Electric brake

Abstract

Provided is an electric brake capable of improving the accuracy of estimating a characteristic related to the position and braking force of an electric motor. The electric brake includes an electric motor, a braking mechanism, and an electric brake ECU. The electric brake ECU controls the electric motor. The electric brake ECU detects a first current value, which is the current value of the electric motor in a region in which the electric motor is driven in a direction in which the braking force is increased, detects a second current value, which is the current value of the electric motor when the electric motor is driven in a direction in which the braking force is reduced in the region in which the first current value was detected, and estimates a characteristic relating to the position and the braking force of the electric motor from the first current value and the second current value.

Description

Electric brake

[0001] The present invention relates to an electric brake that applies braking force to a vehicle such as an automobile.

[0002] For example, Patent Document 1 describes an electric brake device that detects a predetermined motor current when the vehicle is stopped, and then returns the motor a predetermined distance to determine the zero point (pad contact position) where the brake pad begins to contact the brake rotor. Patent Document 2 describes an electric disc brake that returns the motor in a clearance area, removes current pulsation from the frequency characteristics at that time, and estimates the pad contact position.

[0003] JP 2000-055094 A JP 2010-083282 A

[0004] The technology described in Patent Document 1 does not take into account the influence of current pulsation. As a result, it is difficult to ensure accurate estimation of the pad contact position (hereinafter simply referred to as "contact position"). The technology described in Patent Document 2 can only remove frequency components corresponding to one rotation of the motor when it is turned back in the clearance area. As a result, it is unable to remove low-frequency current pulsation (pulsation with a period of more than one rotation of the motor) caused by, for example, gear meshing, making it difficult to ensure accurate estimation.

[0005] An object of the present invention is to provide an electric brake that can improve the accuracy of estimating characteristics related to the motor position and braking force, such as contact position and stiffness.

[0006] One embodiment of the present invention is an electric brake comprising an electric motor, a braking mechanism that generates a braking force by driving the electric motor to press a braking member against a member to be braked, and a control unit that controls the electric motor, wherein the control unit detects a first current value, which is the current value of the electric motor in a region where the electric motor is driven in a direction where the braking force is increased, detects a second current value, which is the current value of the electric motor when the electric motor is driven in a direction where the braking force is decreased in the region where the first current value is detected, and estimates characteristics related to the position and braking force of the electric motor from the first current value and the second current value.

[0007] According to one embodiment of the present invention, it is possible to improve the accuracy of estimating the characteristics relating to the position and braking force of the electric motor.

[0008] 1 is a schematic diagram showing a vehicle equipped with an electric brake according to an embodiment; FIG. 2 is a perspective view showing the electric brake in FIG. 1; FIG. 2 is a cross-sectional view of the electric brake in FIG. 2; FIG. 3 is a characteristic diagram showing an example of the relationship between motor position (motor position) and braking force (clamping force) and motor current (current); FIG. 4 is a characteristic diagram showing the relationship between motor position and braking force in FIG. 4 together with an enlarged view of the vicinity of the contact position; FIG. 4 is a characteristic diagram showing the relationship between motor position and motor current in FIG. 4 together with an enlarged view of the vicinity of the contact position; FIG. 5 is a characteristic diagram showing the relationship between motor position near the contact position and braking force and motor current (enlarged views in FIG. 5 and FIG. 6); FIG. 6 is an explanatory diagram of thrust control without using a thrust sensor (sensorless control using motor current); and FIG. 7 is a flowchart showing processing by a control unit.

[0009] An electric brake according to an embodiment will be described below with reference to the accompanying drawings, taking as an example a case where it is installed in a four-wheeled vehicle. Each step in the flowchart shown in Fig. 9 is represented by the letter "S" (for example, step 1 = "S1"). Lines with two diagonal lines in Fig. 1 represent electrical lines. The suffix "L" corresponds to "left," and the suffix "R" corresponds to "right."

[0010] Fig. 1 shows a vehicle system. In Fig. 1, a vehicle 1 is equipped with a brake system 4 that brakes the vehicle 1 by applying braking force to wheels 2, 3 (front wheels 2L, 2R, rear wheels 3L, 3R). The brake system 4 includes a left front-wheel electric brake 5L (left front-wheel electric brake 5L) provided corresponding to the left front wheel 2L (left front wheel 2L), a right front-wheel electric brake 5R (right front-wheel electric brake 5R) provided corresponding to the right front wheel 2R (right front wheel 2R), a left rear-wheel electric brake 6L (left rear-wheel electric brake 6L) provided corresponding to the left rear wheel 3L (left rear wheel 3L), and a right rear-wheel electric brake 6R (right rear-wheel electric brake 6R) provided corresponding to the right rear wheel 3R (right rear wheel 3R), a brake pedal 7 (operating device) as a brake operation member, a pedal reaction force device 8 (hereinafter referred to as pedal simulator 8) that generates a kickback reaction force in response to operation (depression) of the brake pedal 7, and a pedal stroke sensor 9 as an operation detection sensor that measures the amount of operation of the brake pedal 7 by the driver.

[0011] The left and right front-wheel electric brakes 5L, 5R correspond to the front braking device of the vehicle 1, and the left and right rear-wheel electric brakes 6L, 6R correspond to the rear braking device of the vehicle 1. The left and right front-wheel electric brakes 5L, 5R and the left and right rear-wheel electric brakes 6L, 6R (hereinafter also referred to as electric brakes 5, 6) are configured as, for example, electric disc brakes (electric disc brakes). The electric brakes 5, 6 apply braking force to the wheels 2, 3 (front wheels 2L, 2R, rear wheels 3L, 3R) by driving an electric motor 26. Furthermore, the left and right rear-wheel electric brakes 6L, 6R are equipped with, for example, a parking mechanism (not shown).

