Electric braking system

Abstract

Provided is an electric brake device with which a current-reducing effect can be improved. This electric brake has a first region where braking force increases when a motor current of an electric motor increases, a second region where braking force is maintained when the motor current decreases from an increase to a prescribed current, and a third region where braking force decreases when the motor current decreases from the prescribed current. The electric brake is controlled so that the braking force of at least one or more wheels is maintained at the braking force generated along the third region.

Description

Technical Field

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

Background Art

[0002] An electric brake device includes a braking mechanism that presses a brake pad (braking member) against a disk (braked member), and an electric motor that drives the braking mechanism (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The conventional electric brake device described in Patent Document 1 uses a switching section between positive efficiency and negative efficiency in the relationship between current and braking force, that is, a braking force holding region where the braking force remains constant even when the current is decreased, to hold the braking force. Thereby, in the prior art, the consumption current is suppressed and the electricity cost is improved. However, in the prior art, there is a problem that it is not known how much the current should be decreased, so the current reduction effect cannot be significantly increased including variations.

[0005] The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an electric brake device capable of improving the current reduction effect.

Means for Solving the Problems

[0006] To solve the above-mentioned problems, the present invention provides an electric brake device comprising a braking mechanism that presses a braking member against a member to be braked, and an electric motor that drives the braking mechanism, wherein the device has a first region in which the braking force increases when the current of the electric motor increases, a second region in which the braking force is maintained until the current switches from increasing to decreasing and reaches a predetermined current, and a third region in which the braking force decreases when the current decreases from the predetermined current, and the braking force of at least one wheel is The first region is increased in advance by the amount necessary to detect the transition to the third region, It is characterized by being controlled to be held by the braking force generated along the third region.

[0007] According to an electric brake device of one embodiment of the present invention, the current reduction effect can be improved. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows the system configuration of a vehicle to which electric brakes according to the first and second embodiments of the present invention are applied. [Figure 2] This is a cross-sectional view showing an electric brake according to the first embodiment. [Figure 3] This is a characteristic curve showing the relationship between braking force and motor current in the first embodiment. [Figure 4] The characteristic diagrams for the first embodiment and comparative example show the time variation of required braking force, motor current, motor position, and braking force. [Figure 5] The first modified example and the comparative example are shown in characteristic diagrams illustrating the time variation of required braking force, motor current, motor position, and braking force. [Figure 6] The second modified example and comparative example are shown in characteristic curves illustrating the time variation of required braking force, motor current, motor position, and braking force. [Figure 7] This is a cross-sectional view showing an electric brake according to a second embodiment. [Figure 8] The second embodiment is shown as a characteristic curve illustrating the relationship between braking force and motor current. [Figure 9]The second embodiment and comparative example are shown in characteristic diagrams illustrating the time variation of required braking force, motor current, motor position, and braking force. [Figure 10] The third modified example and comparative example are shown in characteristic diagrams illustrating the time variation of required braking force, motor current, motor position, and braking force. [Figure 11] The fourth modified example and comparative example are shown in characteristic diagrams illustrating the time variation of required braking force, motor current, motor position, and braking force. [Modes for carrying out the invention]

[0009] The following description will refer to the attached drawings and use an example of applying the electric brake system according to the embodiment to a four-wheeled vehicle.

[0010] Figure 1 shows the system configuration of a vehicle 1 to which an electric brake 20, as an electric braking device according to an embodiment, is applied. The brake device 2 mounted on the vehicle 1 includes a hydraulic brake 4 (front braking mechanism) provided corresponding to the left front wheel 3L and the right front wheel 3R facing the direction of vehicle travel, and an electric brake 20 (rear braking mechanism) provided corresponding to the left rear wheel 5L and the right rear wheel 5R. A main ECU 9 is connected to a hydraulic sensor 7 and a pedal stroke sensor 8 that measure the amount of operation of the driver's brake pedal 6. The main ECU 9 receives signals from the hydraulic sensor 7 and the pedal stroke sensor 8 and calculates the target braking force for each wheel (4 wheels) according to a predetermined control program. Based on the calculated braking force, the main ECU 9 transmits braking commands for each of the two front wheels to the hydraulic device ECU 10 via CAN 12 (Controller area network). The main ECU 9 transmits braking commands to the electric brake ECU 11 via CAN 12 for each of the two rear wheels, based on the calculated braking force. The main ECU 9 is also connected to wheel speed sensors 13 located near the front wheels 3L and 3R and the rear wheels 5L and 5R, allowing it to detect the wheel speed of each wheel.

