ELECTRONIC PARKING BRAKE SYSTEM AND CONTROL METHOD FOR IT

Abstract

Electronic parking brake system (30), comprising an electronic parking brake designed to generate a clamping force on a wheel of a vehicle; and a control unit (200) configured to estimate the weight of the vehicle based on a tire pressure and longitudinal acceleration of the vehicle at the time of service braking during driving, to determine a clamping force required for parking during parking operation based on the estimated weight of the vehicle, and to operate the electronic parking brake in such a way as to generate the determined clamping force.

Description

[Technical Field]The disclosure relates to an electronic parking brake system of the brake caliper-mounted electric motor (motor-on-caliper) type and a control method thereof that operates an electric motor united with a brake caliper mounted on a vehicle wheel.[General Art]Generally, an electronic parking brake (EPB) system, particularly an EPB system with a motor-on-caliper (MoC) type electric motor seated on the caliper, increases a torque generated by the electric motor via a reduction gear to generate a clamping force required for parking by a mechanical system within a caliper.An EPB system of the MoC type presses brake pads against a disk that rotates integrally with a vehicle wheel by pressing a piston by an operation of an electric motor, and thereby can generate a clamping force by means of a frictional force between the brake pads and the disk.In a conventional EPB system, the clamping force is controlled based on a maximum weight of the vehicle.However, in the actual driving operation, driving or traveling at the maximum weight does not often occur. Accordingly, the constituent elements of a vehicle are inevitably oversized, resulting in an increase in manufacturing cost.JP 2007-15 602A relates to an electric brake device that converts a rotational motion of a motor into a linear motion and presses a brake pad against a disc to generate a braking force, and a control method thereof. GB 2 535 773 A relates to a system for determining the mass of a vehicle having an engine which exerts a force on the wheels via a drive train. JP 2016-133 375 A provides a vehicle mass estimation apparatus capable of calculating an estimation value of the vehicle mass when the vehicle is braked.[Disclosure][Technical Problem]An aspect of the disclosure provides an electronic parking brake system and a control method thereof, wherein by predicting the actual weight of a vehicle, a clamping force required for parking can be generated while preventing over-dimensioning.[Technical Solution]According to an aspect of the disclosure, there is provided an electronic parking brake system including an electronic parking brake provided to generate a clamping force on a wheel of a vehicle; and a controller configured to estimate a weight of the vehicle based on a tire pressure and a longitudinal acceleration of the vehicle at the time of service braking during travel, determine a clamping force required for parking during parking operation based on the estimated weight of the vehicle, and operate the electronic parking brake to generate the determined clamping force.The controller is configured to determine the clamping force required for parking as a higher value, the heavier the estimated weight of the vehicle.The controller is configured to repeatedly estimate the weight of the vehicle from the time of service braking during running to the start of parking based on the tire pressure and the longitudinal acceleration of the vehicle, and estimate a highest value among the estimated weights of the vehicle as the weight of the vehicle.The controller is configured to repeatedly estimate the weight of the vehicle from the time of service braking during travel to the start of parking operation based on the tire pressure and the longitudinal acceleration of the vehicle, collect the estimated weights of the vehicle, and estimate an average value of the collected weights as the weight of the vehicle.The controller, upon canceling the parking operation after the parking operation, is configured to estimate a weight obtained by increasing or decreasing the estimated weight of the vehicle by a predetermined value as the weight of the vehicle.The electronic parking brake system has a communication interface configured to communicate with a system mounted on the vehicle for obtaining the tire pressure and the longitudinal acceleration of the vehicle, wherein the controller is configured to obtain, via the communication interface, the tire pressure and the longitudinal acceleration of the vehicle at the time of service braking during travel, and estimate the weight of the vehicle on the basis of the obtained tire pressure and the obtained longitudinal acceleration of the vehicle.According to another aspect of the disclosure, there is provided an electronic parking brake system including a motor actuator operated by an electric motor, the electronic parking brake system including a motor drive circuit configured to drive the electric motor; a current sensor configured to detect a current flowing through the electric motor; a communication interface configured to communicate with a vehicle-mounted system to obtain a tire pressure and a longitudinal acceleration of the vehicle; and a controller configured to obtain, via the communication