[0012] The pedal stroke sensor 9 is provided, for example, in the pedal simulator 8. The pedal stroke sensor 9 may also be provided in the brake pedal 7. Furthermore, instead of the pedal stroke sensor 9, a pedal force sensor that measures a pedal force corresponding to the amount of operation of the brake pedal 7 may be used. The pedal stroke sensor 9 is connected to a brake control ECU 10, which is an ECU (Electronic Control Unit) for brake control. The brake control ECU 10 may also be a vehicle control ECU (vehicle main ECU) that performs overall control of the vehicle.

[0013] The brake control ECU 10 (also referred to as ECU 10) is provided in the vehicle 1. The ECU 10 includes a microcomputer having a central processing unit (CPU), a storage device (memory), a control board, etc. The ECU 10 receives a signal from the pedal stroke sensor 9 and calculates the braking force (target braking force) for each wheel (four wheels) according to a predetermined control program.

[0014] The ECU 10 calculates target braking forces to be applied to the front wheels 2L, 2R and the rear wheels 3L, 3R. Based on the calculated target braking forces, the ECU 10 outputs (transmits) braking commands (control commands) for the front wheels 2L, 2R and the rear wheels 3L, 3R to the electric brake ECUs 31, 31 via a CAN 12 (Controller Area Network) serving as a vehicle data bus (communication network).

[0015] In order to perform such braking control, the ECU 10 is provided with a control unit 10A that performs calculations based on input information (e.g., a signal from the pedal stroke sensor 9, etc.) and outputs the calculation results (e.g., a control command according to a target thrust). The ECU 10 receives vehicle information transmitted via the CAN 12 from other ECUs mounted on the vehicle 1 (e.g., a prime mover ECU, a transmission ECU, a steering ECU, an automatic driving ECU, etc., not shown).

[0016] For example, ECU 10 can acquire various vehicle information via CAN 12, such as information on the AT range position or MT shift position, ignition on / off information, engine RPM information, powertrain torque information, transmission gear ratio information, steering wheel operation information, clutch operation information, accelerator operation information, vehicle-to-vehicle communication information, information on the surroundings of the vehicle from an on-board camera, and acceleration sensor information (longitudinal acceleration, lateral acceleration).

[0017] 2 and 3 show the electric brakes 5, 6. The electric brakes 5, 6 include a braking mechanism 21 and an electric motor 26 that constitute actuators, and an electric brake ECU 31. The electric brakes 5, 6 apply braking force to the vehicle 1 by controlling the position and thrust of the braking mechanism 21. To this end, the electric brakes 5, 6 include a rotation angle sensor 32 ( FIG. 3 ) as a position detection means for detecting the motor rotation position, and a current sensor 34 ( FIG. 3 ) as a current detection means for detecting the current (motor current) of the electric motor 26. Note that the electric brakes 5, 6 do not include a thrust sensor that directly detects the thrust (pressing force) of the piston 24. As will be described later, the thrust (pressing force) of the piston 24, which corresponds to the braking force of the electric brakes 5, 6, in other words, the clamping force of the brake pads 25, 25, is estimated from the current (motor current) of the electric motor 26 detected by the current sensor 34.

[0018] The braking mechanism 21 includes, for example, a carrier 22, a caliper 23 serving as a cylinder (wheel cylinder), a piston 24 serving as a pressing member, and brake pads 25 serving as braking members (friction pads). The braking mechanism 21 includes an electric motor 26 for driving the braking mechanism 21, i.e., for generating a braking force by the braking mechanism 21. The braking mechanism 21 also includes a speed reduction mechanism 27, a rotary-to-linear motion conversion mechanism 28, and a fail-open mechanism (return spring) (not shown). The speed reduction mechanism 27, along with an ECU board 31B of the electric brake ECU 31, are covered by a housing 30. The housing 30, the speed reduction mechanism 27, the electric motor 26, the rotation angle sensor 32, and the ECU board 31B constitute a driving member for driving the braking mechanism 21.

[0019] The carrier 22 is fixed to the body of the vehicle 1. The caliper 23 is supported (floatingly supported) by the carrier 22 to allow movement in the axial direction of the disc rotor D. The electric motor 26 rotates when supplied with electric power and propels the piston 24. In this way, the electric motor 26 applies a braking force. The electric motor 26 is controlled by the electric brake ECU 31 based on a braking command (control command) from the ECU 10. The speed reduction mechanism 27 is formed, for example, by a gear reduction mechanism, and reduces the rotation of the electric motor 26 before transmitting it to the rotary-to-linear motion conversion mechanism 28.

[0020] The rotary-linear motion conversion mechanism 28 converts the rotation of the electric motor 26, transmitted via the reduction gear mechanism 27, into axial displacement (linear displacement) of the piston 24. The piston 24 is driven by the electric motor 26 to move the brake pad 25. The brake pad 25 is pressed against the disc rotor D by the piston 24. The pair of brake pads 25, 25 are located on both axial sides of the disc rotor D and are each supported by the carrier 22. The disc rotor D, which serves as a braked member (rotor), rotates together with the wheels 2L, 2R, 3L, 3R.

[0021] A return spring (fail-open mechanism), not shown, applies a rotational force in the brake release direction to the rotating member of the rotary-to-linear motion conversion mechanism 28 when braking is applied. In the braking mechanism 21, the piston 24 is driven by the electric motor 26 to press the brake pads 25 against the disc rotor D. That is, based on a braking request (braking command), the braking mechanism 21 transmits thrust generated by driving the electric motor 26 to the piston 24, which moves the brake pads 25. In this way, the braking mechanism 21 presses the brake pads 25 against the disc rotor D.

