Abstract:
A control system for a hybrid vehicle utilizes telematics and on board sources to obtain information relating to operating conditions. The data is used to modify hybrid-electric drive train operation to extend the life of components of the drive train. In response to requests for propulsion, data relating to expected conditions of operation including one or more of the following, weather, traffic and road conditions, determines what proportion of the request to meet from the internal combustion engine and what proportion to meet from the electrical motor. The proportion of the request for propulsion allocated to the engine is increased where expected conditions of operation impose excessive stress on electrical components of the drive train.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The technical field relates generally to vehicles with a plurality of prime movers and, more particularly, to methods for dynamic allocation of propulsion power demand among the prime movers. 
         [0003]    2. Description of the Technical Field 
         [0004]    Electrical motors generally exhibit greater operating efficiencies than internal combustion engines. In addition, internal combustion engines achieve their maximum efficiencies over relatively narrow RPM and torque ranges in comparison to electrical motors. Consequently, operational rules programmed into vehicle control systems for vehicles which use both electrical traction motors and internal combustion engines for propulsion generally favor using the electrical motors over the internal combustion engine for propulsion absent certain conditions. Conditions which can affect propulsion demand may include, by way of example, conditions of extreme heat and cold which impair operation of a vehicle&#39;s rechargeable energy storage system (RESS), a particular concern where the RESS is constructed from batteries. Vehicles including both internal combustion engines and electric motors for propulsion can include hybrid-electric vehicles with parallel hybrid drive trains, plug in hybrid-electric vehicles (PHEV) and range extended electric vehicles (REEV). The general rule here is that a vehicle&#39;s internal combustion engine is usually run only under certain circumstances, typically relating to a low RESS state of charge (SOC) or, if data relating to such is available, RESS state of energy (SOE). On certain types of hybrid-electric vehicles the internal combustion engine may only be run at its maximum efficiency in response to a low battery SOC or SOE. 
         [0005]    Rules favoring the use of electrical motors have been constrained by various operational limitations. For example, an RESS may be constructed from a number of different power storage elements, for example batteries and capacitors, and may mix those elements. A given RESS design thus may have a quite limited capacity for storage of usable energy per unit mass when contrast to the hydro-carbon fuels usually used with internal combustion engines. The RESS may also exhibit limitations in terms of the rate at which it can be discharged and recharged. If a hybrid-electric vehicle is in use a large proportion of the time and is called on to operate over distances exceeding the capacity of the RESS to carry the vehicle it is unavoidable that the internal combustion engine will be run. 
         [0006]    The use of vehicle telematics technology has become more widespread in recent years. Vehicle telematics offer possibilities for gathering and utilizing information about traffic and other location specific information. Telematics make it possible for a vehicle control system to communicate with the road infrastructure, computers and other vehicles, as well as to obtain GPS location and weather data. Such data have been used to allow drivers to plan routes to avoid traffic congestion and road closures. 
       SUMMARY 
       [0007]    A vehicle comprises a drive train with at least a first configuration of an electrical motor for available for propulsion and an internal combustion engine available for propulsion, a source of generated electricity and a rechargeable energy storage system. A control system dynamically establishes rules for operating the drive-train. The rule provides for handling requests for propulsion, obtaining data relating to expected conditions of operation including one or more of the following, weather, traffic and road conditions and responsive to requests for propulsion and the obtained data determining what proportion of a request for propulsion to meet from the internal combustion engine and what proportion to meet from the electrical motor. The proportion of the request for propulsion allocated to the internal combustion engine is increased in favor of the internal combustion engine where expected conditions of operation stress electrical components of the drive train beyond at least a first predetermined limit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a generalized view of vehicles operating in a telematics enabled environment. 
           [0009]      FIG. 2  is a high level block diagram of a control system for a hybrid-electric drive train for a motor vehicle such as one or more of the vehicles of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    In the following detailed description, like reference numerals and characters may be used to designate identical, corresponding, or similar components in differing drawing figures. 
         [0011]    Referring now to the figures and in particular to  FIG. 1 , a generalized telematics enabled environment  100  is illustrated. Vehicle telematics enabled environment  100  may be implemented for one vehicle  102  or over/between a fleet of vehicles  102 . A given vehicle  102  may be supplied with, or be able to calculate and project, expected delays on a road due to traffic, construction, weather, or emergencies. For a vehicle equipped with a hybrid-electric drive train  20  (See  FIG. 2 ) such delays may be projected as likely to result in a high frequency of cycles in charging and discharging of a vehicle Rechargeable Energy Storage System (RESS), and repeated stopping and starting of an internal combustion engine in a compressed time period to recharge the RESS or to supplement demands for propulsion. Such operating demands can result in overheating of electric traction motors or electrical storage batteries where such batteries serve as the RESS (with resultant increases in resistance leading to still greater heat generation) and other issues. Overheating issues can be made worse on account of weather conditions, particularly high heat and humidity levels, with the consequential effects of such conditions on the ability of a vehicle  102  to reject heat and additional demands for power to support refrigeration. 
         [0012]    Vehicle  102  includes an electronic control system  22  (See  FIG. 2 ) which may be based on controller area networks (CAN) including a public data link  18 . Public data link  18  links numerous controllers on board vehicle  102  for data communication and allows central activation and control of remote data communications services through cellular phone link  108 . CAN  18  may include a node which incorporates an antenna  106  for a global positioning system (GPS) unit for determining a vehicle&#39;s location from the constellation of GPS satellites  110  or incorporate some other mechanism allowing determination of the location of the vehicle. 
         [0013]    Communication between a vehicle  102  and data bases  128  or other vehicles  102  can occur either through road infrastructure sent wirelessly by antenna  108  to the cars around them, via cell towers, or some other means of transmission. Processing of the incoming data could potentially be done in three ways: 
         [0000]    1) The processing is done by vehicle itself on the road, and on-board controller makes localized decisions on how to proceed;
 
