Abstract:
A method for isolating voltage sensor errors from contactor errors in an electrical system includes measuring a voltage between ground and a voltage bus rail when a contactor is open, and comparing the measured voltage to a first threshold voltage corresponding to a calibrated voltage reading that is expected when the contactor is closed. A first diagnostic code is recorded with a stuck-in-range status for the sensor when the measured voltage is greater than 0 and less than the first threshold voltage. A second diagnostic code is recorded with a stuck-closed status for the contactor when the measured voltage is equal to the first threshold voltage. The measured voltage may be compared to a second threshold voltage that exceeds the first threshold voltage, with a third diagnostic code recorded with a shorted value for the sensor when the measured voltage exceeds the first threshold voltage or is less than 0.

Description:
TECHNICAL FIELD 
     The present disclosure relates to a method and a system for isolating voltage sensor and contactor faults in an electrical system. 
     BACKGROUND 
     In hybrid electric and battery electric vehicles, a high-voltage DC battery pack provides some of the power necessary for propelling the vehicle. The battery pack energizes an inverter module over a high-voltage DC bus. The inverter module converts the DC voltage from the battery pack into an AC waveform, and thereafter energizes one or more motor/generator units over a high-voltage AC bus with the AC waveform. Torque from the motor/generator unit(s) may be used thereafter to provide input torque to a transmission or to generate electricity for recharging the battery pack. 
     The battery pack can be electrically isolated from the vehicle chassis and electrical components of the vehicle powertrain in part by selectively opening solid-state contactors under certain operating conditions, for instance upon vehicle shutdown or in the presence of a detected electrical fault. The conductive leads of one or more of the contactors can become stuck or welded closed. However, voltage sensors used for detecting a welded contactor condition can fail, thereby complicating the diagnosis and isolation of welded contactor and stuck-in-range voltage sensor faults. 
     SUMMARY 
     A method is disclosed herein for isolating an electrical fault in an electrical system. The system may be a high-voltage (HV) vehicle such as a hybrid, extended-range, or battery electric vehicle, or any other electrical system using a battery pack, an electrical load, and a contactor that selectively connects/disconnects the battery pack from the electrical load. 
     The method includes measuring, via a voltage sensor, a voltage between ground and a conductive rail of a voltage bus in an electrical system having a voltage source and an electrical load that is selectively connectable to the voltage source via a contactor. The method also includes receiving the measured voltage from the voltage sensor using a controller when the contactor is open, then comparing the received measured voltage signal to a first threshold voltage that corresponds to an expected voltage reading of the voltage sensor when the contactor is closed. 
     A first diagnostic code is recorded in a memory device of the controller, with a stuck-in-range failure status for the voltage sensor, when the received measured voltage signal is greater than 0 and less than the first threshold voltage. A second diagnostic code is recorded in the memory device, with a stuck-closed status for the contactor, when the received voltage signal is equal to the first threshold voltage. 
     The method may include recording a third diagnostic code in the memory device, with a shorted value for the voltage sensor, when the received measured voltage exceeds the first threshold voltage or is less than 0. 
     A system is also disclosed herein that includes a voltage source, a voltage bus, a contactor, an electrical load, a voltage sensor, and a controller. The electrical load is selectively connected to and disconnected from the voltage source over the voltage bus via the contactor. The voltage sensor is configured to measure a voltage between the voltage bus and electrical ground. The controller receives the measured voltage from the voltage sensor when the contactor is open, and then compares the received measured voltage to a first threshold voltage that corresponds to an expected voltage reading when the contactor is closed. 
     The controller also records a first diagnostic code, with a stuck-in-range failure status for the voltage sensor, when the received measured voltage is greater than 0 and less than the first threshold voltage. A second diagnostic code, with a stuck-closed status for the contactor, is recorded in the alternative when the received measured voltage is equal to the first threshold voltage. 
     Additionally, a vehicle includes a battery pack, a transmission, a motor/generator unit connected to the transmission, a voltage bus having a positive and a negative rail, and a pair of contactors, with a first contactor connected to the positive rail and a second contactor connected to the negative rail. The vehicle also includes a power inverter module that is selectively connected to and disconnected from the battery pack over the voltage bus via the pair of contactors, a first voltage sensor that measures a voltage between electrical ground and the positive rail, a second voltage sensor that measures a voltage between electrical ground and the negative rail, and a controller. The controller executes the method noted above to isolate failures of the voltage sensors from failures of the contactors. 
