Abstract:
Electric parking brake devices are configured such that a parking lever is driven by an electric actuator. The electric actuator is provided with: an electric motor drivable in a forward/reverse direction and operationally controlled by a motor control unit according to rotational loads; a conversion mechanism capable of converting a rotational motion into a linear motion, moving the parking lever from a return position toward an operating position through forward rotation of the electric motor, and moving the parking lever from the operating position toward the return position through the reverse rotation of the electric motor; and a load applying mechanism (a stopper and a disc spring assembly) for applying a predetermined rotational load to the electric motor by driving a constituent member of the conversion mechanism after the parking lever is moved from the operating position to the return position through the reverse rotation of the electric motor.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electric parking brake device and, in particular, an electric parking brake device configured such that a parking lever in a drum brake is driven from a return position to an operating position by forward drive of an electric actuator to drive a brake shoe from a return position to an operating position and the parking lever is driven from the operating position to the return position by reverse drive of the electric actuator to drive the brake shoe from the operating position to the return position. 
       BACKGROUND ART 
       [0002]    The electric parking brake device of this type is described in, for example, the following Patent Literature 1. A parking brake switch is actuated and operated to make it possible to drive an electric actuator forward and to make it possible to drive a parking lever from a return position to an operating position (more specifically, to set a parking brake in an operating state (lock state)). When the parking brake switch is operated to be released to make it possible to reversely drive the electric actuator and to make it possible to drive the parking lever from the operating position to the return position (more specifically, to set the parking brake in a release state (release state)). 
       CITATION LIST 
     Patent Literature 
       [0003]    Patent Literature 1: Japanese Unexamined Patent Publication No. H11-105680 
         [0004]    In the electric parking brake device described in the Patent Literature 1, an electric motor (motor) included in the electric actuator is rotated forward to make it possible to drive the electric actuator forward, and when a predetermined current or more flows in the forward-rotating electric motor, the electric motor is stopped to make it possible to always obtain a predetermined parking brake force. The Patent Literature 1 also describes that the electric motor (motor) included in the electric actuator is reversely rotated to make it possible to reversely drive the electric actuator, and, when a current flowing in the reversely rotating electric motor is a no-load current, a power supply to the electric motor is disconnected. 
       SUMMARY OF INVENTION 
       [0005]    In the electric parking brake device described in the Patent Literature 1, depending on a current value flowing in the electric motor, an operation/stop state of the electric motor can be advantageously controlled (a sensor for electrically detecting the state of a parking lever is advantageously unnecessary). However, the brake shoe of the drum brake generally includes a return spring biasing the brake shoe toward the return position. For this reason, when the parking brake is released, the reverse drive of the electric actuator is assisted by the return spring. 
         [0006]    Thus, a timing at which a current flowing in the reverse-rotating electric motor becomes a no-load current may be disadvantageously different from a timing at which the parking lever returns to the return position. For this reason, when the parking brake is released, the parking lever may be incompletely returned or excessively returned disadvantageously. When the parking lever is incompletely returned, for example, the brake is disadvantageously dragged. When the parking lever is excessively returned, for example, a drawback such as a delay of response in the next operation of the parking brake may occur. 
         [0007]    The present invention has been made to solve the above problem (to prevent a parking lever from being incompletely returned or excessively returned in a release state of the parking brake), and has as its object to provide 
         [0008]    an electric parking brake device configured such that a parking lever in a drum brake is driven from a return position to an operating position by forward drive of an electric actuator to drive a brake shoe from a return position to an operating position and the parking lever is driven from the operating position to the return position by reverse drive of the electric actuator to drive the brake shoe from the operating position to the return position, wherein 
         [0009]    the electric actuator includes 
         [0010]    an electric motor which can be rotationally driven forward/reversely and the operation of which can be controlled by a motor control unit depending on a rotational load, 
         [0011]    a conversion mechanism which can convert rotational motion into linear motion, can move the parking lever from the return position to the operating position in a forward drive state in which the electric motor rotates forward, and can move the parking lever from the operating position to the return position in a reverse drive state in which the electric motor reversely rotates, and 
         [0012]    a load applying mechanism drives a constituent member of the conversion mechanism after the parking lever moves from the operating position to the return position by reverse rotation of the electric motor to apply a rotational load increasing depending on a drive amount of the constituent member to the electric motor, and 
         [0013]    the motor control unit includes a calculation unit which calculates a rotational load determination value to determine whether a rotational load applied to the electric motor by the load applying mechanism when the electric motor reversely rotationally drives is a set value or more on the basis of a current supplied to the electric motor, and a reversely rotational drive stop unit which stops the reversely rotational drive of the electric motor when the rotational load determination value is a reference value or more a set time after the reversely rotational drive of the electric motor is started. 