interface, the tire pressure and the longitudinal acceleration of the vehicle at the time of service braking during traveling, estimate, based on the obtained tire pressure and the obtained longitudinal acceleration of the vehicle, the weight of the vehicle, change a target current during parking operation based on the estimated weight of the vehicle, and drive the electric motor via the motor drive circuit such that a motor current detected by the current sensor reaches the changed target current.The controller is configured to change the target current to a higher value the heavier the estimated weight of the vehicle is.The controller is configured to determine a clamping force required for parking based on the estimated weight of the vehicle and change the target current according to the determined clamping force.The controller is configured to repeatedly estimate the weight of the vehicle from the time of service braking during running to the start of parking based on the tire pressure and the longitudinal acceleration of the vehicle, and estimate a highest value among the estimated weights of the vehicle as the weight of the vehicle.According to still another aspect of the disclosure, there is provided a control method for an electronic parking brake system including an electronic parking brake provided to generate a clamping force on a wheel of a vehicle, the control method including estimating a weight of the vehicle based on a tire pressure and a longitudinal acceleration of the vehicle at the time of service braking during travel; determining a clamping force required for parking during parking operation based on the estimated weight of the vehicle; and operating the electronic parking brake so as to generate the determined clamping force.In estimating the weight of the vehicle, the tire pressure and the longitudinal acceleration of the vehicle at the time of service braking during running are detected, and based on the detected tire pressure and the detected longitudinal acceleration of the vehicle, the weight of the vehicle is estimated.In estimating the weight of the vehicle, the tire pressure and the longitudinal acceleration of the vehicle at the time of service braking during traveling are obtained via a communication interface, and the weight of the vehicle is estimated based on the obtained tire pressure and the obtained longitudinal acceleration of the vehicle.In estimating the weight of the vehicle, the weight of the vehicle is repeatedly estimated based on the tire pressure and the longitudinal acceleration of the vehicle from the time of service braking during running to the start of parking operation, and a highest value among the estimated weights of the vehicle is estimated as the weight of the vehicle.In determining the clamping force, the more the estimated weight of the vehicle is, the more the clamping force required for parking is determined to be a higher value.[Advantageous Effects]According to an aspect of the disclosure, a clamping force required for parking may be generated by predicting the actual weight of the vehicle while preventing over-dimensioning.[Description of Drawings]FIG. 1 shows a vehicle to which an electronic parking brake system according to an embodiment is applied. FIG. 2 shows a structure of an electronic parking brake (EPB) applied to an EPB system according to an embodiment. FIG. 3 shows a control block of an EPB system according to an embodiment. FIG. 4 illustrates estimating vehicle weight in an EPB system according to an embodiment. FIG. 5 shows a result of estimating a vehicle weight at the time of service braking during travel in an EPB system according to an embodiment. FIG. 6 shows a clamping force for each vehicle weight estimated in an EPB system according to an embodiment. FIG. 7 shows a control method of an EPB system according to an embodiment. FIG. 8 shows a control method of an EPB system according to another embodiment. FIG. 9 shows a control method of an EPB system according to still another embodiment.[Best Mode of Carrying Out the Disclosure]Like reference numerals throughout the specification designate like elements. In addition, this description does not describe all elements according to embodiments, descriptions well known in the technology related to the disclosure, as well as overlapping portions, have been omitted. Expressions such as "part", "element", "module", "block", and the like may refer to at least one processing processed by at least one hardware or software. According to embodiments, multiple "portions", "elements", "modules", or "blocks" may be embodied as a single element, or a single "portion", "element", "module", or "block" may include multiple elements.It will be appreciated that an element described as being "connected" to another element may be directly or indirectly connected to the other element, where the indirect connection includes a "connection" over a wireless communication network.It will be understood that the term "comprising" used in this specification determines the presence of stated elements, but does not exclude the presence or addition of one or more other elements.It will be understood that when it is stated in this specification that an element is "on" another element, not only can one element contact another element, but there may be another element between the two elements.Although in this disclosure the terms "first", "second", etc. may