Abstract:
An isolation system for traction batteries for a vehicle includes battery contactors having a closed state and an open state. The current drawn from the traction batteries during transitions between the two states is managed by selecting loads for either reduced levels of operation or cutoff to reduce the total current draw. Vehicle operating conditions, such as the direction of the state transition, may control the selection of loads for operation during the transition.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The technical field relates generally to electric vehicles and hybrid-electric vehicles and, more particularly, to control over high voltage battery isolation contactors. 
         [0003]    2. Description of the Problem 
         [0004]    Electric and hybrid electric vehicles carry relatively high voltage battery plants (traction batteries) for supplying power to vehicle traction motors and other vehicle electrical systems. Traction batteries typically have a nominal output voltage sufficient to support of 340 volt rms three phase power, and in some cases 700 volts rms power, from an inverter. In contrast, conventional automotive batteries supply voltage at about 12 volts DC. 
         [0005]    The traction battery plant is usually physically isolated in its own compartment to avoid inadvertent exposure of high voltages to people working on the vehicle. Contactors, which functionally are analogous to circuit breakers, are provided within the compartment for selectively connecting and disconnecting the battery plant from the vehicle electrical system. Under some circumstances the battery plant is electrically isolated by opening the contactors within the compartment to prevent high voltages from appearing at points on the vehicle electrical system outside the battery compartment. 
         [0006]    Electric and hybrid electric vehicles make more extensive use of electrical power than do conventional vehicles to support vehicle functions such as power steering or air conditioning compressor operation from electric motors. On an electric vehicle this is largely unavoidable. On a hybrid vehicle using electric motors to operate an air conditioning or power steering pump makes these functions operationally independent of the vehicle&#39;s internal combustion engine. In addition, contemporary vehicles make extensive use of electronic computers which are consumers of electrical power. As a result, current loads on vehicle traction batteries can become quite high. 
         [0007]    High current loads can compromise fraction battery isolation contactor service life. Relatively high currents, on the order of hundreds of amps, can be drawn by a vehicle if many or all of the vehicle&#39;s potential electrical loads are active. Contactor arcing during opening and particularly on closing can result in isolation contactor degradation and in the development of welds during closing which can hold the contactors in the closed position. Such a result compromises the contactor&#39;s isolation function. 
       SUMMARY 
       [0008]    An isolation system for traction batteries for a vehicle includes battery contactors having a closed state and an open state. The current drawn from the traction batteries during transitions between the two states is managed by selecting loads for either reduced levels of operation or cutoff to reduce the total current draw. Vehicle operating conditions, such as the direction of the state transition, may control the selection of loads for operation during the transition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a high level schematic of a vehicle drive train and vehicle control system for a hybrid-electric vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    In the following detailed description example sizes/models/values/ranges may be given with respect to specific embodiments but are not to be considered generally limiting. Though a parallel hybrid-electric vehicle is used for illustration, the principals taught here are readily extended to an all electric vehicle or a series hybrid-electric vehicle. 
         [0011]    Referring to  FIG. 1 , a high level schematic of a control system  21  which provides control and energy use management for a vehicle drive train  20  is illustrated. An electrical system controller (ESC)  24 , a type of a body computer, operates as a system supervisor and is linked by a public data link  18  to a variety of local controllers which in turn implement direct control over vehicle functions not directly controlled by the ESC  24 . As may be inferred, ESC  24  is typically directly connected to selected inputs (including sensors) and outputs. A sensors package  16  represents such sensors and may include a brake pedal position sensor, a throttle position sensor and abrupt deceleration sensors. In addition ESC  24  communicates with a dash panel  44  from which it may obtain signals indicating ignition state, headlight on/off switch position and provide on/off signals to other items, such as headlights (not shown). Signals relating to a power take-off operation (PTO) are communicated between an in cab switch pack  56  and ESC  24  over a SAE J1708 compliant data link  64 . Data link  64  is a low baud rate data connection, typically about 9.7K baud. 
