Abstract:
A shift-by-wire system, connected to a manual shaft in a vehicle, includes: an electric motor having a rotary shaft which rotates the manual shaft; an angle-of-rotation sensor that detects angle position of the rotary shaft for control of the electric motor; a shaft position sensor that detects angular position of the manual shaft; and a control unit that, when the angle-of-rotation sensor functions normally, controls the electric motor according to the sensed angular position of the rotary shaft, so that the sensed angular position of the shaft comes within a predetermined range, and when the angle-of-rotation sensor does not function normally, initiates sensor-less control of the electric motor while estimating the direction of rotation of the rotation shaft, based on the sensed angular position of the shaft, and ceases sensor-less control when the sensed angular position is within the predetermined range.

Description:
CROSS-REFERENCE 
       [0001]    Japanese Patent Application No. 2009-072065 filed on Mar. 24, 2009 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a shift-by-wire system that is mounted in a vehicle and that actuates an object of actuation by driving a manual shaft on the basis of a shifting manipulation. 
         [0004]    2. Description of the Related Art 
         [0005]    In the past, as this type of shift-by-wire system, a shift-by-wire system that includes a spool position sensor which detects the position of a spool to be used to switch shift positions, and that when any of a parking (P) position, a reverse (R) position, an neutral (N) position, and a drive (D) position is selected using a selector switch (shift switch), controls a motor so that the spool will be located at a position associated with the selected position on the basis of a signal sent from the spool position sensor has been proposed (refer to, for example, JP-A-2007-139102 (patent document 1)). In this system, position switching edges are associated with the D position and P position respectively, and a regulation unit (stopper) is included to regulate the rotation of the motor at the position switching edges. When an abnormality occurs in the position sensor, if the selector switch is set to the D position, the motor is driven until a movement is regulated to a D-position direction. If the selector switch is not set to the D position, the motor is driven until a movement is regulated to a P-position direction (a reverse rotating direction with respect to the D-position direction). Thus, the abnormality in the spool position sensor is coped with. 
         [0006]    As for the foregoing shift-by-wire system, a description has been made of a countermeasure to be taken when an abnormality occurs in the spool position sensor but has not been made of a case where an abnormality occurs in a motor angle sensor to be used to control a brushless motor which drives the spool. When an abnormality occurs in the motor angle sensor, driving the motor is thought to be ceased. However, when consideration is taken into the fact that the shift-by-wire system is mounted in a vehicle, it is desired that even if an abnormality occurs in the motor angle sensor, evacuative driving is enabled or any other appropriate measure is taken. 
       SUMMARY OF THE INVENTION 
       [0007]    A principal object of a shift-by-wire system in accordance with the present invention is to more appropriately cope with an abnormality in an angle-of-rotation sensor to be used to control an electric motor that actuates an object of actuation. 
         [0008]    In order to accomplish the above principal object, the shift-by-wire system in accordance with the present invention adopts pieces of measure presented below. 
         [0009]    The shift-by-wire system in accordance with the present invention is a shift-by-wire system that is mounted in a vehicle and that actuates an object of actuation by driving a manual shaft on the basis of a shifting manipulation, and includes: 
         [0010]    an electric motor that includes a rotation shaft and rotates or drives the manual shaft by rotating or driving the rotation shaft; 
         [0011]    an angle-of-rotation sensor that detects the angle of rotation of the rotation shaft for the purpose of controlling the electric motor; 
         [0012]    a shaft position sensor that detects the rotational position of the manual shaft; and 
         [0013]    a control unit that at an ordinary time at which the angle-of-rotation sensor normally functions, implements ordinary-time control to control the electric motor on the basis of the angle of rotation of the rotation shaft, which is sent from the angle-of-rotation sensor, so that the rotational position of the shaft sent from a shift position sensor will square with a target rotational position within a predetermined range, and that at an unordinary time at which the angle-of-rotation sensor does not normally function, implements unordinary-time control to initiate sensor-less control for controlling the electric motor while estimating the rotating direction of the rotation shaft of the electric motor on the basis of the rotational position of the shaft sent from the shift position sensor, and to cease the sensor-less control when the rotational position sent from the shift position sensor squares with the target rotational position within the predetermined range. 
