Electric parking brake control device and electric parking brake control method

Abstract

The present invention aims at high-precision control of the pressing force regardless of individual differences and usage conditions of the brake device. In the present invention, when controlling the motor (8) that imparts a pressing force to the piston of the pressing brake block, the change in current and voltage during the idling current period, or the change in a function constituted by the current and voltage, is calculated as a plurality of candidate values (c1, c2, c3) during the current change period before the idling current period. Then, at a prescribed time TO in the current change period, one of the plurality of candidate values (c1, c2, c3) is selected on the basis of the current and the voltage, a characteristic parameter of the motor (8) is calculated on the basis of the current and the voltage, or the change in the function, associated with the selected candidate value, and a stop current of the motor (8) is calculated.

Description

TECHNICAL FIELD

[0001] The present application relates to an electric parking brake control device and an electric parking brake control method used in a vehicle such as an automobile. BACKGROUND

[0002] In the related art, as a brake device, there is proposed an electric brake in which a pressing member such as a brake shoe or a drum brake shoe is pressed against a rotating member such as a brake disc or a brake drum by rotation of an electric motor to brake. In the electric brake, in a case where sufficient pressing force is not obtained with respect to necessary braking force, the vehicle cannot be held due to insufficient braking force. In addition, in a case where excessive pressing force is generated, the strength of each part of the brake device needs to be excessively ensured for this.

[0003] Therefore, it is necessary to control the pressing force (hereinafter, referred to as a thrust force) with high accuracy by a simple method regardless of individual differences of the brake device, i.e., a use state or the like. As a technique for controlling the pressing force, for example, there is a technique disclosed in Patent Literature 1.

[0004] PRIOR ART DOCUMENT

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2015-512824 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] In the technique described in Patent Literature 1, there is disclosed a method in which it is described that "in a method in which a clamping force is determined as a function of a motor constant of a brake motor, and the motor constant is calculated from a latest measured value of a motor current (I0, IA) measured in operation of the brake motor, in order to determine the motor constant (KM), an idle voltage (Us0) and an idle current (I0) of the brake motor are measured in an idle stage, and the motor current (IA) is further calculated in a dynamic current change stage", a cutoff current threshold value is determined using the motor constant calculated here, and thereby the thrust force is controlled.

[0009] However, for example, in a case where a gap between a brake pad and a brake disc is small, there is no idle stage, or the like, it is difficult to perform the calculation with high accuracy. In addition, there is a problem in that it is necessary to measure a current and a voltage value for a long time from the current change stage to the idle stage, a storage capacity for storing the measured data increases, and a calculation load increases at the time of calculation from these data, and the calculation accuracy of the pressing force is poor.

[0010] The present application aims to provide an electric parking brake controller and an electric parking brake control method that can improve the calculation accuracy of the pressing force regardless of individual differences and usage conditions of a brake device.

[0011] Method for solving the problem

[0012] To achieve the above object, the present application provides an electric parking brake controller including a controller that controls the pressing force of a piston that presses a brake pad based on the current and voltage through the driving of a motor, characterized in that the controller includes a motor stop current calculation section that calculates the stop current of the motor, calculates the change in the current and voltage, or a function constituted by the current and voltage, during a current change period before an idle current period, as a plurality of candidate values, selects one of the plurality of candidate values based on the current and voltage at a prescribed time in the current change period, calculates a characteristic parameter of the motor based on the change in the current and voltage, or the function, related to the selected candidate value, and calculates the stop current of the motor.

[0013] In addition, the present application provides an electric parking brake control method that controls the pressing force of a piston that presses a brake pad based on the current and voltage through the driving of a motor, characterized in that, during a current change period before an idle current period, the change in the current and voltage, or a function constituted by the current and voltage, during the idle current period is calculated as a plurality of candidate values, one of the plurality of candidate values is selected based on the current and voltage at a prescribed time in the current change period, a characteristic parameter of the motor is calculated based on the change in the current and voltage, or the function, related to the selected candidate value, and the stop current of the motor is calculated.

[0014] Effects of the Invention

[0015] According to the present application, an electric parking brake controller and an electric parking brake control method that can improve the calculation accuracy of the pressing force regardless of individual differences and usage conditions of a brake device can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a sectional view showing the structure of an electric parking brake device according to an embodiment of the present application.

[0017] Figure 2 is a diagram showing an example of the structure of a vehicle including Figure 1 an electric parking brake device.