[0011] Next, the specific configuration of the electric brake 20 according to the first embodiment will be described with reference to Figures 1 and 2.

[0012] The electric brake 20 includes a brake mechanism 21 that transmits thrust generated by the drive of an electric motor 39 to a piston 32 that moves brake pads 22 and 23 pressed against a disc rotor D (disc), a thrust sensor 44 that detects the thrust to the piston 32, a rotation angle sensor 46 that detects the rotational position of the electric motor 39, and an electric brake ECU 11 that acts as a control device that controls the drive of the electric motor 39 based on a braking command. In this case, the disc rotor D is the member being braked. The brake pads 22 and 23 are braking members. The brake mechanism 21 is a braking mechanism.

[0013] As shown in Figure 2, the brake mechanism 21 comprises a pair of inner brake pads 22 and outer brake pads 23, and a caliper 24. The inner brake pads 22 and outer brake pads 23 are arranged on both axial sides of a disc rotor D that is attached to a rotating part of the vehicle 1. The electric brake 20 is configured as a caliper-floating type. The pair of inner brake pads 22 and outer brake pads 23 and the caliper 24 are supported by a bracket 25 fixed to a non-rotating part of the vehicle 1, such as a knuckle. The bracket 25 comprises an inner support portion 26 and an outer support portion 27 that independently support the inner brake pads 22 and outer brake pads 23, respectively.

[0014] The caliper 24 comprises a caliper body 28, which is the main component of the caliper 24, and an electric motor 39 positioned alongside the caliper body 28. The caliper body 28 integrally forms a cylindrical cylinder portion 29, which is located at the base end facing the inner brake pad 22 on the inside of the vehicle and opens in opposition to the inner brake pad 22, and a claw portion 30, which extends from the cylinder portion 29 across the disc rotor D to the outer side and is located at the tip end facing the outer brake pad 23 on the outside of the vehicle.

[0015] In the cylinder part 29, a bottomed cylinder 31 is formed. The piston 32 presses the inner brake pad 22 and is formed in a bottomed cup shape. The piston 32 is housed in the cylinder 31 such that its bottom 33 faces the inner brake pad 22.

[0016] A gear housing 34 is arranged on the bottom wall side of the cylinder part 29 of the caliper body 28. Inside the gear housing 34, a spur multi-stage reduction mechanism 35, a planetary gear reduction mechanism 36, and a control board 38 are housed. The control board 38 is provided with an electric brake ECU 11 as a control device composed of, for example, a microcomputer. The electric brake ECU 11 controls the drive of the electric motor 39 based on a braking command.

[0017] The caliper body 28 includes an electric motor 39, a spur multi-stage reduction mechanism 35 and a planetary gear reduction mechanism 36 which are transmission mechanisms for increasing the rotational torque from the electric motor 39, a ball screw mechanism 41 to which the rotation from the spur multi-stage reduction mechanism 35 and the planetary gear reduction mechanism 36 is transmitted to apply a thrust to the piston 32, a thrust sensor 44 for detecting the reaction force against the thrust (pressing force) from the piston 32 to the inner brake pad 22 and the outer brake pad 23, a return mechanism 45 for storing the rotational force in the backward direction with respect to the push rod 42 when the push rod 42 of the ball screw mechanism 41 propels the piston 32, a rotation angle sensor 46 for detecting the rotation angle of the rotation shaft 40 of the electric motor 39, and a thrust holding mechanism 47 for holding the thrust from the piston 32 to the inner brake pad 22 and the outer brake pad 23 during braking. The spur multi-stage reduction mechanism 35 and the planetary gear reduction mechanism 36 are reduction mechanisms.

