Patent Publication Number: US-2023145033-A1

Title: Electronic parking brake system and control method thereof

Description:
BACKGROUND 
     Field of the Invention 
     The present disclosure relates to an electronic parking brake system and a control method thereof, and more particularly, an electronic parking brake system for determining whether the electronic parking brake is releasable based on a temperature of the parking brake upon a release of the electronic parking brake, and releasing the electronic parking brake through hydraulic assistance if necessary, and a control method thereof 
     Related Art 
     In general, an electronic parking brake generates an apply force required for parking via an electric actuator using an electric motor. When the electric motor rotates a spindle member to advance a nut member, the nut members push a piston to bring a brake pad into contact with a brake disk or bring a brake shoe into contact with a brake drum to thereby generate an apply force. 
     Instead of actuating the electric actuator, the electronic parking brake may generate an apply force by applying a hydraulic pressure to a cylinder provided in the brake and moving the piston to bring the brake pad into contact with the brake disk or by bringing the brake shoe into contact to the brake drum. 
     In this way, the electronic parking brake may thus be applied by hydraulic pressure or motor drive. 
     Meanwhile, a temperature of the brake may be increased due to heat generated during travel, and may be reduced as the heat is released after parking is applied. Alternatively, the temperature of the brake may change due to a sudden change in ambient temperature or the like. 
     If the brake is excessively applied by physical deformation of brake components due to such a change in ambient temperature, problems may occur. For example, the brake may not be released by a torque of the motor itself, and a failure of a motor is detected even when there is no failure in the motor. 
     SUMMARY 
     An aspect of the present disclosure provides an electronic parking brake system for inducing release of an electronic parking brake through hydraulic assistance when the electronic parking brake is excessively applied due to with a change in temperature, and a control method thereof. 
     In an aspect of the present disclosure, there is provided an electronic parking brake system including: an electronic parking brake having an electric motor and a hydraulic cylinder; an ESC actuator configured to generate and supply hydraulic pressure to the hydraulic cylinder; and a controller configured to control the electric motor and the ESC actuator. The controller determines whether or not the electronic parking brake is normally releasable based on the temperature of the electronic parking brake when parking is released, and controls the electric motor to supply hydraulic pressure to the hydraulic cylinder via the ESC actuator and start parking release control when normal release is not possible. 
     The controller may estimate a change in an apply force of the electronic parking brake based on a temperature of the electronic parking brake upon a parking release and a temperature upon a parking apply, and may determine whether or not a normal release of the electronic parking brake is possible based on the estimated change in the apply force of the electronic parking brake. 
     The controller may include a memory for storing a temperature of the electronic parking brake upon the parking apply. 
     The controller may monitor a current or a voltage of the electric motor to determine a failure of the electronic parking brake. 
     The controller may determine a failure of the electronic parking brake after determining whether the electronic parking brake is normally releasable and determining whether to supply a hydraulic pressure. 
     The controller may estimate a temperature of the electronic parking brake based on vehicle state information input via a communication interface. 
     In another aspect of the present disclosure, there is provided a control method of an electronic parking brake system, wherein the electronic parking brake system comprises an electric motor and an electronic parking brake having a hydraulic cylinder, the method including: obtaining a temperature of the electronic parking brake upon a parking release; determining whether the electronic parking brake is normally releasable based on the obtained temperature of the electronic parking brake; supplying a hydraulic pressure to the hydraulic cylinder via an ESC actuator in response to a determination that normal release is not possible; and controlling the electric motor to initiate a parking release. 
     The determining of whether the electronic parking brake is normally releasable may include estimating a change in an apply force of the electronic parking brake based on a temperature of the electronic parking brake upon the parking release and a temperature of the electrical parking brake upon a parking apply. 
     The control method may further include storing a temperature of the electronic parking brake upon the parking apply. 
     The control method may further include monitoring a current or a voltage of the electric motor to determine a failure of the electronic parking brake. 
     The determining of a failure of the electronic parking brake may be performed after determining whether the electronic parking brake is normally releasable and determining whether to supply a hydraulic pressure. 
     The obtaining of a temperature of the electronic parking brake may include estimating a temperature of the electronic parking brake based on vehicle state information input via a communication interface. 
     In an electronic parking brake system and a control method thereof according to the present embodiment, it is possible to prevent an unintended operation of the electronic parking braking system in consideration of a situation depending on temperature. 