2) Processing collections of the data is passed between cars, and then a decision is made and transmitted between the cars; or
 
3) Processing collections of the data and making a decision is done at another location with operational rules then passed to the vehicles on the road.
 
         [0014]    By way of illustration, telematics environment  100  includes a cell phone base station  112  which is linked to a server  114  by land lines. Data transmitted from the vehicle  102  can include information specifying the vehicle&#39;s location. A vehicle  102  may communicate with a vehicle operations server  114  using any convenient means such as a cellular telephone antenna  108  to link with a cellular base station  112 . Cellular base station  112  is linked to server  114  using suitable communication links such as land lines to server  114 . In addition, or alternatively, vehicle  102  may communicate directly or indirectly over one or more base stations  112  with other vehicles  102  in a given geographic region. Alternative communication systems, both public and private can readily be used. A geographic region for which an operational rule for a vehicle  102  is generated may be taken as a particular stretch of road at a particular time. Data available to the vehicle electronic control system  22  from server  114  includes a geographic information system (GIS) database. GIS databases can for example specify the location of public roads and speed limits. Co-location on a road by a group of vehicles  102  may be determined from GPS and GIS data. In return server  114  may access private and public data bases  128  and GIS  116  to return real time traffic and weather information, to the extent available. 
         [0015]    Vehicle on board traffic visualizations of real time traffic, mostly in the form of geographic maps, have become quite popular. Governments (federal and local) and other organizations supply real time traffic data and pollution information in increasing numbers of locales. It is also possible that vehicle to vehicle data could be used to produce real time traffic data without dedicated data bases. The primary influence of this data to date has been to encourage drivers to re-route themselves. Relatively less has been done to change vehicle operational behavior in response to such data. 
         [0016]    Under certain driving conditions, particularly hot climactic conditions, aggressive usage of electric components in a hybrid-electric drive train system may cause de-rating of components in or related to the drive train. Information relating to temperature, humidity, traffic data, and available known route information can allow control system  22  components such as a hybrid controller  48  to make an informed calculation on how to operate the hybrid-electric drive train  20  in order to protect the drive train and related components from premature wear and to maintain safe vehicle operation. For example, the potential for regenerative braking may be limited by ice on roads. Adjusting the engine stop/start algorithm, regenerative braking strategy, and general selection of hybrid operating modes could be implemented to compensate for an expected loss of regenerative braking. 
         [0017]    Data relating to likely traffic delays or other impediments/factors such as weather conditions relating to vehicle  102  operation, wherever or however obtained, may be used by the control system  22  to characterize hybrid-electric drive train  20  operating conditions in terms of stress placed on the hybrid-electric drive train. Stress can be quantized as increased cycling frequency of regenerative braking and electric propulsion or current inflows/outflows to the traction batteries  34  using temperature/humidity as a factor. Such stress can potentially contribute to premature failure of hybrid-electric drive train  20  components or a traction batteries  34  serving as the vehicle RESS. 
         [0018]    Energy efficiency for a rechargeable traction batteries  34  is usually expressed as a percentage of the electrical energy stored in a battery by charging that is recoverable during discharging. For an electrolytic cell this is the fraction, usually expressed as a percentage, calculated as the theoretically required energy divided by the energy actually consumed in the process (production of a chemical, electroplating, etc). The inefficiencies arise from current inefficiencies and the inevitable heat losses due to polarization. 
         [0019]    As most devices (for example, motors, inverters, or the like) that may be coupled to the RESS are characterized and controlled on the basis of the power they consume or generate, the energy flow through them is defined by the integral of power with respect to time (energy=power×time). The commonly reported RESS variable, SOC, represents a percentage of the total capacity of the RESS, is inconsistent with the reckoning of energy flow through the other devices in the system. 
