Patent Publication Number: US-2022212646-A1

Title: Brake control device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a brake control device. 
     BACKGROUND ART 
     In recent years, in vehicles such as passenger cars, a brake device using a hydraulic brake device that generates hydraulic braking force and an electric brake device (electric parking brake (EPB)) that generates electric braking force in combination has been widely adopted. In this brake device, for example, a braking member is pressed by hydraulic pressure toward a member-to-be-braked that rotates integrally with a wheel of a vehicle to generate hydraulic braking force, and the braking member is pressed toward the member-to-be-braked by driving a motor to generate electric braking force. In this case, a braking force obtained by summing the hydraulic braking force and the electric braking force is generated. 
     Therefore, for example, if the target braking force is to be generated by the electric braking force independently of the hydraulic braking force when the hydraulic braking force is generated, an excessive braking force is generated. Therefore, there is a conventional technique in which the generated hydraulic braking force is estimated based on the hydraulic pressure of the master cylinder, and an amount obtained by subtracting the estimated hydraulic braking force from the target braking force is generated by the electric braking force. 
     CITATIONS LIST 
     Patent Literature 
     Patent Literature 1: German Patent Application Publication No. 10150803 
     SUMMARY 
     Technical Problems 
     However, in the case of the above-described conventional technique, for example, in a state where the hydraulic pressure of the master cylinder has not sufficiently reached the wheel cylinder due to sudden brake operation (sudden stepping) or the like by the driver (driver), the estimated hydraulic braking force is smaller than the actually generated hydraulic braking force. In this case, the sum of the estimated hydraulic braking force and the electric braking force becomes smaller than the target braking force. Then, for example, there is a problem that a situation in which the braking force necessary for stopping the vehicle on the slope cannot be realized occurs. 
     Therefore, an object of the present disclosure is to provide a brake control device capable of realizing the necessary braking force even when the hydraulic pressure of the master cylinder does not sufficiently reach the wheel cylinder due to sudden brake operation or the like by a driver in a brake device that uses both a hydraulic brake device and an electric brake device. 
     Solutions to Problems 
     A brake control device according to the present disclosure relates to a brake control device applied to a vehicle including a hydraulic brake device that presses a braking member by hydraulic pressure toward a member-to-be-braked that rotates integrally with a wheel of a vehicle to generate hydraulic braking force, and an electric brake device that presses the braking member toward the member-to-be-braked by driving a motor to generate an electric braking force, the brake control device including a control unit configured to calculate a target current value, which is a target value of current to the motor, based on hydraulic pressure of a master cylinder, and reduce an energization level to the motor when an actual current value, which is an actual value of the current to the motor, reaches the target current value, set a hydraulic pressure threshold value, which is a threshold value of a hydraulic pressure of the master cylinder corresponding to a braking force necessary for the vehicle to stop based on an inclination angle of a road on which the vehicle is stopped, and calculate a time change amount of the hydraulic pressure of the master cylinder, and in a case where the time change amount exceeds a predetermined change amount, increase an energization level to the motor when the hydraulic pressure of the master cylinder subsequently becomes less than or equal to the hydraulic pressure threshold value. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view illustrating an overall outline of a vehicle brake device according to a first embodiment. 
         FIG. 2  is a schematic cross-sectional view of a wheel brake mechanism of a rear wheel system provided in the vehicle brake device of the first embodiment. 
         FIG. 3  is a graph illustrating a relationship between a master cylinder hydraulic pressure and a target current value in the first embodiment. 
         FIG. 4  is a graph illustrating a relationship between a road inclination angle and a hydraulic pressure threshold value in the first embodiment. 
         FIGS. 5A and 5B  are timing charts illustrating an example of a temporal change of each value in the first embodiment. 
         FIG. 6  is a flowchart illustrating a parking brake control process executed by the brake control device of the first embodiment. 
         FIG. 7  is a flowchart illustrating a re-clamp control process executed by the brake control device of the first embodiment. 
         FIGS. 8A and 8B  are timing charts illustrating an example of a temporal change of each value in a second embodiment. 
         FIG. 9  is a flowchart illustrating a parking brake control process executed by the brake control device of the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present disclosure (first embodiment, second embodiment) will be disclosed. The configurations of the embodiment shown below, and the operations and results (effects) provided by the configurations are merely examples. The present disclosure can also be realized with configurations other than the configurations disclosed in the following embodiments. Furthermore, according to the present disclosure, it is possible to obtain at least one of the various effects (including derivative effects) obtained by the following configuration. 