     In the electronic parking brake system and the control method thereof according to this embodiment, it is possible to induce release of the electronic parking brake through hydraulic assistance, thereby preventing erroneous detection of a failure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an electronic parking brake according to an embodiment of the present disclosure. 
         FIG.  2    is a diagram illustrating a driving state when an electronic parking brake according to an embodiment of the present disclosure is applied. 
         FIG.  3    is a block diagram illustrating a schematic configuration of an electronic parking brake system according to an embodiment of the present disclosure. 
         FIG.  4    is a control flow diagram for EPB apply of an electronic parking brake system according to an embodiment of the present disclosure. 
         FIG.  5    is a control flow diagram for EPB release of an electronic parking brake system according to an embodiment of the present disclosure. 
         FIGS.  6  and  7    illustrate a driving state when an electronic parking brake according to an embodiment of the present disclosure is released. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Like reference numerals refer to like elements throughout. The present specification does not describe all elements of embodiments, and common knowledge in the technical field to which the present invention pertains or the same descriptions of the embodiments will be omitted. The term “unit,” “module,” “member,” or “block” may be implemented by using hardware or software. According to embodiments, one component may be implemented by a plurality of “units,” “modules,” “members,” or “blocks,” or one “unit,” “module,” “member,” or “block” may include a plurality of components. 
     Throughout this specification, when a part is referred to as being “connected” to another part, the two parts may not only be directly connected but may also be indirectly connected, and an indirect connection includes a connection via a wireless communication network. 
     When a part is referred to as “including” a component, other components are not excluded therefrom and may be further included unless specified otherwise. 
     Throughout this specification, when a member is referred to as being positioned “on” another member, the member may be in contact with the other member or another member may be interposed between the two members. 
     The terms “first,” “second,” etc. are used to distinguish one component from other components, and components are not limited by the terms. An expression in the singular form includes the plural form unless explicitly stated otherwise. 
     Identification numbers of respective steps are used for convenience of description, and do not describe a sequence of the respective steps. The steps may be carried out in a sequence different from that described unless a particular sequence is specified. 
       FIG.  1    illustrates an electronic parking brake according to an embodiment of the present disclosure and  FIG.  2    illustrates a driving state when an electronic parking brake according to an embodiment of the present disclosure is applied. 
     Referring to  FIG.  1   , an electronic parking brake  10  may be an electric drum brake. In the electronic parking brake  10 , a drum  12  to be rotated with a wheel is provided inside, and a pair of brake shoes  11   a  and  11   b  with brake linings attached thereto expands to brake the drum  12 . 
     The electric drum brake  10  may include the pair of brake shoes  11   a  and  11   b  each having an arc-shaped shape and installed to be movable along a surface of a backing plate coupled to a vehicle body, the drum  12  having a friction surface on an inner circumferential side thereof and rotating with a wheel, an electric actuator  13  configured to apply a force to each of the brake shoes  11   a  and  11   b  in a direction of expanding the pair of braking shoes  11   a  and  11   b , and a wheel cylinder  16 . 
     In the pair of brake shoes  11   a  and  11   b , one ends facing each other are connected to the electric actuator  13  and the wheel cylinder  16 , which are provided on a backing plate. In the pair of brake shoes  11   a  and  11   b , the other side opposite to one side connected to the electric actuator  13  and the wheel cylinder  18  is connected to pins  15   a  and  16   b  of an anchor member  14 , which are fixed to the backing plate. Accordingly, the brake shoes  11   a  and  11   b  do not rotate together with the drum  12 . 
     A strut  17  and a spring  18  are provided between the pair of brake shoes  11   a  and  11   b . The strut  17  serves as an adjuster for adjusting a gap between the pair of brake linings and the friction surface of the drum  12  according to wear of the brake linings. Further, the brake shoes  11   a  and  11   b  are fixed to both ends of the spring  18 , respectively, and are disposed so that the pair of brake shoes are close to each other. 
     The electric actuator  13  may include an electric motor M, a speed reducer, and a pressing mechanism including a ball screw mechanism. As shown in  FIG.  2   , when the electric motor M rotates in one direction, an output shaft rotates, and the rotation of the output shaft is decelerated by the speed reducer. This rotational motion is converted into a linear motion by the ball screw mechanism, and the pair of brake shoes  11   a  and  11   b  are pressed in directions away from each other. As a result, the pair of brake shoes  11   a  and  11   b  with brake linings presses the drum  12  to generate a braking force. Meanwhile, when the electric motor M rotates in the opposite direction, the pair of brake shoes  11   a  and  11   b  pressing the drum  12  and with the brake lining attached thereto are separated from the drum, thereby releasing the braking force. 