         [0020]    Returning to conditions which may affect traction batteries  34  temperature levels may be considered. The condition of batteries  34  may deteriorate more quickly at high temperatures than otherwise if current in flow is not limited. Current outflow from the battery may be aggravated by air conditioning and other refrigeration demands because cooling systems on hybrid-electric vehicles often rely on accessory electric motors  68 ,  70  to run compressors and coolant circulation pumps. Under conditions of extreme cold batteries  34  may be unable to support high current outflows. High current (both root mean square-rms and peak) equate with high energy consumption and accelerated wear or “aging” of drive train components. Stress on a hybrid-electric drive train would increase were such loads allowed. Battery management system strategy should provide a cell/module/pack voltage which allows for stable and repeatable operation. 
         [0021]    Data quantifying such adverse system responses under some conditions allows a cost comparison to be made between the additional costs incurred by operation of the vehicle using its internal combustion (IC) engine  28  (See  FIG. 2 ), mixing propulsion demand between electric motors  32  and the IC engine  28  or propelling the vehicle only from electric motor(s)  32 ,  30 . It can also be used to determine how much regenerative braking to use to meet braking demand. One of the primary disadvantages of electric and hybrid-electric vehicles is the high cost of electric drive train compared to internal combustion engine equipped vehicles. Considering additional warranty cost of electric drive train, the cost disadvantage becomes an even bigger problem. Limiting the exercise of electrical components in a hybrid-electric drive train  20  under adverse conditions can extend the service lives of the components and reduce maintenance costs and vehicle down time by enough to pay for immediate savings in operating costs lost due to increased hydro-carbon fuel consumption. 
         [0022]      FIG. 2  is a high level schematic of a control system  22  for a hybrid-electric drive train  20  which may be used with vehicle  102 . Hybrid-electric drive train  20  illustrates the many possible examples of drive trains where rules of operation may be varied to meet propulsion and braking demand. Hybrid-electric drive train  20  is configurable for series, parallel and mixed series/parallel operation. Illustration of the methods disclosed here is not limited to a particular hybrid-electric system. Nor do hybrid vehicles necessarily combine IC engines and electric machines. IC engines can be replaced with external combustion engines. Another type of motor/pump which can operate with an RESS is a hydraulic motor. For a hybrid-hydraulic drive train a hydraulic accumulator serves as the RESS. 
         [0023]    Hybrid-electric vehicles have generally been of one of two types, parallel and series. In parallel hybrid-electric systems propulsion torque can be supplied to drive wheels by an electrical motor, by a fuel burning engine, or a combination of both. In series type hybrid systems drive propulsion is directly provided only by the electrical motor. An internal combustion engine is used to run a generator which supplies electricity to power the electric traction motor and to charge storage batteries. In a series type system the control system may operate under a rule under which the internal combustion engine is started at a minimum threshold battery SOC, run at its most efficient brake specific fuel consumption output level until the battery reaches a maximum allowed SOC whereupon the IC engine is turned off. 
         [0024]    Hybrid-electric drive train  20  includes an internal combustion (IC) engine  28  and two dual mode electrical machines  30 ,  32  which can be operated either as generators or motors. The dual mode electrical machines (motor/generator)  30 ,  32  can provide for vehicle propulsion. They can also generate electricity as a result either of regenerative braking of drive wheels  26  or by being directly driven by the IC  28  engine. In hybrid-electric drive train  20  the IC machine  28  can provide direct propulsion torque or can be operated in a series type hybrid-electric drive train configuration where it is limited to driving one or both of the electrical motor/generators  30 ,  32 . Hybrid-electric drive train  20  also includes a planetary gear  60  for combining power output from the IC engine  28  with power output from the two electrical motor/generators  30 ,  32 . A transmission  38  couples the planetary gear  60  with the drive wheels  26 . Power can be transmitted in either direction through transmission  38  and planetary gear  60  between the propulsion sources and drive wheels  26 . During braking planetary gear  60  can deliver torque from the drive wheels  26  to the motor/generators  30 ,  32  or, if the vehicle is equipped for engine braking, to engine  28 , distribute torque between the motor/generators  30 ,  32  and IC engine  28 . 