be used to describe various elements, it will be understood that these elements are not intended to be limited by these terms. It is understood that the singular forms are also intended to include the plural forms, unless the context clearly dictates otherwise.Reference numerals used for method steps are used merely for convenience of explanation and not for limiting an order of the steps. Thus, the written order may be implemented in another manner unless the contact clearly dictates otherwise.FIG. 1 shows a vehicle to which an electronic parking brake system according to an embodiment is applied.Referring to FIG. 1, a vehicle may include an electronic brake system 10, a driver assistance system 20, and an electronic parking brake system 30.The electronic brake system 10 may control a brake device in response to a driver braking request through a brake pedal and / or wheel slip.The electronic brake system 10 may be an anti-lock system (ABS) capable of temporarily cancelling braking of vehicle wheels in response to wheel slip detected when a vehicle is braked. Or, the electronic brake system 10 may be an electronic stability control (ESC) capable of selectively cancelling braking of vehicle wheels in response to oversteer and / or understeer detected when steering a vehicle. Or, the electronic brake system 10 may be a traction control system (TCS) capable of temporarily braking vehicle wheels in response to wheel slip detected when a vehicle is running.When a pedestrian and / or an obstacle is present in a detection range, which is dependent on a transmission state, from a front detection range and a rear detection range, when the vehicle is stopped and then starts, the driver assistance system 20 may determine whether emergency braking of the vehicle is necessary depending on the acceleration intention of the driver, and perform emergency braking of the vehicle or warn the driver as a result of the determination. Specifically, when a pedestrian and / or an obstacle is present in the detection area, the driver assistance system 20 may recognize an amount of change of the accelerator pedal from an accelerator pedal position detected by an accelerator pedal sensor, determine whether emergency braking of the vehicle is necessary based on the recognized amount of change of the accelerator pedal, and perform emergency braking of the vehicle when necessary.The driver assistance system 20 may be implemented as a forward collision avoidance (FCA) system, an autonomous emergency braking (AEB) system, a lane departure warning (LDW) system, a lane keeping assist (LKA) system, a smart parking assist (SPAS) system, a driver attention warning (DAC) system, a smart cruise control (SCC) system, a blind spot detection (BSD), and the like.The electronic parking brake system 30 may communicate with the electronic brake system 10 and the driver assistance system 20 via a vehicle communication network (NT). For example, the systems may transmit / receive data via Ethernet, Media Oriented Systems Transport (MOST), FlexRay, a controller area network (CAN), a local interconnect network (LIN), and the likeFIG. 2 shows a structure of an electronic parking brake (EPB) applied to an EPB system according to an embodiment.Referring to FIG. 2, an EPB 100 may include a carrier 110 on which a pair of pad plates 111 and 112 are installed movably back and forth to press a brake disk D rotating with a wheel of a vehicle, a caliper housing 120 slidably disposed on the carrier 110 and having a cylinder 123 in which a piston 121 is disposed movably back and forth by a brake hydraulic pressure, a force conversion unit 130 pressing the piston 121, and a motor actuator 140 supplying a rotational force to the force conversion unit 130 using a motor M.The pair of pad plates 111 and 112 are divided into an inner pad plate 111 disposed to be in contact with the piston 121 and an outer pad plate 112 disposed to be in contact with a finger portion 122 of the caliper housing 120. The pair of facing plates 111 and 112 are configured on the carrier 110 fixed to a vehicle body so that the pair of facing plates 111 and 112 can move toward both sides of the brake disk D. In addition, a brake pad 113 is attached to a surface facing the brake disk D of each of the pair of pad plates 111 and 112.The caliper housing 120 is slidably disposed on the carrier 110. More specifically, the force conversion unit 130 is disposed at a rear side of the caliper housing 120, and the caliper housing 120 includes the cylinder 123 in which the piston 121 is disposed to be movable back and forth and the finger portion 122 bent downward to operate the outer pad 112. The finger portion 122 and the cylinder 123 are integrally formed.The piston 121 is provided in a cylindrical shape having a cup-like inner shape and slidably inserted into the inside of the cylinder 123. The piston 121 presses the inner facing plate 111 toward the brake disk D by an axial force of the force conversion unit 130 receiving the rotational force of the motor actuator 140, and accordingly, the piston 121 moves toward the inner facing plate 111 upon application of the axial force of the force conversion unit 130, thereby pressing the inner facing plate 112. The caliper housing 120 acts in a direction opposite to the piston 121 by a reaction force, and therefore the finger portion 122 presses the outer pad plate 112 toward