Abstract:
Methods and systems for detecting a motor shorting relay failure. Exemplary embodiments include methods and systems for determining a motor shorting relay failure in a motor, the motor having first phase winding in a first leg of the motor, a second phase winding in a second leg of the motor, and a third phase winding in a third leg of the motor, the method including applying a first voltage signal to the first leg, applying a second voltage signal to the second leg, applying a test voltage to a test circuit electrically coupled to the third leg, measuring a third voltage signal in the third leg at a first predetermined time in response to the application of the first and second voltage signals and determining a motor shorting relay in the motor, based on the amplitude of the third voltage signal.

Description:
BACKGROUND 
       [0001]    This invention relates generally to vehicle steering devices, and more particularly, to a system and a method for detecting a motor shorting relay failure. 
         [0002]    The term “active steering” relates to a vehicular control system, which generates an output that is added to or subtracted from the front steering angle, wherein the output is typically responsive to the yaw and/or lateral acceleration of the vehicle. Active front control steering may improve vehicle-handling stability on a variety of road conditions. Stability control may be continuously active. For higher vehicle speeds, vehicle sensitivity of steering may be smaller. At lower vehicle speeds, park solution sensitivity may be increased and driver workload reduced. Thus, in some situations, an active steering control system may react more quickly and accurately than an average driver to correct transient handling instabilities. In addition, active steering can also provide for variable steering ratios in order to reduce driver fatigue while improving the feel and responsiveness of the vehicle. For example, at very low speeds, such as that which might be experienced in a parking situation, a relatively small rotation of the hand-wheel may be supplemented using an active steering system in order to provide an increased steering angle to the steerable road wheels. 
         [0003]    An active rear steering (ARS) system utilizes a three phase brushless DC motor to position rear wheels of a vehicle. When the active rear steering system is not activated, it is desirable to short three phase windings of the DC motor together by closing a pair of electrical contacts to generate a braking force to prevent movement of the rear wheels by the DC motor. If the pair of electrical contacts does not have a closed operational position when the active rear steering system is not activated, the braking force is not generated. 
         [0004]    Alternately, when the active rear steering system is activated, it is desirable to open the pair of electrical contacts to allow desired operation of the DC motor. It is further desired that the electrical conductivity of the two contacts of the motor shorting relay be verified. If the pair of electrical contacts does not have an open operational position when the active rear steering system is activated, the operation of the motor is degraded. In addition, partial failure of the relay cannot be detected. 
         [0005]    There is a recognized need for a system and a method for detecting a motor shorting relay failure. 
       SUMMARY 
       [0006]    Disclosed herein is a method for determining a motor shorting relay failure in a motor, the motor having first phase winding in a first leg of the motor, a second phase winding in a second leg of the motor, and a third phase winding in a third leg of the motor, the method including applying a first voltage signal to the first leg, applying a second voltage signal to the second leg, applying a test voltage to a test circuit electrically coupled to the third leg, measuring a third voltage signal in the third leg at a first predetermined time in response to the application of the first and second voltage signals and determining a motor shorting relay in the motor, based on the amplitude of the third voltage signal. 
         [0007]    Further disclosed herein is a system for determining a motor shorting relay failure in a motor, the motor having first phase winding in a first leg of the motor, a second phase winding in a second leg of the motor, and a third phase winding in a third leg of the motor, the system including a motor circuit having three legs, each of the legs having a drive circuit transistor arrangement, each arrangement being electrically coupled to a respective phase winding, a test circuit electrically coupled to each of the drive circuit test arrangements and a voltage measurement node electrically coupled to each of the drive circuit transistor arrangements, a processor electrically coupled to the motor circuit, the processor configured to induce the motor circuit to apply a first voltage signal to the first leg and a second voltage signal to the second leg, to induce the test circuit in the third leg to induce a test voltage to the third leg, and to measure a response voltage from the third leg. 
         [0008]    Further disclosed herein is a computer-readable medium having computer-executable instructions for performing a method including applying a gate voltage signal to a transistor in a first leg of a drive circuit electrically coupled to a motor circuit, applying a gate voltage signal to a transistor in a second leg of the drive circuit, applying a test voltage to a test circuit electrically coupled to a third leg of the drive circuit, measuring a response voltage from the third leg and determining the presence of a motor shorting relay failure in the motor circuit in response to the response voltage. 
         [0009]    The above-described and other features will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The embodiments will now be described, by way of an example, with references to the accompanying drawings, wherein like elements are numbered alike in the several figures in which: 
           [0011]      FIG. 1  is a block diagram of an active rear steering system of a vehicle having a processor, a motor control circuit, and a motor; 
           [0012]      FIG. 2  is an electrical schematic of the active rear steering system of  FIG. 1 ; 
           [0013]      FIG. 3  is an electrical schematic of the active rear steering system of  FIG. 2  with the inclusion of test circuits; 