         [0025]    A plurality of clutches  52 ,  54 ,  56  and  58  provide various options for configuring the electrical motor/generators  30 ,  32  and the engine  28  to propel the vehicle through application of torque to the drive wheels  26 , to generate electricity by driving the electrical motor/generators  30 ,  32  from the engine, and to generate electricity from the electrical motor/generators  30 ,  32  by back driving them from the drive wheels  26 . Electrical motor/generators  30 ,  32  may be run in traction motor mode to power drive wheels  26  or they may be back driven from drive wheels  26  to function as electrical generators when clutches  56  and  58  are engaged. Electrical motor/generator  32  may be run in traction motor mode or generator mode while coupled to drive wheels  26  by clutch  58 , planetary gear  60  and transmission  38  while at the same time clutch  56  is disengaged allowing electrical motor/generator  30  to be back driven through clutch  54  from engine  28  to operate as a generator. Conversely clutch  56  may be disengaged and clutch  58  engaged and both motor/generators  30 ,  32  run in motor mode. In this configuration motor/generator  32  can propel the vehicle while motor/generator  32  is used to crank engine  28 . Clutch  52  may be engaged to allow the use of IC engine  28  to propel the vehicle or to allow use of a diesel engine, if equipped with a “Jake brake,” to supplement vehicle braking. When clutches  52  and  54  are engaged and clutch  56  disengaged engine  28  can concurrently propel the vehicle and drive motor/generator  30  to generate electricity. Still further operational configurations are possible although not all are used. Elimination of some configurations can allow clutch  58  to be considered as “optional” and to be replaced with a permanent coupling. 
         [0026]    The selective engagement or disengagement of clutches  52 ,  54 ,  56  and (if used)  58  allows hybrid-electric drive train  20  to be configured to operate in a “parallel” mode, in a “series” mode, or in a blended “series/parallel” mode. To configure drive train  20  for series mode operation clutches  54  and  58  could be engaged and clutches  52  and  56  disengaged. Propulsion power is then provided by motor/generator  32  and motor/generator  30  operates as a generator. To implement drive train  20  for parallel mode operation at least clutches  52  and  58  are engaged. Clutch  54  is disengaged. Motor/generator  32  and IC engine  28  are available to provide direct propulsion. Motor/generator  30  may be used for propulsion. A configuration of drive train  20  providing a mixed parallel/series mode has clutches  52 ,  54  and  58  engaged and clutch  56  disengaged. Motor/generator  32  operates as a motor to provide propulsion or in a regenerative mode to supplement braking IC engine  28  operates to provide propulsion and to drive motor/generator  30  as a generator. 
         [0027]    Hybrid-electric drive train  20  draws on two reserves of energy, one for the electrical motor/generators  30 ,  32  and one for the IC engine  28 . Electrical energy for the motor/generators  30 ,  32  is stored in an RESS which may take one of several forms such as capacitors but presently is more commonly constructed from traction batteries  34 . Either storage system is subject to a maximum energy storage limit. Batteries  34  also exhibit rates of charging and discharging which may be limited in comparison to energy flow into or from a fuel tank  62  or capacitors. The availability of power from the electrical power reserve may be referred to as its state of energization (SOE) or, more usually with batteries, as its state of charge (SOC). In either case the value is indicated as a percentage. Combustible fuel for engine  28  is typically a hydro-carbon and, if liquid or gaseous, maybe stored in a fuel tank  62 . The fuel tank  62  is resupplied from external sources and unlike the batteries  34  (which function as the vehicle&#39;s RESS) cannot be regenerated by operation of the vehicle. 
         [0028]    Traction batteries  34  may be charged from external sources or by operation of the drive train  20 . As already described, electrical motor/generators  30  and  32  may operate as generators to supply current to recharge traction batteries  34  over a high voltage energy bus  17  from the high voltage energy distribution sub-system. Hybrid power converter  36  provides voltage step down or step up and, if motor/generators  30 ,  32  are alternating current devices, current rectification and de-rectification between the motor/generators and batteries  34 . Fuel, a form of stored energy, may be converted to electrical energy and thereby moved from the fuel tank  62  to the traction batteries  34 . Traction batteries  34  may also be recharged through regenerative energy capture techniques such as regenerative braking, turbo compounding, regenerative energy capture through coastdown. 