         [0012]    Six representative local controllers in addition to the ESC  24  are illustrated as connected to the public data link  18 . These controllers include an engine controller  46 , a transmission controller  42 , a hybrid controller  48 , a gauge controller  58  and an anti-lock brake system controller (ABS)  50 . It will be understood that other controllers may be installed on the vehicle in communication with data link  18 . These controllers both control various vehicle electrical loads and represent loads themselves. These additional controllers are represented by a generic “load” controller  17  for the control of loads  19 . Various sensors may be connected to several of the local controllers. Data link  18  is preferably the bus for a public controller area network (CAN) conforming to the SAE J1939 standard and under current practice supports data transmission at up to 250K baud. 
         [0013]    Hybrid controller  48 , transmission controller  42  and engine controller  46  coordinate operations of the drive train to select between the engine  28  and the traction motor  32  as the prime mover for the vehicle (or to combine the output of the engine and the fraction motor if called for). During braking these same controllers coordinate disengagement and shut-down of engine  28  and operation of traction motor  32  in its generator mode to recapture the vehicle&#39;s kinetic energy. The ESC  24  and the ABS controller  50  provide data over data link  18  used for these operations, including brake pedal position, data relating to skidding, throttle position and other power demands such as for PTO  22 . The hybrid controller further monitors a proxy relating to battery  34  state of charge (SOC). 
         [0014]    Drive train  20  is a parallel hybrid diesel electric system in which the traction motor/generator  32  is connected in line with an engine  28  through an auto-clutch  30  so that the engine  28 , the traction motor  32 , or both in combination, can function as the vehicle&#39;s prime mover. As with other hybrid designs, the system is intended to recapture a vehicle&#39;s inertial momentum and store it as potential energy for later use including reinsertion to the drive train  20 . In a parallel hybrid-electric vehicle the traction motor/generator  32  is used to recapture vehicle kinetic energy during deceleration by using the drive wheels  26  to back drive the traction motor/generator  32 , capturing a portion of the vehicle&#39;s kinetic energy by generating electricity therefrom. Engine  28  is disengaged from the other components in drive train  20  by opening auto-clutch  30  during periods when the traction motor  32  is back driven. 
         [0015]    Transitions between positive and negative traction motor  32  electrical power consumption are detected and managed by a hybrid controller  48 . Traction motor/generator  32 , during braking, generates three phase alternating current which is applied to an inverter  36  for conversion to direct current (DC) and then through contactors  35  to traction battery plant battery  34 . When the traction motor  32  is used as a vehicle prime mover the flow of power is reversed. Battery  34  is usually a lithium ion battery plant and may be supplemented as a source of stored electrical power, for example, by a conventional 12 volt battery. 
         [0016]    High mass vehicles tend to exhibit poorer gains from hybrid locomotion than do automobiles. Thus electrical power available from fraction battery  34  is often used to power other vehicle systems such as a PTO device  22  based on an electric motor (such PTO systems may include a manned “cherry picker”, a motor for a winch, etc). The traction motor  32  itself may provide the motive power for the PTO device  22  (such as a hydraulic motor). In addition, traction motor/generator  32  may be used for starting engine  28 . If requests for such operations were honored contemporaneously with a transition of contactors  35  to a closed position substantial current could be drawn from the traction battery  34  to support such operations before the contactors  35  closed resulting in arcing before the contactors were fully closed. 
         [0017]    The various local controllers may be programmed to respond to data from ESC  24  passed to data link  18 . Hybrid controller  48  determines, based on available battery charge state, requests for power. Hybrid controller  48  with ESC  24  generates the appropriate signals for application to data link  18  for instructing the engine controller  46  to turn engine  28  on and off and, if on, at what power output to operate the engine. Transmission controller  42  controls engagement of auto clutch  30 . Transmission controller  42  further controls the state of transmission  38  in response to transmission push button controller  72 , determining the gear the transmission is in or if the transmission is to deliver drive torque to the drive wheels  26  or to a hydraulic pump which is part of PTO system  22  (or simply pressurized hydraulic fluid to PTO system  22  where transmission  38  serves as the hydraulic pump) or if the transmission is to be in neutral. 
