Patent Publication Number: US-2003230996-A1

Title: Method and arrangement for a controlling strategy for electronic components in a hybrid elecrtic vehicle

Description:
BACKGROUND OF INVENTION  
       [0001] 1. Industrial Applicability  
       [0002] The present invention finds applicability in the transportation industries, and more specifically private and commercial vehicles. Of particular importance is the invention&#39;s incorporation into hybrid electric vehicles.  
       [0003] 2. Background Art  
       [0004] Generally, a hybrid electric vehicle combines electric propulsion with traditional internal combustion engine propulsion to achieve enhanced fuel economy and/or lower exhaust emissions. Electric propulsion has typically been generated through the use of batteries and electric motors. Such an electric propulsion system provides the desirable characteristics of high torque at low speeds, high efficiency, and the opportunity to regeneratively capture otherwise lost braking energy. Propulsion from an internal combustion engine provides high energy density, and enjoys an existing infrastructure and lower costs due to economies of scale. By combining the two propulsive systems with a proper control strategy, the result is a reduction in the use of each device in its less efficient range. Furthermore, and as shown in FIG. 1 regarding a parallel hybrid configuration, the combination of a downsized engine with an electric propulsion system into a minimal hybrid electric vehicle results in a better utilization of the engine, which improves fuel consumption. Furthermore, the electric motor and battery can compensate for reduction in the engine size.  
       [0005] In typical configurations, the combination of the two types of propulsion systems (internal combustion and electric) is usually characterized as either series or parallel hybrid systems. In a pure series hybrid propulsion system, only the electric motor(s) are in direct connection with the drive train and the engine is used to generate electricity which is fed to the electric motor(s). The advantage of this type of system is that the engine can be controlled independently of driving conditions and can therefore be consistently run in its optimum efficiency and low emission ranges. A key disadvantage to the series arrangement is the loss in energy experienced because of the inefficiencies associated with full conversion of the engine output to electricity. In a pure parallel hybrid propulsion system, both the engine and the electric motor(s) are directly connected to the drive train and either one may independently drive the vehicle. Because there is a direct mechanical connection between the engine and the drive train in a parallel hybrid propulsion system, less energy is lost through conversion to electricity compared to a series hybrid propulsion system. The operating point for the engine, however, can not always be chosen with full freedom.  
       [0006] The two hybrid propulsion systems can be combined into either a switching hybrid propulsion system or a power-split hybrid propulsion system. A switching hybrid propulsion system typically includes an engine, a generator, a motor and a clutch. The engine is typically connected to the generator. The generator is connected through a clutch to the drive train. The motor is connected to the drive train between the clutch and the drive train. The clutch can be operated to allow series or parallel hybrid propulsion.  
       [0007] A power-split hybrid system, as is exemplarily employed with respect to the present invention, includes an engine, a generator and a motor. The engine output is “split” by a planetary gear set into a series path from the engine to the generator and a parallel path from the engine directly to the power train. In a power-split hybrid system, the engine speed can be controlled by varying the power split to the generator by way of the series path, while maintaining the mechanical connection between the engine and drive train through the parallel path. The motor augments the engine on the parallel path in a similar manner as a traction motor in a pure parallel hybrid propulsion system, and provides an opportunity to use energy directly through the series path, thereby reducing the losses associated with converting the electrical energy into, and out of chemical energy at the battery.  
       [0008] In a typical power-split hybrid system, the generator is usually connected to the sun gear of the planetary gear set. The engine is connected to the planetary carrier and the output gears (usually including an output shaft and gears for interconnection with the motor and the wheel-powering, final drive train) are connected to the ring gear. In such a configuration, the power-split hybrid system can generally be operated in four different modes; one electric mode and three hybrid modes.  