     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 an example vehicle having a controller that isolates a voltage sensor fault from a contactor fault. 
         FIG. 2  is a schematic illustration of a control circuit that can be used within the vehicle shown in  FIG. 1 . 
         FIG. 3  is a time plot of example DC reference voltages that describes an aspect of the present method for isolating faults using the circuit shown in  FIG. 2 . 
         FIG. 4  is a flow chart describing an example method for isolating a voltage sensor fault from a contactor fault in the vehicle shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, wherein like reference numbers refer to like components, and beginning with  FIG. 1 , an example vehicle  10  is shown that includes a voltage source in the form of a battery pack  16 , voltage sensors  34 , a set of solid-state contactors  40 , and a controller  50 . As described in detail below with reference to  FIGS. 2-4 , the controller  50  is configured to selectively execute steps of a method  100  to isolate high-voltage electrical faults aboard the vehicle  10 , specifically a “stuck-in-range” fault of the voltage sensors  34  and a “stuck-closed” fault of the contactors  40 . The method  100  may be used in any electrical system employing a voltage source, whether a battery, fuel cell, capacitor, or other electrical or chemical voltage supply, that is disconnected from an electrical load via activation of a mechanical/solid-state switch, relay, or contactor like the contactors  40  described herein. However, for illustrative consistency the example vehicle  10  will be explained in the examples that follow. 
     The vehicle  10  includes at least one motor/generator unit (MGU)  14  having a motor output shaft  22 . The motor output shaft  22 , which is coupled to a transmission  12 , delivers input torque (arrow T I ) to the transmission  12  as needed for powering the vehicle  10 . The transmission  12  may include one or more simple or compound planetary gear sets connected via one or more clutches to a final drive assembly (not shown). Output torque (arrow T O ) from the transmission  12  is ultimately delivered to a set of drive wheels  30  via a drive axle  32 . 
     Depending on the embodiment, other power sources may be used, such as another MGU  15  with a motor output shaft  28  and/or an internal combustion engine  17 , both of which are shown in phantom in  FIG. 1 . When the engine  17  is used as part of the powertrain, an input damping clutch  25  may be used to selectively connect or disconnect the engine  17  from the driveline, and to dampen driveline vibration, e.g., in conjunction with an engine restart event. 
     The battery pack  16  is electrically connected to a power inverter module (PIM)  18  via a high-voltage DC bus  20  and the contactors  40 . In turn, the PIM  18  is electrically connected to the MGU(s)  14  and/or  15  via a high-voltage AC bus  21 . As used herein, the term “high voltage” refers to a voltage level in excess of the auxiliary/12 VDC voltage levels normally used to power auxiliary vehicle systems such as audio systems, lighting, and the like. The battery pack  16  may be rated for approximately 60 VDC to over 300 VDC. In some configurations the battery pack  16  may store 300 VDC or more. The PIM  18  may be controlled via pulse-width modulation and high-speed semiconductor switching, as is well understood in the art, to convert AC power from the MGU(s)  14  and/or  15  into DC power suitable for storage in the battery pack  16 , and to convert stored DC power to AC power as needed for powering the MGU(s)  14  and/or  15 . 
     To facilitate pre-charging of the PIM  18 , i.e., to ensure charge balancing between the battery pack  16  and the PIM  18  prior to closing the contactors  40 , a resistor  58  and an additional contractor  42  may be placed in electrical parallel with the contactors  40  as shown. The controller  50  can close the additional contactor  42  prior to closing the contactors  40 , with the resistor  58  limiting the rate of current flow into the PIM  18 , as will be readily appreciated by one of ordinary skill in the art. Additional contactors (not shown) may be present in the vehicle  10  as needed between a given electrical load and the battery pack  16  or any other voltage source, e.g., a fuel cell. 
     The contactors  40  and any other contactors used aboard the vehicle  10  may be variously embodied as single-pole, single-throw relay devices, as solid-state switches, or as any other physical switching device. Under certain conditions, the contactors  40  may fail in such a manner as to not open or break their respective electrical connections when commanded to do so. For example, a mechanical failure such as a broken spring may prevent the contactor  40  from opening. Likewise, an electrical fault or a control fault could force one of the contactors  40  to either open or close with an excessive or incorrect load across its terminals, which in turn could lead to a welded contactor or other “stuck-closed” contactor condition. 