         [0014]    In the shift-by-wire system according to the present invention, at the ordinary time at which the angle-of-rotation sensor that detects the angle of rotation of the rotation shaft of the electric motor which rotates or drives the manual shaft functions normally, ordinary-time control is implemented to control the electric motor on the basis of the angle of rotation of the rotation shaft, which is sent from the angle-of-rotation sensor, so that the rotational position of the shaft sent from the shift position sensor which detects the rotational position of the manual shaft will square with the target rotational position within the predetermined range. At the unordinary time at which the angle-of-rotation sensor does not normally function, unordinary-time control is implemented to initiate sensor-less control for controlling the electric motor while estimating the rotating direction of the rotation shaft of the electric motor on the basis of the rotational position of the shaft sent from the shift position sensor, and to cease the sensor-less control when the rotational position sent from the shift position sensor squares with the target rotational position within the predetermined range. Therefore, even at the unordinary time at which the angle-of-rotation sensor does not normally function, the rotational position of the manual shaft can be squared with the target rotational position within the predetermined range in order to actuate an object of actuation. As a result, an abnormality in the angle-of-rotation sensor can be more appropriately coped with. 
         [0015]    In the shift-by-wire system according to the present invention, the electric motor may be a three-phase synchronous motor. The angle-of-rotation sensor may include three elements, which are associated with the phases, so as to detect the angle of rotation of a rotor included in the motor. The control unit may be such a mechanism that: when an abnormality occurs in the angle-of-rotation sensor, if the abnormality involves one of the three elements, recognizes the ordinary time, estimates the rotating direction of the electric motor on the basis of the rotational position of the shaft sent from the shaft position sensor, and implements the ordinary-time control on the basis of the estimated rotating direction and signals sent from the two normal elements; and when the abnormality involves two or more out of the three elements, recognizes the unordinary time and implements the unordinary-time control. In this case, even when an abnormality occurs in one of the three elements included in the angle-of-rotation sensor, the same control as the one at the ordinary time can be implemented. 
         [0016]    In the shift-by-wire system according to the present invention, the control unit may be a mechanism configured to control the electric motor so that at the unordinary time, the rotational position of the shaft will be shifted to the target rotational position at a rotating speed lower than the rotating speed attained at the ordinary time. In this case, at the unordinary time, the rotational position of the shaft can be more reliably shifted to the target rotational position. 
         [0017]    In the shift-by-wire system according to the present invention, the vehicle may have an automatic transmission, which includes clutches that convey power fed from a power plant to an axle, mounted therein. The control unit may be a mechanism configured to control the clutches so that when a predetermined time has elapsed since initiation of the unordinary-time control, the control of the electric motor will be ceased in order to disconnect the power plant from the axle. In this case, even when the unordinary-time control is not normally implemented, unexpected power can be suppressed to be outputted to the axle. 
         [0018]    Further, in the shift-by-wire system according to the present invention, the vehicle may have an automatic transmission, which includes clutches that are actuated with a fluid pressure fed via a manual valve interlocked with the manual shaft, mounted therein. The object of actuation may be the manual valve, or may be a parking lock mechanism that is actuated along with driving of the manual shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a configuration diagram showing the outline of the configuration of an automobile in which a shift-by-wire system that is an embodiment of the present invention is mounted; 
           [0020]      FIG. 2  is an explanatory diagram showing an actuation table for an automatic transmission; 
           [0021]      FIG. 3  is a configuration diagram showing the outline of the configuration of a hydraulic circuit; 
           [0022]      FIG. 4  is a construction diagram showing the outline of the construction of a driving system for a manual valve; 
           [0023]      FIG. 5  is a configuration diagram showing the outline of the configuration of an SBWECU; 
           [0024]      FIG. 6  is a flowchart showing an example of a control mode designating processing routine to be executed by the SBWECU; 
           [0025]      FIG. 7  is a flowchart showing an example of an ordinary-time control routine; 
           [0026]      FIG. 8  is an explanatory diagram showing the relationship among a shaft position POS, a valve position, and the number of motor rotations; 
           [0027]      FIG. 9  is a flowchart showing an example of a failing-time control routine; 
           [0028]      FIG. 10  is an explanatory diagram showing the relationship between the number of motor rotations and a driving time; and 
           [0029]      FIGS. 11A and 11B  are construction diagrams showing the outline of the construction of a driving system for a parking lock mechanism. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0030]    Next, the best mode for carrying out the invention will be described by taking an embodiment for instance. 