[0018] The thrust sensor 44 is a thrust detection unit that detects the thrust generated in the brake mechanism 21 (braking mechanism). Specifically, the thrust sensor 44 detects the thrust to the piston 32. The thrust sensor 44 is installed so as to be sandwiched between the base nut 43 constituting the ball screw mechanism 41 and the bottom of the cylinder 31.

[0019] The spur gear multi-stage reduction mechanism 35 and the planetary gear reduction mechanism 36 reduce and amplify the rotation of the electric motor 39 at a predetermined reduction ratio and transmit it to the carrier 37 of the planetary gear reduction mechanism 36. The rotation from the carrier 37 is transmitted to the push rod 42 of the ball screw mechanism 41.

[0020] The ball screw mechanism 41 is a rotation-to-linear motion conversion mechanism. The ball screw mechanism 41 converts the rotational motion from the spur gear multi-stage reduction mechanism 35 and the planetary gear reduction mechanism 36, i.e., the rotational motion of the electric motor 39, into linear motion (hereinafter referred to as linear motion for convenience) and imparts thrust to the piston 32. The ball screw mechanism 41 consists of a push rod 42 as a shaft member to which the rotational motion from the spur gear multi-stage reduction mechanism 35 and the planetary gear reduction mechanism 36 is transmitted, and a base nut 43 as a nut member that is screw-engaged to the outer circumferential surface of the push rod 42. The base nut 43 is fitted by a fitting part (not shown) so as not to rotate relative to the cylinder 31. The push rod 42 can move forward while rotating relative to the base nut 43 while pressing the base nut 43 against the thrust sensor 44. Furthermore, the push rod 42 is connected to the piston 32 via a thrust bearing attached to its tip so as to be able to rotate relative to it. Therefore, the piston 32 can be advanced, and the piston 32 can press the inner brake pad 22 against the disc rotor D.

[0021] The return mechanism 45 is sometimes called a fail-open mechanism. The return mechanism 45 releases the braking force from the inner brake pads 22 and outer brake pads 23 to the disc rotor D by the piston 32 in the event that the electric motor 39 or control board 38 fails during braking.

[0022] The rotation angle sensor 46 is an electric motor position detection unit that detects the rotation angle of the rotation shaft 40 of the electric motor 39. The rotation angle sensor 46 comprises a magnetic member 46A attached to the rotation shaft 40 of the electric motor 39 and a magnetic detection IC chip 46B. By detecting the change in magnetic flux from the rotating magnetic member 46A using the magnetic detection IC chip 46B, the control board 38 can calculate and detect the rotation angle of the rotation shaft 40 of the electric motor 39. The rotation angle sensor 46 constitutes a rotation angle detection means for detecting the rotation position of the electric motor 39 as the motor position.

[0023] The return spring 48 is made of a coil spring. The return spring 48 can store a rotational force in the backward direction relative to the push rod 42. The current sensor 49 is mounted in the motor drive circuit on the control board 38 so as to be able to detect the motor current supplied to the electric motor 39. The current sensor 49 outputs a signal corresponding to the motor current.

[0024] The electric brake ECU 11 receives the requested braking force as a braking command from the main ECU 9. In addition, the electric brake ECU 11 receives the thrust detected by the thrust sensor 44, the motor position detected by the rotation angle sensor 46, and the motor current detected by the current sensor 49. Based on the motor current, motor position, and thrust, the electric brake ECU 11 controls the drive of the electric motor 39 so that the braking force generated by the electric brake 20 becomes the requested braking force specified in the braking command.

[0025] Next, the braking and brake release functions of the electric brake 20 during normal driving will be explained.