     Hereinafter, the first EPB operation may be referred to as a clamp, and the second EPB operation for the subsequent braking force adjustment may be referred to as a re-clamp. The first embodiment and the second embodiment are different in that the first embodiment performs the re-clamping after the clamping is completed, and the second embodiment starts the re-clamping after the clamping is forcibly terminated in the middle. 
     In a first embodiment and a second embodiment, a vehicle brake device in which a disc brake type EPB is applied to the rear wheel system will be described by way of an example. 
     First Embodiment 
       FIG. 1  is a schematic view showing an overall outline of a vehicle brake device according to a first embodiment.  FIG. 2  is a schematic cross-sectional view of a wheel brake mechanism of the rear wheel system provided in the vehicle brake device of the first embodiment. 
     As shown in  FIGS. 1 and 2 , the vehicle brake device according to the first embodiment includes a service brake  1  (hydraulic brake device) that presses a brake pad  11  (braking member) by hydraulic pressure toward a brake disc (member-to-be-braked) that rotates integrally with a wheel of a vehicle to generate hydraulic braking force (service brake force), and an EPB  2  (electric brake device) that presses the brake pad  11  toward the brake disc  12  by driving an EPB motor  10  to generate electric braking force. 
     The service brake  1  is a hydraulic brake mechanism that generates brake hydraulic pressure based on the depression of the brake pedal  3  by the driver and generates service brake force based on this brake hydraulic pressure. Specifically, the service brake  1  boosts the pedaling force corresponding to the depression of the brake pedal  3  by the driver with a booster  4 , and then generates a brake hydraulic pressure corresponding to the boosted pedaling force in a master cylinder (M/C)  5 . Then, the brake hydraulic pressure is transmitted to a wheel cylinder (W/C)  6  provided in a wheel brake mechanism of each wheel to generate a service brake force. Furthermore, an actuator  7  for controlling brake hydraulic pressure is provided between the M/C  5  and the W/C  6 . The actuator  7  adjusts the service brake force generated by the service brake  1  and performs various controls (e.g., anti-skid control etc.) for improving the safety of the vehicle. 
     Various controls using the actuator  7  are executed by an electronic stability control (ESC)-ECU  8  that controls the service brake force. For example, the ESC-ECU  8  outputs a control current for controlling various control valves provided in the actuator  7  and a motor for driving the pump to control the hydraulic circuit provided in the actuator  7 , and control the W/C pressure transmitted to the W/C  6 . Wheel slip is thereby avoided, and the safety of the vehicle is improved. For example, the actuator  7  is configured to include, for each wheel, a pressure increasing control valve that controls the application of the brake hydraulic pressure generated in the M/C  5  or the brake hydraulic pressure generated by the pump drive with respect to the W/C  6 , a pressure reducing control valve that reduces the W/C pressure by supplying brake fluid in each W/C  6  to a reservoir, and the like, and can perform pressure increasing, maintaining, and reducing control of the W/C pressure. Furthermore, the actuator  7  can realize the automatic pressurizing function of the service brake  1 , and can automatically pressurize the W/C  6  even in a state where there is no brake operation based on the control of the pump drive and various control valves. 
     The EPB  2  generates an electric braking force by driving the wheel brake mechanism by the EPB motor  10 , and is configured to include an EPB-ECU  9  (control unit) that controls the drive of the EPB motor  10 . The EPB-ECU  9  and the ESC-ECU  8  transmit and receive information by, for example, Controller Area Network (CAN) communication. 
     The wheel brake mechanism is a mechanical structure that generates a brake force (braking force) in the vehicle brake device of the first embodiment, and has a structure in which a wheel brake mechanism of the front wheel system first generates a service brake force by the operation of the service brake  1 . On the other hand, the wheel brake mechanism of the rear wheel system has a shared structure that generates a brake force for both the operation of the service brake  1  and the operation of the EPB  2 . The wheel brake mechanism of the front wheel system is a wheel brake mechanism that has been conventionally used in general, in which a mechanism for generating the electric braking force based on the operation of the EPB  2  is omitted, as opposed to the wheel brake mechanism of the rear wheel system, and thus the description thereof will be omitted here, and the wheel brake mechanism of the rear wheel system will be described below. 