[0022] As shown in Fig. 1, an electric brake ECU 31 is provided for each braking mechanism 21. The electric brake ECU 31 includes, for example, a microcomputer having a central processing unit (CPU), a storage device (memory), a control board, etc., and a drive circuit (e.g., an inverter) for supplying power to the electric motor 26. As shown in Fig. 3, the electric brake ECU 31 includes an ECU board 31B incorporating the arithmetic circuit, etc. The electric brake ECU 31 controls the electric motor 26 that operates the braking mechanism 21 based on commands from the ECU 10.

[0023] The electric brake ECU 31 includes a control unit 31A (in other words, an ECU board 31B) that performs calculations based on input information (e.g., signals corresponding to control commands) and outputs the calculation results (e.g., electric motor drive commands corresponding to the control commands). The electric brake ECU 31, together with the ECU 10, constitutes a control device (brake control device) that controls the electric motor 26.

[0024] In this case, the electric brake ECU 31 controls the drive of the electric motor 26 based on a braking command (control command) input to the electric brake ECU 31. Furthermore, for example, the electric brake ECU 31 on the rear wheel side controls the drive (apply, release) of the parking mechanism based on a parking operation command input to the electric brake ECU 31. A signal corresponding to the braking command and a signal corresponding to the parking operation command are input to the electric brake ECU 31 from the ECU 10. The parking mechanism (not shown) is a mechanism that maintains the generated thrust (clamping force) even when power to the motor is stopped based on the parking operation command.

[0025] The rotation angle sensor 32 detects the rotation angle (motor rotation angle) of the rotary shaft 26A of the electric motor 26. The rotation angle sensor 32 is provided corresponding to each electric motor 26 of each braking mechanism 21, and constitutes position detection means that detects the rotation position of the electric motor 26 (motor rotation position), and ultimately the position of the piston 24 (piston position).

[0026] The rotation angle sensor 32 is composed of, for example, a magnet 32A, which is a magnetic member attached to the rotating shaft 26A of the electric motor 26, and a magnetic detection IC chip 32B, which is a magnetic signal receiver provided in the electric brake ECU 31 (ECU board 31B). The electric brake ECU 31 (ECU board 31B) can calculate and detect the rotation angle of the rotating shaft 26A of the electric motor 26 by detecting changes in the magnetic flux of the rotating magnet 32A using the magnetic detection IC chip 32B.

[0027] The current sensor 34 is mounted on the ECU board 31B. The current sensor 34 detects the current (motor current) supplied to the electric motor 26. A current sensor 34 is provided corresponding to each electric motor 26 of each braking mechanism 21, and constitutes current detection means that detects the current (motor current, motor torque current) supplied to the electric motor 26. The rotation angle sensor 32 and the current sensor 34 are connected to the electric brake ECU 31.

[0028] The electric brake ECU 31 (and the ECU 10 connected to this electric brake ECU 31 via the CAN 12) can obtain the rotation angle of the electric motor 26 based on a signal from the rotation angle sensor 32. The electric brake ECU 31 (and the ECU 10) can obtain the motor current supplied to the electric motor 26 based on a signal from the current sensor 34. The electric brake ECU 31 (and the ECU 10) can estimate the thrust (braking force) based on the motor current.

[0029] Next, the braking and braking release operations of the electric brakes 5, 6 will be described. Note that the following description will be given taking as an example the operations when the driver operates the brake pedal 7. However, in the case of automatic braking, the operations are almost the same except that, for example, an automatic braking command is output from the automatic driving ECU, the automatic braking ECU, or the ECU 10 to the electric brake ECU 31.

[0030] For example, when the driver depresses the brake pedal 7 while the vehicle 1 is traveling, the ECU 10 outputs a command corresponding to the depression of the brake pedal 7 (a control command corresponding to the target thrust command value) to the electric brake ECU 31 based on a detection signal input from the pedal stroke sensor 9. The electric brake ECU 31 drives (rotates) the electric motor 26 in the forward direction, i.e., in the braking direction, based on the command from the ECU 10. The rotation of the electric motor 26 is transmitted to the rotary-to-linear motion conversion mechanism 28 via the speed reducer 27, and the piston 24 moves forward toward the brake pad 25.

[0031] This presses the brake pads 25 against the disc rotor D, applying a braking force. At this time, the drive of the electric motor 26 is controlled based on detection signals from the pedal stroke sensor 9, the rotation angle sensor 32, the current sensor 34, etc., thereby establishing a braking state. During this braking, a return spring provided in the braking mechanism 21 applies a force in the braking release direction to the rotating member 28A of the rotary-to-linear motion conversion mechanism 28, and ultimately to the rotating shaft 26A of the electric motor 26.

[0032] On the other hand, when the brake pedal 7 is operated to the release side, the ECU 10 outputs a command corresponding to this operation (a control command corresponding to the target thrust command value) to the electric brake ECU 31. The electric brake ECU 31 drives (rotates) the electric motor 26 in the reverse direction, i.e., in the direction of braking release, based on the command from the ECU 10. The rotation of the electric motor 26 is transmitted to the rotary-to-linear motion conversion mechanism 28 via the speed reducer 27, and the piston 24 moves backward in a direction away from the brake pads 25. Then, when the brake pedal 7 is completely released, the brake pads 25 move away from the disc rotor D, and the braking force is released. In this non-braking state where the braking is released, the return spring provided in the braking mechanism 21 returns to its initial state.

[0033] The braking force (braking force) of the electric brakes 5, 6 is generated by pressing the brake pads 25 against the disc rotor D. At this time, the electric brake ECU 31 (ECU board 31B) drives the electric motor 26 based on the braking command transmitted via the CAN 12. The torque generated by the electric motor 26 is amplified by the reduction mechanism 27 and converted into thrust by the rotary-to-linear motion conversion mechanism 28, i.e., thrust in the axial direction of the piston 24, and the brake pads 25 are pressed against the disc rotor D by the piston 24.