     The wheel cylinder  16 , which is a hydraulic cylinder, may apply a force to the pair of brake shoes  11   a  and  11   b  by hydraulic pressure being supplied. When the braking hydraulic pressure is supplied from the outside, a piston provided in the hydraulic cylinder moves and the pair of brake shoes  11   a  and  11   b  are respectively pressed in directions away from each other. As a result, the pair of brake shoes  11   a  and  11   b  with brake linings presses the drum  12 , thereby generating a braking force. Meanwhile, when the supply of the hydraulic pressure is cut off, the pair of brake shoes  11   a  and  11   b  with brake linings are, while pressing the drum  12 , separated from the drum  12 , thereby releasing a braking force. 
       FIG.  1    shows a case where the electric actuator  13  and the wheel cylinder  16  are connected in parallel to each other between the pair of brake shoes  11   a  and  11   b , but, in another embodiment, the electric actuator  13  and the wheel cylinder  16  may be configured as one cylinder and a piston inside the cylinder may be installed so as to move forward and backward by braking hydraulic pressure, so that the piston can move forward and backward even by a pressurization mechanism of the electric actuator. 
     On the other hand, in another embodiment of the disclosed invention the electronic parking brake may be a disc brake rather than a drum brake as disclosed in  FIG.  1   . In another embodiment, an electronic parking brake may include a carrier on which a pair of pad plates are provided to be movable back and forth so as to press a brake disk rotating together with a wheel of a vehicle, a caliper housing provided with a cylinder slidably mounted on the carrier and having a piston mounted to be capable of moving forward and backward by braking hydraulic pressure, a power conversion unit for pressing the piston, and an electric actuator for transmitting a rotational force to the power conversion unit using an electric motor M. 
     With the above-described configuration, the electronic parking brake  10  may be able to press the brake shoes or the brake pad using the electric motor M when the EPB is applied. The electronic parking brake  10  may perform a apply operation that generates a apply force as the brake shoe or brake pad pressed by the electric motor M are brought into contact with the drum or disk. 
     In addition, in the case of releasing the parking, the electronic parking brake  10  may be released from the pressure by retracting a member pressing the brake shoes or the brake pad using the electric motor M. As the brake shoes or brake pad become to be spaced from the drum or disc by release of the pressing on the brake shoes or brake pad, the electronic parking brake  10  may perform a release operation to releases the generated apply force. 
       FIG.  3    is a block diagram illustrating a schematic configuration of an electronic parking brake system according to an embodiment of the present disclosure 
     Referring to  FIG.  3   , the electronic parking brake  10  may be provided at rear left and right wheels RL and RR of the vehicle. 
     The electronic parking brake system may include a controller  200 , an ESC actuator  210 , an EPB switch  220 , and a current sensor  230 . 
     The controller  200  may be called an Electronic Control Unit (ECU). 
     The controller  200  may include a processor and a memory. The processor may control the overall operation of the electronic parking brake system. The memory may store programs for processing or control of the processor and various data for operation of the electronic parking brake system. The memory may include a volatile memory such as an S-RAM and a D-RAM, as well as a non-volatile memory, such as a flash memory, a Read Only Memory (ROM), and an Erasable Programmable Read Only memory (EPROM). 
     The controller  200  may include an ESC control module  201  for controlling the operation of the ESC actuator  210 , and an EPB control module  202  for controlling the operation of an electric motor M of the electronic parking brake  10 .The ESC control module  201  and the EPB control module  202  may be implemented by software provided in a single integrated ECU, or may be separate ECUs connected to a communication interface. 
     The controller  200  may estimate a temperature of the electronic parking brake  10  based on vehicle state information which is input via the communication interface. The controller  200  may estimate a temperature of the electronic parking brake  10  based on wheel speed information and brake pressure information, which are input via the communication interface  60 . 