     In the wheel brake mechanism of the rear wheel system, not only when the service brake  1  is operated but also when the EPB  2  is operated, the brake pad  11 , which is the friction material shown in  FIG. 2 , is pressed to sandwich the brake disc  12  ( 12 RL,  12 RR,  12 FR,  12 FL) which is a friction object material by the brake pad  11 , thus generating a frictional force between the brake pad  11  and the brake disc  12 , and generating a brake force. 
     Specifically, the wheel brake mechanism rotates the EPB motor  10  directly fixed to the body  14  of the W/C  6  for pressing the brake pad  11  as shown in  FIG. 2  in the caliper  13  shown in  FIG. 1  to rotate a spur gear  15  provided on a drive shaft  10   a  of the EPB motor  10 . Then, the brake pad  11  is moved by transmitting the rotational force (output) of the EPB motor  10  to a spur gear  16  engaged with the spur gear  15 , and the electric braking force by the EPB  2  is generated. 
     In the caliper  13 , in addition to the W/C  6  and the brake pad  11 , a part of the end face of the brake disc  12  is accommodated so as to be sandwiched by the brake pad  11 . The W/C  6  can generate the W/C pressure in a hollow portion  14   a,  which is the brake fluid accommodation chamber, by introducing the brake hydraulic pressure into the hollow portion  14   a  of the cylindrical body  14  through a passage  14   b,  and is configured to include a rotary shaft  17 , a propulsion shaft  18 , a piston  19 , and the like in the hollow portion  14   a.    
     The rotary shaft  17  has one end connected to the spur gear  16  through an insertion hole  14   c  formed in the body  14 , so that when the spur gear  16  is turned, the rotary shaft  17  is turned with the turning of the spur gear  16 . A male screw groove  17   a  is formed on the outer peripheral surface of the rotary shaft  17  at the end of the rotary shaft  17  opposite to the end coupled to the spur gear  16 . On the other hand, the other end of the rotary shaft  17  is axially supported by being inserted into the insertion hole  14   c.  Specifically, the insertion hole  14   c  is provided with a bearing  21  together with an O-ring  20 , so that the O-ring  20  prevents the brake fluid from leaking out between the rotary shaft  17  and the inner wall surface of the insertion hole  14   c,  and the bearing  21  axially supports the other end of the rotary shaft  17 . 
     The propulsion shaft  18  is configured by a nut including a hollow tubular member, and has a female screw groove  18   a  to be screw fitted with the male screw groove  17   a  of the rotary shaft  17  formed on the inner wall surface. The propulsion shaft  18  is configured, for example, in a circular column shape or a polygonal column shape provided with a key for preventing rotation, so that even if the rotary shaft  17  is turned, it cannot be turned about the turning center of the rotary shaft  17 . Therefore, when the rotary shaft  17  is turned, the rotational force of the rotary shaft  17  is converted to a force for moving the propulsion shaft  18  in the axial direction of the rotary shaft  17  by the engagement between the male screw groove  17   a  and the female screw groove  18   a . When the drive of the EPB motor  10  is stopped, the propulsion shaft  18  stops at the same position due to the frictional force from the engagement between the male screw groove  17   a  and the female screw groove  18   a,  where if the drive of the EPB motor  10  is stopped when the target electric braking force is obtained, the propulsion shaft  18  can be held at that position, desired electric braking force can be maintained and self-locking (hereinafter simply referred to as “lock”) can be performed. 
     The piston  19  is arranged so as to surround the outer periphery of the propulsion shaft  18 , and is formed by a bottomed cylindrical member or a polygonal cylindrical member and arranged such that the outer peripheral surface comes into contact with the inner wall surface of the hollow portion  14   a  formed in the body  14 . A structure is such that a seal member  22  is provided on the inner wall surface of the body  14  and W/C pressure can be applied to the end face of the piston  19  so that brake fluid does not leak out between the outer peripheral surface of the piston  19  and the inner wall surface of the body  14 . The seal member  22  is used to generate a reaction force for returning the piston  19  at the time of release control after the lock control. Since the seal member  22  is provided, basically, even if the brake pad  11  and the piston  19  are pushed in within a range not exceeding the elastic deformation amount of the seal member  22  by the tilted brake disc  12  during turning, they are pushed back toward the brake disc  12  so that the gap between the brake disc  12  and the brake pad  11  is held at a predetermined clearance. 