[0034] Furthermore, the rotation angle of the electric motor 26 is detected by a rotation angle sensor 32. The electric brake ECU 31 (ECU board 31B) controls the electric motor 26 using the rotation angle of the electric motor 26 (the rotation angle of the rotating shaft 26A). That is, the electric motor 26 is controlled by detecting changes in the magnetic flux of a magnet 32A, which rotates together with the rotating shaft 26A, using a magnetic detection IC chip 32B, which serves as a magnet signal receiver. At this time, the electric brake ECU 31 (ECU board 31B) controls the position of the piston 24 using the rotation angle of the electric motor 26 detected by the rotation angle sensor 32. In this way, the electric brake ECU 31 (ECU board 31B) adjusts (controls) the amount of clearance between the brake pads 25 and the disc rotor D and the thrust (clamping force) with which the brake pads 25 press against the disc rotor D.

[0035] Here, the electric brakes 5, 6 of the embodiment are not equipped with a thrust sensor. That is, in the embodiment, as shown in Fig. 8, the "position where the brake pad 25 contacts the disc rotor D (contact position)" and the "thrust of the brake pad 25 (clamping force)" are estimated from the current of the electric motor 26 (motor current). In such thrust control using the motor current (sensorless control), in order to reduce drag of the brake pad 25, that is, to accurately maintain the amount of clearance between the brake pad 25 and the disc rotor D when braking is not being applied, it is important to estimate the "contact position," which is the point at which braking force (thrust) is generated.

[0036] Furthermore, for highly accurate thrust control, it is also important to estimate the "thrust-position characteristics (stiffness)" which are the brake characteristics of the electric brakes 5 and 6. The "thrust-position characteristics" are the relationship between the braking force (thrust) and the position (rotational position) of the electric motor 26. The "thrust-position characteristics" are used for controlling the electric brakes 5 and 6 (electric motor 26) as, for example, a map (thrust position characteristics map, stiffness map) corresponding to the relationship between thrust (clamping force) and position (motor rotational position).

[0037] That is, once the "contact position" and "thrust-position characteristics" are known, a motor rotation angle command for realizing a thrust command can be calculated. The motor rotation angle can be detected by the rotation angle sensor 32. That is, using the motor rotation angle detected by the rotation angle sensor 32 and the motor current detected by the current sensor 34, the electric motor 26 is controlled by feedback control so that it matches the thrust command, thereby realizing thrust sensorless control. Meanwhile, the "contact position" and "thrust-position characteristics" change due to wear and temperature changes of the brake pads 25, as well as replacement of the brake pads 25. For this reason, the "contact position" and "thrust-position characteristics" are estimated and updated (corrected), for example, from the motor rotation angle and motor current detected when thrust is generated.

[0038] Specifically, as shown in FIG. 4, the "contact position" can be estimated using the motor rotation angle and motor current. That is, the "contact position" can be estimated and updated (corrected) from the point at which the motor current rises. The "thrust-position characteristics" can be estimated using the motor rotation angle and motor current because the relationship between the thrust and the motor current (the relationship between the motor current and the thrust) is constant. That is, the "thrust-position characteristics" can be estimated and updated (corrected) from the relationship between the motor rotation angle and the current corresponding to the thrust. However, the motor current has pulsation. This pulsation reduces the estimation accuracy. For this reason, it is necessary to remove the pulsation from the motor current.

[0039] That is, thrust sensorless control is preferable for electric brakes in terms of miniaturization (shortening shaft length) and cost reduction. However, even if the electric brake is thrust sensorless, high-precision control is required to ensure vehicle safety and comfort, more specifically, to enable independent control of each wheel with high response and high performance. In particular, it is important to accurately estimate the contact position. This is because accurate estimation of the contact position allows for accurate control of the electric brake piston position and, ultimately, the pad clearance, reducing drag between the brake pads and the disc rotor. This can extend the driving range of electric vehicles and reduce environmental impact.

[0040] However, when estimating the contact position and thrust using the motor current when the piston is advanced, the estimation accuracy may be reduced due to current pulsation caused by the reducer, etc., i.e., current pulsation dependent on the rotation angle. Therefore, in the embodiment, the influence of current pulsation is reduced, thereby enabling the contact position and thrust to be estimated using the motor current with high accuracy.

[0041] Specifically, current pulsation has a characteristic in which only the positive and negative polarities are reversed for the same motor rotation angle during power increase and power decrease. Therefore, by calculating the difference between the current during power increase and the current during power decrease, it is possible to remove current pulsation (including low frequencies) that depends on the rotation angle. Therefore, in this embodiment, as shown in FIGS. 6 and 7 , the difference between the current during power increase and the current during power decrease is calculated to remove current pulsation that depends on the rotation angle, thereby improving the accuracy of estimating the contact position and thrust. In FIGS. 6 and 7 , solid line 51 corresponds to the current during power increase, solid line 52 corresponds to the current during power decrease, and dashed line 53 corresponds to the current obtained by adding the current during power increase and the current during power decrease.

[0042] According to this embodiment, it is possible to remove current pulsation that depends on the rotation angle, thereby improving the accuracy of contact position estimation and thrust force estimation. In particular, in contact position estimation, it is expected that the sensitivity of the current to the thrust force in the thrust force hysteresis characteristic region will be improved. Furthermore, according to this embodiment, it is possible to perform estimation using the motor current with high accuracy without increasing the accuracy of mechanical components such as reducers. This reduces the cost of mechanical components.

[0043] In other words, in the embodiment, by using the motor current during force increase and the motor current during force decrease, it is possible to remove current pulsation. Therefore, it is possible to improve the accuracy of estimating the contact position compared to the above-mentioned Patent Document 1. Furthermore, in the embodiment, by using the motor current not only in the clearance region but also in the region where thrust is generated, it is possible to remove even low-frequency current pulsation. Therefore, it is possible to improve the accuracy of estimating the contact position and thrust compared to the above-mentioned Patent Document 2. These points will be explained in detail below.