       [0009] In the electric mode, the power-split hybrid system propels the vehicle utilizing only stored electrical energy and the engine is turned off. The tractive torque is supplied from the motor, the generator, or a combination of both. This is the preferred mode when the desired power is low enough that it can be produced more efficiently by the electrical system than by the engine and when the battery is sufficiently charged. This is also a preferred mode for reverse driving because the engine cannot provide reverse torque to the power train in this configuration.  
       [0010] In the parallel hybrid mode, the engine is operating and the generator is locked. By doing this, a fixed relationship between the speed of the engine and the vehicle speed is established. The motor operates as either a motor to provide tractive torque to supplement the engine&#39;s power, or can be operated to produce electricity as a generator. This is a preferred mode whenever the required power demand requires engine operation and the required driving power is approximately equal to an optimized operating condition of the engine. This mode is especially suitable for cruising speeds exclusively maintainable by the small internal combustion engine fitted to the hybrid electric vehicle.  
       [0011] In a positive split hybrid mode, the engine is on and its power is split between a direct mechanical path to the drive train and an electrical path through the generator. The engine speed in this mode is typically higher than the engine speed in the parallel mode, thus deriving higher engine power. The electrical energy produced by the generator can flow to the battery for storage or to the motor for immediate utilization. In the positive split mode, the motor can be operated as either a motor to provide tractive torque to supplement the engine&#39;s power or to produce electricity supplementally with the generator. This is the preferred mode whenever high engine power is required for tractive powering of the vehicle, such as when high magnitude acceleration is called for, as in passing or uphill ascents. This is also a preferred mode when the battery is charging.  
       [0012] In a negative split hybrid mode, the engine is in operation and the generator is being used as a motor against the engine to reduce its speed. Consequently, engine speed, and therefore engine power, are lower than in parallel mode. If needed, the motor can also be operated to provide tractive torque to the drive train or to generate electricity therefrom. This mode is typically never preferred due to increased losses at the generator and planetary gear system, but will be utilized when engine power is required to be decreased below that which would otherwise be produced in parallel mode. This situation will typically be brought about because the battery is in a well charged condition and/or there is low tractive power demand. In this regard, whether operating as a generator or motor, the torque output of the generator is always of the same sense (+/−); that is, having a torque that is always directionally opposed to that of the engine. The sign of the speed of the generator, however, alternates between negative and positive values depending upon the direction of rotation of its rotary shaft, which corresponds with generator vs. motor modes. Because power is dependent upon the sense of the speed (torque remains of the same sense), the power will be considered to be positive when the generator is acting as a generator and negative when the generator is acting as a motor.  
       [0013] When desiring to slow the speed of the engine, the current being supplied to the generator is changed causing the speed of the generator to slow. Through the planetary gear set, this in turn slows the engine. This effect is accomplished because the resistive force acting against the torque of the generator is less at the engine than at the drive shaft which is connected to the wheels and is being influenced by the entire mass of the vehicle. It should be appreciated that the change in speed of the generator is not equal, but instead proportional to that of the engine because of gearing ratios involved within the connection therebetween.  
       [0014] In conventional vehicles, the cooling system has a variety of components that require cooling by a fluid cooling system, radiator and fan. Fluid cooled components typically include the engine and transmission. A fluid coolant circulates through a closed cooling loop, passes through each component to absorb heat, and then passes through the radiator. The radiator exposes the coolant to the fan&#39;s airflow and releases the heat. A controller monitors engine and transmission temperatures and adjusts fan speed to maintain acceptable coolant temperature for the cooling loop. In addition to the fluid cooled components, the air conditioning (A/C) condenser requires cooling from airflow that comes from the fan(s) to keep the A/C compressor head pressures at acceptable levels.  
       [0015] In electric and hybrid electric vehicles the high voltage system and other electronic components unique to such vehicles require cooling. However, the conventional cooling system described above does not provide an appropriate temperature differential to remove the heat which builds up in the electronic components. Therefore a separate cooling system is commonly used to cool the electronic components of an electric or hybrid electric vehicle.  