[0026] During braking in normal driving, the electric motor 39 is driven by a command from the electric brake ECU 11, and its rotation in the forward direction, i.e., the braking direction (force amplification direction), is reduced and amplified at a predetermined reduction ratio via the spur gear multi-stage reduction mechanism 35 and the planetary gear reduction mechanism 36, and transmitted to the carrier 37 of the planetary gear reduction mechanism 36. Then, the rotation from the carrier 37 is transmitted to the push rod 42 of the ball screw mechanism 41.

[0027] Next, as the carrier 37 rotates, the push rod 42 begins to rotate as well. The push rod 42 presses the base nut 43 against the thrust sensor 44 and moves forward while rotating relative to the base nut 43. As the push rod 42 moves forward while rotating relative to the base nut 43, the piston 32 moves forward and presses the inner brake pad 22 against the disc rotor D. Then, due to the reaction force to the pressing force on the inner brake pad 22 by the piston 32, the caliper body 28 moves to the right in Figure 2 relative to the bracket 25, pressing the outer brake pad 23 attached to the claw portion 30 against the disc rotor D. As a result, the disc rotor D is clamped between the inner brake pad 22 and the outer brake pad 23, generating friction, which in turn generates braking force for the vehicle 1.

[0028] Subsequently, as the disc rotor D is clamped between the inner brake pad 22 and the outer brake pad 23 and braking force begins to be generated, the reaction force is applied to the thrust sensor 44 via the push rod 42 and base nut 43 from the inner brake pad 22 side, and via the claw portion 30 and the bottom of the cylinder 31 from the outer brake pad 23 side. The thrust sensor 44 then detects the thrust force from the inner brake pad 22 and the outer brake pad 23 to the disc rotor D due to the forward movement of the piston 32.

[0029] From this point onward, the return spring 48 stores a rotational force in the backward direction relative to the push rod 42. Subsequently, the drive of the electric motor 39 is controlled by detection signals from the rotation angle sensor 46 and the thrust sensor 44, etc., and a braking state is established.

[0030] On the other hand, when the brake is released, a command from the electric brake ECU 11 causes the rotation shaft 40 of the electric motor 39 to rotate in the opposite direction, i.e., the brake release direction (force reduction direction), and this reverse rotation is transmitted to the push rod 42 via the spur gear multi-stage reduction mechanism 35 and the planetary gear reduction mechanism 36. As a result, the push rod 42 begins to retract while rotating relative to the other gear in the opposite direction, reducing the thrust on the disc rotor D. The restoring force of the inner brake pad 22 and outer brake pad 23, which were compressed by the thrust, causes the caliper body 28 to move to the left in Figure 2 relative to the bracket 25, and the piston 32 retracts. This returns the return spring 48 to its initial state, and the braking force from the inner brake pad 22 and outer brake pad 23 on the disc rotor D is released.

[0031] The piston 32 retracts due to the restoring force of the pads until the restoring forces of the inner brake pad 22 and outer brake pad 23 balance the sum of the sliding resistance between each pad and its bracket and the sliding resistance between the piston 32 and the cylinder 31. To further retract the piston 32 thereafter, the electric motor 39 must be driven further in the deceleration direction to retract the push rod 42 further, which then engages with a groove on the inner wall surface of the piston. The force is then transmitted to the piston 32 via a retaining ring that restricts the relative linear displacement between the piston 32 and the push rod 42.

[0032] The residual thrust between the inner brake pad 22 and the outer brake pad 23, which is prevented from retracting due to sliding resistance between the pads and the bracket, and between the piston 32 and the cylinder 31, becomes a resistance torque (drag torque) when the vehicle is running, i.e., when the disc rotor D rotates, and affects the vehicle's fuel efficiency. Therefore, in the electric brake 20, when there is no braking command from the main ECU 9, or if there is no such command, the electric motor 39 is driven in the deceleration direction, and a gap (clearance) is created between the piston 32 and the inner brake pad 22, thereby reducing the residual thrust and the drag torque. Although not shown, it is also possible to create a clearance between the disc rotor D and the inner brake pad 22 by fitting the piston 32 and the inner brake pad 22 together so that they move linearly as a single unit. It is also possible to create a clearance between the disc rotor D and the outer brake pad 23 by providing a spring between the inner brake pad 22 and the outer brake pad 23 that is biased to move away from the disc rotor D. These methods can further reduce drag torque.