         [0018]    PTO control is implemented through one or more remote power modules (RPMs)  40 . Remote power modules  40  are data linked expansion input/output modules dedicated to the ESC  24 , which is programmed to utilize them. RPMs  40  function as the controller for PTO  22 , and provide any hardwire outputs  70  and hardwire inputs  66  associated with the PTO device  22  and possibly to and from a PTO load  23 . Requests for operation of load  23  and potentially response reports are applied to the data link  74  for transmission to the ESC  24 , which translates them into specific requests for the other controllers, e.g. a request for power. ESC  24  is also programmed to control valve states through RPMs  40  in PTO device  22 . Remote power modules are more fully described in U.S. Pat. No. 6,272,402 which is assigned to the assignee of the present invention and is fully incorporated herein by reference. At the time the &#39;402 patent was written what are now termed “Remote Power Modules” were called “Remote Interface Modules”. 
         [0019]    If a supplementary 12 volt system is present some electrical power may be diverted from hybrid inverter  35  to maintain the charge of a conventional 12-volt DC chassis battery  60  through a DC/DC inverter  62 . Twelve volt DC motor vehicle power systems based on an engine driven alternator and 12 volt, 6 cell lead acid batteries have been in use for decades and are well known to those skilled in the art. In vehicles contemporary to the writing of this application numerous 12 volt applications remain in common use and a hybrid electric vehicle incorporating drive train  20  may be equipped with a supplemental 12 volt system to support such systems. In such cases electrical power may be diverted from hybrid inverter  36  to a DC/DC inverter  62  which steps power down to maintain a charge on a conventional 12-volt DC chassis battery  60 . Inclusion of such a parallel system would allow the use of readily available and inexpensive components designed for motor vehicle use, such as incandescent bulbs for illumination. Otherwise the use of 12 volt components carries a weight penalty and adds complexity to the vehicle. Battery  34  is sometimes referred to as a traction battery to distinguish it from the supplemental 12 volt battery  60 . 
         [0020]    Transmission controller and ESC  24  both operate as portals and/or translation devices between the various data links  68 ,  18 ,  74  and  64 . Data links  68  and  74  may be proprietary and operate at substantially higher baud rates than does the public data link  18 , and accordingly, buffering is provided for a message passed from one link to another. Additionally, a message may have to be reformatted, or a message on one link may require another type of message on the second link, e.g. a movement request over data link  74  may translate to a request for transmission engagement from ESC  24  to transmission controller  42 . Data links  18 ,  68  and  74  are usually controller area network buses and may conform to the SAE J1939 protocol. 
         [0021]    On heavy hybrid vehicles where the high voltage isolation contactors  35  separate the stored energy in the hybrid system&#39;s traction batteries  34  from the rest of the hybrid, the movable parts can become welded together as a result of transitions (the opening and closing) of the high voltage isolation contactors  35  while the high voltage system is under load. Welding can be further exacerbated by additional current loads originating from the chassis&#39; electrical system and sub-electrical systems which are carried by the hybrid high voltage system by way of the hybrid system&#39;s DC to DC converters  62  at the time of the high voltage isolation contactor  35  transitions resulting in arcing and welding of the contactors. 
         [0022]    Control system  21  implements cooperation of the control elements to order vehicle operations to minimize current draw during contactor  35  transitions. Chassis imposed electrical loads are reduced before, during and after the opening and or closing of the high voltage hybrid isolation contactors  35 . A reconfigurable software and an electrical hardware architecture coordinates the turning on and turning off of current loads imposed by the chassis electrical system and or its sub-electrical system coordinated with the opening and closing of the hybrid system&#39;s high voltage contactors. Changes of state occurring among sensors  16  or on dash panel  44  can operate as indicators of an incipient demand for a transition of contactors  35 . For example, movement of an ignition switch from OFF to ON or START will likely trigger a demand to close contactors  35 . An indication of abrupt deceleration from sensors used to trigger deployment of air bags may be used as a trigger to open the contactors  35 . 
         [0023]    The existing vehicle data link environment allows control over the operation of the vehicle&#39;s hybrid-electric drive train  20  and various loads represented by loads  19 , PTO  22 , DC/DC inverter  62  and the various local controllers, for example the ABS controller  50 , all of which draw power. Vehicle components, systems and subsystems such as: the chassis load manager, electric condenser pusher fans, electrified accessories (AC compressor, power steering, air compressor DC to DC converters and the like), truck equipment manufacture (TEM) installed equipment (lights, motors, solenoids and the like) are all subject to central control. With fully integrated load management system between the chassis, TEM installed equipment and the hybrid electric power electronics system electrical current loads are reduced as much as possible during the actual opening and closing of the hybrid high voltage contactors. 