         [0014]    In the electric parking brake device according to the present invention, the motor control unit can obtain a parking brake operation such that the electric motor is rotated forward by an actuating operation of the parking brake switch, and the forward-rotating electric motor is stopped by a current value obtained when a rotational load acting on the forward-rotating electric motor becomes a set value. At this time, when the parking brake switch is actuated and operated, the electric motor rotates forward, and the parking lever at the return position is driven from the return position to the operating position by forward drive of the electric actuator to drive a brake shoe from the return position to the operating position. At this time, since the device is set such that the forward-rotating electric motor is stopped by a current value (target current value) obtained when the rotational load (load obtained when the brake shoe moves to the operating position and is brought into press contact with the brake drum) acting on the forward rotating electric motor becomes the set value, predetermined parking brake force can be always obtained. 
         [0015]    The motor control unit is set such that the electric motor is reversely rotated by a releasing operation of the parking brake switch, and the reversely rotating electric motor is stopped by a current value obtained when a rotational load acting on the reversely rotating electric motor becomes a set value, so as to make it possible to release the parking brake. At this time, when the parking brake switch is released, the electric motor reversely rotates, and the parking lever at the operating position is driven from the operating position to the return position by reverse drive of the electric actuator to drive the brake shoe from the operating position to the return position. At this time, since the device is set such that the reversely rotating electric motor is stopped by a current value obtained when the rotational load (load obtained by the load applying mechanism) acting on the reversely rotating electric motor becomes the set value, the parking lever can always be stopped in a state in which the parking lever is always returned to the predetermined return position. 
         [0016]    Thus, in the electric parking brake device according to the present invention, the parking lever can be prevented from being incompletely returned or excessively returned when the parking brake is released. In this manner, a drawback (for example, drag of the brake) caused by incomplete return of the parking lever can be prevented, and a drawback caused by excessive return of the parking lever (for example, delay of response in the next operation of the parking brake) can be prevented. 
         [0017]    In the electric parking brake device according to the present invention, the operation/stop of the electric motor can be advantageously controlled by a current value supplied to the electric motor (a sensor for electrically detecting the state of the parking lever is advantageously unnecessary), and the motor control unit can be simply configured at low costs. Since the motor control unit includes the calculation unit and the reversely rotational drive stop unit, the reversely rotational drive of the electric motor can be accurately stopped, and a rotational load required by the load applying mechanism can be set to be small. As a result, the load applying mechanism can be miniaturized and manufactured at low costs. 
         [0018]    In execution of the present invention described above, 
         [0019]    the rotational load determination value is a current value supplied to the electric motor, and a sum of a no-load current value detected in a reversely rotational drive state of the electric motor and a preset predetermined current value can also be defined as the reference value. 
         [0020]    In this case, a sum of the no-load current value and the preset predetermined current value is defined as the reference value, and the no-load current value serves as a part of the reference value. For this reason, a fluctuation in performance caused by a manufacturing error or the like in the conversion mechanism or the load applying mechanism can be excluded. Thus, determination accuracy when the reversely rotational drive of the electric motor is stopped can be improved, and a rotational load required by the load applying mechanism can be reduced. As a result, the load applying mechanism can be miniaturized and manufactured at low costs. 
         [0021]    In execution of the present invention described above, 
         [0022]    the rotational load determination value is a differential value of a current value supplied to the electric motor, and the preset predetermined value can also be defined as the reference value. 
         [0023]    In this case, since the rotational load determination value is the differential value of the current value supplied to the electric motor, in comparison with the case in which the sum of the no-load current value detected in the reversely rotational drive state of the electric motor and the preset predetermined current value is defined as the reference value, a stop timing can be more quickly determined. For this reason, determination accuracy when the reversely rotational drive of the electric motor can be improved, and the load applying mechanism can be further miniaturized and manufactured at low costs. 
         [0024]    In each of the cases of the present invention, 
         [0025]    the motor control unit can also include an abnormal-state reversely rotational drive stop unit which, when it is determined that the rotational load determination value is a reference value or more within the set time except for an operation initial time zone in which a current supplied to the electric motor is unstable from the start of the reversely rotational drive of the electric motor, stops the reversely rotational drive of the electric motor, and an abnormality notification unit which notifies of abnormality. In this case, the abnormal electric actuator in the device can be rapidly detected to stop the abnormal operation and to make it possible to notify of the abnormal operation. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1  is a perspective view showing an embodiment of an electric parking brake device according to the present invention. 