[0018] Figure 3This is a block diagram showing the structure of the control device 11.

[0019] Figure 4 This is a cross-sectional view showing the electric parking brake device when it is clamped.

[0020] Figure 5 This is a flowchart illustrating the operation of the control device 11.

[0021] Figure 6 It is a graph showing the historical waveforms of application commands, thrust, motor current, and terminal voltage at specific moments.

[0022] Figure 7 This is a flowchart showing the sequence of current calculations for stopping the motor.

[0023] Figure 8 This is a schematic diagram illustrating the general outline of waveform measurement and calculation. Detailed Implementation

[0024] Hereinafter, embodiments of the electric parking brake device of the present invention will be described based on the accompanying drawings.

[0025] Furthermore, the present invention is not limited to the following embodiments, and various modifications and applications of the technical concept of the present invention are also included within its scope. Hereinafter, a disc brake is described in particular, but it is also applicable to other types of braking devices such as drum brakes.

[0026] (Example 1)

[0027] First, use Figures 1-8 Example 1 of the braking device of the present invention is described. Figure 1 This is a cross-sectional view showing the structure of the electric parking brake device according to an embodiment of the invention. Figure 2 It means including Figure 1 A diagram illustrating the structure of a vehicle with an electric parking brake system.

[0028] like Figure 2 As shown, the braking device used in this embodiment is a disc brake device 1a, 1b (1a and 1b have the same structure), which is installed on the left and right rear wheel sections of the vehicle 21. The disc brake devices 1a, 1b obtain braking force by pressing the brake pads against the brake discs 2a, 2b that rotate together with the rear wheels.

[0029] The vehicle 21 includes: a brake pedal 22 operated by the driver; a master cylinder 23 that generates pressure by moving an internal piston through operation of the brake pedal 22; pipes 24a, 24b, and 24c that transmit pressure to the left and right front wheels and the rear wheels; and disc brake devices 25a and 25b for the front wheels (a and b have the same structure). Furthermore, a hydraulic control device 27, including a sideslip prevention device, is disposed between the master cylinder 23 and the pipes 24 of each wheel to control the hydraulic pressure.

[0030] like Figure 1 As shown, the disc brake device 1 (a and b have the same structure and will be omitted hereafter) installed on the rear wheel consists of a planetary gear carrier 3 fixed to the non-rotating part of the vehicle 21 and located inside the brake disc rotor (rotating component) 2; a cylinder 4 supported and axially floating towards the brake disc rotor 2; brake blocks (pressing components) 5a and 5b arranged on both sides of the brake disc rotor 2; a piston 6 that slides within the cylinder 4; a pressure chamber 7; and an electric motor 8 that drives the piston 6. The output shaft of the electric motor 8 is connected to a reducer 9, and the output shaft of the reducer 9 is connected to a rotary-to-linear conversion mechanism 10. The piston 6 is designed to move in the linear motion direction via the rotary-to-linear conversion mechanism 10. The electric motor 8 is connected to a control device 11 via a wire 12. The pressure chamber 7 is connected to a piping 24. The rotation control of the electric motor 8 is performed by the control device 11 (control unit).

[0031] Figure 3 This is a block diagram showing the structure of the control device 11. For example... Figure 3 As shown, the control device 11 includes: a current detection unit 31 for detecting the current during the driving of the motor 8; a motor stop current calculation unit 32 for calculating the stop current of the motor 8 based on the current detected by the current detection unit 31 during the driving of the motor 8; a timer 33 for measuring the detection time of the current detection unit 31; and a drive circuit 34 for controlling the motor 8 based on the current value detected by the current detection unit 31 and the result calculated by the motor stop current calculation unit 32. The motor stop current calculation unit 32 performs calculations based on a control program stored in a storage unit (not shown).

[0032] Additionally, the control unit 11 is connected to a driver-operated parking brake switch 35, various sensors 36 for acceleration, vehicle speed, etc., a CAN bus 37 for acquiring information about various parts of the vehicle 21, and a power supply 38, which controls the power supply to the motor 8 according to their respective signals. Furthermore, a notification unit 39, such as a warning light, is connected to the control unit 11 as needed. The various sensors 36 include a power sensor for detecting power supply and a voltage sensor for detecting the voltage of the motor.