           [0014]      FIG. 4  illustrates an exemplary methodology for the detection of a motor shorting relay failure; 
           [0015]      FIG. 5  illustrates an equivalent circuit of two drive legs and a test leg; 
           [0016]      FIGS. 6 and 7  illustrate exemplary voltage and current responses for various values of the test resistor with a V test ; and 
           [0017]      FIG. 8  illustrates an exemplary output voltage and current response for a variation of L a . 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0018]    Referring to  FIG. 1 , a vehicle  10  having an active rear steering system  12  is illustrated. The active rear steering system  12  has an active operational state where the system  10  is utilized to move the rear vehicle wheels  32 ,  34  to desired rotational positions. Further, the active rear steering system  12  has an inactive operational state where the system  10  does not move the rear vehicle wheels  32 ,  34 . The active rear steering system  12  includes a motor  14 , a drive mechanism  18 , a steering rack  20 , a rack shaft  22 , tie rods  24 ,  26 , knuckle arms  28 ,  30 , rear vehicle wheels  32 ,  34 , a processor  36 , and a motor control circuit  38 . 
         [0019]    The motor  14  is provided to drive the drive mechanism  18  for moving the vehicle wheels  32 ,  34  to predetermined positions. Referring also now to  FIG. 2 , which is an electrical schematic of the active rear steering system of  FIG. 1 , the motor  14  includes phase windings  40 ,  42 ,  44 , electrical contacts  46 ,  48 ,  49  and the rotor  45 . The phase winding  40  is electrically coupled between a node of  46  and a node  47 . The phase winding  42  is electrically coupled between node  48  and the node  47 . Further, the phase winding  44  is electrically coupled between a node  49  and the node  47 . The phase windings  40 ,  42 ,  44  can be energized via the motor control circuit  38  to induce the rotor shaft  45  to rotate in either a first direction or a second direction opposite the first direction. The drive mechanism  18  converts the rotational motion of the rotor shaft  45  to a linear motion of the steering rack  20  and the rack shaft  22 . The rack shaft  22  is operably coupled to the tie rods  24 ,  26  that are further operably coupled to the knuckle arms  28 ,  30 , respectively. Further, the knuckle arms  24 ,  26  are operably coupled to the rear vehicle wheels  32 ,  34  respectively. When the motor shaft  45  rotates in a first rotational direction, the rack shaft  22  is moved in a first linear direction. In response, the tie rods  24 ,  26  and the knuckle arms  28 ,  30  induce the vehicle wheels  32 ,  34 , respectively, to rotate in a first predetermined direction about steering axes  39 ,  41 , respectively, associated with the vehicle wheels  32 ,  34 , respectively, toward a desired rear vehicle wheel steering angle. Alternately, when the motor shaft  45  rotates in a second rotational direction, the rack shaft  22  is moved in a second linear direction, opposite the first linear direction. In response, the tie rods  24 ,  26  and the knuckle arms  28 ,  30  induce the vehicle wheels  32 ,  34 , respectively, to rotate in a second predetermined direction about steering axes  39 ,  41  respectively, associated with the vehicle wheels  32 ,  34 , respectively, toward a desired rear vehicle wheel steering angle. 
         [0020]    When the active rear steering system  12  is in an inactive operational state, the electrical contacts  86 ,  88  are provided to have closed operational states, triggered by motor relay  95 . When the electrical contacts  86 ,  88  have the closed operational state, the motor  14  is prevented from rotating the rotor shaft  45  in response to voltage signals from the transistors. When the active rear steering system  12  is in an active operational state, the electrical contacts  86 ,  88  are provided to have open operational states, triggered by motor relay  95 , to allow the motor  14  to rotate the rotor shaft  45  in response to voltage signals from the transistors. 
         [0021]    The processor  36  is provided to generate command signals that induce the motor control circuit  38  to generate voltage signals that are applied to the phase windings  40 ,  42 ,  44  to induce rotation of the rotor  45 . Further, the processor  36  is provided to generate command signals that induce the motor control circuit  38  to generate voltage signals that are applied to the phase windings  40 ,  42  for determining operational states of the electrical contacts  86 ,  88 . The processor  36  is electrically coupled to the gate drive  50  and to the nodes  46 ,  48 ,  49  of the motor  14 . Processor  36  also controls engine relay  95  and can process algorithms to detect motor and motor relay shorts as well as shorting relay failures. 
         [0022]    The motor control circuit  38  is provided to generate voltage signals that are applied to the phase windings  40 ,  42 ,  44  in response to command signals received from the processor  36 . The motor control circuit  38  includes a gate drive  50 , transistors  52 ,  54 ,  56 ,  58 ,  60 ,  62 , a voltage source  64 , resistors  70 ,  72 ,  74  and capacitors  80 ,  82 ,  84 . 
         [0023]    The gate drive  50  is provided to control operation of the transistors  52 ,  54 ,  56 ,  58 ,  60  and  62  in response to command signals received from the processor  36 . The gate drive  50  is electrically coupled to gates of the transistors  52 ,  54 ,  56 ,  58 ,  60  and  62 . 