           [0027]      FIG. 2  is a front view of the electric parking brake device shown in  FIG. 1 . 
           [0028]      FIG. 3  is a sectional view showing a configuration of an electric actuator in the electric parking brake device shown in  FIG. 1  and  FIG. 2 , and shows a cross-sectional plan view of a coupling part between a parking lever and a rod along  3 - 3  line in  FIG. 4 . 
           [0029]      FIG. 4  is a front view showing the parking lever and the rod shown in  FIG. 3  and a coupling mechanism coupling the parking lever and the rod. 
           [0030]      FIG. 5  is a flow chart showing a main routine executed by an electric control device shown in  FIG. 3 . 
           [0031]      FIG. 6  is a flow chart showing a sub-routine executed in a lock control process shown in  FIG. 5 . 
           [0032]      FIG. 7  is a flow chart showing a sub-routine executed in a release control process shown in  FIG. 5 . 
           [0033]      FIG. 8  is a flow chart showing a sub-routine executed in an in-abnormal-state process shown in  FIG. 7 . 
           [0034]      FIG. 9  is a flow chart showing a sub-routine executed in an in-normal-state process shown in  FIG. 7 . 
           [0035]      FIG. 10  is a graph showing a relationship between a time (time in which the electric motor reversely rotates) in which the sub-routines shown in  FIG. 7 ,  FIG. 8 , and  FIG. 9  are executed and a motor current (current supplied to the electric motor). 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0036]    Embodiments of the present invention will be described below with reference to the accompanying drawings.  FIG. 1  to  FIG. 4  show an embodiment of an electric parking brake device according to the present invention. The electric parking brake device according to the embodiment includes a drum brake  10  having a parking brake mechanism and an electric actuator  20  driving the parking brake mechanism. 
         [0037]    The drum brake  10 , as shown in  FIG. 1  and  FIG. 2 , includes a disk-like back plate  11 , one pair of brake shoes  12  and  13  assembled on the back plate  11 , an anchor block  14 , a wheel cylinder  15 , and the like. The back plate  11  is configured to be fixed to an attaching part (not shown) on a vehicle body side. 
         [0038]    The brake shoes  12  and  13  are assembled on the back plate  11  such that the brake shoes  12  and  13  can move in a specific direction (direction along a plate plane) with reference to the back plate  11 , and integrally include arc-shaped linings  12   a  and  13   a  pressed against a brake drum (not shown) in a brake operating state, respectively. A coupling member  16  with adjustment mechanism and return springs S 1  and S 2  are assembled between the brake shoes  12  and  13 . 
         [0039]    The brake shoe  12  on the left in  FIG. 1  and  FIG. 2  is configured to be engaged with a left piston (not shown) of the wheel cylinder  15  at an upper end of the brake shoe  12 , engaged with the anchor block  14  at the lower end, and pressed and spread to the left toward the brake drum (not shown) in a brake operation state. A parking lever  17  is swingably assembled on the brake shoe  12 . 
         [0040]    On the other hand, the brake shoe  13  on the right in  FIG. 1  and  FIG. 2  is configured to be engaged with a right piston (not shown) of the wheel cylinder  15  at an upper end of the brake shoe  13 , engaged with the anchor block  14  at the lower end, and pressed and spread to the right toward the brake drum (not shown) in a brake operation state. A return spring S 3  (the spring S 3  has an upper end locked on the back plate  11  and a lower end locked on the brake shoe  13 ) is assembled on the brake shoe  13 . 
         [0041]    The anchor block  14  is fixed to a lower part of the back plate  11  in the drawing by using one pair of fixtures  14   a  and  14   b . The wheel cylinder  15  is fixed to an upper part of the back plate  11  in the drawing by using one pair of fixtures  15   a  and  15   b . The wheel cylinder  15  includes one pair of pistons (not shown) which come away from the left and right sides in the operation of the brake to open the left and right brake shoes  12  and  13 , the wheel cylinder  15  housing the pair of pistons therein. 
         [0042]    A coupling member  16  is tiltably engaged with an upper part of the brake shoe  12  at a left-end part and tiltably engaged with an upper part of the parking lever  17 , and tiltably engaged with an upper part of the brake shoe  13  at a right-end part. The coupling member  16  is configured to have a length which can be automatically adjusted (increasable) by a known adjustment mechanism  16   a  depending on amounts of abrasion of the linings  12   a  and  13   a.    
