volt, 60 cycle power; or 200-240 volt, 50 cycle power. An inverter charger  66  may be provided which accepts utility mains input power by a “shore power” connection and produces a direct current output of the appropriate voltage on power bus  16 . The output of the inverter charger  66  is connected to the alternator side of power bus  16  relative to contactor  58 . Inverter charger  66  may also pass the shore power to an onboard AC distribution system and may allow for connections to alternative sources of power. A connection is provided allowing control and data signals to be communicated between the vehicle controller  31  and the inverter charger  66 . 
         [0019]    An electric starter or cranking motor  26  draws energization from cranking battery  68  upon application of an input or starter signal from the vehicle control system (an alternative ignition path based on ignition key  54  position and clutch position sense switch  52  also exists). The starter signal is applied to a starter relay  56  which in turn engages a starter solenoid  24  in line with the cranking motor  26 . 
         [0020]    Operation of the control system  11  in relation to handling of recharging of the chassis and cranking batteries  12 ,  13  by the electrical power system  10  is described by reference to the flow chart of  FIG. 3 . During periods when a vehicle is parked, and continuous operation of the vehicle&#39;s internal combustion engine  14  discouraged notwithstanding ongoing demands for electrical power, the vehicle may be placed in an automatic (duration limited) idling mode where the engine is started and run for limited periods as required to recharge the chassis battery  12  and potentially the cranking battery  13 . 
         [0021]    The recharging routine can provide for cranking battery  13  temperature protection as well as protection from excessive current inrush. From the battery power consumption management routine (step  78 ) execution advances to step  80  for determination of the position of the idling switch  50 . If the idling switch  50  is off temperature protection only is at issue. Advancing along the “OFF” branch from step  80  it is determined if the vehicle ignition key position is “ON” or “OFF”. IF “OFF”, it is next determined at step  84  if shore power is available. If shore power is not available along this processing progression recharging cannot occur and the routine is exited back to the battery management routine  78 . The same result obtains if the ignition key  54  is detected as being ON at step  82  but the engine is “OFF” as determined at step  86  and shore power (step  84 ) is not available or OFF. 
         [0022]    If the engine is determined to be ON at step  86 , or if shore power is ON (determined at step  84 ), the process advances to step  88  for control over battery charging. The default state for contactor  58  is the open state and the default state for the precharge circuit is non-conductive. At step  88  it is determined from thermistor  62  or BMS  64  if the temperature of the cranking battery  13  is above the minimum which allows for charging and below a safe limit. If NO then step  90  confirms that the contactor  58  is open and the precharge circuit  60  is non-conductive (open). Next the status of the HVAC system  72  is checked. If ON the routine loops back to step  88 . If OFF then the HVAC system  72  is turned on (step  94 ) to heat or cool the battery compartment  68  in order to adjust the temperature of cranking battery  13  so that it falls within the temperature limits for charging. 
         [0023]    Once battery compartment  68  temperature is within the preselected limit, the YES branch is followed from step  88  to step  96  where the relative voltages of the chassis battery  12  (Vpb) and cranking battery  13  (Vli-ion) are compared. If the voltage difference exceeds a maximum allowed difference than the precharge circuit  60  is turned on (the contactor  58  remains open) (step  100 ). The process loops until the voltage difference is less than the allowed difference whereupon step  98  is executed to turn off the precharge circuit  60  and close the contactor  58 . The process is exited to the battery management routine  78 . 
         [0024]    Returning to decision step  80  the process following detection of an “ON” idling switch  50  is followed. Idling switch  50  is ON only if the default state of the internal combustion engine  14  is “OFF”. Idling switch  50  is conventionally used when a vehicle is parked and electrical power demands on the chassis battery  12  are expected. At step  102  the state of charge of the batteries is checked. If the state of charge for chassis battery  12  and cranking battery  13  meet or exceed a minimum limit process execution is returned to the battery power management routine  78  along the YES branch. As described above a proxy for state of charge, such as terminal to terminal voltage indicated by Vbat may be used. 
         [0025]    If the battery state of charge does not meet the minimum threshold, indicating a need for recharging, the NO branch is followed from decision step  102  to step  104  where it is confirmed that power is not being conducted between the chassis battery  12  and alternator  20  to cranking battery  13 . The default open state of contactor  58  is confirmed at step  104 . Next, at step  106  signal line  22  goes high to initiate engine cranking (step  106 ). Self sustained engine  14  operation is monitored for at step  108 , with the monitoring process looping back to maintain engine cranking following the “OFF” branch from step  108  through steps  110  and  112 . Steps  110  and  112  implement a time out procedure limiting how long engine cranking is maintained (or more precisely, how many times the engine is allowed to crank). If cranking fails an abort provision is provided (step  112 ) for advising the vehicle operator. Once engine  14  is running the “ON” branch if followed from step  108  to step  114  where it is determined if chassis battery  12  voltage and cranking battery  13  voltage are close enough to allow unimpeded power flow between the batteries. 
         [0026]    From step  114  the process can follow the NO path indicating a voltage difference which is exceeds the limit for unimpeded power flow. At step  116  the precharge circuit  60  is turned on allowing limited current flow, typically from the chassis battery  12  side of the power bus  16  to the cranking battery  13  side of the power bus. This state is maintained until the voltage difference diminishes enough to allow closing the contactor  58  to permit unimpeded power flow, as provided along the YES branch from step  114  to step  118  where it is indicated that the precharge circuit  60  is turned off or “opened” and the contactor  58  is closed. Once the chassis and cranking batteries  12 ,  13  are fully charged (as determined at step  120 ) the engine  14  is turned off (step  124 ). A NO branch loop back on step  120  is omitted but will be understood to be inherent. Once the engine  14  is turned off the process returns to battery management  78 . Hysteresis is built into the system in that the state of charge level which initiates charging is less than the state of charge required to shut down the engine  14 .