Abstract:
A vehicle includes a high-voltage (HV) energy storage system (ESS), an HV power bus, a DC-DC power converter electrically connected to the HV power bus, an HV bus connector, a low voltage (LV) battery power bus, and a pair of LV bus connectors. The vehicle includes a vehicle module electrically connected to the HV and LV bus connectors, an LV power bus electrically connected to the DC-DC power converter and to the module, and a controller. The controller has an algorithm that controls the converter to power the module via one of the LV bus connectors during a transient LV condition. The converter and a method of controlling the same are also provided, with the method including determining the LV condition, powering the vehicle module via one of the LV bus connectors during the transient LV condition, and powering the module via the other LV connector otherwise.

Description:
TECHNICAL FIELD 
     The present invention relates to an apparatus and method for supplying low-voltage power aboard a vehicle during a transient low-voltage condition. 
     BACKGROUND OF THE INVENTION 
     One method of reducing vehicle fuel consumption is to selectively shut down the engine when engine output torque is not required, such as when the vehicle is temporarily parked at a stop light or idling in heavy traffic. Power delivered by an engine-driven generator to onboard low-voltage (LV) loads is discontinued when the engine is off. Therefore, LV loads are typically supplied by a 12-volt battery, another LV power source, and/or an LV battery/standard vehicle power bus. 
     Various onboard control modules are used to ensure proper vehicle functionality and control. Such modules may include a Traction Power Inverter Module or TPIM adapted for inverting direct current (DC) power to alternating current (AC) power and vice versa, a Vehicle Integration Control Module or VICM adapted for supplying power to a set of high-voltage (HV) battery relays or contactors, i.e., for HV contactor control, engine controllers, Vehicle Braking Modules, Vehicle Steering Modules, etc. Some or all of these vehicle modules may automatically reset whenever a voltage level on the standard vehicle power bus drops below a minimum threshold voltage. 
     SUMMARY OF THE INVENTION 
     Accordingly, a vehicle is provided herein that includes an engine, a high-voltage (HV) energy storage system (ESS), an HV power bus electrically connected to the ESS, a low-voltage (LV) battery power bus, and a DC-DC power converter electrically connected to the HV power bus. The DC-DC converter has an HV bus connector and a pair of different LV bus connectors, i.e., a power feed from the LV battery power bus and an independent buffered supply, thus supplying redundant LV power. Additionally, the vehicle includes one or more vehicle modules each electrically connected to the different LV bus connectors of the DC-DC converter, with the LV battery power bus being electrically connected to the DC-DC power converter and the vehicle module(s). Aboard the vehicle, a controller having a power flow control algorithm controls the DC-DC power converter. In particular, the controller powers the vehicle module(s) via the different LV bus connectors during a predetermined transient LV condition. 
     A DC-DC power converter is also provided for a vehicle having an HV ESS, an HV power bus, an LV battery power bus, and a vehicle module that is electrically connected to the DC-DC power converter. The converter includes HV and LV bus connectors as noted above, and powers the vehicle module(s) via a different LV feed during the transient LV condition, and via the other LV connector when the predetermined transient LV condition is no longer present. 
     A method is also provided for controlling a DC-DC power converter aboard a vehicle having an HV ESS, an HV power bus, an LV battery power bus, and a vehicle module that is electrically connected to the converter. The method includes determining the presence of a predetermined transient LV condition aboard the vehicle, powering the vehicle module with LV via one of a pair of LV bus connectors during the transient LV condition, and powering the vehicle module via the other LV bus connector when the transient LV condition is no longer present. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a vehicle having a DC-DC power converter, and a controller adapted for controlling an operation of the DC-DC power converter; 
         FIG. 2  is a schematic electric logic diagram for a vehicle module usable with the vehicle shown in  FIG. 1 ; 
         FIG. 3  is a table describing possible low-voltage levels for the vehicle modules of the vehicle shown in  FIG. 1 ; and 
         FIG. 4  is a flow chart describing an algorithm for controlling the DC-DC power converter aboard the vehicle shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures,  FIG. 1  shows a vehicle  10 . The vehicle  10  may be configured as any vehicle having a secondary power source, including but not limited to a hybrid electric vehicle (HEV). The vehicle  10  includes an internal combustion engine (E)  14  having an output member  20 . The vehicle  10  also includes a transmission (T)  16  having an input member  22  and an output member  24 . Output member  20  of engine  14  may be selectively connected to the input member  22  of the transmission  16  via a clutch  18 . The transmission  16  may be configured as an electrically-variable transmission or any other suitable transmission capable of transmitting torque to wheels  17  via the output member  24 . 