         [0043]    The parking lever  17  is disposed along the left brake shoe  12  in the drawing and tiltably (rotatably) coupled to the brake shoe  12  at the upper-end part by using a pin  17   a  and a clip  17   b . The parking lever  17  is configured such that the parking lever  17 , at the lower end, as shown in  FIG. 3 , is engaged with a coupling mechanism  29  on the electric actuator  20  and driven in the left-right direction by the coupling mechanism  29  (rotatably driven around the pin  17   a ). 
         [0044]    The electric actuator  20 , as shown in  FIG. 1  and  FIG. 2 , is disposed in the drum brake  10 . The electric actuator  20 , as shown in  FIG. 3 , includes an electric motor  21 , a conversion mechanism  22 , and a stopper  27  and a disk spring assembly  28  which function as a load applying mechanism, and also includes the coupling mechanism  29 . The electric motor  21  can be rotationally driven forward/reversely, and is configured to be operated with a motor control unit (electric control device) ECU depending on a current value changing depending on a rotational load. The current value depending on the rotational load can be detected by a current monitor IM included in the motor control unit (electric control device) ECU. 
         [0045]    The conversion mechanism  22  can convert rotational motion of the electric motor  21  into linear motion of a rod (screw shaft)  22   e  (swinging operation of the parking lever  17  through the coupling mechanism  29 ), can axially move the rod  22   e  from a return position (position in  FIG. 3 ) to an operating position (position on the right of the position in  FIG. 3  by a predetermined length) in a forward drive state in which the electric motor  21  rotates forward, and can axially move the rod  22   e  from the operating position to the return position in a reverse drive state in which the electric motor  21  reversely rotates. 
         [0046]    The conversion mechanism  22  includes a pinion  22   a  integrally disposed on a rotating shaft  21   a  of the electric motor  21 , a first intermediate gear  22   b   1  and a second intermediate gear  22   b   2  which are rotationally driven with the pinion  22   a , an output gear  22   c  rotationally driven with the second intermediate gear  22   b   2 , a screw mechanism  22   d  disposed at the center (center of axis) of the output gear  22   c , and the rod  22   e  coupled to the output gear  22   c  through the screw mechanism  22   d . The first intermediate gear  22   b   1  and the second intermediate gear  22   b   2  decrease rotation of the rotating shaft  21   a  to transmit the rotation to the output gear  22   c.    
         [0047]    The first intermediate gear  22   b   1 , the second intermediate gear  22   b   2 , and the output gear  22   c  are rotatably assembled in a housing  22   g . A thrust bearing  22   h  which receives reaction force (force to the left in  FIG. 3 ) from the parking lever  17  is assembled between the output gear  22   c  and the housing  22   g . The output gear  22   c  is configured to be able to move in an axial direction with reference to the housing  22   g . The electric motor  21  and the housing  22   g  are fixed to the back plate  11  by using a fixture (not shown). 
         [0048]    The screw mechanism  22   d  includes a female screw part formed at the center (center of axis) of the output gear  22   c  and a male screw part formed from an intermediate part of the rod  22   e  to the right end thereof, and the female screw part and the male screw part are meshed with each other. In the screw mechanism  22   d , when axial movement (movement to the left in the drawing) of the output gear  22   c  is regulated, rotation (rotational motion) of the output gear  22   c  is converted into axial movement (linear motion) of the rod  22   e . When axial movement (movement to the left in the drawing) of the rod  22   e  is regulated by the stopper  27 , rotation (rotational motion) of the output gear  22   c  is converted into axial movement of the output gear  22   c.    
         [0049]    In the screw mechanism  22   d , leads of the female screw part and the male screw parts are arbitrarily set, and the output gear  22   c  is set not to be rotated by reaction force (axial force) from the parking lever  17 . The male screw part formed on the rod  22   e  is covered and protected with a boot  22   j  disposed between the distal-end part (left-end part) of the rod  22   e  and the housing  22   g . The boot  22   j  is configured to extend and contract with the axial movement of the rod  22   e.    
         [0050]    The stopper  27  and the disk spring assembly  28  which function as the load applying mechanism are designed to function after the parking lever  17  moves from the operating position to the return position, and the stopper  27  is fixed to the back plate  11  by using a fixture (not shown). The stopper  27 , after the parking lever  17  moves from the operating position to the return position, as shown  FIG. 3 , is engaged with a first coupling pin  29   a  of the coupling mechanism  29  to regulate axial movement of the rod  22   e  in a return direction (to the left in the drawing). 