the brake disk D side. Consequently, the braking can be performed.The force conversion unit 130 may receive the rotational force from the motor actuator 140 and act to press the piston 121 toward the inner facing plate 111 side.The force conversion unit 130 may include a nut member 131 disposed inside the piston 121 so as to be in contact with the piston 121, and a spindle member 135 screwed to the nut member 131.The nut member 131 is disposed inside the piston 121 in a state where its rotation is restricted, and is screwed to the spindle member 135.The nut member 131 may include a head portion 132 provided to be in contact with the plunger 121, and an engaging portion 133 extending from the head portion 132 and in which an internal thread for screwing to the spindle member 135 is formed on an inner circumferential surface.The nut member 131 moves forward or backward depending on a rotation direction of the spindle member 135, and may serve to press the piston 121 or release the pressure on the piston 121. In this case, the forward direction may be a moving direction in which the nut member 131 approaches the piston 121. The rearward direction may be a moving direction in which the nut member 131 moves away from the piston 121. In addition, the forward direction may be a moving direction in which the piston approaches the brake pads 113. The rearward direction may be a moving direction in which the piston 121 moves away from the brake pads 113.The spindle member 135 may include a shaft portion 136 that passes through a rear portion of the caliper housing 120 and rotates upon receiving the rotational force from the motor actuator 140, and a flange portion 137 that extends radially from the shaft portion 136. The shaft portion 136 may have one side that is rotatably configured and passes through a rear side of the cylinder 123, and another side disposed inside the piston 121. In this case, the one side of the shaft portion 136 passing through the cylinder 123 is connected to an output shaft of a reduction gear 142 for receiving the rotational force of the motor actuator 140.The motor actuator 141 may include an electric motor 141 and the reduction gear 142.The electric motor 141 moves the nut member back and forth by rotating the spindle member 135, thereby pressing the piston 121 or releasing the pressure on the piston 121.The reduction gear 142 may be provided between an output side of the electric motor 141 and the spindle member 135.By the above configuration, the EPB 100 can rotate the spindle member 135 in one direction in a parking operation mode using the motor actuator 140, thereby moving the nut member 131 and pressing the piston 121. The piston 121 pressed by the movement of the nut member 131 presses the inner pad plate 111, whereby the brake pads 131 come into close contact with the brake disc D and thereby can generate a clamping force.And in a parking operation cancel mode, the EPB 100 may rotate the spindle member 135 in the opposite direction using the motor actuator 140, thereby moving the nut member 131 pressed by the piston 121 backward. By the rearward movement of the nut member 131, the pressure on the piston 121 can be released. As a result of the release of the pressure on the piston 121, the brake pads 113 can be moved away from the brake disc D, thereby releasing the generated clamping force.FIG. 3 shows a control block of an EPB system according to an embodiment.Referring to FIG. 3, the EPB system 30 may include a controller 200 that performs all of the control operation related to the operation of the EPB system 100.An input side of the controller 200 is electrically connected to a current sensor 300.An input / output side of the controller 200 is electrically connected to a communication interface 310.An output side of the controller 200 is electrically connected to a motor drive circuit 320.The current sensor 300 may detect a current flowing through the electric motor 141. For example, the current sensor 300 may detect a motor current flowing through the electric motor 141 using a shunt resistor or a Hall sensor. Besides the shunt resistor or the Hall sensor, various methods for detecting the motor current may be applied to the current sensor 300. The current sensor 300 may send information regarding the detected motor current to the controller 200.The communication interface 310 may transmit and receive communication signals to and from the electronic brake system 10 and the driver assistance system 20 via a vehicle communication network (NT). The communication interface 310 may include a CAN transceiver.The motor drive circuit 320 can rotate the electric motor 141 forward or backward. For example, the motor drive circuit 320 may include an H-bridge circuit including a plurality of electric switching devices to rotate the electric motor 141 forward or backward. During a parking operation operation in which the electric motor 141 rotates in one direction by the motor drive circuit 320, the rotation of the drive motor 141 in the one direction is decelerated by the reduction gear 142, whereby the spindle member 135 can be rotated in one direction with a large force. When the spindle member 135 rotates in the one direction, the nut member 131 may be moved in the spindle direction. When the nut member 131 presses the piston 121, two brake pads 113 press the brake disk D, whereby the vehicle wheel can be braked. In