       [0016] For example, in a typical hybrid electric vehicle, a DC/AC inverter and a DC/DC converter require cooling below the temperature range typically found in conventional internal combustion engine cooling systems. Without an adequate cooling system, the build up of the heat load during operation of a converter and/or an inverter threatens the operation and efficiency of these electrical devices as well as the operation of the vehicle itself. The present approach to eliminate or at least reduce heat build up includes the use of a separate radiative cooling system with a liquid coolant temperature significantly lower than the liquid coolant used to cool an internal combustion engine of a vehicle.  
       [0017] Even with use of a separate cooling system for the inverter and/or converter, the electrical components are threatened by the build up of heat during hot ambient conditions or extreme operating conditions. When such conditions occur, the present electronics cooling strategy calls for the electronic device to monitor its own temperature and shut down thereby preventing damage due to overheating. Such shut downs deprive the user of a fully functional hybrid electric vehicle.  
       [0018] Several deficiencies associated with the use of known hybrid electric vehicle designs and methods of operating the same have been described hereinabove. Several inventive arrangements and methods for operating hybrid electric vehicles are described hereinbelow that minimize, or remedy these deficient aspects of known designs, and/or provide benefits, in and of themselves, to the user. These new, improved and otherwise potentiated solutions are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.  
       SUMMARY OF INVENTION  
       [0019] In one aspect, a cooling arrangement for electronic components in a hybrid electric vehicle is disclosed. The arrangement includes an electronics cooling loop aboard a hybrid electric vehicle in which a DC/DC converter, DC/AC inverter and an electronics radiator are fluidly connected to each other to cool the converter and inverter. In a preferred embodiment, a electronics radiator fan is positioned near the electronics radiator to cause or enhance air flow across the electronics radiator. In yet another embodiment, a coolant pump is fluidly connected to the electronics cooling loop to cause fluid circulation. A temperature sensor in the cooling loop senses a temperature which is communicated to a supervisory module. The temperature sensor may be located at or near a cooling inlet of the DC/DC converter or between the DC/DC converter and DC/AC inverter. Based on the temperature input, the supervisory module controls the operation of the DC/DC converter. In a preferred embodiment, the supervisory module controls the DC/DC converter based on ambient outside temperature, radiator fan speed, air conditioning system operational modes, lighting system operation modes, and battery system energy capacity. By controlling the operation of the DC/DC converter, the heat contribution from the converter to the electronic cooling loop can be reduced or eliminated. While the DC/DC converter is shut down to reduce or eliminate the heat load of the electronics cooling system, electrical power can be supplied by the 12-volt battery and/or a conventional alternator driven by the internal combustion engine. In a preferred embodiment, the DC/DC converter is located upstream of the DC/AC inverter in the electronics cooling loop.  
       [0020] In yet another preferred embodiment, the supervisory module further controls the operating capacity of the DC/AC inverter based on the temperature in the electronics cooling loop. The supervisory module&#39;s control over the DC/AC inverter allows the operating capacity of the inverter to be varied in response to a temperature of the electronics cooling system, thereby varying the heat contribution from the inverter to the electronics cooling loop. By reducing the operational capacity of the inverter, a corresponding heat load reduction occurs in the electronics cooling loop, thereby extending the duration of operating the hybrid electric vehicle under extreme operating scenarios and especially in hot ambient environments.  