[0044] FIG. 4 shows the braking characteristics of the electric brakes 5 and 6, specifically, the relationship between the "motor position (motor position [rev])," the "clamping force (kN])," and the "motor current (Iq [A])." The "motor position" corresponds to the rotational position of the electric motor 26 (the position of the piston 24, the axial position). The "clamping force" corresponds to the braking force of the electric brakes 5 and 6 (the thrust and pressing force of the piston 24). The "motor current" corresponds to the current value of the electric motor 26. In thrust control (sensorless control) using the motor current, the contact position gradually advances due to wear, etc., of the braking members (brake pads 25 and 25) and the member to be braked (disc rotor D).

[0045] Furthermore, the stiffness (thrust-position characteristics) of the electric brakes 5, 6 changes not only due to wear and uneven wear of the braking members (brake pads 25, 25) and the member to be braked (disc rotor D), but also due to changes in the temperature and efficiency of the actuator including the electric motor 26. In particular, high-frequency and low-frequency current pulsations occur due to the component precision and assembly precision of the speed reduction mechanism 27, which is a gear reducer. For this reason, if the contact position and stiffness (thrust-position characteristics) are estimated without taking these factors into consideration, the estimation results will vary, and control precision will deteriorate.

[0046] That is, due to component precision and assembly precision of the reduction mechanism 27, which is a gear reducer, the meshing gears become eccentric, and the distance between the gear centers fluctuates as the gears rotate, generating current pulsation. Fluctuations in the distance between the gear centers cause fluctuations in the meshing ratio, which in turn fluctuates in efficiency, so the torque required to rotate the gears fluctuates depending on the rotation angle. This causes fluctuations in the output torque of the electric motor 26, which in turn fluctuates the current (generating current pulsation that depends on the rotation angle).

[0047] The eccentricity between the gears remains the same regardless of the rotational direction, regardless of the rotational angle. Therefore, the generated current pulsation has the characteristic that only the positive and negative signs are reversed with respect to the motor rotation angle when the motor is being increased or decreased, as shown in Figures 4, 6, and 7. Furthermore, due to the material characteristics of the brake pads 25, 25, when they are pressed once and then released, there is a delay before the compressed brake pads 25, 25 return to their original state. Therefore, as shown in Figures 5 and 7, the braking force has a hysteresis characteristic (a region in which braking force is present when the motor is being increased and the braking force is zero when the motor is being decreased).

[0048] Therefore, in this embodiment, as shown in Figures 6 and 7, the current during force increase (solid line 51) and the current during force decrease (solid line 52) are added together to remove the current pulsation that depends on the rotation angle. That is, the current pulsation (wave-like vibration) is removed by obtaining the corrected current characteristic (dashed line 53) from the current characteristic before current pulsation correction (solid lines 51 and 52). The corrected current characteristic (dashed line 53) is a current characteristic in which the amplitude of vibration due to the current pulsation (wave-like vibration) is suppressed, allowing for accurate estimation of the contact position.

[0049] The contact position corresponds to the position where the current rises. Therefore, if the uncorrected current characteristics (solid lines 51 and 52) are used as is, the amplitude of the current pulsation is large, which may result in an erroneous determination of the contact position. In contrast, in this embodiment, the contact position is estimated based on the current characteristics (dashed line 53) in which the amplitude of the current pulsation (wave-like vibration) is suppressed, making this estimation easy and highly accurate. Furthermore, since the vibration of the current pulsation is removed when estimating stiffness (thrust-position characteristics), only the current that generates the thrust can be extracted. This also improves the accuracy of estimating stiffness (thrust-position characteristics).

[0050] Next, the process shown in FIG. 9 , i.e., the process for eliminating the influence of current pulsation, will be described. The process shown in FIG. 9 is performed, for example, by the electric brake ECU 31. For this purpose, a processing program for executing the process flow shown in FIG. 9 is stored (contained) in the memory of the electric brake ECU 31. Note that the process shown in FIG. 9 reduces the thrust generated by the electric brake 5 (6) of at least one wheel. In contrast, if the vehicle can be maintained stationary while stopped, the thrust (braking force) of the electric brake 5 (6) generated on any wheel can be changed. Therefore, for example, if the vehicle (automobile) is equipped with electric brakes 5, 6 on four wheels, the thrust of the electric brakes 5, 6 other than the wheel (operating wheel) performing the process shown in FIG. 9 is increased so that the braking force is maintained by the electric brakes 5, 6 other than the wheel (operating wheel). This maintains the vehicle 1 stationary.

[0051] The electric brake ECU 31 starts the process of Fig. 9 based on, for example, a command from the ECU 10. The electric brake ECU 31 also starts the process of Fig. 9 at predetermined time intervals, for example. When the process of Fig. 9 starts, the electric brake ECU 31 determines in S1 whether preparation for the contact position and stiffness estimation operation is complete. In S1, the electric brake ECU 31 determines whether the preparation is complete, for example, whether the vehicle is stopped. In other words, if the vehicle is stopped, it can be determined that preparation for the estimation operation is complete.

[0052] In S1, in addition to determining whether the vehicle is stopped, it may also be determined whether a predetermined time has elapsed since the previous estimation. That is, it may be determined that preparation for the estimation operation is complete when the vehicle is stopped and a predetermined time has elapsed since the previous estimation. The predetermined time may be set, for example, as an appropriate time for updating the contact position and stiffness. For example, the predetermined time may be set so that the contact position and stiffness can be updated at times when the contact position and stiffness change, such as when the vehicle is started, when the vehicle environment changes, or when the brake pads 25, 25 are replaced.