the process for canceling the parking operation, the operations may be performed in a manner reverse to the parking operation.The controller 200 may be referred to as an electronic control unit (ECU).The controller 200 may include a processor 210 and a memory 220.The memory 220 may store a program for processing or controlling the processor 210 and various data for operating the electronic brake system.The memory 220 may include a volatile memory such as a static random access memory (S-RAM) and a dynamic random access memory (D-RAM), and a nonvolatile memory such as a flash memory, a read only memory (ROM), an erasable programmable read only memory (EPROM), and the like.The processor 210 may control the overall operation of the EPB system 30.The controller 200 described above may rotate the electric motor 141 back or forth through the motor drive circuit 320.The controller 200 may perform a parking operation mode or a parking operation cancel mode by an operation signal from a parking switch operated by the driver or an operation signal generated by a program related to an operation of the EPB.In the parking operation mode, the controller 200 may rotate the electric motor 141 in a direction, thereby moving the nut member 131 forward and pressing the piston 121. Accordingly, a parking operation operation may be performed in which the brake pads 113 come into close contact with the brake disc D to generate a clamping force.In the parking operation release mode, the controller 200 may rotate the electric motor 141 in the opposite direction to move the nut member 131 backward, thereby releasing the pressure on the piston 121. Accordingly, the controller may perform a parking operation canceling operation to cancel the generated clamping force by separating the brake pads 113 from the brake disc D.The controller 200 may request and obtain information required for estimating a vehicle weight from the electronic brake system 10 and / or the driver assistance system 20 via the communication interface 310.The controller 200 may request and receive a brake pedal signal, a brake pressure signal, and a vehicle acceleration signal from the electronic brake system 10 and / or the driver assistance system 20 via the communication interface 310.The brake pedal signal may be a brake pedal signal output from a pedal displacement sensor configured in the electronic brake system 10 to detect an operation of the brake pedal. The brake pressure signal may be a pressure signal output from a brake pressure sensor installed in the electronic brake system 10 to detect a brake pressure. The brake pressure signal may be a tire pressure signal output from a tire pressure sensor for detecting the tire pressure of a wheel on which the EPB 100 is installed. The vehicle acceleration signal may be an acceleration signal output from a longitudinal acceleration sensor configured in the driver assistance system 20 to detect the longitudinal acceleration of the vehicle. Incidentally, if a system is capable of providing the brake pedal signal, the brake pressure signal, and the vehicle acceleration signal, the controller 200 may receive the above-described signals from this system instead of the electronic brake system 10 and the driver assistance system 20.When the brake pedal signal is received, the controller 200 may request and receive the brake pressure signal and the vehicle acceleration signal from the electronic brake system 10.FIG. 4 illustrates estimating vehicle weight in an EPB system according to an embodiment.Referring to FIG. 4, the controller 200 may estimate a weight of the vehicle based on a tire pressure and a vehicle acceleration.The controller 200 may estimate the weight of the vehicle based on the tire pressure and the vehicle acceleration.The controller 200 may estimate the weight of the vehicle based on the tire pressure and the vehicle acceleration at the time of service braking during travel.When the brake pedal is operated, the controller 200 may estimate the weight of the vehicle based on the tire pressure and the vehicle acceleration.By inversely calculating a pressure P that generates a braking force of the vehicle and using a relationship between the pressure P and a force with which a piston of a caliper acts on brake pads when the pressure P acts on the caliper, the following relational expression for the weight W of the vehicle and the vehicle acceleration can be derived.The above [Equation 1] can be rearranged and expressed as.Here, A cylinder denotes the cross-sectional area of the piston, N piston denotes the number of pistons, BF denotes a braking factor (generally, 2 μ pad; where μ pad is the brake pad friction coefficient), η denotes the efficiency, R tire denotes the tire radius, and R eff denotes the effective disk radius.FIG. 5 shows a result of estimating a vehicle weight at the time of service braking during travel in an EPB system according to an embodiment.Referring to FIG. 5, the vertical axis shows the estimated vehicle weight and the horizontal axis shows the number of estimates.The vehicle weight may be repeatedly estimated and stored based on tire pressure and vehicle acceleration until a start of a parking operation each time service braking is performed during driving.The highest value among a plurality of estimated vehicle weights may be estimated as a final vehicle weight.Or, the plurality of estimated vehicle weights