[0033] If the electric motor 39 or control board 38 fails during braking, the biasing force stored in the return spring 48 during braking causes the push rod 42 to retract while rotating relative to it in the opposite direction, releasing the braking force from the inner brake pad 22 and outer brake pad 23 to the disc rotor D.

[0034] Thus, the electric brake 20 is equipped with a rotation angle sensor 46 that can detect the rotation angle of the electric motor 39, a thrust sensor 44 that can detect the thrust of the piston 32, and a current sensor 49 that can detect the motor current, in order to perform position control and thrust control of the piston 32. In addition, it is equipped with a return mechanism 45 (fail-open mechanism) that can release the thrust in case of a malfunction during thrust generation.

[0035] Incidentally, the electric brake 20 is configured such that the reduction mechanism (spur gear multi-stage reduction mechanism 35, planetary gear reduction mechanism 36) and the rotation-to-linear motion conversion mechanism (ball screw mechanism 41) can operate with input from either the input side or the output side. In this case, as shown in Figure 3, there is a first region in which the braking force increases when the current of the electric motor 39 increases, a second region in which the braking force is maintained until the current decreases from increasing to reaching a predetermined current, and a third region in which the braking force decreases when the current decreases from the predetermined current. This predetermined current is set to the current value at which the braking force switches from being maintained to decreasing. For example, Figure 3 shows an example of the relationship between motor current and braking force when the braking force is increasing (increasing force) and decreasing (decreasing force). At this time, the braking force is roughly the same as the braking force obtained from the thrust detected by the thrust sensor 44.

[0036] As shown by the dashed line in Figure 3, the characteristics between motor current and braking force vary due to changes in the efficiency of the reduction mechanism and the rotary-to-linear motion conversion mechanism. Specifically, variations in the efficiency of movable parts such as the reduction mechanism and the rotary-to-linear motion conversion mechanism cause variations in the slope of the braking force relative to the motor current during power increase and power decrease. In addition, variations in the sliding resistance of the movable parts cause variations in the difference in motor current between power increase and power decrease. For this reason, the second region is not constant.

[0037] In response to this, the electric brake ECU 11 of the electric brake 20 controls the motor current supplied to the electric motor 39 so that, in the case of the electric brake 20 of a wheel for which a hold command has been received from the main ECU 9, which is a higher-level controller, the braking force generated along the third region is used for holding. This makes it possible to significantly reduce the motor current while reliably maintaining the braking force. This control is applied not only to constant braking, but also to at least one wheel, such as only the inner wheel during turning, or only the wheel with a higher ECU temperature than the other wheels. For this reason, if electric brakes 20 are applied to all four wheels, the above control may be applied only to the front or rear wheels. Furthermore, the decision to maintain the braking force may be made based on the hold command from the higher-level controller, or it may be made by a control device (electric brake ECU 11) that controls the electric brake 20 based on a change in the braking command (braking force command) from the higher-level controller.

[0038] Next, the operation of the electric brake 20 will be explained using the timing chart in Figure 4. Figure 4 shows the time variation of the requested braking force, motor current, motor position (thrust), and braking force when a trapezoidal wave braking force is requested by the higher-level controller (main ECU 9). At this time, the motor position roughly corresponds to the thrust generated by the brake mechanism 21. The solid line in Figure 4 shows the characteristics of the first embodiment, in which motor current is supplied in the third region when the braking force is maintained. The dashed line in Figure 4 shows the characteristics of a comparative example, in which motor current is supplied in the first region when the braking force is maintained.

[0039] As shown by the solid line in Figure 4, when the braking force increases, the electric brake ECU 11 increases the motor current to satisfy the required braking force. Then, when it recognizes the need to maintain the braking force, the electric brake ECU 11 reduces the motor current. When it detects that the motor position or thrust has decreased, the electric brake ECU 11 maintains the motor current at that point in time.