         [0051]    By reverse rotation of the output gear  22   c  with reverse rotation of the electric motor  21 , after the parking lever  17  moves from the operating position to the return position, in a state in which the first coupling pin  29   a  is engaged with the stopper  27  to regulate the axial movement of the rod  22   e  with the stopper  27 , when the output gear  22   c  moves from the return position in an operating direction (to the right in the drawing) in  FIG. 3  with the reverse rotation of the output gear  22   c , the disk spring assembly  28  is engaged with the right end of the output gear  22   c  to elastically regulate the axial movement (movement to the right) of the output gear  22   c  so as to apply a rotational load to the output gear  22   c . The rotational load described above increases depending on a drive amount (axial movement) of the output gear  22   c , and the rotational load applied to the electric motor  21  increases accordingly. 
         [0052]    The disk spring assembly  28 , in the housing  22   g , is disposed coaxially with the output gear  22   c  between the housing  22   g  and the right end of the output gear  22   c . The disk spring assembly  28  includes a holder  28   a , three disk springs  28   b , and a thrust plate  28   c . The holder  28   a  is to movably support the three disk springs  28   b  and the thrust plate  28   c  in a small-diameter cylindrical part, is disposed coaxially with the output gear  22   c , and is fixed to the housing  22   g  in a large-diameter part. 
         [0053]    The three disk springs  28   b  are disposed between the large-diameter part of the holder  28   a  and the thrust plate  28   c  alternatively as shown in the drawing (such that the large-diameter parts contact with each other and the small-diameter parts contact with each other), and are almost freely disposed in the illustrated state. The thrust plate  28   c  is disposed between the disk spring  28   b  at the left end in the drawing and the right end of the output gear  22   c , and can rotatably bear the right end of the output gear  22   c . The thrust plate  28   c , at the position in  FIG. 3 , is fixed to the small-diameter cylindrical part of the holder  28   a  not to be removed therefrom (not to move to the left). 
         [0054]    The coupling mechanism  29 , as shown in  FIGS. 3 and 4 , includes the first coupling pin  29   a , a second coupling pin  29   b , and one pair of coupling plates (coupling members)  29   c . The first coupling pin  29   a  is assembled on a distal end (end part) of the rod  22   e , orthogonal to the rod  22   e , and disposed in parallel with the pin (support shaft)  17   a  of the parking lever  17 . An intermediate part of the first coupling pin  29   a  is integrally fitted and fixed to an attaching hole  22   e   1  formed in the distal end (end part) of the rod  22   e . Both the end parts of the first coupling pin  29   a  are assembled on first hole parts  29   c   1  each having an oval shape and formed in the coupling plates  29   c  such that both the end parts can relatively rotate and move in a long-diameter direction (left-right direction in  FIG. 3  and  FIG. 4 ). When the rod  22   e  returns and moves to the return position, as shown in  FIG. 3 , both the end parts of the first coupling pin  29   a  are set to be able to contact with the stopper  27 . 
         [0055]    The second coupling pin  29   b  is assembled on a swinging end part  17   c  of the parking lever  17  and disposed in parallel with the first coupling pin  29   a . The second coupling pin  29   b  is relatively rotatably assembled on a circular assembling hole  17   c   1  formed in the swinging end part  17   c  at the intermediate part and relatively rotatably assembled on circular second hole parts  29   c   2  formed in coupling plates  29   c  at both the end parts. The second coupling pin  29   b  has both ends each having a diameter larger than that of the intermediate part to prevent the second coupling pin  29   b  from being removed. 
         [0056]    Each of the coupling plates  29   c  can rotate in a first hole part  29   c   1  assembled in the first coupling pin  29   a  in the circumferential direction of the first coupling pin  29   a  with reference to the end part of the rod  22   e , can rotate in the second hole part  29   c   2  assembled in the second coupling pin  29   b  in the circumferential direction of the second coupling pin  29   c   2  with reference to the parking lever  17 , and couples the first coupling pin  29   a  and the second coupling pin  29   b  to each other. 
         [0057]    In the configuration, on the parking lever  17  and the rod  22   e  coupled by the coupling mechanism  29 , a swinging surface of the parking lever  17  and an axial line of the rod  22   e  are disposed on the same plane. For this reason, in the embodiment, driving force of the electric actuator  20  can be smoothly transmitted to the swinging end part  17   c  of the parking lever  17 . 