         [0024]    The transistors  52 ,  54 ,  56 ,  58 ,  60 ,  62  are provided to supply voltage signals to the phase windings  40 ,  42 ,  44  of the motor  14 . The transistor  52  has a gate terminal (G 1 ) electrically coupled to the gate drive  50  (bDriveHi), a drain terminal (D 1 ) electrically coupled to the voltage source  64 , and a source terminal (S 1 ) electrically coupled to both a drain terminal (D 2 ) of the transistor  54  and the node  46 . The transistor  54  has a gate terminal (G 2 ) electrically coupled to the gate drive  50  (bDriveLo), a drain terminal (D 2 ) electrically coupled to both a source terminal (S 1 ) of the transistor  52  and the node  46 , and a source terminal (S 2 ) electrically coupled to electrical ground. A series combination of the resistor  70  and the capacitor  80  are electrically coupled between the node  46  and electrical ground. The transistor  56  has a gate terminal (G 3 ) electrically coupled to the gate drive  50  (aDriveHi), a drain terminal (D 3 ) electrically coupled to the voltage source  64 , and a source terminal (S 3 ) electrically coupled to both a drain terminal (D 4 ) of transistor  58  and the node  48 . The transistor  58  has a gate terminal (G 4 ) electrically coupled to the gate drive  50  (aDriveLo), a drain terminal (D 4 ) electrically coupled to both a source terminal (S 3 ) of the transistor  56  and the node  48 , and a source terminal (S 4 ) electrically coupled to electrical ground. A series combination of the resistor  72  and the capacitor  82  are electrically coupled between the node  48  and electrical ground. The transistor  60  has a gate terminal (G 5 ) electrically coupled to the gate drive  50  (cDriveHi), a drain terminal (D 5 ) electrically coupled to the voltage source  64 , and a source terminal (S 5 ) electrically coupled to both a drain terminal (D 6 ) of the transistor  62  and the node  49 . The transistor  62  has a gate terminal (G 6 ) electrically coupled to the gate drive  50  (cDriveLo), a drain terminal (D 6 ) electrically coupled to both a source terminal (S 5 ) of the transistor  60  and the node  49 , and a source terminal (S 6 ) electrically coupled to electrical ground. A series combination of the resistor  74  and capacitor  84  is electrically coupled between the node  49  and electrical ground. In general, transistor pairs  52  and  54 ,  56  and  58 , and  60  and  62  can all be considered a “leg” of the motor and drive circuit as described. 
         [0025]      FIG. 3  is an electrical schematic of the active rear steering system of  FIG. 2  with the inclusion of test circuits. Each leg a, b, c of the motor and drive circuit described above is provided with a test circuit, on each of the respective legs a, b, c. The test circuits include transistors  102 ,  108 ,  112  that are used to provide voltage signals to the respective test circuit as described further below. The transistor  102  has a gate terminal (G 7 ) electrically coupled to the gate test drive  55  (bTest), a drain terminal (D 7 ) electrically coupled to the test voltage source  100 , and a source terminal (S 7 ) electrically coupled in series to test resistor  103  that is coupled to node  104  electrically coupled between node  46  and resistor  70 . The transistor  108  has a gate terminal (G 8 ) electrically coupled to the gate test drive  55  (aTest), a drain terminal (D 8 ) electrically coupled to the test voltage source  100 , and a source terminal (S 8 ) electrically coupled in series to test resistor  109  that is coupled to node  110  electrically coupled between node  48  and resistor  72 . The transistor  112  has a gate terminal (G 9 ) electrically coupled to the gate test drive  55  (cTest), a drain terminal (D 9 ) electrically coupled to the test voltage source  100 , and a source terminal (S 9 ) electrically coupled in series to test resistor  113  that is coupled to node  114  electrically coupled between node  49  and resistor  74 . The test circuits further include voltage test points  120 , coupled to respective nodes  104 ,  110 ,  114 , which are the motor connection of the legs a, b, c. The test points  120  are further coupled between source (S 1 ) of transistor  52  and drain (D 2 ) of transistor  54 , source (S 3 ) of transistor  56  and drain (D 4 ) of transistor  58 , and source (S 5 ) of transistor  60  and drain (D 6 ) of transistor  60 . 
         [0026]    It is appreciated that the addition of the test circuit to the ARS system as described above allows for detection of a motor shorting relay failure. Software algorithms can be implemented to provide detection as described. The detection methodology is now described with respect to  FIG. 4 , which illustrates an exemplary methodology for the detection of a motor shorting relay failure. 
         [0027]    In general, prior to operating the ARS system, the motor and relay circuit are checked by turning on two of the DriveLo FETs transistors  50 , that is any two of aDriveLo, bDriveLo, cDriveLo, at step  405 . In addition, at step  410 , the drive circuit of the third leg, that is any one of aTest, bTest, cTest, is also turned on. At step  415 , the voltage at the test leg is then read at V aOut , V bOut , V cOut . 
         [0028]    At step  420 , it is determined whether or not the voltage reading of the third leg is 0 volts. If the voltage reading is immediately 0 volts at step  420 , then the cause of the 0 volt reading is determined at step  425 . In general, if the reading is 0 volts at step  420 , the reason determined at step  425  can include, but is not limited to: the relay is closed; there is a short in the motor; there is a short across the relay, etc. These reasons can be predetermined at step  430 . 
         [0029]    If the voltage reading is not immediately 0 volts, and the voltage has not decayed, then the circuit is open. Then, at step  420 , then it is determined whether or not all of the test leg pairs have been tested at step  435 . If all of the test leg pairs have not been tested at step  435 , then the motor and relay circuit are checked by turning on the next two of the DriveLo FETs transistors  50 , that is any two of aDriveLo, bDriveLo, cDriveLo, at step  440 . In addition, at step  410 , the drive circuit of the third leg, that is any one of aTest, bTest, cTest, is also turned on. The process is then repeated until all of the test leg pairs have been tested and reasons for a 0 volt reading have been determined. It is appreciated that testing each leg of the circuit is performed to verify each winding and relay contact. For example, an open circuit on Lc can be verified by enabling aDriveLo, bDriveLo and aTest, and checking for signal decay at VaOut. A short between Lb and Lc is verified by a normal operation with bDriveLo, cDriveLo and aTest enabled, and an immediate reading of 0 volts at Vcout with aDriveLo, bDriveLo and cTest enabled. 
         [0030]    It is further appreciated that time delays, as waiting periods, can be added to the algorithm as discussed above, in order to test for decays. For example, in a circuit with R aTest =10Ω and V test =12V, the algorithm is: 
         [0000]    
       