may be collected and an average value of the collected values estimated as the final vehicle weight.Meanwhile, when the parking operation is canceled after the execution of the parking operation, with respect to an already estimated vehicle weight, a value obtained by increasing or decreasing the already estimated vehicle weight by a predetermined value (delta weight) may be estimated as a final vehicle weight, or the previously estimated vehicle weight may be reset to zero, and the vehicle weight may then be re-estimated.FIG. 6 shows a clamping force for each vehicle weight estimated in an EPB system according to an embodiment.Referring to FIG. 6, the vertical axis shows the estimated vehicle weight and the horizontal axis shows the clamping force.As the estimated vehicle weight increases, the clamping force may be increased.The appropriate clamping force required for parking may be changed in such a way as to change a target current of the EPB system.The appropriate clamping force corresponding to the vehicle weight may be generated by the current supplied to the electric motor 141 reaching the changed target current.FIG. 7 shows a control method of an EPB system according to an embodiment.Referring to FIG. 7, the controller 200 may estimate the vehicle weight ( 400).The controller 200 may determine whether a parking operation is started ( 402). In this case, the controller 200 may determine that the parking operation is started when a parking switch is turned on.If it is determined as a result of the determination at operation 402 that the parking operation is not started, the controller 200 may return to operation 400 and perform a subsequent operation.Meanwhile, if it is determined that the parking operation is being started as a result of the determination at operation 402, the controller 200 may determine a clamping force corresponding to the vehicle weight ( 404).The controller 200 may control the electric motor 141 according to the determined clamping force to generate the determined clamping force ( 406).Since the weight state of a vehicle cannot be identified in the related art, the clamping force for the parking operation is set based on the maximum weight of the vehicle even if traveling or traveling at the maximum weight does not often occur. Accordingly, the structural components of the vehicle are inevitably oversized, resulting in an increase in manufacturing cost.However, according to one embodiment, the EPB system may change the clamping force required for parking by predicting the vehicle weight on the basis of the tire pressure and the vehicle acceleration at the time of service braking during running, and thereby flexibly change the clamping force for each vehicle weight state. Accordingly, the clamping force required for parking can be generated by predicting the actual vehicle weight while preventing over-dimensioning.FIG. 8 shows a control method of an EPB system according to another embodiment.Referring to FIG. 8, the controller 200 may determine whether to begin a parking operation ( 500).If it is determined as a result of the determination at operation 500 that the parking operation is not being initiated, the controller 200 may receive a brake pedal signal ( 502), a tire pressure signal ( 504), and a vehicle acceleration signal ( 506) from another system in the vehicle via the communication interface 310.When the brake pedal is operating, the controller 200 may calculate the vehicle weight based on the tire pressure and the vehicle acceleration ( 508).Meanwhile, when it is determined that the parking operation is started as a result of the determination at operation 500, the controller 200 may determine a clamping force corresponding to the vehicle weight ( 210).The controller 200 may control the electric motor 141 according to the determined clamping force to generate the determined clamping force ( 512).FIG. 9 shows a control method of an EPB system according to still another embodiment.Referring to FIG. 9, the controller may determine whether the vehicle is in a service braking state during travel ( 600).If, as a result of the determination at operation 600, the vehicle is determined to be in the service braking state, the controller may determine the vehicle weight based on the tire pressure and the vehicle acceleration detected or obtained from another system ( 602).The controller 200 may store the calculated vehicle weight in the memory 220 in the vehicle ( 604).The controller 200 may determine a final vehicle weight from the vehicle weights stored in the memory 220 ( 606). The highest value among the stored vehicle weights may be determined as the final vehicle weight.Meanwhile, if it is determined as a result of the determination at operation 600 that the vehicle is not in the service braking state during travel, the controller 200 may determine whether to begin a parking operation ( 608).If it is determined that park operation is being initiated as a result of the determination at operation 608, the controller 200 may determine a clamping force corresponding to the final vehicle weight ( 610).The controller 200 may control the electric motor 141 according to the determined clamping force to generate the determined clamping force ( 612).As described above, by predicting the actual vehicle weight, the disclosure can generate a clamping force required for parking while preventing over-dimensioning.