         [0031]      FIG. 1  is a configuration diagram showing the outline of the configuration of an automobile  10  in which a shift-by-wire system that is an embodiment of the present invention is mounted.  FIG. 2  shows an actuation table for an automatic transmission  20 .  FIG. 3  is a configuration diagram showing the outline of the configuration of a hydraulic circuit  50 .  FIG. 4  is a construction diagram showing the outline of the construction of a driving system for a manual valve  56 . The automobile  10  concerning the embodiment includes: as shown in  FIG. 1 , an engine  12  that is an internal combustion engine which outputs power through explosion and combustion of a hydrocarbon fuel such as gasoline or light oil; an engine electronic control unit (hereinafter, an engine ECU)  16  that operates or controls the engine  12 ; a lock-up clutch inclusive torque converter  24  attached to a crankshaft  14  of the engine  12 ; a stepped automatic transmission  20  that has an input shaft  21  thereof coupled to the output side of the torque converter  24 , has an output shaft  22  thereof coupled to driving wheels  18   a  and  18   b  via a gear mechanism  26  and a differential gear  28 , and changes gears to convey power inputted to the input shaft  21  to the output shaft  22 ; an automatic transmission electronic control unit (hereinafter, an ATECU)  29  that controls the automatic transmission  20  and a shift-by-wire system electronic control unit (hereinafter, a SBWECU)  80 ; and a main electronic control unit (hereinafter, a main ECU)  90  that controls the whole of the vehicle. 
         [0032]    The automatic transmission  20  is, as shown in  FIG. 1 , constructed as a stepped transmission for changing six speed stages, and includes a single-pinion type planetary gear mechanism  30 , a Ravigneaux type planetary gear mechanism  40 , three clutches C 1 , C 2 , and C 3 , two brakes B 1  and B 2 , and a one-way clutch F 1 . The single-pinion type planetary gear mechanism  30  includes a sun gear  31  serving as an external gear, a ring gear  32  serving as an internal gear disposed concentrically with the sun gear  31 , plural pinion gears  33  that mesh with both the sun gear  31  and ring gear  32 , and a carrier  34  that sustains the plural pinion gears  33  so that the pinion gears can rotate or revolve. The sun gear  31  is locked in a case, and the ring gear  32  is connected to the input shaft  21 . The Ravigneaux type planetary gear mechanism  40  includes two sun gears  41   a  and  41   b  that are external gears, a ring gear  42  that is an internal gear, plural short pinion gears  43   a  that mesh with the sun gear  41   a , plural long pinion gears  43   b  that mesh with both the sun gear  41   b  and plural short pinion gears  43   a , and also mesh with the ring gear  42 , and a carrier  44  that links the plural short pinion gears  43   a  and plural long pinion gears  43   b , and sustains the pinion gears so that the pinion gears can rotate or revolute. The sun gear  41   a  is connected to the carrier  34  of the single-pinion type planetary gear mechanism  30  via the clutch C 1 . The sun gear  41   b  is connected to the carrier  34  via the clutch C 3  and also connected to the case via the brake B 1 . The ring gear  42  is connected to the output shaft  22 , and the carrier  44  is connected to the input shaft  21  via the clutch C 2 . The rotation of the carrier  44  can be freed or fixed according to the ON or OFF of the brake B 2 , and is regulated to one direction by the one-way clutch F 1 . 
         [0033]    In the thus constructed automatic transmission  20 , as seen from the actuation table of  FIG. 2 , the first to sixth speeds for advancement, reverse and neutral can be switched according to the combination of the ONs or OFFs (ON may be referred to as engagement, OFF may be referred to as disengagement, and the same applies to a description to be made below) of the clutches C 1  to C 3  and the ONs or OFFs of the brakes B 1  and B 2 . As shown in  FIG. 2 , the state of the first speed for advancement is attained by bringing the clutch C 1  to ON and the clutches C 2  and C 3  and brakes B 1  and B 2  to OFF (in the case of an engine brake, the brake B 2  is brought to ON). The state of the second speed for advancement is attained by bringing the clutch C 1  and brake B 1  to ON and the clutches C 2  and C 3  and brake B 2  to OFF. The state of the third speed for advancement is attained by bringing the clutches C 1  and C 3  to ON and the clutch C 2  and brakes B 1  and B 2  to OFF. The state of the fourth speed for advancement is attained by bringing the clutches C 1  and C 2  to ON and the clutch C 3  and brakes B 1  and B 2  to OFF. The state of the fifth speed for advancement is attained by bringing the clutches C 2  and C 3  to ON and the clutch C 1  and brakes B 1  and B 2  to OFF. The state of the sixth speed for advancement is attained by bringing the clutch C 2  and brake B 1  to ON and the clutches C 1  and C 3  and brake B 2  to OFF. The state of a reverse is attained by bringing the clutch C 3  and brake B 2  to ON and the clutches C 1  and C 2  and brake B 1  to OFF. The state of a neutral is attained by bringing all the clutches C 1  to C 3  and brakes B 1  and B 2  to OFF. 