         [0058]    The motor control unit (electric control device) ECU, for example, has a function of stopping an operation (forward rotational drive) of the electric motor  21  when a rotational load reaches a set value (obtained by moving the parking lever  17  to the operating position) in a forward rotational drive state of the electric motor  21 , and a function of stopping an operation (reversely rotational drive) of the electric motor  21  when the rotational load reaches a predetermined value in a reversely rotational drive state of the electric motor  21 . 
         [0059]    The motor control unit (electric control device) ECU is configured such that the motor control device ECU is also connected to a parking lock switch SW 1  and a parking release switch SW 2  (when any one of the switches is turned on, the other is turned off) which are disposed in the driver seat of the vehicle (see  FIG. 3 ), and, as shown in  FIG. 5 , when the parking lock switch SW 1  is turned on in a state in which a parking brake release state (release state) is stored, a lock control process in step  100  and an end process in step  99  are executed to end the program. When the parking release switch SW 2  is turned on in a state in which a parking brake operating state (lock state) is stored, a release control process in step  200  and the end process in step  99  are executed to end the program. The release state is configured to be stored when the reversely rotational drive of the electric motor  21  is normally completed, and the lock state is configured to be stored when the forward rotational drive of the electric motor  21  is normally completed. 
         [0060]    When the motor control unit (electric control device) ECU executes the lock control process in step  100  in  FIG. 5 , a lock control process routine in  FIG. 6  is executed. In the lock control process routine in  FIG. 6 , the process is started in step  101 , forward rotational drive of the electric motor  21  is started in step  102 , and an elapsed time T is counted up (Tup) in step  103 . In step  104 , it is determined whether the elapsed time T is a predetermined value T1 or longer. The predetermined value T1 corresponds to a time required until a current supplied to the electric motor  21  at the beginning of the forward rotational drive of the electric motor  21  becomes stable, and steps  103  and  104  are repeatedly executed until the elapsed time T reaches the predetermined value T1. 
         [0061]    In this manner, when the elapsed time T reaches the predetermined value T1, step  105  is executed to determines whether a current value A (This is calculated on the basis of an output from the current monitor IM.) supplied to the electric motor  21  is a target current value A1 or more. The target current value A1 is obtained when the parking lever  17  moves from the return position to the operating position to make a rotational load (load obtained when the brake shoes  12  and  13  move to the operating positions to bring the linings  12   a  and  13   a  into press contact with the brake drum) obtained by the forward rotational drive of the electric motor  21  becomes a set value, and steps  105  and  106  are repeatedly executed until the current value A reaches the target current value A1. In step  106 , a condition establishment duration Ta is reset. 
         [0062]    When the current value A reaches the target current value A1, steps  107  and  108  are executed to determine whether the condition establishment duration Ta is a predetermined value T2 or more. The predetermined value T2 is to determine a stop timing of the electric motor  21 , and is arbitrarily set. Steps  105 ,  107 , and  108  are repeatedly executed until the condition establishment duration Ta reaches the predetermined value T2. When the condition establishment duration Ta reaches the predetermined value T2, “Yes” is determined in step  108 , steps  109  to  112  are executed to return the ECU to the main routine in  FIG. 5 . The forward rotational drive of the electric motor  21  is stopped in step  109 , the lock state is stored in step  110 , and the elapsed time T and the condition establishment duration Ta are reset in step  111 . In step  112 , the return process is performed to end the program in step  99  in  FIG. 5 . 
         [0063]    On the other hand, when the motor control unit (electric control device) ECU executes the release control process in step  200  in  FIG. 5 , a release control process routine in  FIG. 7  is executed. In the release control process routine in  FIG. 7 , the process is started in step  201 , reversely rotational drive of the electric motor  21  is started in step  202 , and the elapsed time T is counted up in step  203 . In step  204 , it is determined whether the elapsed time T is a predetermined value T3 or longer. The predetermined value T3 corresponds to a time required until a current supplied to the electric motor  21  at the beginning of the reversely rotational drive of the electric motor  21  becomes stable (see T3 in  FIG. 10 ), and steps  203  and  204  are repeatedly executed until the elapsed time T reaches the predetermined value T3. 