     In addition, to prevent the piston  19  from turning about the turning center of the rotary shaft  17  even if the rotary shaft  17  rotates, when the propulsion shaft  18  is provided with a rotation prevention key, the piston is provided with a key groove in which the key slides, and when the propulsion shaft  18  has a polygonal column shape, the piston has a polygonal cylindrical shape corresponding thereto. 
     The brake pad  11  is arranged at the distal end of the piston  19 , and the brake pad  11  is moved in the left-right direction in the plane of drawing accompanying the movement of the piston  19 . Specifically, the piston  19  is movable in the left direction in the plane of drawing accompanying the movement of the propulsion shaft  18 , and is movable in the left direction in the plane of drawing independently from the propulsion shaft  18  when the W/C pressure is applied to the end of the piston  19  (the end opposite to the end where the brake pad  11  is arranged). Then, if the brake hydraulic pressure in the hollow portion  14   a  is not applied (W/C pressure=0) when the propulsion shaft  18  is at the release position (the state before the EPB motor  10  is rotated), which is the standby position in the normal release, the piston  19  is moved in the right direction in the plane of drawing by the elastic force of the seal member  22  to be described later, and the brake pad  11  can be separated away from the brake disc  12 . Furthermore, when the EPB motor  10  is rotated and the propulsion shaft  18  is moved in the left direction in the plane of drawing from the initial position, even if the W/C pressure becomes 0, the movement of the piston  19  in the right direction in the plane of drawing is regulated by the moved propulsion shaft  18  and the brake pad  11  is held in place. 
     In the wheel brake mechanism configured as described above, when the service brake  1  is operated, the piston  19  is moved in the left direction in the plane of drawing based on the W/C pressure generated thereby so that the brake pad  11  is pressed against the brake disc  12  and the service brake force is generated. Furthermore, when the EPB  2  is operated, the spur gear  15  is rotated by driving the EPB motor  10 , and the spur gear  16  and the rotary shaft  17  are accordingly rotated, so that the propulsion shaft  18  is moved toward the brake disc  12  (left direction in the plane of drawing) based on the engagement between the male screw groove  17   a  and the female screw groove  18   a.  The distal end of the propulsion shaft  18  thereby abuts the bottom surface of the piston  19  and presses the piston  19 , whereby the piston  19  is also moved in the same direction, so that the brake pad  11  is pressed against the brake disc  12  and an electric braking force is generated. Therefore, a shared wheel brake mechanism that generates a brake force for both the operation of the service brake  1  and the operation of the EPB  2  can be adopted. 
     Furthermore, it is possible to confirm the generation state of the electric braking force by the EPB 2  or recognize the current detection value by confirming the current detection value of the current sensor (not shown) for detecting the current of the EPB motor  10 . 
     A front-rear G sensor  25  detects G (acceleration) in the front-rear direction (advancing direction) of the vehicle and transmits a detection signal to the EPB-ECU  9 . 
     An M/C pressure sensor  26  detects the M/C pressure in the M/C  5  and transmits a detection signal to the EPB-ECU  9 . 
     A temperature sensor  28  detects the temperature of the wheel brake mechanism (e.g., a brake disc) and transmits a detection signal to the EPB-ECU  9 . 
     A wheel speed sensor  29  detects the rotation speed of each wheel and transmits a detection signal to the EPB-ECU  9 . Although one wheel speed sensor  29  is actually provided for each wheel, detailed illustration and description thereof will be omitted here. 
     The EPB-ECU  9  is configured by a well-known microcomputer equipped with CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), I/O, and the like, and performs parking brake control by controlling the rotation of the EPB motor  10  following the program stored in the ROM and the like. 
     The EPB-ECU  9  inputs, for example, a signal corresponding to the operation state of an operation switch (SW)  23  provided on an instrumental panel (not shown) in the vehicle compartment, and drives the EPB motor  10  according to the operation state of the operation SW  23 . Furthermore, the EPB-ECU  9  executes lock control, release control, and the like based on the current detection value of the EPB motor  10 , and recognizes that the lock control is being performed based on the control state or that the wheel is in the lock state by the lock control, and that the release control is being performed or that the wheel is in the release state (EPB release state) by the release control. Then, the EPB-ECU  9  outputs a signal for performing various displays to an indicator lamp  24  provided on the instrumental panel. 