         
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Enable cDriveLo and bDriveLo 
               
               
                   
                 Enable cTest 
               
               
                   
                 Wait 0.1 μs 
               
               
                   
                 Read V aout   
               
               
                   
                 If Vaout&gt;5 V then no short in leg a 
               
               
                   
                 Wait 30 μs 
               
               
                   
                 If Vaout&lt;5 V then no open leg a 
               
               
                   
                   
               
             
          
         
       
     
         [0031]    To further illustrate the aforementioned example,  FIG. 5  illustrates the equivalent circuit of cDriveLo and bDriveLo are on with V in  at the node between the test transistor (FET) and the test resistor of the motor phase a. The values of R aSunb  and C aSnub  are given in order to provide the snub circuit. Analyzing each of the paths individually for illustrative purposes, the time constant for the inductor path is R aTest /(1.5*La), and the time constant for the capacitor circuit is 1/(R aTest +R aSnub )*C aSnub . Therefore, R aTest  is chosen to balance the time constant of the inductor circuit, the time constant of the capacitor circuit, and the current drawn through the test FET. In an exemplary implementation, a slow time constant is selected for the inductor circuit, a fast time constant is selected for the capacitor circuit, and a low current is drawn for a small test FET. 
         [0032]      FIGS. 6 and 7  illustrate exemplary voltage and current responses for various values of the test resistor with a V test  of 12V. In general,  FIGS. 6 and 7  illustrate that decreasing R aTest  increases the fall time for the output, but increases current draw. 
         [0033]    It is appreciated that the previously described circuits can be simplified as shown by the equivalent circuit in  FIG. 5 , and the diagnostic is robust to variations in the inductance of the motor windings.  FIG. 8  illustrates an output voltage and current response for a 50% variation of L a , and R test =10Ω. As illustrated, it is appreciated that there is sufficient time to check the voltage before it decays. 
         [0034]    As described above, the present invention for the detection of a motor shorting relay failure can be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. The present invention can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. The present invention can also be embodied in the form of computer program code, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits. 
         [0035]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. Terms such as “first” and “second” are used herein merely to distinguish between two like elements, and are not intended to imply an order such as of importance or location. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.