     For example, when a driver of the vehicle presses a brake pedal to reduce the speed during travel of the vehicle, the brake shoes  11   a  and  11   b  with the brake lining apply pressure to the drum  12 . When a frictional force is generated by contact between the drum  12  and the brake lining, the kinetic energy of the vehicle is converted into frictional energy between the drums  11  and the brake lining. The frictional energy is converted into thermal energy, some of which may escape into the air and be absorbed by the drum  12 . The thermal energy absorbed by the drum  12  increases the temperature of the drum. In contrast, while the vehicle is traveling or stopped without braking, the thermal energy absorbed by the drum  12  is released into the surrounding connected components or atmosphere in ways of conduction, convection, and radiation, and thus, the temperature is lowered. This thermal energy conversion process may be used to create a mathematical model that calculates the temperature of the drum  12  and the electronic parking brake  10 . The frictional energy generated by the frictional force is converted into thermal energy and absorbed by the drum  12 .The thermal energy generated by the friction force may be a function of the friction coefficient of the brake lining, the braking pressure, the wheel speed, etc. Thermal energy, which has been absorbed by drum  12  when the vehicle is traveling without braking or is stopped, is transferred to the surrounding atmosphere or connected components in ways of conduction, convection, radiation, etc. The sum of the thermal energy exiting the drum  12  in ways of conduction, convection and radiation may be calculated by adding all of the respective thermal energy. Depending on a speed of the vehicle, the thermal energy to be cooled may be expressed as a function of wheel speed, ambient temperature, etc. A final temperature of the drum  12  is determined by a difference between thermal energy absorbed for a certain time and thermal energy transferred to the outside. A current temperature of the drum  12  may be determined by a change in temperature due to the difference between the two thermal energies. The temperature of the drum  12  may be continuously calculated while the vehicle travels. In addition, the controller  20  may directly detect a temperature of the drum  12  through a temperature sensor that detects the temperature of the drum  12 . 
     The ESC actuator  210  may supply brake oil pressure to wheel cylinders  16   rl  and  16   rr  of electronic parking brakes  10   rl  and  10   rr  of rear left and right wheels RL and RR so as to brake the rear left and right wheels RL and RR. 
     The ESC actuator  210  is connected to a master cylinder MC coupled with a reservoir R, which stores brake oil, via brake pipes. 
     The ESC actuator  210  is connected to the wheel cylinder  16   rl  of the electronic parking brake  10   rl  of the left rear wheel RL, and to the wheel cylinders  16   rr  of the electronic parking brake  10   rr  of the right rear wheel RR via the brake pipes. 
     The ESC actuator  210  may include a master cylinder MC for generating a brake oil pressure by operation of a brake pedal BP, a reservoir R for storing brake oil, an open/close valve for adjusting the brake oil pressure supplied to the wheel cylinders  16   rl  and  16   rr  during a braking control, and a hydraulic circuit for supplying the brake oil generated by the master cylinder MC to the wheel cylinders  17   rl  and  17   rr  or for generating brake oil using a hydraulic pressure generating device such as a motor pump or a hydraulic piston and supplying the generated brake oil to the wheel cylinders  17   rl  or  17   rr , 
     The ESC actuator  210  having the above-described configuration generates a braking force required for the wheels, by supplying the brake oil pressure generated in the master cylinder MC to the wheel cylinders  16   rl  and  16   rr  by the operation of the brake pedal BP and driving the opening/closing valve as necessary, or by supplying the brake oil pressure generated by the fluid pressure circuit to the wheel cylinders  16   rl  and  16   rr  and driving the opening/closing valve as necessary. The brake oil pressure supplied to the wheel cylinders  16   rl  and  16   rr  may generate a braking force on the left and right rear wheels RL and RR by pressing the pistons to bring the brake shoes  11   a  and  21   b  into close contact with the drum  12 . 
     The EPB switch  220  is a switch for receiving an input of a driver’s operation to the electronic parking brake  10 , and may be provided in the vicinity of the driver’s seat of the vehicle. 
     The EPB switch  220  is provided to be turned on or off by the driver. 
     The EPB switch  220  transmits a signal corresponding to an EPB apply command, which is a parking operation command, to the controller  200  in ON operation, and a signal corresponding to an EPB release command, which is a parking release command, in OFF operation. 
     The controller  200  may perform an EPB apply mode or an EPB release mode in order to apply or release the electronic parking brake  10  in accordance with an operation signal of the EPB switch  220  operated by the driver or an operation signal generated by a program associated with an electronic parking brake operation. 