     The vehicle brake device configured as described above basically performs an operation of generating a braking force in the vehicle by generating the service brake force by the service brake  1  when the vehicle is traveling. Furthermore, when the vehicle is stopped by the service brake  1 , the driver performs operations such as pressing the operation SW  23  to operate the EPB  2  and generate the electric braking force thus maintaining the stop state, and releasing the electric braking force thereafter. That is, as the operation of the service brake  1 , when the driver operates the brake pedal  3  while the vehicle is traveling, the brake hydraulic pressure generated in the M/C  5  is transmitted to the W/C  6  thus generating the service brake force. Moreover, as the operation of the EPB  2 , the piston  19  is moved by driving the EPB motor  10 , and the electric braking force is generated by pressing the brake pad  11  against the brake disc  12  to have the wheels in the lock state, or the electric braking force is released by separating the brake pad  11  from the brake disc  12  to have the wheels in the release state. 
     Specifically, the electric braking force is generated or released by the lock/release control. In the lock control, the EPB  2  is operated by forward rotating the EPB motor  10 , the rotation of the EPB motor  10  is stopped at a position where a desired electric braking force can be generated by the EPB  2 , and this state is maintained. A desired electric braking force is thereby generated. In the release control, the EPB  2  is operated by reverse rotating the EPB motor  10 , and the electric braking force generated in the EPB  2  is released. 
     More specifically, the EPB-ECU  9  calculates a target current value which is a target value of the current to the EPB motor  10  based on the hydraulic pressure of the M/C  5 , and reduces the energization level to the motor when the actual current value which is an actual value of the current to the EPB motor  10  reaches the target current value. When the hydraulic pressure of the M/C  5  is equal to the hydraulic pressure of the W/C  6 , the target braking force can be realized by this control. However, with only this control, in a state where the hydraulic pressure of the M/C  5  does not sufficiently reach the M/C  5  due to sudden brake operation (sudden stepping) or the like by the driver, the realized braking force becomes smaller than the target braking force. Therefore, the following control is also performed. 
     The EPB-ECU  9  sets a hydraulic pressure threshold value, which is a threshold value of the hydraulic pressure of the M/C  5  corresponding to the braking force necessary for the vehicle to stop, based on the inclination angle of the road where the vehicle is stopped. Note that the inclination angle of the road can be recognized (calculated) on the basis of, for example, detection signals by the front-rear G sensor  25 . 
     In addition, the EPB-ECU  9  calculates the time change amount of the hydraulic pressure of the M/C  5 , and in a case where the time change amount exceeds a predetermined change amount (threshold value), increases the energization level to the EPB motor  10  (performs re-clamping) when the hydraulic pressure of the M/C  5  becomes less than or equal to the hydraulic pressure threshold value thereafter. 
     Note that, for example, the EPB-ECU  9  determines the hydraulic pressure threshold value based on the actual current value at the time point when the reduction in the energization level to the EPB motor  10  is started. For example, the EPB-ECU  9  sets the hydraulic pressure threshold value to be smaller as the actual current value at the time point when the reduction in the energization level to the EPB motor  10  is started is larger. Hereinafter, processing and the like of the EPB-ECU  9  will be described in detail with reference to  FIG. 3  and subsequent drawings. 
     Here, meanings of main symbols used in the following description will be described. Pm is the hydraulic pressure of the M/C  5 . Ia is an actual current value of the EPB motor  10 . It is a target current value of the EPB motor  10 . Ix is an actual current value (start actual current value) at the time point when the reduction in the energization level to the EPB motor  10  is started. 
     Zit is a calculation map of the target current value of the EPB motor  10 . Ka is a road inclination angle. dP is a time change amount of the M/C hydraulic pressure Pm (differential value of Pm: hydraulic pressure gradient). px is a predetermined change amount (threshold value) with respect to the time change amount dP. Pz is a hydraulic pressure threshold value. Zpz is a calculation map of the hydraulic pressure threshold value Pz. 
       FIG. 3  is a graph illustrating a relationship (calculation map Zit) between the M/C hydraulic pressure Pm and the target current value It in the first embodiment. In the graph of  FIG. 3 , the vertical axis represents the target current value It, and the horizontal axis represents the M/C hydraulic pressure Pm. By using this calculation map Zit, the target current value It can be generally determined to be smaller as the M/C hydraulic pressure Pm is larger. This is because when the target braking force is the same, the electric braking force may be smaller as the hydraulic braking force is larger. 