         [0034]    The clutches C 1  to C 3  and brakes  81  and B 2  of the automatic transmission  20  are driven by the hydraulic circuit  50 . The hydraulic circuit  50  includes: as shown in  FIG. 3 , a mechanical oil pump  52  that sucks a working fluid from a strainer  51  using power fed from the engine  12 , and feeds it with a pressure; a regulator valve  54  that adjusts the pressure of the working fluid (line pressure PL) fed from the mechanical oil pump  52  with a pressure; a linear solenoid SLT that drives the regulator valve  54  using a modulator pressure PMOD inputted via a modulator valve that is not shown and derived from the line pressure PL; a manual valve  56  including an input port  56   a  through which the line pressure PL is inputted, a D-position output port  56   b , and an R-position output port  56   c ; and a linear solenoid SLC 1  that inputs a drive pressure PD through the D-position output port  56   b  of the manual valve  56 , adjusts it, and outputs it to the clutch C 1 . In the embodiment, the hydraulic systems for the clutches C 2  and C 3  other than the clutch C 1  and for the brakes B 1  and B 2  are omitted. The hydraulic systems can be configured using known linear solenoids and others. 
         [0035]    The manual valve  56  includes: as shown in  FIG. 4 , a manual plate  62  attached to a manual shaft  60 ; a spool  64  having a hook  64   a , which is shaped like letter L and caught in an elongated hole  62   a  formed at a position (end) deflected from the axis of rotation of the manual shaft  60  in the manual plate  62 , formed at the distal end thereof; and a land  57  formed on the spool  64 . A rotational motion of the manual shaft  60  is converted into a linear motion of the spool  64  by driving an electric motor  66  whose rotation shaft  66   a  is connected to the manual shaft  60  via a reduction gear  68 , whereby a state in which the communications of the input port  56   a  with the output ports  56   b  and  56   c  are interrupted, a state in which the input port  56   a  and D-position output port  56   b  are communicated with each other and the communication between the input port  56   a  and R-position output port  56   c  is interrupted, and a state in which the communication between the input port  56   a  and D-position output port  56   b  is interrupted and the input port  56   a  and R-position output port  56   c  are communicated with each other are switched according to a magnitude of a stroke of the spool  64 . The manual plate  62  is provided with a detent mechanism  70  including a plate-like detent spring  74  whose proximal end is locked in the case of the automatic transmission  20  with a bolt, and a roller  76  that is attached to the distal end of the detent spring  74  so that it can freely revolve, and that is abutted with a pressure against a cam surface  72  having ridges and valleys alternatively formed on the edge of the manual plate  62 . 
         [0036]    The ATECU  29  is configured as a microprocessor having a CPU centered, though it is not shown in detail. The ATECU  29  includes, in addition to the CPU, a ROM in which processing programs are stored, a RAM in which data is temporarily stored, input and output ports, and a communication port. To the ATECU  29 , the number of input-shaft rotations Nin sent from a number-of-rotations sensor attached to the input shaft  21 , and the number of output-shaft rotations Nout sent from a number-of-rotations sensor attached to the output shaft  22  are inputted via the input port. From the ATECU  29 , driving signals for solenoids including the linear solenoids SLT and SLCI are outputted via the output port. The ATECU  29  communicates with the main ECU  90 , controls the automatic transmission  20  (hydraulic circuit  50 ) according to a control signal sent from the main ECU  90 , and, if necessary, outputs data concerning the state of the automatic transmission  20  to the main ECU  90 . 
         [0037]    The SBWECU  80  is, as shown in  FIG. 5 , configured with a CPU  82 , which serves as a central processing circuit, as a center. The SBWECU  80  includes, in addition to the CPU  82 , a  5 V power circuit  81  that feeds power to components, a CAN circuit  84  that performs CAN communication with the main ECU  90 , an electric motor  66  that is a three-phase brushless motor for driving the manual shaft  60  along with rotational driving of the rotation shaft  66   a , a drive circuit  85  that drives the electric motor  66 , a shaft position sensor  86  that detects an angle of rotation of the manual shaft  60  of the manual valve  56 , and a brushless motor control motor angle sensor  88  that detects an angle of rotation of the electric motor  66 . The motor angle sensor  88  includes three hole ICs associated with the phases (U phase, V phase, and W phase) of the electric motor  66 , and detects the magnetic-pole position of the rotor by detecting output voltages of the hole ICs that are switched in units of an electrical angle of 60°. 