         [0029]    Control over drive train  20 , the power converter  36  and traction batteries  34  is implemented by a control system  22 . Control system  22  may be implemented using two controller area networks (CAN) based on a public data link  18  and a hybrid system data link  44 . Control system  22  coordinates operation of the elements of the drive train  20  and the service brakes  40  in response to operator/driver commands to move (ACC/TP) and stop (BRAKE) the vehicle received through an electronic system controller (ESC)  24 . Energy reserves in terms of the SOC of traction batteries  34  are managed taking into account the operator commands. The control system  22  selects how to respond to the operator commands to meet programmed objectives including efficiently maintaining the SOC of traction batteries  34  as well as protecting drive train  20  components. 
         [0030]    In addition to the data links  18 ,  44 , control system  22  includes the controllers which broadcast and receive data and instructions over the data links. Among these controllers is the ESC  24 . ESC  24  is a type of body computer and is not assigned to a particular vehicle system. ESC  24  has various supervisory roles and is connected to receive directly or indirectly various operator/driver inputs/commands including brake pedal position (BRAKE), ignition switch position (IGN) and accelerator pedal/throttle position (ACC/TP). ESC  24 , or sometime the engine controller  46 , can also be used to collect other data such as ambient air temperature (TEMP). In response to these and other signals ESC  24  generates messages/commands which may be broadcast over data link  18  or data link  44  to an anti-lock brake system (ABS) controller  50 , the transmission controller  42 , the engine control unit (ECU)  46 , hybrid controller  48  and a pair of accessory motor controllers  12 ,  14  and includes data transmission to and from a global positioning system unit  64  and a two way telematics unit  16 . 
         [0031]    Accessory motor controllers  12 ,  14  control for high voltage accessory motors  13 ,  15  in response to directions from other CAN nodes. High voltage accessory motors  13 ,  15  are direct current motors to support the operation of components such as an air conditioning compressor (not shown), a battery cooling loop pump (not shown) or a power steering pump (not shown). On many hybrid-electric vehicles there is no option to power such components directly from the internal combustion engine and the motors driving these components are parasitic loads on a motor/generator operating in generator mode or they draw power over a high voltage power distribution sub-system  19  from the traction batteries  34 . Under conditions where a vehicle  102  is caught in slow moving traffic greater demands may be made on power steering. Under conditions of high heat and humidity greater demands are likely to be placed on air conditioning and for battery cooling. When these circumstances coincide the greatest stress due to heat is likely to be placed on the drive train  20  components particularly motor internal resistances rise and batteries  34  temperatures with increased frequency and depth and charging and discharging cycles. 
         [0032]    Operator demand for power on drive train  20  power is a function of accelerator/throttle position (ACC/TP). ACC/TP is an input to the ESC  24  which passes the signal to the hybrid supervisory control module  48 . Where engine  28  is supplying power both for propulsion and for charging of the traction batteries  34  an allocation of the available power from engine  28  is made by the hybrid supervisory control module  48 . 
         [0033]    Table I illustrates possible drive train  20  configurations related to traction batteries  34  SOC and vehicle operating conditions. The possible configurations are mixed series/parallel, parallel and series. The term “Regen Mode” refers to one of the motor/generators operating as a generator while being back driven from the drive wheels  26 . A motor operating in a generator mode is driven by the engine  28 . Clutch  58  is engaged for all examples. Propelling source, charging source and propel less charging source are listed in propel units. The table reflects a possible set rules for configuration of hybrid-electric drive train  20  to meet loads that may be imposed on the system. 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                 Comment 
                 Light Load 
                 Urgent SOC 
                 Mid-Load 
                 Max. Load 
                 Heavy Load 
               