[0040] When the required braking force decreases, the electric brake ECU 11 controls the motor current to compensate for the difference between the required braking force and the actual braking force when the current is zero, in accordance with the decrease in braking force. However, when the required braking force decreases, the electric brake ECU 11 may also compensate for the difference between the required braking force and the actual braking force and then control the motor current to match the required braking force. As a result, the braking force will be less than the required braking force, but it will be negligible, or it will be compensated for by other wheels so as not to affect the feel.

[0041] On the other hand, as shown by the dashed line in Figure 4, in the comparative example, when maintaining braking force, the motor current supplied when increasing braking force is maintained at the same rate. Therefore, in the comparative example, the motor current when maintaining braking force increases compared to the first embodiment. Consequently, the difference between the solid line and the dashed line in Figure 4 between the first embodiment and the comparative example where braking force is maintained in the first region represents the effect of reducing current consumption.

[0042] Thus, in the first embodiment, the electric brake 20 has a first region in which the braking force increases when the motor current of the electric motor 39 increases, a second region in which the braking force is maintained when the motor current decreases from an increasing value to a predetermined current, and a third region in which the braking force decreases when the motor current decreases from the predetermined current, and the braking force of at least one wheel is controlled to be maintained at the braking force generated along the third region.

[0043] This reduces the current consumption while maintaining braking force, thereby improving energy efficiency. Furthermore, by detecting a third region, current consumption can be significantly reduced without being affected by variations in efficiency, and braking force can be reliably maintained. Additionally, the reduced energization time decreases self-heating and heat exposure time, improving the reliability of the electric brake ECU 11.

[0044] The electric brake 20 includes a spur gear multi-stage reduction mechanism 35 and a planetary gear reduction mechanism 36 as reduction mechanisms for reducing the rotational motion from the electric motor 39, and a ball screw mechanism 41 as a rotation-to-linear motion conversion mechanism that converts the rotational motion of the reduction mechanism into linear motion and pushes the inner brake pad 22 and outer brake pad 23 as braking members. The reduction mechanism and the rotation-to-linear motion conversion mechanism are configured to operate with input from either the input side (e.g., the electric motor 39 side) or the output side (e.g., the inner brake pad 22 and outer brake pad 23 side). The braking force generated along the third region is controlled to be maintained by maintaining the motor current of the electric motor 39. Therefore, compared to the case where the braking force is maintained in the second region, the motor current supplied to the electric motor 39 can be reduced, and the power consumption can be improved.

[0045] The electric brake 20 includes a rotation angle sensor 46 as an electric motor position detection unit that detects the rotational position of the electric motor 39, and the rotation angle sensor 46 determines that a braking force is being generated along the third region. The electric brake 20 generates a braking force corresponding to the rotational position of the electric motor 39. Therefore, the electric brake ECU 11 can determine that a braking force is being generated along the third region by detecting the rotational position of the electric motor 39.

[0046] Furthermore, the electric brake 20 is equipped with a thrust sensor 44 as a thrust detection unit that detects the thrust generated in the brake mechanism 21, which is a braking mechanism. Therefore, the electric brake ECU 11 may determine that a braking force is being generated along the third region based on the thrust detected by the thrust sensor 44. When the braking force is estimated based on the rotational position of the electric motor 39, estimation errors may occur, which may reduce the accuracy of the braking force detection. In contrast, when the thrust detected by the thrust sensor 44 is used, such estimation errors are eliminated, and the accuracy of the braking force detection can be improved.

[0047] As shown in Figure 4, in the first embodiment, the electric brake ECU 11 of the electric brake 20 reduces the motor current from the moment it recognizes that the main ECU 9, which is a higher-level controller, has requested that the braking force be maintained, and maintains the braking force in the third region.