Claims

An electronic parking brake system (30) comprising: an electronic parking brake provided for generating a clamping force on a wheel of a vehicle; and a controller (200) configured to estimate a weight of the vehicle based on a tire pressure and a longitudinal acceleration of the vehicle at the time of service braking during travel, determine a clamping force required for parking during a parking operation based on the estimated weight of the vehicle, and operate the electronic parking brake so as to generate the determined clamping force.The electronic parking brake system (30) according to claim 1, wherein the controller (200) is configured to determine the clamping force required for parking as a higher value, the heavier the estimated weight of the vehicle isThe electronic parking brake system (30) according to claim 1, wherein the controller (200) is configured to repeatedly estimate the weight of the vehicle from the time of service braking during driving to the start of parking operation based on the tire pressure and the longitudinal acceleration of the vehicle, and estimate a highest value among the estimated weights of the vehicle as the weight of the vehicle.The electronic parking brake system (30) according to claim 1, wherein the controller (200) is configured to repeatedly estimate the weight of the vehicle from the time of service braking during driving to the start of parking operation based on the tire pressure and the longitudinal acceleration of the vehicle, collect the estimated weights of the vehicle, and estimate an average value of the collected weights as the weight of the vehicle.The electronic parking brake system (30) according to claim 1, wherein the controller (200), upon canceling the parking operation after the parking operation, is configured to estimate a weight obtained by increasing or decreasing the estimated weight of the vehicle by a predetermined value as the weight of the vehicle.The electronic parking brake system (30) according to claim 1, comprising a communication interface (310) configured to communicate with a system mounted on the vehicle for obtaining the tire pressure and the longitudinal acceleration of the vehicle, wherein the controller (200) is configured to obtain, via the communication interface (310), the tire pressure and the longitudinal acceleration of the vehicle at the time of service braking during driving, and estimate the weight of the vehicle based on the obtained tire pressure and the obtained longitudinal acceleration of the vehicle.An electronic parking brake system (30) comprising a motor actuator (140) operated by an electric motor (141), the electronic parking brake system (30) comprising: a motor drive circuit (320) configured to drive the electric motor (141); a current sensor (300) configured to detect a current flowing through the electric motor (141); a communication interface (310) configured to communicate with a vehicle-mounted system to obtain a tire pressure and a longitudinal acceleration of the vehicle; A controller (200) configured to obtain, via the communication interface (310), tire pressure and longitudinal acceleration of the vehicle at the time of service braking during traveling, estimate a weight of the vehicle based on the obtained tire pressure and longitudinal acceleration of the vehicle, change a target current during parking operation based on the estimated weight of the vehicle, and drive the electric motor (141) via the motor drive circuit (320) such that a motor current detected by the current sensor reaches the changed target current.The electronic parking brake system (30) of claim 7, wherein the controller (200) is configured to change the target current to a higher value the heavier the estimated weight of the vehicle is.The electronic parking brake system (30) according to claim 7, wherein the controller (200) is configured to determine a clamping force required for parking based on the estimated weight of the vehicle and change the target current according to the determined clamping force.The electronic parking brake system (30) according to claim 7, wherein the controller (200) is configured to repeatedly estimate the weight of the vehicle from the time of service braking during driving to the start of parking operation based on the tire pressure and the longitudinal acceleration of the vehicle, and estimate a highest value among the estimated weights of the vehicle as the weight of the vehicle.A control method for an electronic parking brake system (30) having an electronic parking brake provided for generating a clamping force on a wheel of a vehicle, the control method comprising: estimating a weight of the vehicle based on a tire pressure and a longitudinal acceleration of the vehicle at the time of service braking during travel; determining a clamping force required for parking during parking operation based on the estimated weight of the vehicle; and operating the electronic parking brake so as to generate the determined clamping force.The control method according to claim 11, wherein in estimating the weight of the vehicle, the tire pressure and the longitudinal acceleration of the vehicle are detected at the time of service braking during running, and based on the detected tire pressure and the detected longitudinal acceleration of the vehicle, the weight of the vehicle is estimated.The control method according to claim 11, wherein in estimating the weight of the vehicle, the tire pressure and the longitudinal acceleration of the vehicle at the time of service braking during travel are obtained via a communication interface (310), and the weight of the vehicle is estimated based on the obtained tire pressure and the obtained longitudinal acceleration of the vehicle.The control method according to claim 11, wherein in estimating the weight of the vehicle, the weight of the vehicle from the time of service braking during running to the start of parking operation is repeatedly estimated based on the tire pressure and the longitudinal acceleration of the vehicle, and a highest value among the estimated weights of the vehicle is estimated as the weight of the vehicle.The control method according to claim 11, wherein in determining the clamping force, the more heavy the estimated weight of the vehicle, the more clamping force required for parking is determined to be a higher value.

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