         [0024]    Implementation of load control is through a controller area network (CAN) communication strategy where different CAN modules/local controllers communicate over a data link environment (including data link  18 ) to control various chassis electrical loads (including loads  19  and PTO  22 ) and the various local controllers in conjunction with the opening and closing of two hybrid high voltage isolation contactors  35 . High voltage isolator contactors  35  have a default open state and an energized (closed) state. For example, a transition from the open state to their closed state would be associated with cycling of the in-can key switch to its “On” state initializing the hybrid electric system and the vehicle control system. 
         [0025]    The hybrid controller  48 , which typically controls the hybrid high voltage isolation contactors  35  (alternatively these may be controlled by the ESC  24 ), sends an encoded digital message to the body controller (ESC  24 ) over the data  18  requesting the ESC, through its own physical outputs  44  or through a secondary CAN module such as the remote power module (RPM)  40 , turn off or reduce all “non-critical” electrical loads  19 ,  22  in anticipation of the hybrid controller  48  closing of the hybrid high voltage isolation contactors  35 . Once the ESC  24  (either directly, through the RPM  40  or through other controllers) has turned “Off” and, or reduced all available electrical loads under the present vehicle mode of operation, or delayed a load from turning on, the ESC  24  then transmits encoded digital message over the data link  18  containing the instant loading status of the chassis electrical system. This status communication can be as simple as broadcasting a discrete message indicating that the electrical loads that can be turned “Off”, or be reduced, have been turned “Off” or reduced to their fullest extent. The status communication could also contain actual or calculated current loads. Once the hybrid controller  48  receives the ESC  24  status message, it then can decide to transition the hybrid high voltage isolation contactors  35  from their current state or maintain them in their present state based on the information contained in the message status. 
         [0026]    PTO devices  22  are a good example of the flexibility which may be incorporated into the present system. Normally PTO  22  would be a lead candidate for shut down or reduced level operation on a contactors  35  transition. However, whether or not operation of the PTO  22  can be discontinued on particular transition event can be left to the operator&#39;s determination based on the character and circumstances of the transition event. 
         [0027]    An initialization timer is also provided, typically through appropriate programming of the ESC  24 . The purpose of the initialization timer is to create an interval of time during the activation of the hybrid system (such as turning “On” the in-cab key switch) which automatically turns “Off” or reduces a series of predetermined loads. These loads are turned “Off” or reduced for a programmable interval of time minimizing the current loading imposed on the hybrid high voltage isolation contactors  35  prior to all associated controllers involved in the normal load management process becoming fully initialized. By the time the initialization timer expires, all involved controllers should have had adequate time to initialize and assume the normal mode of load management functionality as describe in the first part of this teaching. 
         [0028]    By managing loads the amount of current being carried through the hybrid high voltage isolation contactors  25  during their transitions is reduced whereby premature failure and weld issues are mitigated. 
         [0029]    The control of various loads originating from the chassis&#39; electrical system and sub-electrical systems is based on “logical” and data link signals. This allows for customization of vehicle equipment features and functionality with little to no changes to actual vehicle hardware architecture. Due to the data link and software driven character of the control arrangements the control of particular loads may be conditional upon the operating mode of the vehicle and allows selection of vehicle loads to cut off or restrict based on whether the transition is from opened to closed or closed to opened. For example, windshield wiper function through the dash panel  44  or load controller  17  may be shed if the vehicle is in a stationary mode of operation and the headlights are off. Under other circumstances windshield wipers may be a priority function which is maintained through a transition of the contactors  35 . Examples of loads that may be considered for mode sensitive availability for turning off or reducing for transitions include headlights, marker lights, heating, ventilation and air conditioning blower motors, electrically powered power steering, electric air compressors, truck equipment manufacturer (TEM) accessories, electric cooling fans, various system controllers (e.g. the ABS controller  50  if the vehicle is stationary and the parking brake is set). 
         [0030]    Costs are reduced since this system uses the existing vehicle architecture. System robustness is enhanced by using the data link and controller environment. Increased robustness enhances safety by improving the chances that contactors  35  will open in case of a accident to reduce voltages on exposed portions of the vehicle electrical system.