[0053] If S1 returns "NO", that is, if it is determined that the vehicle is not stopped (or the predetermined time has not elapsed), the process returns to the start and the processes from S1 onwards are repeated. On the other hand, if S1 returns "YES", that is, if it is determined that the vehicle is stopped (and the predetermined time has elapsed), the process proceeds to S2 onwards. In this case, the process proceeds to the operation processing for learning the "motor position - motor current" characteristics (S2, S3, S4), and the processing for estimating the contact position and stiffness of the brake pads 25, 25 (S5).

[0054] First, it is necessary to return the rotational position (motor position) of the electric motor 26 to the clearance area of ​​the electric brake 5 (6). Therefore, in S2, based on the previously stored contact position, the electric motor 26 is driven in the force reduction direction from this contact position to a position where a predetermined amount of clearance is achieved, and the rotational position (motor position) of the electric motor 26 is rotated to a position corresponding to the clearance area. This position is then determined to be the clearance area.

[0055] When the electric brake 5 (6) is operated for the first time, such as when the electric brake 5 (6) is assembled, the electric motor 26 is driven in the force reduction direction from the contact position stored at the time of assembly to a position where a predetermined amount of clearance is achieved, and the rotational position (motor position) of the electric motor 26 is rotated to a position corresponding to the clearance area. The predetermined amount of clearance can be set as a clearance amount that can obtain a current value required to estimate the contact position and stiffness.

[0056] S3 and S4 following S2 correspond to a process for learning the "motor position-motor current" characteristics. In S3, the electric motor 26 is driven in the power-up direction until the motor position reaches a predetermined stroke amount, and the "motor position-motor current" characteristics at this time, i.e., a function (characteristics, data map, etc.) corresponding to the motor position x when driven in the power-up direction, represented as "I_inc(x)," is stored. At this time, it is desirable to operate (drive) at a constant speed (constant speed) to avoid the influence of viscosity differences due to speed differences between power-up and power-down and inertia due to acceleration on the current characteristics. Furthermore, the predetermined stroke amount is set so that it is always equal to or greater than the position at which thrust is generated, regardless of, for example, pad wear, uneven wear, disc rotor inclination, temperature, efficiency of the brake mechanism 21, pulsation, etc.

[0057] In the next step S4, the electric motor 26 is driven in the deceleration direction by the same stroke amount as in step S3, and the "motor position-motor current" characteristics at this time, i.e., a function (characteristics, data map, etc.) corresponding to the motor position x when driven in the deceleration direction, represented as "I_dec(x)," are stored. After the "motor position-motor current" characteristics (function, data map) have been stored in steps S3 and S4, the process proceeds to step S5. In step S5, a correction current, i.e., "I_inc(x) + I_dec(x)," is calculated based on the data stored in steps S3 and S4, i.e., the "motor position-motor current" characteristics (function, data map). Then, the contact position and stiffness are estimated from this correction current, and the contact position and stiffness information is updated to the estimated contact position and stiffness. After the contact position and stiffness have been estimated and updated in step S5, the process returns.

[0058] In this manner, in the embodiment, pulsation in the motor current can be removed by calculating the correction current, i.e., "I_inc(x) + I_dec(x)." This improves the accuracy of the contact position estimation, the accuracy of the stiffness estimation, and ultimately the accuracy of the thrust force estimation calculated based on the stiffness. In particular, the contact position estimation is expected to improve the sensitivity of the current to the thrust force in the thrust force hysteresis characteristic region. Furthermore, current-based estimation can be performed with high accuracy without increasing the accuracy of mechanical components such as reducers. This reduces the cost of mechanical components.

[0059] In addition to the processing (basic operation) shown in FIG. 9 , current pulsation may be corrected using, for example, the current characteristics when increasing and decreasing the braking force during normal braking (including pedal operation, automatic braking, emergency braking, parking brake operation, etc.). However, in this case, braking force must be increased or decreased depending on the driver's operation, and the speed of the electric motor is usually not constant. For this reason, it is necessary to correct the effects of viscosity, which depends on speed, and inertia, which depends on acceleration. Furthermore, if the braking force increase operation does not reach a predetermined stroke amount, the correction current is not calculated.

[0060] 1 to 3 , the electric brakes 5 and 6 include the electric motor 26, the braking mechanism 21, and the electric brake ECU 31 (ECU board 31B) as a control unit. The braking mechanism 21 generates a braking force by driving the electric motor 26 to press the brake pads 25, 25 as braking members against the disc rotor D as a member to be braked. The electric brake ECU 31 (ECU board 31B) controls the electric motor 26. The electric brake ECU 31 controls the electric motor 26 based on characteristics related to the position of the electric motor 26 and the braking force (e.g., the contact position where the brake pads 25 come into contact with the disc rotor D, the relationship between the motor current and motor position of the electric motor 26 corresponding to the stiffness of the electric brakes 5 and 6, etc.).

[0061] As shown in FIGS. 6 and 7 , the electric brake ECU 31 (ECU board 31B) detects a first current value (solid line 51), which is the current value of the electric motor 26 when the electric motor 26 is driven in a direction that increases the braking force. Furthermore, the electric brake ECU 31 (ECU board 31B) detects a second current value (solid line 52), which is the current value of the electric motor 26 when the electric motor 26 is driven in a direction that decreases the braking force, in the region where the first current value (solid line 51) is detected. This detection region includes not only the clearance region but also the region where thrust is generated. Furthermore, the electric brake ECU 31 (ECU board 31B) can detect the current value via the current sensor 34. The first current value (solid line 51) corresponds to "I_inc(x)" stored in the process of S3 in FIG. 9 . The second current value (solid line 52) corresponds to "I_dec(x)" stored in the process of S4 in FIG. 9 .