[0033] Next, the operation of braking device 1 will be explained. First, the operation of braking device 1 when used as a service brake will be explained. When the driver operates the brake pedal 22, hydraulic pressure is generated by the master cylinder 23. This hydraulic pressure passes through the pipe 24 and the pressure chamber 7, so the force generated by this pressure pushes the piston 6, thereby generating a force on the brake disc rotor 2 to press the brake blocks 5a and 5b, thus generating braking force. In addition, in braking devices with hydraulic control devices such as 27, regardless of the driver's operation of the brake pedal 22, the necessary hydraulic pressure may be generated by the hydraulic control device 27, and similarly, braking force is generated by the generated hydraulic pressure.

[0034] Next, the operation of the parking brake will be explained. The system detects whether the driver's parking brake switch 35 is engaged or the vehicle's status, and generates braking force based on an application command 41 generated from the thrust from the control device 11. The electric motor 8 is driven based on this command, and the driving force of the electric motor 8, via the reducer 9 and the rotary-to-direct-actuation conversion mechanism 10, generates thrust on the piston 6. Figure 4 The middle character indicates the action.

[0035] Figure 4 This is a cross-sectional view showing the electric parking brake device when it is clamped. For example... Figure 4 As shown, piston 6 abuts against brake block 5b. Additionally, in cylinder 4, a force is generated in the direction that presses brake block 5a against brake disc rotor 2, thereby generating braking force by clamping brake disc rotor 2 with brake blocks 5a and 5b. When the necessary braking force is obtained, the drive of motor 8 is stopped.

[0036] exist Figure 5 The text in the image represents the flowchart at this point. Figure 5 This is a flowchart illustrating the operation of the control device 11.

[0037] First, in the motor stop current calculation unit 32 of the control device 11, when a start application command is determined (Yes in step S50), the motor 8 is driven (step S51). When no start application command is determined (No in step S51), the determination of the start application command is repeated.

[0038] Next, in the control device 11, after the motor 8 is driven, it is determined whether the current has reached its maximum value. If the current has reached its maximum value (Yes in step S52), a motor stop current calculation is performed (step S53). In the motor stop current calculation (step S53), specific parameters are calculated (step S54), and the motor stop current is calculated based on the specific parameters (step S55). The process of the motor stop current calculation (step S53) will be described in detail below.

[0039] When it is determined that the motor current 43 (current) exceeds the calculated motor stop current 44, or a predetermined time has elapsed after the motor current 43 exceeds the calculated motor stop current 44 (Yes in Step S56), the motor 8 is stopped (Step S57).

[0040] In addition, in Figure 6 The time history waveforms of the application command 41, the thrust 42, the motor current 43, and the voltage between the motor terminals at this time are shown in FIG. 6. When the application command 41 is input, the motor 8 is driven and the piston 6 moves in the direction of approaching the brake block 5b. Then, the piston 6 runs empty to abut against the brake block 5b. At this time, the load on the motor 8 is small, and the motor current 43 remains at a substantially constant low value (idling current 45). The motor current 43 converges after flowing through a surge current after the motor starts to be driven, and the current flowing during the period until the piston 6 abuts against the brake block 5b after the convergence of the motor current 43 becomes the idling current 45. Here, the period before the predetermined time To is set as a current change period 47, and the period after the current change period 47 is set as an idling current period 48. The predetermined time To is set as a boundary point at which the motor current 43 changes from the state of changing to a substantially constant value.

[0041] Then, when the piston 6 and the brake block 5b abut against each other, the thrust 42 of the piston 6 rises, and along with the rise of the thrust 42, the pressing force of the brake block 5b against the brake disc rotor 2 also starts to rise, and the load on the motor 8 gradually increases, and along with this, the motor current 43 increases.

[0042] Further, in the case where the motor current 43 exceeds the motor stop current 44, the motor 8 is stopped. Alternatively, the current detected by the sensor is collected every certain sampling time, so even if the detected current exceeds the motor stop current 44 a predetermined number of times (for example, three times), the motor 8 can be stopped.

[0043] The motor stop current 44 is calculated using Figure 7 The determination method of the motor stop current 44 (motor stop current calculation S53) will be described in detail. Figure 7 is a flowchart showing the sequence of the motor stop current calculation.

[0044] The motor stop current calculation S53 of Step S53 is constituted by a step S54 of calculating a characteristic parameter based on the current and voltage of the portion of the current change period 47 when the motor current 43 is the current change period 47, and a motor stop current calculation step S55 of calculating the motor stop current 44 from the calculated characteristic parameter. The characteristic parameter is a parameter of the characteristic variation unique to the motor.