     The vehicle  10  includes a top-level controller (C)  12  having a power flow control algorithm  100 , which is described in detail below with reference to  FIG. 4 . The controller  12  is adapted for controlling power flow aboard the vehicle  10 , and in particular for coordinating, via a DC-DC power converter  28 , a secondary LV power output or bus connector independently of the main functionality of the converter, and that allows dedicated power feeds to be routed to designated vehicle control modules. Power may be routed to these modules during a predetermined transient LV condition, e.g., a cold engine cranking and starting event according to one possible embodiment. 
     The vehicle  10  also includes at least one HV electric motor/generator unit (MGU), e.g., a multi-phase electric machine of approximately 60 volts to approximately 300 volts or more depending on the vehicle design. In the embodiment shown in  FIG. 1 , the vehicle  10  is configured as a two-mode HEV having first and second MGUs, i.e., MGU  26 A and  26 B, respectively. Each MGU is electrically connected to an HV DC power bus  29  via an HV alternating current (AC) power bus  29 A, a Traction Power Inverter Module (TPIM)  27 , i.e., a control module adapted for inverting DC power to AC power and vice versa as needed, and a Vehicle Integration Control Module (VICM)  31 , i.e., a control module adapted for supplying power to HV battery contactors  11 . The vehicle  10  includes an HV energy storage system (ESS)  25 , e.g., a rechargeable battery, that may be selectively recharged using the MGUs  26 A and/or  26 B when the MGUs are operating as generators, for example by capturing energy during a regenerative braking event. 
     As understood by those of ordinary skill in the art, cranking and starting of an engine exerts a substantial, albeit a transient, LV electrical load on the onboard power supplies, thus causing an auxiliary voltage level aboard the vehicle  10  to rapidly drop. The reduced LV level may be sustained for as long as  100  milliseconds after initiation of the cranking and starting event. Such an LV level could cause the TPIM  27  and/or the VICM  31 , or other vehicle modules or HV loads  33 , to automatically reset as noted above, with a temporary loss of their respective functionalities. 
     Still referring to  FIG. 1 , the DC-DC power converter  28  is electrically connected to the HV ESS  25  via the HV power bus  29 . Converter  28  is also electrically connected to an auxiliary battery  41 , e.g., a 12-volt DC battery, via an LV battery power bus  19 , referred to also as an LV bus for simplicity, ultimately energizing one or more LV auxiliary systems  45 , e.g., windshield wipers, radio, seat warmers, etc. Converter  28  includes internal LV bus connectors  50 A,  50 B, which are connected in parallel without the possibility of back-feeding, as is understood in the art, and which feed the LV bus  19 , i.e., the standard bus, and an independent buffered LV supply  99 . LV supply  99  provides a fixed voltage that can power designated vehicle modules via the DC-DC power converter  28 . 
     As noted above, the designated vehicle modules may include, according to one possible embodiment, the TPIM  27  and/or the VICM  31 , with other vehicle modules being usable with the DC-DC power converter  28  depending on the design of vehicle  10 . Converter  28  may be configured as either or both of a step-down/buck converter and a step-up/boost converter. Converter  28  provides redundant LV power to the designated vehicle modules via the LV bus connectors  50 A,  50 B, LV power bus  19 , and LV supply  99 , respectively. Hardware and software complexity, as well as buck circuit-related power loss, may be sufficiently reduced by removing LV boost circuitry that would otherwise be required. 
     Controller  12  may be configured as a single or a distributed control device that is electrically connected to or otherwise in hard-wired or wireless communication with each of the engine  14 , the MGUs  26 A and  26 B, the ESS  25 , the DC-DC converter  28 , the TPIM  27 , the VICM  31 , and auxiliary battery  41  via one or more control channels (arrow  51 ). Control channels  51  may include any required transfer conductors, e.g., a hard-wired or wireless control link(s) or path(s) suitable for transmitting and receiving the necessary electrical control signals for proper power flow control and coordination aboard the vehicle  10 . The controller  12  may include such modules and capabilities as might be necessary to execute all required power flow control functionality aboard the vehicle  10  in the desired manner. 