       [0021] In another aspect, a method of controlling a cooling arrangement for electronic components in a hybrid electric vehicle is disclosed. In the most basic form, the method of control includes arranging an electronics cooling loop aboard a hybrid electric vehicle in which a DC/DC converter, DC/AC inverter and an electronics radiator are placed in fluid connection with each other to cool the converter and inverter, sensing a temperature in the electronics cooling loop, and selectively operating the DC/DC converter based on the sensed temperature in the electronics cooling loop. A preferred method of control includes controlling a pump that is fluidly connected to the electronics cooling loop for varying fluid flow, and controlling an electronics radiator fan, which in operation, causes air flow across the electronics radiator. In addition to, or apart from the control methods described above, selective operation of the DC/DC converter is based upon the cooling loop temperature sensed, ambient outside temperature, lighting system operational modes, and battery system energy capacity. As well as controlling the DC/DC converter to alter the heating load of the cooling loop, the speed of the electronics radiator fan can be controlled. In addition to or apart from the control methods described above, selective variation of the DC/AC inverter&#39;s operating capacity occurs based upon the temperature sensed in the electronics cooling loop. As can be appreciated by those skilled in the art, the basic and alternative methods of controlling the converter and/or the inverter, as set forth, reduces the heat load of the electronics cooling loop. In doing so, a smaller electronics radiator can be utilized thereby saving on space and weight in the hybrid electric vehicle.  
       [0022] The general beneficial effects described above apply generally to the exemplary descriptions and characterizations of the devices, mechanisms and methods disclosed herein. The specific structures and steps through which these benefits are delivered will be described in detail hereinbelow.  
     
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
     [0023] In the following, the invention will be described in greater detail by way of examples and with reference to the attached drawings, in which:  
     [0024]FIG. 1 is a graphical comparison of torque generated by a parallel hybrid and systems that have either an engine or motor.  
     [0025]FIG. 2 is a perspective of a hybrid electric vehicle showing exemplarily system component locations on the vehicle.  
     [0026]FIG. 3 is a schematic depicting the architecture of a power-split hybrid electric vehicle.  
     [0027]FIG. 4 is a schematic depicting the layout of the electronics cooling loop and the control relationships between the vehicle control unit and the electronics cooling loop.  
     [0028]FIG. 5 is a schematic depicting control relationships between the various systems of a hybrid electric vehicle as coordinated utilizing the CAN.  
     [0029]FIG. 6 is a functional schematic depicting the processes, tasks and controls of the various systems of the exemplary hybrid electric vehicle. 
    
    
     DETAILED DESCRIPTION  
     [0030] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention(s) that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention.  
     [0031] As depicted in FIGS. 1 and 2, a hybrid electric transporting vehicle  10  has a power train system (having components generally designated with reference numbers from the 500&#39;s series) included therein for providing propulsion, as well as serving supplemental functions which are described in greater detail herein. Predominantly, the power train system is positioned in an engine room  11  located near a passenger compartment  12  of the vehicle  10 . A battery compartment or housing  14 , also positioned near the passenger compartment  12  holds one or more batteries  410 . As will be appreciated by those skilled in the art, the positioning of the engine room  11  and battery housing  14  is not limited to the locations set forth in FIG. 2. For example, the engine room  11  may be positioned in front of, or behind the passenger compartment  12 .  
     [0032] As depicted in FIG. 2, the overall systems architecture of the electric hybrid vehicle  10  comprises an engine system  510 , including an internal combustion engine  511  (petrol, diesel or the like), that is mechanically connected by an output shaft system  520  to a transaxle system  530 . The transaxle system  530  is further connected to a drive shaft system  540  utilized to rotate one or more drive wheels  20  that propel the hybrid electric transporting vehicle  10 . In a preferred embodiment, the combustion engine  511  is controlled by an engine control module (ECM) or unit  220  which is capable of adjusting, among possible parameters, airflow to, fuel flow to and/or ignition at the engine  511 . The engine  511  is mechanically connected via an output shaft  522  to the transaxle system  530 . A planetary gear set  535  establishes interconnection between the engine  511  (via the output shaft  522 ), a generator  532 , and the drive shaft system  540  (via the transaxle system  530 ). A motor  531  is also coupled to the drive shaft system  540 , also possibly via the transaxle system  530 .  