[0045] In the step S54 of characteristic parameter operation, the current and the voltage, or a function composed of the current and the voltage are measured (step S58). Then, the current and the voltage, or a function composed of the current and the voltage in the idling current period 48 are assumed as a plurality of candidate values (cl ~ cn) (step S59), and an approximation formula of the reproduced measured value is obtained using each candidate value (step S60). The plurality of assumed candidate values (cl ~ cn) are stored in a memory or the like of the motor stop current operation section 32 in the control device 11. Then, a candidate value capable of most accurately reproducing the measured value is selected from the plurality of candidate values (cl ~ cn) at a prescribed time To (step S61), and the characteristic parameter is operated using the candidate value (step S62).

[0046] Hereinafter, a specific flow of the step S56 in the characteristic parameter operation will be described in detail. First, the main behavior of the electric parking brake device is represented by the following equation (1).

[0047]

[0048] In the equation (1), Kt represents a torque constant, I represents a current, K represents a rotation / linear motion conversion coefficient of the rotation linear motion conversion mechanism 10, FCLP represents a pressing thrust, J represents an inertia coefficient (Jdω / dt is an inertia term), Tfric represents a friction torque of the rotation linear motion conversion mechanism 10 from the motor 8 to the power transmission mechanism, λ represents a viscosity coefficient, and ω represents a rotational speed.

[0049] When the equation (1) is transformed, the current when the pressing force becomes FCLP can be calculated.

[0050]

[0051] Therefore, in a case where the pressing force to be maintained is set as FCLP, if the current value I obtained in (2) stops, the pressing force becomes FCLP, so this value is set as the motor stop current 44. However, in order to set this value, the values of the parameters and variables of (2) (hereinafter, referred to as characteristic parameters. For example, the torque constant Kt, the friction torque Tfric, the viscosity coefficient λ, and the rotational speed ω) are required. The values vary depending on the individual variation of each, and the environment such as temperature, voltage, and the like, so in order to control the thrust with high accuracy, it is necessary to consider these variations and set the motor stop current 44. Therefore, in the present embodiment, the characteristic parameters are estimated from the variations of the current and voltage, or a function constituted by the current and voltage. Thus, the environment and the solid variation are considered, and even in a condition where the mechanical efficiency and the motor performance are low and it is difficult to generate the thrust, it is possible to always ensure the necessary thrust (for example, the thrust required for a car to be able to stop on a slope), and to generate the necessary or more thrust in an individual where the mechanical efficiency and the motor characteristics are good, and to suppress excessive stress on the mechanism system of the electric parking brake device.

[0052] The following shows the estimation method of the characteristic parameters in the present embodiment. The current waveform after the start of the motor is determined from the equation of the circuit and the motion equation. The equation of the circuit is expressed by the following formula (3).

[0053]

[0054] Here, R represents the resistance, and L represents the inductance. In addition, FCLP = 0 before the thrust is generated in (1), and since this term can be ignored, the motion equation is expressed as (4).

[0055]

[0056] It is difficult to strictly explain these two calculation formulas, but Ldl / dt in (3) is a term that rapidly decreases within several ms, so it is ignored, and in addition, Tfric in (4) is also smaller than the other terms, so it can be solved approximately as (5). Furthermore, in the present embodiment, the case where Tfric is smaller than the other terms is shown, but in a case where λω is small, Tfric cannot be ignored, and λω can also be ignored and solved approximately.

[0057]

[0058] Here, generally, the lower the temperature, the larger the torque constant Kt, the lower the temperature, the smaller the resistance R, and in addition, the lower the temperature, the larger the viscosity coefficient. In addition, similarly, the individual variation of the motor and the characteristic variation of the grease used, and the like, affect the characteristic parameters. (5) indicates that the characteristic parameter variations caused by these temperature and variations are expressed as the variations of the current and voltage.

[0059] Therefore, in the present embodiment, the characteristic parameters are calculated using this relationship. For example, a method is given in which the waveform of current ÷ voltage after starting is measured, and the characteristic parameters on the right side of equation (5) are determined (5) in a manner consistent with this waveform. Figure 8 is a schematic diagram showing the outline of the waveform measurement and calculation, and Figure 8 In the graph of

[0060]

[0061] Thus, equation (5) becomes equation (7).