         [0038]    The main ECU  90  is configured as a microprocessor having a CPU centered, though it will not be shown in detail. The main ECU  90  includes, in addition to the CPU, a ROM in which processing programs are stored, a RAM in which data is temporarily stored, input and output ports, and a communication port. To the main ECU  90 , a shift position SP sent from a shift position sensor  92  that detects the manipulated position of a shift lever  91 , an accelerator pedal angle Acc sent from an accelerator pedal position sensor  94  that detects a magnitude of a stroke imposed on an accelerator pedal  93 , a brake switch signal BSW sent from a brake switch  96  that detects a stroke imposed on a brake pedal  95 , and a vehicle speed V sent from a vehicle speed sensor  98  are inputted via the input port. From the main ECU  90 , a lighting signal for an alarm lamp  99  is outputted via the output port. The main ECU  90  is, as mentioned above, connected to the engine ECU  16 , ATECU  29 , and SBWECU  80  via the communication port, and transfers various control signals and data to or from the engine ECU  16 , ATECU  29 , and SBWECU  80 . 
         [0039]    In the thus configured automobile  10  of the embodiment, at the ordinary time, the main ECU  90  transmits a shift command signal consistent with the position of the shift lever  91  to the SBWECU  80  and ATECU  29 . The SBWECU  80  having received the shift command signal (shift position SP) uses the drive circuit  85  to drive or control the electric motor  66  on the basis of the shaft position POS sent from the shaft position sensor  86 , so that the manual valve  56  will be moved to a valve position associated with the shift position SP. The ATECU  29  having received the shift command signal controls the respective linear solenoids on the basis of the shift position SP, so that the clutches C 1  to C 3  and brakes B 1  and B 2  will be brought to ON or OFF. When the shift lever  91  is shifted or manipulated to the drive (D) position, the accelerator pedal angle Acc sent from the accelerator pedal position sensor  94  and the vehicle speed V sent from the vehicle speed sensor  98  are transmitted to the ATECU  29 . The ATECU  29  having received the accelerator pedal angle Acc and vehicle speed V uses a shift map to designate any of the first to sixth speeds for advancement on the basis of the accelerator pedal angle Acc and vehicle speed y, and drives or controls the linear solenoids according to the designated speed stage, so that the necessary clutches and brakes out of the clutches C 1  to C 3  and brakes B 1  and  82  will be brought to ON. 
         [0040]    Next, a description will be made of the actions of the thus configured automobile  10 , or more particularly, the actions of the SBWECU  80  to be made in case of a failure in the motor angle sensor  88 .  FIG. 6  is a flowchart showing an example of a control mode designating processing routine to be executed by the SBWECU  80 . The routine is repeatedly executed at intervals of a predetermined time (for example, several tens of milliseconds). 
         [0041]    When the control mode designating processing routine is executed, the CPU  82  of the SBWECU  80  first executes the processing of inputting data items, such as, the shaft position POS sent from the shaft position sensor  86  and the hole IC signals HU, HV, and HW sent from the three hole ICs of the motor angle sensor  88  (step S 100 ). 
         [0042]    Thereafter, a failure in a hole IC is decided (step S 110 ). For deciding the failure in a hole IC, for example, the rotating direction of the electric motor  66  is decided by deciding based on a magnitude of a temporal change in the shaft position POS, which is detected by the shaft position sensor  86 , whether the rotating direction of the manual shaft  60  is the direction of forward rotation or reverse rotation. 
         [0043]    Signals to be detected next by the motor angle sensor  88  are inferred from the rotating direction of the electric motor  66 , the hole IC signals detected previously by the motor angle sensor  88 , and a signal pattern shown in  FIG. 5 . The inferred signals are compared with the hole IC signals HU, HV, and HW actually detected this time by the motor angle sensor  88 . The comparison is performed for each of the signals HU, HV, and HW, and a failure is decided individually for each of the hole ICs. 
         [0044]    If all of the three hole ICs are decided to be normal (step S 120 ), an ordinary-time control mode in which the hole IC signals HU, HV, and HW sent from the motor angle sensor  88  are used to control the electric motor  66  is designated (step S 130 ). If any of the three hole ICs is decided to have failed, whether the number of failing hole ICs is one is decided (step S 140 ). If the number of failing hole ICs is one, the foregoing ordinary-time control mode is designated in order to control the electric motor  66  using the signals of the two normal hole ICs (step S 130 ). If the number of failing hole ICs is two or more, a failing-time control mode in which the electric motor  66  is controlled in a sensor-less manner without use of the hole IC signals HU, HV, and HW sent from the motor angle sensor  88  is designated (step S 150 ). The routine is then terminated. 