     The controller  12  may be configured as a general purpose digital computer generally comprising a microprocessor or central processing unit, read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) and digital-to-analog (D/A) circuitry, and input/output circuitry and devices (I/O), as well as appropriate signal conditioning and buffer circuitry. Any algorithms resident in the controller  12  or accessible thereby, including the algorithm  100  in accordance with the invention as described below with reference to  FIG. 4 , may be stored in ROM and executed by the controller  12  to provide the respective functionality. 
     Referring to  FIG. 2 , the designated vehicle module to be supplied with LV power is represented as the TPIM  27  or the VICM  31 . Internally, the voltage connections are identical, and therefore the actual vehicle module may vary without departing from the intended inventive scope. The vehicle module is supplied via LV bus connectors  50 A,  50 B, which selectively powers the module via the LV bus  19  and the redundant LV power supply  99 , respectively. A first voltage level (V 1 ) is present via LV connector  50 A and LV bus  19 , while a second voltage level (V 2 ) is present on LV bus connector  50 B and supply  99 . Voltages (V 1 , V 2 ) may be comparatively processed by an OR gate  61  or other suitable logic. Gate  61  feeds the designated vehicle module(s) power supply  64 . Gate  61  may be configured to ensure that the voltage from one of the LV bus connectors  50 A,  50 B feeds designated vehicle module(s) power supply  64  with at least a threshold voltage level. 
     Referring to  FIG. 3 , a voltage table  70  shows possible values for V 1  and V 2  on LV power bus  19  and supply  99  respectively, as shown in  FIG. 2 . For example, if V 1  is 4.5 VDC and V 2  is 13.0 VDC, with a threshold of 9.0 VDC, the designated vehicle module(s) power supply  64  may be fed by V 2  and LV supply  99 , i.e., a fixed 13.0 VDC supply in one embodiment, up to approximately 16.0 VDC in another embodiment. If V 1  on LV power bus  19  is 13.8 VDC and V 2  on supply  99  is any other value, the designated vehicle module(s) power supply  64  may be fed by V 1 , i.e., by LV bus connector  50 A connecting to the LV power bus  19  reducing the DC-DC conversion losses. 
     Referring to  FIG. 4  in conjunction with the vehicle  10  shown in  FIG. 1 , the algorithm  100  begins at step  102 , wherein a predetermined transient LV condition is detected. For example, if the engine  14  is cranked and started, the algorithm  100  proceeds to step  104 , otherwise repeating in a loop until the transient LV condition is detected. 
     At step  104 , the algorithm  100  determines whether the LV levels to the designated vehicle module(s) are sufficiently high. If so, the algorithm  100  proceeds to step  108 . If not, the algorithm  100  proceeds to step  106 . 
     At step  106 , LV power is designated via the LV power bus  19  via bus connector  50 A. The algorithm  100  then proceeds to step  110 . 
     At step  108 , the LV bus connector  50 B of DC-DC power converter  28  powers the designated vehicle module, e.g., the TPIM  27  or VICM  31  in one embodiment, via LV power supply  99 . The algorithm  100  then proceeds to step  110 . 
     At step  110 , LV voltages and other LV loads are continuously monitored, with the algorithm periodically repeating step  104  to determine if there has been a change. 
     Using the algorithm  100 , the DC-DC power converter  28  can output a voltage in the range of approximately 9.0 VDC to approximately 16.0 VDC, and with a nominal output of approximately 13.8 VDC, to any designated modules, using the LV power bus  19  and supply  99 . If the HV level on the HV power bus  29  drops below a threshold, as may be determined by the lower limit of the operating range of the DC-DC power converter  28 , the LV bus connector  50 A allows the LV power bus  19  to supply substantially all of the power needed to sustain the designated vehicle modules on the LV power bus alone. The LV bus connectors  50 A,  50 B may be adapted to use forward bias/reverse bias diode properties in order to turn the converter  28  on and off as needed to selectively feed the designated vehicle modules, or to connect the modules to the LV power bus  19 . 
     Throughout execution of algorithm  100 , the designated vehicle modules can monitor the voltage on the LV power bus  19 , i.e., the standard vehicle bus voltage, on the anode-side of the LV bus connectors  50 A,  50 B, thus verifying and providing feedback that the DC-DC power converter  28  is still providing a voltage output to these modules, and that the standard LV bus voltage is still available. DC-DC converter  28  thus provides an independent feed to designated vehicle modules, such that the LV levels on the LV bus  99  are not pulled down if the DC-DC converter  28  fails to provide power to the LV power bus  19  and a transient event occurs. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.