     Additionally, the voltage sensors  34  may experience a stuck-in-range fault, or may simply fail to work at all. Diagnosis of the voltage sensors  34  depends on the properly diagnosed open/closed state of the contactors  40 . However, the accurate detection of an open/closed state of the contactors  40  depends on the validity of the voltage measurements provided by the voltage sensors  34 . The present method  100 , as executed by the controller  50 , therefore allows the controller  50  to distinguish a stuck-in-range failure of the voltage sensors  34  from a stuck-closed fault of the contactors  40  using the same measured voltage signals (arrows  55 ) as provided by the voltage sensors  34 . 
     With respect to the controller  50  shown in  FIG. 1 , this hardware/software device receives the voltage signals (arrows  55 ) over a controller area network (CAN) bus or other suitable communications channel, and then executes recorded instructions or code embodying the method  100  from a tangible, non-transitory memory device  54 . Execution of the method  100  allows a processor  54  to perform the various required calculations and threshold comparisons as explained in detail below with reference to  FIGS. 2-4 . 
     The controller  50  may be configured as a digital computer having the processor  52  and memory device  54  as two of its main components. The memory device  54  maybe embodied as read only memory (ROM), flash memory, or other suitable magnetic or optical storage media. The controller  50  may also include any required amount of transitory memory such as random access memory (RAM) and electrically-erasable programmable read only memory (EEPROM). Other components may include 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. 
     Referring to  FIG. 2 , an example control circuit  13  includes an auxiliary voltage source  38 , as well as the voltage sensors  34  and the controller  50  noted above with reference to  FIG. 1 . The auxiliary voltage source  38  provides a reference voltage (arrow V R ), e.g., 5 VDC. The auxiliary voltage source  38  may be configured as a DC battery or as a reduced-voltage DC output from a DC-DC converter (not shown). One voltage sensor  34  is used per conductor or rail of the high-voltage DC bus  20  shown in  FIG. 1 , with the rails  20 + and  20 − representing the respective positive and negative rails of the high-voltage DC bus  20 . In some embodiments, only one voltage sensor  34  and only one conductive rail may be used. While the use of dual positive and negative rails  20 +,  20 − provides a current path in the event of a stuck-closed fault of one of the rails  20 + or  20 −, and thus retention of some level of electrical functionality relative to a single rail embodiment, execution of the present method  100  proceeds in the same manner regardless of the number of rails that are used. 
     The reference voltages (arrows V R ) as shown in  FIG. 2  drive the voltage sensors  34 . When two voltage sensors  34  are used as shown, one voltage sensor  34  reads a first voltage (V 1 ) between electrical ground, e.g., the chassis ground  26 , and the positive rail  20 + while the other voltage sensor  34  reads a second voltage (V 2 ) between the chassis ground  26  and the negative rail  20 −. The chassis ground  26  in a non-vehicular embodiments may be any grounded component of a given system being diagnosed via the method  100 . The voltage sensors  34  transmit their respective measured voltages as voltage signals (arrows  55 ) to a corresponding pin  56  or  59  of the controller  50 , with the first voltage (V 1 ) being transmitted to pin  56  and the second voltage (V 2 ) being transmitted to pin  59 . The controller  50  then processes the received voltage signals (arrows  55 ) and generates a suitable diagnostic output signal (arrow  60 ) as a control action. 
     Referring to  FIG. 3 , a time plot  70  is used to describe an example range of DC voltage outputs from the voltage sensors  34  shown in  FIGS. 1 and 2 . A typical embodiment is a voltage sensor  34  rated for 5 VDC. In such a design, the DC voltage range is 0-5 VDC, and the reference voltage (arrows V R ) of  FIG. 2  is 5 VDC. Because the actual voltage rating of the battery pack  16  shown in  FIG. 1  can vary with the application, the sensor output range of the voltage sensors  34  is indexed to the actual operating range of the power source. 
     As an example, the battery pack  16  of  FIG. 1  may have a nominal rating of 300 VDC. In this instance, when a single contactor  40  is used for a single bus rail, 4.5 VDC corresponds to 300 VDC and 0.5 VDC corresponds to 0 VDC, leaving a 0.5 VDC voltage offset at the upper and lower ends of the DC voltage range. In the embodiment of  FIG. 1  in which the DC bus  20  has two conductive rails  20 + and  20 −, each rail carries 50% of the voltage of the battery pack  16 , for instance 150 VDC. 