     [0033] In one embodiment, and which is illustrated in FIG. 3, a one way clutch  521  is engageable with the output shaft  522 , which in turn is connected to the engine  511  and to the planetary gear set  535 . The function of the one-way clutch  521  is to limit the engine to being only a power/torque input to the planetary gear set  535 , and with only one direction of rotation. Consequently, the one-way clutch  521  prevents power or torque from being transmitted from the planetary gear set  535  back to the engine  511 .  
     [0034] Based on the above disclosed system architecture, implementation of an energy management strategy, which is a focus of the hybrid electric vehicle  10 , starts at a high level within a vehicle control unit or vehicle systems controller (VCU)  100  as schematically shown in FIGS. 4, 5 and  6 . The vehicle systems controller  100  is programmed with control strategies for the drive train system and battery system, as well as others. The vehicle systems controller  100  is responsible for interpreting inputs, coordinating the component controllers, and determining vehicle system operating states. The VCU  100  also generates commands to appropriate component sub-systems based on defined vehicle systems controller  100  functions, and sends those commands to the component controllers that, based thereon, take appropriate actions. The vehicle systems controller  100  also acts as a reference signal generator for the sub-system controllers. The vehicle systems controller  100  may take the form of a single, integrated microprocessor, or comprise multiple microprocessors that are suitably interconnected and coordinated.  
     [0035] A primary function of the vehicle systems controller  100  is to carry out vehicle mode processes and tasks (also known as the sequential control process), as well as make torque determinations, set reference values and perform energy management processes. Certain systems of the vehicle  10  are managed or monitored by a vehicle management (VM) unit or controller  105  which carries out sequential control processes, including ascertaining the position of the vehicle key and gear selector positioning, among others. It is at this level that certain inputs from the driver and conditions of the vehicle are synthesized for utilization as command inputs for subsystem controllers.  
     [0036] At the lower level of the VCU  100 , three sub-component controllers are illustrated in FIG. 6. The first is a high voltage DC controller (HVDC)  115 ; the second is a battery management unit or controller  110  (BMU); and the third is a drive train controller  120  (DTC). As indicated above, certain inputs and processes are taken from the driver and the vehicle&#39;s systems at the vehicle management unit  105 . Conversely, certain outputs relevant to the driver will be transmitted and displayed at the dashboard display unit  107  from the VCU  100  or the VM  105 .  
     [0037] The HVDC  115  is responsible for coordinating operation of the high voltage components. The positioning of this controller is schematically shown in FIG. 6. The HVDC contains contactors or breakers which are normally positioned to an open configuration that prevents electricity from flowing thereacross. But when called on to take action and engage the battery  410 , for instance when starting of the engine  511  is required, these contractors (usually a pair) close completing an appropriate connective circuit.  
     [0038] As shown in FIG. 5, the HVDC serves as a shield or buffer between the high voltage battery  410 , and the inverters  534 , as well as other auxiliary loads run off of the electric power of the battery  410 . An example of such a high voltage auxiliary load may include an electrically run air-conditioning compressor system. In order to act as such a buffer, the high voltage output from the battery  410  must be relatively slowly “brought-up” to operating levels at the inverter  534  and/or auxiliary loads. In order to accept this “run-up” of the voltage, relatively small capacity contactors are initially closed that cause voltage from the battery to pass to a capacitor in either the inverter  534  or the appropriate auxiliary load, across a resistive circuit (a circuit containing buffering resistors). Once an appropriate pre-charge is built-up in the capacitor, primary contractors are then closed which complete the high voltage circuit between the batteries  410  and the capacitor contained within the receiving component which may be exemplified by the DC to AC inverter(s)  534 , or an auxiliary load such as an electric air-conditioning system as indicated hereinabove. In this manner, a potentially damaging high voltage is prevented from being introduced too quickly to the receiving components.  
     [0039] The HVDC  115  also carries out certain diagnostic functions regarding the components of the HVDC  115 , such as the contactors within the HVDC  115  itself, and also possibly the several systems interconnected through the HVDC, such as the battery  410 , the inverters  534 , or an electrically driven air-conditioning compressor which has not been illustrated in the Figures. Among other parameters, these diagnostics may be performed based on measurements of voltage and/or current.  