[0062] y = a exp(-bt) + c... (7)

[0063] Here, the three unknowns a, b, c can also be found by optimization or the like in a manner in which y approaches the measured value ym, but in a manner in which the calculation can be performed in a short time by a simpler method, a method of finding the unknowns by the least squares method is explained here. Taking the logarithm of both sides of equation (7), equation (8) is set,

[0064] Y = ln(y - c), A = ln a... (8)

[0065] This can be handled as a problem of finding an approximate straight line as in equation (9).

[0066] Y = -bt + A... (9)

[0067] Here, in order to find b and A of equation (9), c is needed. On the other hand, if the time t of equation (7) is advanced, y asymptotically approaches c, but the value of c is not known at the TO point at which the current change period 47 ends. In accordance with this, in the present embodiment, c is assumed to be a plurality of candidate values as shown in Figure 8 b and A (= In a) are found in each of the candidate values, and using c assumed to be these candidate values, each of the calculated curves yp is found. Then, a, b, c of the calculated curve in which the measured value ym is reproduced with the highest accuracy among the calculated curves yp found are adopted. Then, the characteristic parameters are calculated based on equation (10) obtained by solving the simultaneous equations of equation (6) using these values. Furthermore, as a criterion for adopting the values, for example, the parameter in which the squared error of the calculated value yp and the measured value ym is the smallest can also be selected.

[0068]

[0069] Finally, the obtained characteristic parameters are substituted into equation (2) to obtain the motor stopping current 44. At this time, as an example, K and Tfric, which are not obtained as characteristic parameters, are obtained by using the assumed worst value (the value of minimum thrust) and ω is obtained as a function of voltage V.

[0070] Furthermore, the method of assuming multiple candidate values ​​for the unknown c can also be as follows. As shown in equation (6), c is a function of the torque constant Kt, resistance R, and viscous resistance λ. Therefore, if these values ​​are known as design values ​​or specifications, c obtained from these values ​​can be set as candidate value c1. Moreover, other candidate values ​​can be set as ratios relative to c1, such as using c2 = c1 × 0.9, c3 = c1 × 0.8, etc. Alternatively, the final value of the measured value during the current change period 47 can be set as c1. In addition, in the case of multiple operations, the candidate value c selected in the previous operation can be set as c1 for this operation. In these cases, multiple candidate values ​​are pre-calculated before the start of driving the motor 8 and stored, for example, in the memory of the motor stop current calculation unit 32, so the calculation of the motor stop current can be accelerated.

[0071] According to Example 1, the motor stopping current 44 is obtained through the structure described above. Thus, regardless of the presence or absence of idling current, the characteristic parameters can be calculated in a short time. As a result, an electric parking brake control device and an electric parking brake control method with high-precision thrust control through a simple method can be provided.

[0072] (Example 2)

[0073] Next, Embodiment 2 of the present invention will be described. In Embodiment 1, a method is given, for example, storing the measured value during the current change period 47 to a predetermined time T0, and performing calculations at T0 to obtain the motor stopping current 44. However, in Embodiment 2, a method is given, in which calculations are performed sequentially at predetermined time intervals (measurement times), without storing the measured value to T0.

[0074] Specifically, such as Figure 8 As shown, the data of current ÷ voltage are measured at specified time intervals. Figure 8 (12 times), and at each measurement time, the accumulated values ​​calculated according to the least squares method are calculated successively, thereby obtaining A and b in equation (9). In this case, the unknown c needs to be assumed at the beginning of the calculation, and thus, as shown in Example 1, it can also be obtained according to the known design value and specifications. In addition, in the case of multiple operations, the value c of the previous operation can also be used.

[0075] The characteristic parameter can be calculated in the same manner as in Embodiment 1 using A and b obtained by repeating the above calculation for the number of measurements until a predetermined time To, and the motor stop current 44 can be obtained. According to this method, if only the cumulative value is stored, the previous measurement value does not need to be stored, so the number of measurements can be increased without increasing the storage capacity. Accordingly, an electric parking brake control device and an electric parking brake control method that can perform high-precision force control by a simple method can be provided.

[0076] Further, in the above, the case of the disc brake was described as an example of the embodiment, but the brake device of the present application can also be applied to a drum brake. In addition, the brake device of the present application is not limited to a vehicle such as an automobile, and can be used as long as a braking force is required.