[0062] The electric brake ECU 31 (ECU board 31B) then estimates the characteristics related to the position and braking force of the electric motor 26 from the first current value (solid line 51) and the second current value (solid line 52). That is, the electric brake ECU 31 (ECU board 31B) estimates the characteristics of the electric brakes 5, 6 equipped with the electric motor 26 from the first current value (solid line 51) in the braking force increasing direction and the second current value (solid line 52) in the braking force decreasing direction in the region where the first current value (solid line 51) is detected. In this case, the electric brake ECU 31 (ECU board 31B) estimates the characteristics related to the position and braking force of the electric motor 26 by subtracting the second current value (solid line 52) from the first current value (solid line 51).

[0063] In other words, the position and braking force characteristics of the electric motor 26 are estimated by adding together a "first current value (solid line 51)" and a "second current value (solid line 52) whose sign is opposite to that of the first current value (solid line 51)." The current obtained by adding together the first current value (solid line 51) and the second current value (solid line 52) corresponds to the correction current calculated in the process of S5 in FIG. 9, i.e., "I_inc(x)+I_dec(x)." Furthermore, the first current value (solid line 51) and the second current value (solid line 52) are values ​​detected in the same region (same rotational position).

[0064] FIG. 8 shows an example of a characteristic relating to the position and braking force of the electric motor 26. That is, the characteristic relating to the position and braking force of the electric motor 26 is stiffness, i.e., the relationship between thrust and position (thrust-position characteristic). Furthermore, the characteristic relating to the position and braking force of the electric motor 26 is the contact position of the braking member (brake pads 25, 25) with the member to be braked (disc rotor D). Furthermore, as shown in FIG. 7 , the electric brake ECU 31 (ECU board 31B) estimates the contact position based on the characteristics of the rotor rotation position (e.g., motor position) of the electric motor 26 and the physical quantity relating to the braking force (e.g., clamping force) from the first current value (solid line 51) and the second current value (solid line 52) in a region (e.g., region H) where the physical quantity is within a predetermined value (e.g., 0) when the electric motor 26 is driven in a direction in which the braking force is reduced.

[0065] That is, the electric brake ECU 31 (ECU board 31B) estimates the contact position from the first current value (solid line 51) and the second current value (solid line 52) in a hysteresis region H where a physical quantity related to braking force (clamping force) is within a predetermined value (zero) when driven in a direction in which the braking force is reduced. More specifically, the contact position is estimated from a corrected current value (dashed line 53) obtained by adding the first current value (solid line 51) and the second current value (solid line 51). The hysteresis region H corresponds to a region where braking force is present when braking force is increased and where the braking force is zero when braking force is decreased due to the hysteresis characteristic.

[0066] As described above, according to this embodiment, the position and braking force characteristics of the electric motor 26 are estimated from the first current value (solid line 51), which is the current value of the electric motor 26 in a region where the electric motor 26 is driven in a direction where the braking force is increased, and the second current value (solid line 52), which is the current value of the electric motor 26 when the electric motor 26 is driven in a direction where the braking force is decreased in the region where the first current value (solid line 51) is detected. As shown in FIGS. 4 , 6 , and 7 , the first current value (solid line 51) and the second current value (solid line 52) are in phase and magnitude, with only the positive and negative signs reversed. For example, when the electric motor 26 is unloaded (when the electric motor 26 is running idle), the "current during power increase (first current value)" and the "current during power decrease (second current value)" are line-symmetrical with respect to a line extending in the X-axis direction at 0 A.

[0067] In other words, the change in current (second current value) when the electric motor 26 is rotated in the force-decrease direction is the negative version of the change in positive current (first current value) that occurs when the electric motor 26 is rotated in the force-increase direction, but with the same phase and magnitude. Conversely, the change in current (first current value) when the electric motor 26 is rotated in the force-increase direction is the positive version of the change in negative current (second current value) that occurs when the electric motor 26 is rotated in the force-decrease direction, but with the same phase and magnitude. Therefore, the first current value (solid line 51) and the second current value (solid line 52) can be used to improve the accuracy of estimating the characteristics related to the position and braking force of the electric motor 26.

[0068] In this case, the accuracy of estimating the characteristics related to the position and braking force of the electric motor 26 can be improved in the region from the clearance region of the electric brake 5 (6) (clearance region between the brake pads 25, 25 and the disc rotor D) to the region where maximum thrust is generated. That is, by using the first current value (solid line 51) and the second current value (solid line 52) not only in the clearance region but also in the region where thrust is generated, it is possible to remove not only high-frequency pulsation but also low-frequency pulsation. This also improves the accuracy of estimating the characteristics related to the position and braking force of the electric motor 26.

[0069] According to this embodiment, the characteristics related to the position and braking force of the electric motor 26 are estimated by subtracting the second current value (solid line 52) from the first current value (solid line 51). Therefore, the characteristics related to the position and braking force of the electric motor 26 can be estimated using the current value (dashed line 53) from which the current pulsation has been removed. In other words, the pulsation can be removed by subtracting the second current value (solid line 52) from the first current value (solid line 51). This improves the accuracy of estimating the characteristics related to the position and braking force of the electric motor 26.

[0070] According to the embodiment, the characteristic relating to the position and braking force of the electric motor 26 is stiffness (thrust-position characteristic). Therefore, it is possible to improve the accuracy of estimating the stiffness (thrust-position characteristic). Also, according to the embodiment, the characteristic relating to the position and braking force of the electric motor 26 is the contact position of the brake pads 25, 25 with respect to the disc rotor D. Therefore, it is possible to improve the accuracy of estimating the contact position.