     [0040] The HVDC  115  also provides interconnection between an exterior charger connection (see ext. charger in FIG. 5), thereby allowing the battery  410  to be “plugged-in” for charging from an external power source.  
     [0041] The battery management controller (BMU)  110  handles control tasks relative to the battery system  410 . Among other characteristics, the BMU  110  can estimate and measure state-of-charge (SOC) levels, and voltage and current parameters. It can also sense/determine and maintain maximum and minimum voltage and current levels with respect to the battery  410 . Based on these determinations or sensed quantities/qualities, the VM  105 , via such control modules as the DTC  120 , can direct certain operations for affecting changes in the SOC of the battery  410 . Other characteristics which may be monitored include operating temperature(s) of the battery  410 , and voltages at the individual battery cells. Similarly, pressure within the cells can also be monitored. Failures may be detected and reported, at least back to the VCU; but there is also the possibility of the information being passed to the operator via the dashboard display unit  107 .  
     [0042] The DTC  120  makes the mode selection under which the several powering components will cooperate. That includes choices between parallel and split modes, as well as positive and negative split modes. The operational points for the several components of the drive train are also specified by the DTC  120 . Still further, reference values are provided by the DTC  120  for the several sub-systems, including the transaxle management control modules or unit (TMU)  230  and the engine control module or unit (ECM)  220 . From among the possible settings established by the DTC  120 , battery charging/discharging mode is a possibility, as well as specifying whether the generator  532  and/or motor  531  should be used in their powering capacity as a motor, or their generating capacity as a generator. Torque references for the generator and motor are also issued from the TMU  230 .  
     [0043] As a sub-component under the TMU  230 , the transaxle control unit TCU  232  handles the transaxle  530  with respect to torque compensation when starting and stopping the engine  511 . The TCU  232  uses and controls two slave processors characterized as a generator control unit GCU  236  and a motor control unit MCU  234 . The GCU  236  handles the current and torque control of the generator  532 ; typically, via the inverter  534 . The GCU  236  receives its torque and speed reference information from the TCU  232  as its immediate controller. The TCU  232  receives a total torque reference for the transaxle  530  and the speed reference value for the engine  511 , together with mode reference information regarding cooperation between the engine  511  and generator  532 ; such as, whether parallel-, positive-split, or negative-split mode configurations will be assumed. The TCU  232  generates the torque reference parameters for the generator  532  and motor  531 , each of which are implemented under the control of the GCU  236  and MCU  234 , respectively. The specified torque settings are accomplished by controlling the current provided to the respective generator/motor controllers  236 ,  234 .  
     [0044] Based on a map of optimal engine torque vs. speed curves, engine speed and torque are selected by the DTC  120  so that the engine system  510  can deliver the desired engine power and simultaneously lie on one of the engine&#39;s optimized efficient curves. If the DTC  120  determines that the speed of the engine  511  is too for efficient operation, then the engine  511  is turned (or left) off by the engine control unit  220 . If the power train control module  120  determines that the speed of the engine  511  is too high to be controlled by the generator  532  (based on SOC and generator limitations), the engine  511  is set to a slowed operational speed by the ECM  220 .  
     [0045] Once the speed, torque and power of the engine  511  are determined by the vehicle systems controller  100 , particularly at the DTC  120  of the controller  100 , then the DTC  120  further determines the required speed and torque of the generator  532  to control the engine  511 . The DTC  120 , using this information, then determines the required speed and torque of the motor  531  to meet the difference, if any, between driver power (torque) demand and the engine power (torque).  
     [0046] Torque determination and monitoring is also carried out at the VCU  100 . This function further ensures that torque delivered to the drive wheel(s)  20  is substantially equal to the torque (acceleration) demanded by the driver. The VCU  100  also monitors and controls the torque from the engine  511  and transaxle system  530  by comparing a sensed torque against the torque demanded by the driver. Torque management by the VCU  100  interprets driver inputs and speed control demands to determine regenerative brake torque and desired output shaft torque.  