         [0045]    Next, actions in the ordinary-time control mode will be described below.  FIG. 7  is a flowchart showing an example of an ordinary-time control routine. In the routine, data items such as the shift position SP detected by the shift position sensor  92  and transmitted from the main. ECU  90  through communication, and the shaft position POS sent from the shaft position sensor  86  are inputted (step S 200 ). A target valve position VP* that is a target position of the manual valve  56  is designated based on the inputted shift position SP, and a valve position VP indicating the current position of the manual valve  56  is designated based on the inputted shaft position POS (step S 210 ). The target valve position VP* and current valve position VP are compared with each other (step S 220 ). Herein, as for the valve position VP, the relationship between shaft positions POS and valve positions VP is obtained in advance and stored as a map in the ROM. When the shaft position POS is given, the associated valve position VP is deduced from the map.  FIG. 8  shows an example of the map. When the target valve position VP* and current valve position VP square with each other, the manual valve  56  need not be moved. The routine is therefore terminated. When the target valve position VP* and current valve position VP do not square with each other, the hole IC signals HU, HV, and HW are inputted from the motor angle sensor  88  (step S 230 ). If all of the three hold ICs of the motor angle sensor  88  are decided to be normal through the control mode designating processing routine, an angle of motor rotation θm is designated based on the inputted hole IC signals HU, HV, and HW (step S 250 ). A pulse width modulation (PWM) signal for driving the electric motor  66  is produced based on the target valve position VP*, the current valve position VP, and the angle of motor rotation θm (step S 280 ). The produced PWM signal is outputted to the drive circuit  85  in order to drive or control the electric motor  66  (step S 290 ). The shaft position POS is inputted (step S 300 ), and the current valve position VP is designated based on the inputted shaft position POS (step S 310 ). If the target valve position VP* and current valve position VP do not square with each other (step S 320 ), the routine returns to the step S 230 , and the pieces of processing of steps S 230  to S 320  are repeated. If the target valve position VP* and current valve position VP square with each other, the routine is terminated. 
         [0046]    If any of the three hole ICs of the motor angle sensor  88  is decided to have failed at step S 240 , a control signal for use in lighting the alarm lamp  99  is transmitted to the main ECU  90  (step S 260 ). The angle of motor rotation θm is designated based on two of the signals fed from the three hole ICs and the shaft position POS sent from the shaft position sensor  86  (step S 270 ). The pieces of processing of step S 280  and subsequent steps are then carried out. Since the three hole IC signals HU, HV, and HW are out of phase by an electrical angle of 60°, when the rotating direction of the electric motor  66  is specified based on the magnitude of a temporal change in the shaft position POS, the remaining signal can be inferred from the rotating direction of the electric motor  66 , the two hole IC signals, and the cycle of the hole IC signals. Therefore, even if any of the three hole ICs of the motor angle sensor  88  fails, the angle of motor rotation θm can be designated. The electric motor  66  can be controlled based on the angle of motor rotation θm. 
         [0047]    Next, actions in the failing-time control mode will be described below.  FIG. 9  is a flowchart showing an example of a failing-time control routine. In the routine, data items such as the shift position SP and shaft position POS are inputted (step S 400 ). The target valve position VP* is designated based on the inputted shift position SP, and the current valve position VP is designated based on the inputted shaft position POS (step S 410 ). The target valve position VP* and current valve position VP are compared with each other (step S 420 ). If the target valve position VP* and current valve position VP square with each other, the manual valve  56  need not be moved. The routine is therefore terminated. If the target valve position VP* and current valve position VP do not square with each other, a timer T is started (step S 430 ). Forcible commutation (commutation unrelated to the rotor position of the electric motor  66 ) is performed to forcibly drive the electric motor  66  in a sensor-less manner (step S 440 ).  FIG. 10  shows the relationship between motor rotating speeds and driving times. As illustrated, in the ordinary-time control routine, the electric motor  66  is driven with a high current at a high frequency in order to raise the rotating speed so that the manual valve  56  will be quickly moved to a target position. In the failing-time control routine, the electric motor  66  is driven using a current and a frequency, which are lower than the current and frequency employed at the ordinary time, in order to lower the rotating speed so that the manual valve  56  will be reliably moved to the target position. Whether a predetermined time has elapsed since the timer T is started (whether the time is up) is decided (step S 450 ). If a decision is made that the time is not up, the rotating direction of the manual shaft  60  is, as mentioned above, decided based on the magnitude of a temporal change in the shaft position POS detected by the shaft position sensor  86  (step S 460 ). Whether the decided rotating direction of the manual shaft  60  squares with a direction in which the manual valve  56  approaches to the target valve position VP* is decided (step S 470 ). If the rotating direction squares with the direction, the shaft position POS is inputted (step S 480 ). The current valve position VP is designated based on the inputted shaft position POS (step S 490 ). If the target valve position VP* and current valve position VP do not square with each other (step S 500 ), the routine returns to step S 440 , and the pieces of processing of steps S 440  to S 500  are repeated. If the target valve position VP* and current valve position VP square with each other, the routine is terminated. 