         [0064]    In this manner, when the elapsed time T reaches the predetermined value T3, step  205  is executed to determine whether the current value A supplied to the electric motor  21  is an abnormality determination current value A2 or more. The abnormality determination current value A2, for example, is obtained when rotational load obtained by the reversely rotational drive of the electric motor  21  is an abnormal value (see a virtual line and A2 in  FIG. 10 ) when the parking lever  17  moves from the operating position to the return position (for example, an abnormally high rotational resistance is generated on the screw mechanism  22   d  of the conversion mechanism  22 ). At this time, “Yes” is determined in step  205  to execute an in-abnormal-state process in step  210 . 
         [0065]    When the motor control unit (electric control device) ECU executes the in-abnormal-state process in step  210  in  FIG. 7 , an in-abnormal-state process routine in  FIG. 8  is executed. In the in-abnormal-state process routine in  FIG. 8 , the process is started in step  211 , and an abnormal condition establishment duration Tb is counted up (Tbup) in step  212 . In step  213 , it is determined whether the abnormal condition establishment duration Tb is a predetermined value T4 or more. The predetermined value T4 is to determine a stop timing of the electric motor  21  (see T4 in  FIG. 10 ), and is arbitrarily set. Until the abnormal condition establishment duration Tb reaches the predetermined value T4, “No” is determined in step  213 , and step  205  in  FIG. 7  and steps  211  to  213  in  FIG. 8  are repeatedly executed. 
         [0066]    When the abnormal condition establishment duration Tb reaches the predetermined value T4, “Yes” is determined in step  213 , and steps  214  to  217  are executed. The electric motor  21  is stopped in step  214 , an alarm for abnormality is generated in step  215 , and the elapsed time T and the abnormal condition establishment duration Tb are reset in step  215 . In step  217 , the return process is performed to end the program in step  99  in  FIG. 5 . 
         [0067]    In a period in which the elapsed time T falls within the range of the predetermined value T3 to a set value T5, when the current value A supplied to the electric motor  21  does not increase not to reach the abnormality determination current value A2 (more specifically, as indicated by a solid line or a broken line in  FIG. 10 , when the electric motor  21  normally operates), steps  205  to  208  in  FIG. 7  are repeatedly executed. “No” is determined in step  205 , the elapsed time T is counted up in step  206 , the abnormal condition establishment duration Tb is reset in step  207 , and “No” is determined in step  208 . The set value T5 is set on the basis of a time required when the parking lever  17  moves from the operating position to the return position by normal reversely rotational drive of the electric motor  21 . 
         [0068]    In this manner, when the elapsed time T reaches the set value T5, “Yes” is determined in step  208  in  FIG. 7 , and an in-normal-state process is executed in step  220 . When the motor control unit (electric control device) ECU executes the in-normal-state process in step  220  in  FIG. 7 , an in-normal-state process routine in  FIG. 9  is executed. In the in-normal-state process routine in  FIG. 9 , the process is started in step  221 , a no-load current value Ao is calculated in step  222 , and it is determined in step  223  whether the current value A supplied to the electric motor  21  is a load determination current value (Ao+A3) or more. The no-load current value Ao is a current value supplied to the electric motor  21  before the first coupling pin  29   a  is brought into contact with the stopper  27  by the reversely rotational drive of the electric motor  21  (more specifically, in a no-load state set until the first coupling pin  29   a  contacts with the stopper  27  after the elapsed time T becomes the set value T5). A predetermined value A3 corresponds to a current value increasing depending on an increase in load obtained by the load applying mechanism (the stopper  27  and the disk spring assembly  28 ), and is arbitrarily set. Until the current value A reaches the load determination current value (Ao+A3), “No” is determined in step  223 , and steps  223  to  229  in  FIG. 9  are repeatedly executed. In step  229 , a load condition establishment duration Tc is reset. 
         [0069]    Until the current value A reaches the load determination current value (Ao+A3), “Yes” is determined in step  223 , and steps  224  to  225  are executed. The load condition establishment duration Tc is counted up in step  224  (Tcup), and it is determined in step  225  whether the load condition establishment duration Tc is a predetermined value T6 or more. The predetermined value T6 is to determine a stop timing of the electric motor  21  (see T6 in  FIG. 10 ), and is arbitrarily set. Until the load condition establishment duration Tc reaches the predetermined value T6, “No” is determined in step  225 , and steps  223  to  225  are repeatedly executed. 
         [0070]    When the load condition establishment duration Tc reaches the predetermined value T6, “Yes” is determined in step  225 , steps  226  to  228  are executed. The reversely rotational drive of the electric motor  21  is stopped in step  226 , the release state is stored and the elapsed time T and the load condition establishment duration Tc are reset in step  227 , and the return process is performed in step  228  to end the program in step  99  in  FIG. 5 . 