     [0047] From the VCU  100 , commands and references are distributed over a controller area network (CAN)  300  to component controllers generally referenced herein utilizing reference numbers in the  200 &#39;s series. As indicated above, these controllers include the ECM  220  and the TMU  230  that together control the power train system to achieve efficient energy management, partition torque, determine engine  511  operating point (s), and decide on, and coordinate engine  511  start/stops. Commands and references from the VCU  100  to a series regenerative brake controller determine regeneration torque limitations, desired regenerative torque and zero vehicle speed control.  
     [0048] Finally, if and/or when individual system components are rendered inoperative, such as the motor  531  becomes disabled, the VCU  100  is configured to provide limited operating control over the power train system to allow the hybrid engine vehicle  10  to “limp” home.  
     [0049] As shown in FIG. 4, a preferred embodiment of an electronics cooling system  800  includes an electronics cooling loop  803 , an DC/AC inverter  534 , a DC/DC converter  405 , a electronics coolant pump  820  and a electronics radiator  805  in fluid communication with each other. The electronics coolant pump  820  may be located upstream of the DC/DC converter  405 . The electronics coolant flowing in the electronics cooling loop  803  transfers heat from the inverter  534  and/or converter  405  to the electronics radiator  805 . As the electronics coolant passes through the electronics radiator  805  heat is rejected from the electronics cooling loop  803 . In an alternative configuration, an electronics radiator fan  810  draws air across the electronics radiator  805  to promote the rejection of heat from the electronics cooling loop  803 .  
     [0050] As can be appreciated by those skilled in the art, a significant portion of the heat load from the electronics cooling system  800  can be shifted to the cooling system of the internal combustion engine  511  by including an alternator (driven by the internal combustion engine  511 ) in the 12 volt electrical system of the hybrid electric transporting vehicle  10 . Operation of the alternator (and therefore supply of 12 volt power) would not be affected by shut down of the DC/DC converter  405  due to heat. Such an independent source for the 12 volt system effectively shifts the heat load from the electronics cooling system  800  to the cooling system of the internal combustion engine  511  which is the drive source for the alternator. The use of the alternator with the DC/DC converter  405  provides redundancy in the 12 volt electrical system. Furthermore, the use of the alternator allows the DC/DC converter  405  to be reduced in size or completely eliminated. If small enough, the DC/DC converter  405  can be removed from the electronics cooling system  800 . By utilizing the alternator and/or properly positioning the DC/AC inverter  534 , DC/DC converter  405 , and radiator  805  in the engine room  11 , the electronics cooling pump  820  and/or the electronics radiator fan  810  can be reduced in size or even eliminated from the electronics cooling loop  803  without compromising the cooling capabilities of the electronics cooling system  800 . For example, by placing the electronics radiator  805  near the radiator or radiator fan for the internal combustion engine  511 , the electronics radiator fan  810  can be eliminated. Such reductions in size or elimination of components reduces vehicle weight and increases the amount of usable volume for other components of the hybrid electric transporting vehicle  10 .  
     [0051] In any of the embodiments described above, a temperature sensor  815  is positioned in the electronics cooling system  800  to sense a temperature condition in the electronics cooling loop  803 . The temperature sensor  815  communicates the temperature condition to a supervisory module. In a preferred embodiment, the temperature sensor  815  is positioned at the coolant inlet  817  of the DC/AC inverter  534 . In another embodiment, the temperature sensor  815  is positioned between the DC/DC converter  405  and the DC/AC inverter  534  to sense the temperature condition in the electronics cooling loop  803  as electronics coolant flows from the DC/DC converter  405  to the DC/AC inverter  534 .  