         [0048]    If it is found at step S 470  that the rotating direction of the manual shaft  60  does not square with the direction in which the manual valve  56  approaches to the target valve position VP*, driving the electric motor  66  is suspended (step S 510 ). The routine returns to step S 440 , and the electric motor  66  is forcibly driven through forcible commutation. When the driving control for the electric motor  66  is not completed within the predetermined time but the time is up (step S 450 ), a control command for bringing the clutches C 1  to C 3  and brakes  51  and  52  to OFF is transmitted to the ATECU  29  so that the crankshaft  14  of the engine  12  will be disconnected from the axle (step S 520 ). The routine is then terminated. 
         [0049]    According to the foregoing shift-by-wire system of the embodiment, whether the motor angle sensor  88  that detects an angle of rotation of the rotation shaft  66   a  (rotor) of the electric motor  66  which actuates the manual valve  56  has failed is decided. If the motor angle sensor does not fail, the electric motor  66  is controlled based on the angle of motor rotation θm sent from the motor angle sensor  88  so that the manual valve  56  will be moved to a valve position associated with the shift position SP sent from the shift lever  91  (ordinary-time control mode). If the motor angle sensor  88  has failed, the electric motor  66  is forcibly driven through forcible commutation while the rotating direction of the manual shaft  60  (the rotating direction of the electric motor  66 ) is checked based on the magnitude of a temporal change in the shaft position POS sent from the shaft position sensor, so that the manual valve  56  will be moved to a valve position associated with the shift position SP sent from the shift lever  91  (failing-time control mode). Therefore, even if the motor angle sensor  88  fails, the failure can be appropriately coped with. In the failing-time control mode, compared with the ordinary-time control mode, the electric motor  66  is driven with a lower current at a lower frequency in order to suppress the rotating speed. Therefore, the manual valve  56  can be more reliably moved to a position associated with the shift position SP. 
         [0050]    According to the shift-by-wire system of the present embodiment, when one of the three hole ICs of the motor angle sensor  88  has failed, the angle of motor rotation θm is estimated based on the remaining two hole ICs, the rotating direction of the manual shaft  60  (the rotating direction of the electric motor  66 ), and the cycle of the hole IC signals. The electric motor  66  is controlled based on the estimated angle of motor rotation θm. Therefore, the manual valve  56  can be actuated through the same control as the control implemented at the ordinary time. 
         [0051]    For the shift-by-wire system of the present embodiment, a description has been made by applying the present invention to the processing to be performed in a case where the motor angle sensor  88  of the electric motor  66  which actuates the manual valve  56  has failed. The present invention is not limited to the case. As illustrated in  FIGS. 11A and 11B , the present invention may be applied to the processing to be performed in a case where a motor angle sensor of an electric motor  166  that actuates a parking lock mechanism  180  has failed. The parking lock mechanism  180  includes: a parking gear  182  included in the gear mechanism  26  of the automatic transmission  20 ; a parking pole  184  that is engaged with the parking gear  182  to lock the parking gear with the rotation of the parking gear ceased; a parking rod  186 ; and a parking cam  188  that is attached to the distal end of the parking rod  186  and that along with the slide of the parking rode  186 , presses the parking pole  184  onto the parking gear  182  side or releases the parking pole  184 . The proximal end of the parking rod  186  is formed as a hook  186   a  shaped like letter L. The hook  186   a  is caught in a hole formed at a position deflected from the axis of rotation of a manual shaft  160  in a manual plate  162 . Therefore, when the manual shaft  160  is rotated forward by an electric motor  166 , the parking gear  182  is locked (see  FIG. 11A ). When the manual shaft  160  is rotated reversely, the parking gear  182  is unlocked (see  FIG. 11B ). The manual plate  162  is, similarly to the embodiment, provided with a detent mechanism  170  including a detent spring  174  and a roller  176  abutted with a pressure against a cam surface  72  formed on the edge of the manual plate  162 . 