     In the EPB apply mode, the controller  200  may perform EPB apply in which the brake shoes  11   a  and  11   b  are brought into close contact with the drum  12  by pressing the piston by rotating the electric motor M of the electric actuators  13   rl  and  13   rr  in one direction to generate an apply force. 
     In the EPB release mode, the controller  200  may perform EPB release in which the apply force generated by releasing the brake shoes  11   a  and  11   b  closely contacting to the drum  12  is released by releasing the pressure of the piston by rotating the electric motor M of the electric actuators  13   rl  and  13   rr  in opposite directions. 
     The current sensor  230  detects a current flowing through the electric motor M of the electronic parking brakes  10   rl  and  10   r . The current sensor  230  may detect a motor current flowing through the electric motor M using a shunt resistor or a Hall sensor. In the current sensor  230 , various methods for sensing a motor current in addition to the shunt resistor or Hall sensor may be applied 
     In the EPB apply mode, the controller  200  may rotate the electric motor M in one direction until a current value reaches a target current value corresponding to an apply force required for parking, and then may stop the motor M to complete an EPB apply operation. 
     In the EPB release mode, the controller  200  may stop the electric motor M to complete the EPB release operation after a predetermined time has elapsed after the motor M is rotated. 
     The controller  200  may monitor a current or voltage of the electric motor M to determine a failure of the electronic parking brake  10 . 
     The controller  200  controls to supply an electric current to the electric motor M in the EPB apply mode and in the EPB release mode. At this time, it is possible to monitor the current supplied to the electric motor M or the voltage applied to the motor M and to determine a failure of the electronic parking brake  10  when an abnormal pattern occurs. For example, the controller  200  may determine a failure by setting various conditions as an abnormal pattern, such as conditions in which a current value I_rsh of an in-rush interval in an initial stage of operation is higher than a set current value, there is no in-rush interval, or a time for which a current input to the electric motor M continues to be higher than a set load current I_load becomes longer than a predetermined time. 
     The controller  200  may include a memory for storing a temperature of the electronic parking brake  10  upon a parking apply. 
     The controller  200  may supply a hydraulic pressure to the wheel cylinders  16   rl  and  16   rr  of the electronic parking brakes  10   rl  and  10   rr  through an ESC cooperative control by the ESC actuator  210  before the electric actuator  13  is actuated. 
     When it is necessary to increase the hydraulic pressure of the wheel cylinders  16   rl  and  16   rr , the controller  200  may generate a brake hydraulic pressure with a hydraulic pressure generating device such as a motor pump and a hydraulic piston of the ESC actuator  210  and supply the brake oil pressure to the wheel cylinders  16   rl  and  16   rr . 
     As described above, a phenomenon occurs in which an apply force changes due to a physical change such as thermal contraction or thermal expansion of a brake component due to a temperature change. When the electronic parking brake  10  is applied with too great an apply force due to a temperature change, the electronic parking brake  10  may not be properly released due to a lack of torque of the electric motor M upon an EPB release or the apply force may not be sufficiently reduced, thereby resulting in a drag of the vehicle. 
     For example, the brake actuation during traveling causes a temperature of the brake to increase and the EPB apply is made in with the drum  12  being expanded, thereby fixing the position of the braking shoes  11   a  110b. Then, when the drum  12  contracts due to lowering of the temperature, not just the drum  12  and the brake shoes  11   a  and  11   b  strongly comes into contact with each other, but also the components of the electric actuator  13  becomes to be tightly engaged with each other. Thus, the electronic parking brake  10  is applied with a greater apply force than in a case where the electronic parking brake  10  is applied without a change in temperature. 
     As such, a large torque is required to initially drive the electric actuator  13  when the parking is released with the electronic parking brake  10  applied with a large apply force. Due to this, the torque of the motor itself alone may not be released, or may be less released such that a residual apply force remains after the release. 
     In the disclosed invention, the change in temperature upon EPB apply and EPB release affects the initial drive of the electric actuator  13  upon EPA release, and this may be solved through a hydraulic cooperative control. First, upon an EPB apply, the controller  200  estimates and stores a temperature of the electronic parking brake based on the vehicle state information. Upon an EPB release, the controller  200  determines whether the electronic parking brake is normally releasable or not, based on the temperature of the electronic parking brake estimated based on the vehicle state information and the temperature at the times of EPB apply. When normal release is not possible, the controller  200  requests a hydraulic cooperative control to perform an EPB release control. 