               
                   
               
             
             
               
                 Configuration 
                 Series/Par 
                 Series 
                 Parallel 
                 Parallel 
                 Parallel 
               
               
                 Propelling 
                 Motor/Gen 
                 Motor/Gen 32 
                 Both 
                 Both Motor/ 
                 Both 
               
               
                 Source 
                 32 
                   
                 Motor/Gen 
                 generators 
                 Motor/generators, 
               
               
                   
                   
                   
                   
                 Engine 
                 Engine 
               
               
                 Charging 
                 Motor/Gen 
                 Motor 32 in 
                 Both motors in 
                 Motor 32 in 
                 Both motors in 
               
               
                 Source 
                 32 in 
                 Regen mode, 
                 Regen mode 
                 Regen mode, 
                 Regen mode 
               
               
                   
                 Regen 
                 motor/gen 30 
                   
                 motor/gen 30 in 
               
               
                   
                 mode 
                 in generator 
                   
                 generator mode 
               
               
                   
                   
                 mode 
               
               
                 Clutch 52 
                 Disengaged 
                 Disengaged 
                 Disengaged 
                 Disengaged 
                 Engaged 
               
               
                 Clutch 56 
                 Disengaged 
                 Disengaged 
                 Engaged 
                 Engaged 
                 Engaged 
               
               
                 Clutch 54 
                 Disengaged 
                 Engaged 
                 Disengaged 
                 Engaged 
                 Disengaged 
               
               
                 ACC/TP % 
                 20 
                 50 
                 50 
                 80 
                 60 
               
               
                 SOE/SOC % 
                 80 
                 20 
                 80 
                 50 
                 70 
               
               
                 Propelling S. 
                 150 
                 150 
                 300 
                 471 
                 471 
               