       FIG. 4  is a graph illustrating a relationship (calculation map Zpz) between the road inclination angle Ka and the hydraulic pressure threshold value Pz in the first embodiment. In the graph of  FIG. 4 , the vertical axis represents the hydraulic pressure threshold value Pz, and the horizontal axis represents the road inclination angle Ka. In addition, the calculation map Zpz moves downward as the start actual current value Ix is larger, and moves upward as the start actual current value Ix is smaller. 
     By using this calculation map Zpz, the hydraulic pressure threshold value Pz can be generally determined to be larger as the road inclination angle Ka is larger. This is because the braking force required to maintain the stopped state of the vehicle is larger as the road inclination angle is larger. 
     By using the calculation map Zpz, the hydraulic pressure threshold value Pz can be determined to be smaller as the start actual current value Ix is larger. This is because as the start actual current value Ix is larger, the already realized electric braking force is larger and the hydraulic braking force required for maintaining the stopped state of the vehicle is smaller. 
     Next, an example of a temporal change in each value in the first embodiment will be described with reference to  FIGS. 5A and 5B .  FIGS. 5A and 5B  are timing charts illustrating an example of a temporal change in each value in the first embodiment. In (a), the vertical axis represents a current value, and the horizontal axis represents time. 
     In (b), the vertical axis represents the braking force, and the horizontal axis represents time. Bt is the target braking force. Bm is a braking force conversion value of the M/C hydraulic pressure Pm. Bw is a braking force conversion value of the hydraulic pressure of the W/C  6 . Ba is the sum of the W/C hydraulic braking force conversion value Bw and the electric braking force (total braking force). Bn is a braking force conversion value of the hydraulic pressure threshold value Pz. 
     When there is an operation request of the EPB  2  at time t 1 , the operation control of the EPB  2  is performed by the EPB-ECU  9 , and the actual current value Ia rapidly increases due to the inrush current and then decreases thereafter and becomes a stable value at time t 2 . Thereafter, when the driver performs a sudden brake operation between times t 3  and t 5 , the M/C hydraulic braking force conversion value Bm increases, and the target current value It decreases accordingly. After time t 3 , the W/C hydraulic braking force conversion value Bw also increases, but the increase is slower than the increase in the M/C hydraulic braking force conversion value Bm. 
     The actual current value Ia increases from time t 4 , reaches the target current value It at time t 6 , and becomes 0 when the operation of the EPB  2  ends. Although the target current value It decreased from time t 3  to time t 5 , the total braking force Ba does not reach the target braking force Bt at the time point of time t 6  since the W/C hydraulic braking force conversion value Bw is smaller than the M/C hydraulic braking force conversion value Bm. 
     After time t 6 , the M/C hydraulic braking force conversion value Bm decreases from time t 7  and becomes equal to the W/C hydraulic braking force conversion value Bw at time t 8 . When the M/C hydraulic braking force conversion value Bm decreases from time t 7 , the EPB-ECU  9  then increases the target current value It by that amount. The target current value It starts to increase from time t 7  and increases until time t 10  at which the decrease of the M/C hydraulic braking force conversion value Bm stops. 
     When the M/C hydraulic braking force conversion value Bm decreases to the hydraulic pressure threshold value braking force conversion value Bn at time t 9 , the EPB  2  is driven by the EPB-ECU  9  to energize the EPB motor  10 , and the actual current value Ia rapidly increases due to the inrush current, slightly decreases, and then increases until time t 11 . Then, the total braking force Ba starts to increase from time t 9  and reaches the target braking force Bt at the time point of time t 11 . 
     Next, parking brake control process executed by the brake control device of the first embodiment will be described with reference to  FIG. 6 .  FIG. 6  is a flowchart illustrating a parking brake control process executed by the brake control device of the first embodiment. It is assumed that there is an operation request of the EPB  2  at the start of the control of  FIG. 6 . 
     In step S 1 , the EPB-ECU  9  reads the M/C hydraulic pressure Pm and the actual current value Ia. Next, in step S 2 , the EPB-ECU  9  calculates a target current value It based on the M/C hydraulic pressure Pm ( FIG. 3 ). 
     Next, in step S 3 , the EPB-ECU  9  calculates the M/C hydraulic pressure time change amount dp based on the M/C hydraulic pressure Pm. Next, in step S 4 , the EPB-ECU  9  controls the actual current value Ia to increase. That is, the energization level of the EPB  2  to the EPB motor  10  is increased. 