[0077] The above describes the embodiments of the present application in detail, but the present application is not limited to the above-described embodiments, and various design changes can be made within the scope of the gist of the present application described in the claims. For example, the above-described embodiments are embodiments described in detail in order to easily understand the present application, and are not necessarily limited to all the structures described. In addition, a part of the structure of an embodiment can be replaced with the structure of another embodiment, and in addition, the structure of an embodiment can be added with the structure of another embodiment. Furthermore, a part of the structure of each embodiment can be added, deleted, or replaced with another structure.

[0078] Explanation of Reference Numerals

[0079] 1 … brake device

[0080] 1a, 1b … disc brake device

[0081] 2 … brake disc rotor (rotating member)

[0082] 3 … planetary gear carrier

[0083] 4 … cylinder

[0084] 5a, 5b … brake pad (pressing member)

[0085] 6 … piston

[0086] 7 … pressure chamber

[0087] 8 … motor

[0088] 9 … speed reducer

[0089] 10 … rotary linear conversion mechanism

[0090] 11 … control device

[0091] 12 … electric wire

[0092] 21 … vehicle

[0093] 22 brake pedal

[0094] 23 master cylinder

[0095] 24, 24a, 24b, 24c piping

[0096] 25a, 25b disc brake device of front wheel

[0097] 27 hydraulic control device

[0098] 31 current detection section

[0099] 32 motor stop current operation section

[0100] 33 timer

[0101] 34 drive circuit

[0102] 35 parking brake switch

[0103] 36 sensor

[0104] 38 power supply

[0105] 39 notification unit

[0106] 41 application instruction

[0107] 42 thrust

[0108] 43 motor current

[0109] 44 motor stop current

[0110] 45 idle current

[0111] 47 current change period

[0112] 48 idle current period

Claims

1. An electric parking brake control device, comprising a control unit that controls the thrust of a piston pressing a brake block based on current and voltage via a motor drive, characterized in that: The control device includes a motor stop current calculation unit that calculates the stop current of the motor. The motor stop current calculation unit Before the motor starts driving, the changes in the current and voltage, or a function of the current and voltage, during the idle current period are pre-calculated as multiple candidate values. After the motor starts driving, During a predetermined time period of current change preceding the idle current period, based on the current and the voltage, one of the pre-calculated candidate values ​​is selected. The characteristic parameters of the motor are calculated based on the changes in the current and voltage, or the function, in relation to the selected candidate values, and the stopping current of the motor is also calculated.

2. The electric parking brake control device as described in claim 1, characterized in that: The plurality of candidate values ​​are calculated based on the current and voltage within the specified time period.

3. The electric parking brake control device as described in claim 1 or 2, characterized in that: The specified time is the time from the state of the current change to the boundary point where the current becomes approximately constant.

4. The electric parking brake control device as described in claim 1, characterized in that: The plurality of candidate values ​​are calculated based on the changes in the current and voltage, or the function, selected during the previous operation.

5. The electric parking brake control device as described in claim 1, characterized in that: The characteristic parameters are obtained by successively calculating the calculated values ​​of the current and voltage, or the function, at each measurement moment.

6. A control method for an electric parking brake, wherein the thrust of a piston pressing the brake block is controlled by a motor based on current and voltage, characterized in that: Before the motor starts driving, the changes in the current and voltage, or a function of the current and voltage, during the idle current period are pre-calculated as multiple candidate values. After the motor starts driving, During a predetermined time period of current change preceding the idle current period, based on the current and the voltage, one of the pre-calculated candidate values ​​is selected. The characteristic parameters of the motor are calculated based on the changes in the current and voltage, or the function, in relation to the selected candidate values, and the stopping current of the motor is also calculated.

7. The electric parking brake control method as described in claim 6, characterized in that: The plurality of candidate values ​​are calculated based on the current and voltage within the specified time period.

8. The electric parking brake control method as described in claim 6 or 7, characterized in that: The specified time is the time from the state of the current change to the boundary point where the current becomes approximately constant.

9. The electric parking brake control method as described in claim 6, characterized in that: The plurality of candidate values ​​are calculated based on the changes in the current and voltage, or the function, selected during the previous operation.

10. The electric parking brake control method as described in claim 6, characterized in that: The characteristic parameters are obtained by successively calculating the calculated values ​​of the current and voltage, or the function, at each measurement moment.

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