         [0052]    Now, a hybrid automobile in which an engine, a first motor, a planetary gear mechanism that includes three rotating elements to which the crankshaft of the engine, a rotation shaft of the motor MG 1 , and a driving shaft coupled to the axle are connected, and a second motor connected to the driving shaft are mounted will be discussed. Since the hybrid automobile need not include a hydraulic circuit but can be driven by freely changing gears so as to output power, which is fed from the engine, to the driving shaft, as described above, a shift-by-wire system is thought to be such that: when the shift lever is manipulated into the parking (P) position, the parking lock mechanism  180  is actuated; and when the shift lever is manipulated into a position other than the P position (for example, the drive (D) position or neutral (N) position), the actuation of the parking lock mechanism  180  is canceled. In the shift-by-wire system, the position of the manual plate  162  is switched between only two positions. Therefore, assuming that the electric motor  166  is driven so that the roller  176  will be abutted against a wall formed at a moving end on the cam surface  172  of the detent mechanism  170 , a shaft position sensor need not be attached to the manual shaft  160 . However, since changing the positions is accompanied by a mechanical impact, when durability is discussed, the manual plate  162  has to be made thick or large in size in order to improve strength. This is disadvantageous to mounting in a vehicle in which preservation of a space is hard to do. If the CPU  102  of the SBWECU  100  fails, the position of the manual shaft  160  remains unknown. The ATECU  29  has to bring all the clutches to OFF so as to realize the neutral (N) position. This disables evacuative driving. In a variant, a shaft position sensor  108  is attached to the manual shaft  160  in order to avoid the foregoing drawback. Therefore, even the variant can be applied to the same pieces of processing as the embodiment can. 
         [0053]    In the shift-by-wire system of the present embodiment, when one of the three hole ICs of the motor angle sensor  88  fails, two remaining normal hole ICs are used to estimate the angle of motor rotation θm, and the electric motor  66  is driven or controlled in the ordinary-time control mode. Alternatively, the electric motor  66  may be driven or controlled in a sensor-less manner in the failing-time control mode. 
         [0054]    The shift-by-wire system of the present embodiment shall be adapted to a stepped transmission for changing six speed stages. The present invention is not limited to the transmission but may be applied to a stepped transmission for changing plural speed stages ranging from two speed stages to five speed stages, or a stepped transmission for changing seven or more speed stages. 
         [0055]    In the shift-by-wire system of the embodiment, the main ECU  90  and ATECU  29  are realized with two electronic control units. Alternatively, the main ECU  90  and ATECU  29  may be realized with three or more electronic control units, or may be realized with a single electronic control unit. 
         [0056]    The shift-by-wire system of the embodiment shall be adapted to the automobile  10  in which the engine  12  is mounted as an internal combustion engine. Alternatively, the shift-by-wire system of the embodiment may be adapted to a hybrid vehicle including both the internal combustion engine and an electric motor, or may be adapted to an electric automobile in which only an electric motor for driving is mounted. 
         [0057]    Now, a description will be made of the relationship of correspondence between the major components of the embodiment with the major components of the present invention described in Disclosure of the Invention. In the embodiment, the electric motor  66  serving as a brushless motor is equivalent to an “electric motor.” An angle-of-motor rotation sensor  114  that detects an angle of rotation of the rotation shaft  66   a  of the electric motor  66  is equivalent to an “angle-of-rotation sensor.” The shaft position sensor  86  is equivalent to a “shaft position sensor.” The SBWECU  80  is equivalent to a “control unit.” The “electric motor” is not limited to the brushless motor, but may be a synchronous electric motor such as a DC brushless motor or a switched reluctance (SR) motor, or any other electric motor as long as the electric motor is of a type that detects the rotational position of the rotation shaft and implements control using the detected rotational position. The relationship of correspondence between the major components of the embodiment and the major components of the invention set forth in Disclosure of the Invention shall not restrict the components of the invention set forth in Disclosure of the Invention, because the embodiment is an example for use in concretely explaining the best mode for carrying out the invention described in Disclosure of the Invention. Namely, the invention described in Disclosure of the Invention should be interpreted based on the description in Disclosure of the Invention. The embodiment is a mere concrete example of the invention described in Disclosure of the Invention. 
         [0058]    The best mode for carrying out the invention has been described using the embodiment. The present invention is not limited to the embodiment but may be implemented in various forms within the scope of the invention without a departure from the gist thereof. 
         [0059]    The present invention can be utilized in the automobile industry.