     Next, in step S 5 , the EPB-ECU  9  determines whether or not “M/C hydraulic pressure time change amount dp≥predetermined change amount px”, and if Yes, the process proceeds to step S 6 , and if No, the process proceeds to step S 7 . 
     In step S 6 , the EPB-ECU  9  determines that re-clamping is necessary, and proceeds to step S 7 . In step S 7 , the EPB-ECU  9  determines whether or not the actual current value Ia has reached the target current value It, and if Yes, the process proceeds to step S 8 , and if No, the process returns to step S 1 . 
     In step S 8 , the EPB-ECU  9  stores the actual current value Ia at that time as the start actual current value Ix. Next, in step S 9 , the EPB-ECU  9  controls the actual current value Ia to decrease. That is, the energization level of the EPB  2  to the EPB motor  10  is reduced. 
     Next, in step S 10 , the EPB-ECU  9  determines whether or not re-clamping is necessary, and if Yes (in a case where the process has passed through step S 6 ), the process proceeds to step S 11 , and if No (in a case where the process has not passed through step S 6 ), the process proceeds to step S 12 . In step S 12 , the EPB-ECU  9  ends the clamping. 
       FIG. 7  is a flowchart illustrating the re-clamping control process (step S 11  in  FIG. 6 ) executed by the brake control device of the first embodiment. In step S 21 , the EPB-ECU  9  reads the M/C hydraulic pressure Pm, the actual current value Ia, the road inclination angle Ka, and the start actual current value Ix. 
     Next, in step S 22 , the EPB-ECU  9  calculates a hydraulic pressure threshold value Pz based on the road inclination angle Ka and the start actual current value Ix ( FIG. 4 ). 
     Next, in step S 23 , the EPB-ECU  9  determines whether or not “M/C hydraulic pressure Pm≤hydraulic pressure threshold value Pz”, and if Yes, the process proceeds to step S 24 , and if No, the process returns to step S 21 . 
     In step S 24 , the EPB-ECU  9  calculates a target current value It based on the M/C hydraulic pressure Pm ( FIG. 3 ). 
     Next, in step S 25 , the EPB-ECU  9  controls the actual current value Ia to increase. That is, the energization level of the EPB  2  to the EPB motor  10  is increased. 
     Next, in step S 26 , the EPB-ECU  9  determines whether or not the actual current value Ia has reached the target current value It, and if Yes, the process proceeds to step S 27 , and if No, the process returns to step S 21 . 
     In step S 27 , the EPB-ECU  9  controls the actual current value Ia to decrease. That is, the energization level of the EPB  2  to the EPB motor  10  is reduced. 
     As described above, according to the brake control device of the first embodiment, the re-clamping is performed when the hydraulic pressure of the M/C  5  is suddenly increased (Yes in step S 5  in  FIG. 6 ), so that the necessary braking force can be realized even when the hydraulic pressure of the M/C  5  does not sufficiently reach the W/C  6  due to the sudden brake operation or the like by the driver. 
     Specifically, when the hydraulic pressure of the M/C  5  is suddenly increased, the re-clamping is performed after the condition of “M/C hydraulic pressure Pm hydraulic pressure threshold value Pz” is satisfied (after Yes in step S 23  of  FIG. 7 ) instead of the re-clamping being performed immediately after the end of the clamping, so that it is possible to realize an appropriate braking force without excess or deficiency by reliably equalizing the hydraulic pressure of the M/C  5  and the hydraulic pressure of the W/C  6  while preventing the vehicle from sliding down with the hydraulic braking force. 
     In addition, the hydraulic pressure threshold value Pz can be appropriately determined based on the actual current value (start actual current value Ix) at the time point when the reduction in the energization level to the EPB motor  10  is started ( FIG. 4 ). Specifically, the hydraulic pressure threshold value Pz can be appropriately set to be smaller the larger the start actual current value Ix ( FIG. 4 ). 
     On the other hand, for example, in the conventional technique, when the hydraulic braking force is generated, if the target braking force is to be generated by the electric braking force independently thereof, an excessive braking force is generated, and a situation in which an excessive hard load is applied to the caliper  13  occurs. 
     In addition, for example, in another conventional technique, if the generated hydraulic braking force is estimated based on the hydraulic pressure of the master cylinder, and an amount obtained by subtracting the estimated hydraulic braking force from the target braking force is to be generated by the electric braking force, a situation in which the necessary braking force cannot be realized occurs if there is a sudden brake operation (sudden stepping) or the like by the driver. Such a situation occurs particularly at a low temperature at which the brake fluid is less likely to flow. 