     The controller  200  may estimate a change in the apply force of the electronic parking brake  10  based on a temperature of the electronic parking brake  10  upon a parking release and a temperature thereof upon a parking apply, and may determine whether or not it is possible to normally release the electronic parking brake  10  based on an estimated apply force thereof. 
     When it is not determined that the electronic parking brake  10  is normally releasable, thee controller  200  may supply a hydraulic pressure via the EPB actuator  210  and initiate a parking release control of the electric motor M. 
     Therefore, in the disclosed invention, since a required torque of the electric actuator  13  can be reduced through the hydraulic supply when the EPB is released, it is possible to prevent the problems that the electronic parking brake  10  is not released with the torque in the electric motor M itself and that an apply force remains after the release because the electronic parking brake  10  is not properly released. In doing so, the disclosed invention is able to more accurately and reliably perform the EPB release operation. 
     The disclosed invention makes it possible to reduce the incidence of erroneous control such as less or too much release of the EPB and the resulting effects (overfriction, etc.) in consideration of the effects of temperature changes upon an EPB apply and an EPB release. 
     The disclosed invention may prevent a false detection of a failure of the motor when the EPB apply is not released by the torque of the engine itself due to a temperature change during the EPB release. 
     The disclosed invention may increase a product life by reducing the number of cases of control with an excessive torque of the electric actuator  13  when the EPB is released. 
       FIG.  4    is a control flow diagram for an EPB apply of an electronic parking brake system according to an embodiment of the present disclosure 
     Referring to  FIG.  4   , the controller  200  determines whether EPB apply is requested in operation  300 . 
     When the EPB apply is requested, the controller  200  first receives vehicle state information through the communication interface in operation  310 . 
     The controller  200  estimates a temperature of the electronic parking brake  10  based on the received vehicle state information in operation  320 . This may be the same as the temperature estimating process described above with reference to  FIG.  3   . 
     The controller  200  stores the temperature of the electronic parking brake  10  upon a parking apply in operation  330 . 
     Then, the controller  200  initiates and performs an EPB apply in operation  340 . When a motor current detected through the current sensor  230  reaches the target current corresponding to the EPB apply after the electric motor M is rotated in one direction, the controller  200  may determine that the EPB apply is completed and may complete the EPB apply operation. 
       FIG.  5    is a control flow diagram for EPB release of an electronic parking brake system according to an embodiment of the present disclosure. 
     Referring to  FIG.  5   , the controller  200  determines whether EPB release is requested in operation  400 . 
     When the EPB release is requested, the controller  200  first receives vehicle state information through a communication interface in operation  410 . 
     The controller  200  estimates a temperature of the electronic parking brake  10  based on the input vehicle state information in operation  420 . This may be the same as the temperature estimating process described above with reference to  FIG.  3   . 
     The controller  200  determines whether or not the electronic parking brake  10  is normally releasable based on the temperature of the electronic parking brake in operation  430 . 
     The controller  200  may estimate a change in the apply force of the electronic parking brake  10  based on the temperature of the electronic parking brake upon a parking release and the temperature of the electronic parking brake  10  upon a parking apply. The controller  200  may determine whether the electronic parking brake  10  is normally releasable based on the estimated change in the apply force of the electronic parking brake  10 . 
     To this end, controller  200  may retrieve a stored temperature of electronic parking brake  10  upon a parking apply. 
     When it is determined that normal release is not possible, the controller  200  supplies a hydraulic pressure to the hydraulic cylinder via the ESC actuator  210  in operation  435 . As such, the controller  200  may reduce the required torque of the electric actuator  13  by supplying the hydraulic pressure via the ESC actuator  210 . 
     When it is determined that the normal release is possible, or after the hydraulic pressure is supplied to the hydraulic cylinder via the ESC actuator  210 , the controller  200  controls the electric motor M to initiate the parking release in operation  440 . 
     The controller  200  monitors a current or voltage of the electric motor  450 . The controller  200  determines a failure of the electronic parking brake  10  based on the monitored current or voltage in operation  460 . 
     The controller  200  may determine a failure of the electronic parking brake  10  after determining whether to supply the hydraulic pressure by determining whether normal release is possible. The controller  200  may prevent erroneous detection of a failure by determining a failure of the electronic parking brake  10  after determining whether the hydraulic pressure is supplied. For example, when normal release is not possible with the electric motor M alone but is possible through hydraulic assistance of the ESC actuator  210 , the controller  200  may detect a failure after the supply of the hydraulic pressure, so that the electric motor M can operate normally and it is not determined as a failure. 