               
                 Charging S 
                 15 
                 165 
                 30 
                 165 
                 30 
               
               
                 Propel less 
                 135 
                 −15 
                 270 
                 306 
                 441 
               
               
                 charging 
               
               
                   
               
             
          
         
       
     
         [0034]    Maintaining batteries  34  SOC is subject to various constraints including the present SOC of the traction batteries  34  and a dynamic limit on the rate at which the traction batteries  34  can accept charge. The traction batteries  34  and engine  28  can be selected so that the engine can be run at its most efficient brake specific fuel consumption during pure charging operation up to a nominal SOC, usually 80% of a full charge. Thus the dynamic limit on the rate of charge can be disregarded during periods when both charging and propulsion are demanded from the drive train  20 . The hybrid controller  48  monitors batteries  34  SOC and when charging of batteries  34  is indicated allocates available torque from the engine  28  or from the drive wheels  26  during dynamic regenerative braking to motor/generators  30  and/or  32  to generate electricity for charging traction batteries  34 . 
         [0035]    Consideration of modification of the operational rules for a control algorithm based on traffic, road and weather conditions can now be considered. Any control algorithm includes a number of definitions. 
         [0036]    RESS (Rechargeable Energy Storage System) Management System: For a typical hybrid-electric vehicle this is known as a battery management system (BMS). This component monitors the state of the battery in terms of useable energy, power capability, health, voltage and temperature. 
         [0037]    RESS State of Health: A quantitative measure of the health of the RESS. Avoiding declines in the State of Health of the RESS is a factor guiding rule selection and/or parameter value selection. 
         [0038]    RESS State of Charge and State of Energy: Quantitative measures of the amount of useful energy contained in the RESS. 
         [0039]    Expected RESS Load for the Next Driving Period how the battery will be used in the near future. This is derived from weather, road condition and traffic data as well as the vehicle load. For example, the frequency of stops may be projected from traffic conditions and GIS information about the projected route of the vehicle. 
         [0040]    Preferred charge rate for RESS life, charger life, temperature distribution: The vehicle system, especially the HEV components, has designated operational limits. These limits are in place to preserve the performance level and reliability/durability of the components. For example the battery cells have a charge-rate limit to preserve the battery&#39;s useful lifetime. These rates can vary with operating temperature. 
         [0041]    Determination of maximum allowed RESS load for a particular class of vehicle and particular hybrid-electric drive train can be developed from long term operational histories and stored on data bases  128  or locally on the vehicle. Such values are subject to being updated over time and for upgrades or changes in drive train components. 
         [0042]    Knowledge of likely vehicle speed and probability of variation in speed, along with changes in parasitic demand and losses stemming from weather conditions allows for power demand and opportunities for regenerative braking to be projected. A target or maximum allowed RESS Load may be provided and operational rules may be varied in an attempt to reduce Expected RESS Load to this maximum allowed level, or at least to minimize occasions of exceeding it. Alternatively, short term and long term maximum allowed RESS load can be provided. Transients above a long term limit may be allowed but limited in duration and frequency. IC engine  28  operation may be expanded as called for to reduce Expected RESS Load in any drive train  20  configuration. Service brake  40  operation or IC engine  28  braking (if not disallowed by local ordinance) may be substituted for regenerative braking to avoid over heating and/or stress on the batteries  34 . Loss of opportunities for regenerative braking may be used to force greater IC engine  28  operation at a base output level to meet high voltage accessory motor demand plus a varying output level to support propulsion demand and thereby minimize current flow into and out of the batteries  34 . For drive train  20 , because it can be reconfigured between serial, parallel and mixed serial/parallel operation it is possible to specify changes in configuration not withstanding a rule which would usually entail operation in a particular configuration. This could be done to allow increased reliance on IC engine  28 . Analogous values may be developed for other components in drive train  20  which may be subject to heat accelerated aging, such as the motor/generators  30 ,  32  or the hybrid power converter  36 .