         [0071]    In the embodiment described above, although the determination is made by setting the durations Ta, Tb, and Tc to avoid an erroneous determination caused by signal noise or the like, the determination can also be made without setting the durations Ta, Tb, and Tc (executed such that, after T becomes T1, the forward rotational drive of the electric motor  21  is stopped when A reaches A1, the reversely rotational drive of the electric motor  21  is stopped when T is T3 to T5 and A reaches A2, and the reversely rotational drive of the electric motor  21  is stopped after T becomes T5 and when A reaches (Ao+A4)). 
         [0072]    As described above, in short, in the embodiment, in the electric parking brake device according to the present invention, the operation/stop of the electric motor  21  can be advantageously controlled by a current value A supplied to the electric motor  21  (a sensor for electrically detecting the state of the parking lever  17  is advantageously unnecessary), and the motor control unit (electric control device) ECU can be simply configured at low costs. Since the motor control unit (electric control device) ECU includes the calculation unit (steps  222  and  223 ) and the reversely rotational drive stop unit (steps  223  to  226 ) and is configured to stop the reversely rotational drive of the electric motor  21  when it is determined that the rotational load determination value (current value A) is the reference value (Ao+A3) or more the set time after the reversely rotational drive of the electric motor  21  is started (T=0) (T≧T5), the reversely rotational drive of the electric motor  21  can be accurately stopped, and a rotational load required for the load applying mechanism (the stopper  27  and the disk spring assembly  28 ) can be set to be small. As a result, the load applying mechanism (the stopper  27  and the disk spring assembly  28 ) can be miniaturized and manufactured at low costs. 
         [0073]    In the embodiment, the sum (Ao+A3) of the no-load current value Ao and the preset predetermined current value A3 is defined as a reference value for reversely rotational drive stop determination of the electric motor  21 , and the no-load current value Ao serves as a part of the reference value. For this reason, a fluctuation in performance caused by a manufacturing error or the like in the conversion mechanism  22  or the load applying mechanism (the stopper  27  and the disk spring assembly  28 ) can be excluded. Thus, determination accuracy when the reversely rotational drive of the electric motor  21  is stopped can be improved, and a rotational load required by the load applying mechanism (the stopper  27  and the disk spring assembly  28 ) can be reduced. As a result, the load applying mechanism (the stopper  27  and the disk spring assembly  28 ) can be miniaturized and manufactured at low costs. 
         [0074]    In the embodiment, when it is determined that the rotational load determination value (current value A) is the reference value (A2) or more within the set time (time zone from T3 to T5) except for an operation initial time zone (time zone from 0 to T3) in which a current is unstable from the start of the reversely rotational drive (T=0) of the electric motor  21 , the abnormal-state reversely rotational drive stop unit (step  214 ) for stopping the reversely rotational drive of the electric motor  21  and the abnormality notification unit (step  215 ) for notifying of abnormality are included in the motor control unit (electric control device) ECU. For this reason, abnormality in the electric actuator  20  in the device is detected to make it possible to stop an abnormal operation and to notify of the abnormal operation. 
         [0075]    In the embodiment, the program is executed such that the sum (Ao+A3) of the no-load current value Ao and the preset predetermined current value A3 is defined as the reference value for determining a timing of stopping the reversely rotational drive of the electric motor  21  and the current value A supplied to the electric motor  21  is defined as the rotational load determination value. However, in execution of the present invention, a differential value of the current value A supplied to the electric motor  21  may be employed as the rotational load determination value. In this case, the stop timing can be determined rapidly more than that in the embodiment, determination accuracy at which the reversely rotational drive of the electric motor  21  is stopped can be improved, and the load applying mechanism can be further miniaturized and manufactured at low costs. 
         [0076]    In the embodiment, the determination is made such that the sum (Ao+A3) of the no-load current value Ao and the preset predetermined current value A3 is defined as the reference value for determining a timing of stopping the reversely rotational drive of the electric motor  21  and the current value A supplied to the electric motor  21  is defined as the rotational load determination value. However, in execution of the present invention, the determination can also be made such that the set value A4 (see  FIG. 10 ) larger than (Ao+A3) is employed as the reference value. 
         [0077]    In the embodiment, an abnormality determination is made by the current value A supplied to the electric motor  21 . However, for example, the abnormality determination can also be made by a differential value of the current value A supplied to the electric motor  21 , and various changes can be effected without departing from the contents described in the scope of claims.