     According to the brake control device of the first embodiment, these situations can be avoided. 
     Second Embodiment 
     Next, a brake control device of a second embodiment will be described. The description on the matters same as in the first embodiment will be omitted as appropriate. 
       FIGS. 8A and 8B  are timing charts illustrating an example of a temporal change in each value in the second embodiment. The description on the matters same as  FIGS. 5A and 5B  will be omitted as appropriate. 
     Time before time t 23  is similar to time before time t 3  in  FIGS. 5A and 5B . The actual current value Ia rises from time t 24  after time t 23 . Furthermore, when the driver performs a sudden brake operation between times t 23  and t 26 , the M/C hydraulic braking force conversion value Bm increases, and the target current value It decreases accordingly. After time t 23 , the W/C hydraulic braking force conversion value Bw also increases, but the increase is slower than the increase in the M/C hydraulic braking force conversion value Bm. 
     At time t 25 , the EPB-ECU  9  determines that the time change amount of the hydraulic pressure of the M/C  5  has exceeded the predetermined change amount. Then, the EPB-ECU  9  forcibly ends the clamping, and the actual current value Ia becomes 0. Note that the total braking force Ba has not reached the target braking force Bt at the time point of time t 26 . 
     After time t 26 , the M/C hydraulic braking force conversion value Bm decreases from time t 27  and becomes equal to the W/C hydraulic braking force conversion value Bw at time t 28 . Furthermore, as the M/C hydraulic braking force conversion value Bm decreases from time t 27 , the EPB-ECU  9  thereafter increases the target current value It accordingly. The target current value It starts to increase from time t 27  and increases until time t 30  at which the decrease of the M/C hydraulic braking force conversion value Bm stops. 
     When the M/C hydraulic braking force conversion value Bm decreases to the hydraulic pressure threshold value braking force conversion value Bn at time t 29 , the EPB  2  is driven by the EPB-ECU  9  to energize the EPB motor  10 , and the actual current value Ia rapidly increases due to the inrush current, slightly decreases, and then increases until time t 31 . Then, the total braking force Ba starts to increase from time t 29  and reaches the target braking force Bt at the time point of time t 31 . 
     Next, parking brake control process executed by the brake control device of the second embodiment will be described with reference to  FIG. 9 .  FIG. 9  is a flowchart illustrating a parking brake control process executed by the brake control device of the second embodiment. It is assumed that there is an operation request of the EPB  2  at the start of the control of  FIG. 9 . 
     Steps S 1  to S 4  are similar to those in  FIG. 6 . Next, in step S 5 , the EPB-ECU  9  determines whether or not “M/C hydraulic pressure time change amount dp predetermined change amount px”, and if Yes, the process proceeds to step S 11 , and if No, the process proceeds to step S 7 . 
     Steps S 7  to S 9  are similar to those in  FIG. 6 . After step S 9 , the process proceeds to step S 12 . Furthermore, details of step S 11  are similar to those in  FIG. 7 . 
     As described above, according to the brake control device of the second embodiment, even when the clamping is forcibly ended in a case where the hydraulic pressure of the M/C  5  is suddenly increased, an effect of realizing the necessary braking force can be obtained by performing the re-clamping thereafter, similarly to the case of the first embodiment. 
     The embodiments and modified examples of the present disclosure have been described above, but the above-described embodiments and modified examples are merely examples, and they are not intended to limit the scope of the disclosure. The novel embodiments and modified examples described above can be implemented in various forms, and various omissions, substitutions, or modifications can be made without departing from the gist of the disclosure. Furthermore, the embodiments and modified examples described above are included in the scope and gist of the disclosure, and are included in the disclosure described in the Claims and the equivalent scope thereof. 
     For example, in the embodiments described above, the rear wheels are electric braking wheels, but this is not the sole case, and the front wheels may be electric braking wheels. 
     In addition, instead of determining whether or not “M/C hydraulic pressure Pm hydraulic pressure threshold value Pz” in step S 23  of  FIG. 7 , whether or not a predetermined time (preset) in which the deviation is considered to be eliminated when the driver suddenly performs the brake operation and the hydraulic pressure of the M/C  5  and the hydraulic pressure of the W/C  6  are deviated has elapsed may be determined.