[0071] According to this embodiment, the contact position is estimated based on the characteristics of the rotational position (rotor rotational position) of the electric motor 26 and the physical quantity related to the braking force (e.g., clamping force) from the first current value (solid line 51) and the second current value (solid line 52) in a region (e.g., hysteresis region H in FIGS. 5 and 7 ) in which the physical quantity is within a predetermined value (e.g., 0) when the electric motor 26 is driven in a direction in which the braking force is reduced. Therefore, the contact position can be estimated with high accuracy based on the characteristics of the rotational position (rotor rotational position) of the electric motor 26 and the physical quantity related to the braking force (clamping force). In other words, the contact position is estimated using the first current value (solid line 51) and the second current value (solid line 52) in a region (hysteresis region H in FIGS. 5 and 7 ) in which no pulsation due to the braking force occurs, and therefore the contact position can be estimated with high accuracy.

[0072] In the embodiment, the braking mechanism 21 has been described as a so-called floating caliper type disc brake in which the piston 24 is provided on the inner side of the caliper 23. However, the braking mechanism is not limited to this, and may be, for example, a so-called opposed piston type disc brake in which a piston is provided on each of the inner and outer sides of the caliper.

[0073] In the embodiment, the brake mechanism 21 is a disc brake. However, the brake mechanism is not limited to this. For example, the brake mechanism may be a drum brake in which a shoe (friction pad) is pressed against a drum rotor (rotor) that rotates together with the wheel.

[0074] In the embodiment, an example has been described in which all four wheels are equipped with electric brakes operated by the electric motor 26. However, the present invention is not limited to this, and for example, the front wheels may be equipped with hydraulic brakes and the rear wheels with electric brakes, or the front wheels may be equipped with electric brakes and the rear wheels with hydraulic brakes.

[0075] In the embodiment, the vehicle braking control device (ECU) is described as including the ECU 10 and the electric brake ECU 31. However, the present invention is not limited to this, and for example, the ECU 10 may be configured with a plurality of ECUs, or the ECU 10 and the electric brake ECU 31 may be configured with a single ECU.

[0076] According to the embodiment described above, the characteristics related to the position and braking force of the electric motor are estimated from a first current value, which is the electric motor current value in a region where the electric motor is driven in a direction where the braking force is increased, and a second current value, which is the electric motor current value when the electric motor is driven in a direction where the braking force is decreased in the region where the first current value is detected. The first current value and the second current value have the same phase and magnitude, but are inverted in sign. Therefore, the first current value and the second current value can be used to improve the accuracy of estimating the characteristics related to the position and braking force of the electric motor. In this case, the accuracy of estimating the characteristics related to the position and braking force of the electric motor in the region from the clearance region of the electric brake to the region where maximum thrust is generated can be improved. In other words, by using the first current value and the second current value not only in the clearance region but also in the region where thrust is generated, not only high-frequency pulsation but also low-frequency pulsation can be removed. This also improves the accuracy of estimating the characteristics related to the position and braking force of the electric motor.

[0077] According to this embodiment, the characteristics related to the position and braking force of the electric motor are estimated by subtracting the second current value from the first current value. Therefore, the characteristics related to the position and braking force of the electric motor can be estimated using a current value from which current pulsation has been removed. In other words, by subtracting the second current value from the first current value, the pulsation can be removed. This improves the accuracy of estimating the characteristics related to the position and braking force of the electric motor.

[0078] According to the embodiment, the characteristic relating to the position and braking force of the electric motor is the stiffness, which improves the accuracy of estimating the stiffness.

[0079] According to the embodiment, the characteristic relating to the position of the electric motor and the braking force is the contact position of the braking member with the member to be braked, which improves the accuracy of estimating the contact position.

[0080] According to this embodiment, the contact position is estimated from the first current value and the second current value in a region where the physical quantity is within a predetermined value when the electric motor is driven in a direction that reduces the braking force, based on the characteristics of the rotor rotation position of the electric motor and the physical quantity related to the braking force. Therefore, the contact position can be estimated with high accuracy based on the characteristics of the rotor rotation position of the electric motor and the physical quantity related to the braking force. In other words, the contact position can be estimated with high accuracy because the contact position is estimated using the first current value and the second current value in a region where no pulsation due to the braking force occurs.

[0081] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0082] This application claims priority to Japanese Patent Application No. 2024-092740, filed June 7, 2024. The entire disclosure of Japanese Patent Application No. 2024-092740, filed June 7, 2024, including the specification, claims, drawings, and abstract, is incorporated herein by reference in its entirety.

[0083] 5 Electric brake 5L Left front wheel electric brake 5R Right front wheel electric brake 6 Electric brake 6L Left rear wheel electric brake 6R Right rear wheel electric brake 21 Braking mechanism 25 Brake pad (braking member) 26 Electric motor 31 Electric brake ECU (control unit) D Disc rotor (braked member)

Claims

1. An electric brake comprising: an electric motor; a braking mechanism that generates a braking force by driving the electric motor to press a braking member against a member to be braked; and a control unit that controls the electric motor, wherein the control unit detects a first current value, which is the current value of the electric motor in a region where the electric motor is driven in a direction where the braking force is increased; detects a second current value, which is the current value of the electric motor when the electric motor is driven in a direction where the braking force is decreased in the region where the first current value is detected; and estimates characteristics related to the position and braking force of the electric motor from the first current value and the second current value.

2. An electric brake according to claim 1, wherein the characteristics relating to the position and braking force of the electric motor are estimated by subtracting the second current value from the first current value.

3. An electric brake according to claim 1 or 2, wherein the characteristic relating to the position and braking force of the electric motor is stiffness.

4. An electric brake according to claim 1 or 2, wherein the characteristic relating to the position of the electric motor and the braking force is the contact position of the braking member with the member to be braked.

5. An electric brake according to claim 4, wherein the contact position is estimated based on the rotor rotation position of the electric motor and the characteristics of a physical quantity related to braking force, from the first current value and the second current value in a region where the physical quantity falls within a predetermined value when the electric motor is driven in a direction that reduces the braking force.

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