     When an abnormality is determined even in a case where a state of the electronic parking brake  10  is determined after determining whether or not to supply the hydraulic pressure, the controller  200  detects a failure of the electronic parking brake  10  in operation  470 . When a failure of the electronic parking brake  10  is detected, the controller  200  generates an indication signal  480  for indicating the failure to the driver. 
       FIGS.  6  and  7    illustrate a driving state when an electronic parking brake according to an embodiment of the present disclosure is released. 
     Referring to  FIG.  6   , it can be seen that, in the EPB-applied electronic parking brake  10 , the drum  12  is contracting due to a temperature change and is pressing the brake shoes  11   a  and  11   b . As a result of such contraction of the drum  12 , the brake shoes  11   a  and  11   b  are not only firmly adhered to the drum, but also press (F_T) the electric actuator  13  connected to the brake shoes  11   a  and  11   b . In response to the pressing, the electric actuator  13  forms a reaction force F_M1, and accordingly, the components of the electric actuators  12  are strongly engaged. 
     As shown in  FIG.  6   , when the electric actuator  13  is strongly pressed by the brake shoes  11   a  and  11   b , the electronic parking brake  10  may not be released only by a torque of the electric motor M itself. 
     When it is determined that the electronic parking brake  10  is not normally releasable due to a temperature change, as shown in  FIG.  6   , the controller  200  generates hydraulic pressure via the ESC actuator  210  and supplies the hydraulic pressure to the wheel cylinder  16 . 
     Referring to  FIG.  7   , it can be seen that hydraulic pressure is supplied to the wheel cylinder  16  via the ESC actuator  210 . The wheel cylinder  16  with the hydraulic pressure supplied presses (F_W) the brake shoes  11   a  and  11   b  in directions away from each other. As the wheel cylinder  16  presses the brake shoes  11   a  and  11   b , the reaction force F_M2 formed by the electric actuator  13  is reduced (F_M2&lt;F_M1). Therefore, a force with which the components of the electric actuator  13  are engaged is also reduced, and the EPB release may be performed by rotating the electric motor M. At this time, the controller  200  may release the hydraulic pressure of the wheel cylinder  16  after the EPB release operation is initiated and the electric motor M is initially driven or after the EPB release operation is completed. 
     As such, in the disclosed invention, upon an EPB release, whether the electronic parking brake is normally releasable is determined based on the temperature of the electronic parking brake  10  before the electric motor M is activated, and when the electronic parking brake is not normally releasable, hydraulic pressure is supplied to reduce a force applied to the electric actuator and then the EPB release operation is performed. Therefore, in the disclosed invention, since a required torque of the electric motor M can be reduced through the hydraulic supply when the EPB is released, and thus, it is possible to perform an EPB release operation more accurately and reliably. 
     Meanwhile, the aforementioned controller and/or components thereof may include one or more processors/microprocessor(s) coupled with a computer-readable recording medium that stores computer readable code/algorithm/software. The processor/microprocessor(s) may execute the computer-readable code/algorithm/software stored on a computer readable recording medium to perform the functions, operations, steps, etc. described above. 
     The aforementioned controller and/or components thereof may further include a memory implemented in a non-transitory computer-readable recording medium or a transitory computer readable recording medium. The memory may be controlled by the aforementioned controller and/or components thereof, and may be configured to store data that is transmitted to or received from the aforementioned controller and or components thereof or may be configured to store data which has been processed or is to be processed by the aforementioned controller and/or components thereof. 
     The disclosed embodiments may also be implemented as computer-readable codes/algorithms/software on a computer readable recording medium. The computer readable recording medium may be a computer-readable non-transitory recording medium such as a data storage device capable of storing data readable by a processor/microprocessor. Examples of the computer-readable recording medium include a hard disk drive (HDD), a solid state drive (SSD), a silicon disc drive (SDD), a read only memory (ROM), a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like. 
     The embodiments have been described above with reference to the accompanying drawings. Those of ordinary skill in the art to which the present invention pertains will appreciate that the present invention can be carried out in forms different from the disclosed embodiments without changing the technical spirit or essential characteristics of the present invention. The disclosed embodiments are exemplary and should not be interpreted as restrictive.