     [0052] Based upon the sensed temperature condition of the electronics cooling loop  803 , the supervisory module controls the operation of the DC/DC converter  405 . In a preferred embodiment, the supervisory module also controls the operational capacity of the DC/AC inverter  534  based upon the sensed temperature condition of the electronics cooling loop  803 . The supervisory module may also control the operation of the electronics radiator fan  810  and/or the electronics coolant pump  820  based upon the sensed temperature condition of the electronics cooling loop  803 .  
     [0053] In a preferred embodiment, the VCU  100  is the supervisory module and carries out control of the DC/DC converter  405 , DC/AC inverter  534 , electronics coolant pump  820 , and electronics radiator fan  810 . In addition to receiving and controlling in response to the sensed temperature of the electronics cooling loop  803 , the VCU  100  (or supervisory module) may consider ambient outside temperature, electronics radiator fan  810  speed, air conditioning system operational modes, lighting system operational modes, and/or battery system energy capacity and state-of-charge. Each of these aspects contribute individually and collectively to the cooling loop&#39;s  803  heat load. In the most preferred embodiment, control of the DC/AC inverter  534  is carried out at a lower level of the VCU  100 , namely the TMU  230 .  
     [0054] Another aspect of the present invention is a method of controlling the electronics cooling system  800 . The cooling method includes: arranging an electronics cooling loop  803  aboard a hybrid electric transport vehicle  10  in which a DC/DC converter  405 , DC/AC inverter  534  and an electronics radiator  805  are placed in fluid communication with each other, for cooling the DC/DC converter  405  and the DC/AC inverter  534 ; sensing a temperature condition in the electronics cooling loop  803 ; and discontinuing operation of the DC/DC converter  405  when a predetermined upper threshold temperature is sensed in the electronics cooling loop  803 . In an alternative method, the cooling method further includes reducing the operating capacity of the DC/AC inverter  534  when the predetermined upper threshold temperature condition is sensed. In a preferred alternative method, a stepped reduction of the DC/AC inverter&#39;s  534  operating capacity continues until the predetermined upper threshold temperature condition is sensed. In the most preferred alternative method, the stepped reduction results in discontinuing operation of the DC/DC converter  405  when the predetermined upper threshold temperature condition is sensed. The method contemplates the lower threshold temperature having a magnitude of approximately 57 centigrade when measuring the electronics coolant flowing between the DC/DC converter  405  and the DC/AC inverter  534 . The control method further contemplates the upper threshold temperature having a magnitude of approximately 60° centigrade when measuring the electronics coolant flowing between the DC/DC converter  405  and the DC/AC inverter  534 .  
     [0055] The control method may include the step of resuming operation of the DC/DC converter  405  after a predetermined time period elapses from the time of shutting down the DC/DC converter  405 . The method may also include the step of resuming operation of the DC/DC converter  405  when a predetermined resumptive temperature condition is sensed in the electronics cooling loop  803  before the expiration of the predetermined time period. The control method contemplates the predetermined resumptive temperature having a magnitude of approximately 55° centigrade when measuring the electronics coolant flowing between the DC/DC converter  405  and the DC/AC inverter  534 . The control method contemplates the predetermined time period to be calculated based on ambient outside temperature, electronics radiator fan  810  speed, air conditioning system operational modes, lighting system operational modes and/or battery system energy capacity. The control method may include a resumptive step which resumes operation of the DC/DC converter  405  when the predetermined resumptive temperature is lower than the predetermined lower threshold temperature. The control method may also include a resumptive step which resumes operation of the DC/DC converter  405  when a predetermined resumptive lower voltage (energy) limit of the 12 volt battery is lower than the predetermined lower threshold voltage (energy) level. In the most general form, the most preferred control method contemplates a hysteresis-type control strategy to shut down and resume operation of the DC/DC converter  534 .  
     [0056] Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken as a limitation. The spirit and scope of the present invention are to be limited only by the terms of any claims presented hereafter.