     The 0.5 VDC voltage offset can be used to diagnose an additional fault condition. Results falling above 4.5 VDC (region  72 ) or below 0.5 VDC (region  74 ) respectively correspond to shorted/out-of-range high and shorted/out-of-range low faults for the voltage sensors  34 . Regions  78  and  79  correspond to stuck-in-range faults for the voltage sensors  34 . Region  75  corresponds to stuck-closed fault of the contactor  40 . Region  76  corresponds to a passing diagnostic if a measured value falls in this region when the contactors  40  are open. If a measurement falls within region  76  when the contactors  40  are closed, this corresponds to one of two fault conditions: an open contactor  40  or a stuck-in-range fault for the voltage sensors  34 . Placement of a particular measurement in one of these regions is achieved via execution of the method  100 , an example of which is now described with reference to  FIG. 4 . 
     Referring to  FIG. 4  in conjunction with the structure shown in  FIGS. 1 and 2 , the controller  50  determines at step  102  whether a set of enabling conditions are present for performing voltage fault isolation. Because the contactors  40  are automatically opened when the vehicle  10  is not running, for instance while the vehicle  10  is parked in a garage or while the battery pack  16  is actively charging, step  102  may include detecting whether the vehicle  10  is “awake” or otherwise operating in a state in which the contactors  40  are commanded open. For other configurations evaluating different contactors  40 , i.e., at a location other than between the battery pack  16  and the PIM  18  as shown in  FIG. 1 , the enabling conditions of step  102  may be different. Once suitable enabling conditions have been detected at step  102 , the method  100  proceeds to step  104 . 
     At step  104 , the controller  50  receives the measured voltage signals (arrows  55 ) from the voltage sensor(s)  34 , temporarily records these values via the memory device  54 , and then proceeds to step  106 . 
     At step  106 , the controller  50  next determines whether the received voltage measurements (arrows  55 ) from step  104  is greater than 0 VDC but less than a voltage expected when the contactor  40  is closed, i.e., 50% of the maximum output voltage of the battery pack  16  when dual contactors  40  are used. If so, the method  100  proceeds to step  108 . The method  100  also proceeds to step  108  when the received voltage signals (arrows  55 ) exceed the voltage expected when the contactor  40  is in a closed position. The value when the contactor  40  is closed corresponds, as noted above with reference to  FIG. 3 , to 4.5 VDC when using a 5 VDC max sensor rating. Thus, values corresponding to the criteria of step  106  fall within the regions  78  and  79  shown in  FIG. 3 . If neither case applies, the method  100  proceeds in the alternative to step  110 . 
     At step  108 , the controller  50  records, via a diagnostic signal (arrow  60 ) of  FIGS. 1 and 2 , a diagnostic code having a status indicating that the voltage sensor  34  is stuck-in-range. Suitable control actions may be taken as needed after recording this status, for instance repair or replacement of the voltage sensor(s)  34 . 
     At step  110 , the controller  50  determines whether the received voltage signals (arrows  55 ) from step  104  convey a value that is equal to the voltage expected when the contactor  40  is closed, e.g., 2.25 VDC for a single contactor  40  in the dual contactor configuration of  FIG. 1 , i.e., region  75  of  FIG. 3 . If so, the method  100  proceeds to step  112 . Otherwise, the method  100  proceeds to step  111 . 
     At step  111 , the controller  50  next determines whether an out-of-range high or an out-of-range low value is present. If so, the method  100  proceeds to step  114 . Otherwise, the method  100  proceeds to step  116 . 
     At step  112 , the controller  50  records, via diagnostic signal (arrow  60 ) of  FIGS. 1 and 2 , a diagnostic code having a status indicating that contactor  40  is stuck-closed. As with step  108 , suitable control actions may be taken as needed as part of step  112  after recording this status, for instance repair or replacement of the contactor(s)  40 . 
     At step  114 , the controller  50  records, via the diagnostic signal (arrow  60 ) of  FIGS. 1 and 2 , a diagnostic code having a status indicating that one of two conditions is present: a shorted/out-of-range high fault (region  72  of  FIG. 1 ) and a shorted/out-of-range low fault (region  74  of  FIG. 3 ) for the voltage sensor(s)  34 . Suitable control actions may be taken as needed as part of step  114  after recording this status, for instance repair or replacement of the voltage sensor(s)  34 . 
     At step  116 , the controller  50  records, via the diagnostic signal (arrow  60 ) of  FIGS. 1 and 2 , a diagnostic having a status indicating that all diagnostics have passed for the contactors  40  and the sensor(s)  34 . 
     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.