[0048] The present invention is not limited to this, and as shown in the first modified example in Figure 5, when the electric brake ECU 11 recognizes that the main ECU 9 has requested that the brake force be maintained, it may increase the motor current by the amount necessary to detect the transition to the third region, and then decrease the motor current. In the first embodiment, since the brake force is maintained after detecting the third region, the brake force in the maintained state tends to be lower than the required brake force. In contrast, in the first modified example, the brake force is increased in advance by the amount necessary to detect the third region, and then the motor current is decreased to detect the third region. As a result, the brake force in the maintained state can be brought closer to the required brake force.

[0049] Furthermore, in the first modified example, when increasing braking force, the braking force generated by the brake mechanism 21 is increased in accordance with the increase in the required braking force, similar to the first embodiment. The present invention is not limited to this, and as shown in the second modified example in Figure 6, when increasing braking force, a motor current that has been pre-added (increased) by the amount necessary for detecting the third region may be supplied. Subsequently, when the main ECU 9 recognizes that braking force maintenance has been requested, the electric brake ECU 11 reduces the motor current to detect the transition to the third region. After detecting the third region, the electric brake ECU 11 fixes the value of the motor current and maintains the braking force in the third region. In the second modified example, similar to the first modified example, the braking force in the maintained state can be brought closer to the required braking force. In addition, in the second modified example, the motor current can be reduced from the time it is recognized that braking force maintenance has been requested. For this reason, the braking force can be maintained earlier compared to the first modified example.

[0050] Furthermore, in order to detect the third region, when detecting a decrease in motor position or thrust, the motor current may be maintained after considering recognition errors, etc. In addition, Figures 4 to 6 illustrate the case where the braking force is reduced after the motor current is maintained (after the braking force is maintained). The present invention is not limited to this, and after the motor current is maintained, the motor current may be increased up to the first region as an upper limit, for example, in response to a command from ADAS (Advanced Driver-Assistance Systems) or in a situation where emergency braking may be necessary (such as a sudden decrease in the distance to the vehicle in front or behind).

[0051] Next, Figures 1, 7 to 9 show a second embodiment. The characteristic of the second embodiment is that at least one of the reduction mechanism and the rotary-to-linear motion conversion mechanism is configured in such a way that it cannot be operated by an input on either the input side or the output side, and the braking force generated along the third region is controlled to be maintained by de-energizing the electric motor. In the second embodiment, the same reference numerals are used for the same components as in the first embodiment described above, and their descriptions are omitted.

[0052] As shown in Figures 1 and 7, the electric brake 50 of the second embodiment, like the electric brake 20 of the first embodiment, is equipped with a brake mechanism 51, a thrust sensor 44, a rotation angle sensor 46, and an electric brake ECU 53. In this case, the brake mechanism 51 is configured in substantially the same way as the brake mechanism 21 of the first embodiment. Therefore, the brake mechanism 51 is equipped with a spur gear multi-stage reduction mechanism 35 and a planetary gear reduction mechanism 36 as reduction mechanisms, as well as a trapezoidal screw mechanism 52 as a rotation-to-linear conversion mechanism. However, the trapezoidal screw mechanism 52 can be operated by input from the input side, the electric motor 39 side (reduction mechanism side), but cannot be operated by input from the output side, the piston 32 side. Therefore, when the supply of motor current to the electric motor 39 is stopped (motor current becomes zero), the position of the piston 32 is maintained. As a result, even when the supply of motor current is stopped, the thrust from the inner brake pad 22 and outer brake pad 23 to the disc rotor D is maintained, and the braking force is maintained.

[0053] Furthermore, a configuration in which operation by input from the output side is impossible is not limited to the case where a rotary-to-linear motion conversion mechanism is provided. A configuration in which operation by input from the output side is impossible may be provided by a reduction mechanism, or by both a reduction mechanism and a rotary-to-linear motion conversion mechanism.

[0054] The electric brake ECU 53 is configured similarly to the electric brake ECU 11 in the first embodiment. The electric brake ECU 53 receives the requested braking force as a braking command from the main ECU 9. In addition, the electric brake ECU 53 receives the thrust detected by the thrust sensor 44, the motor position detected by the rotation angle sensor 46, and the motor current detected by the current sensor 49. Based on the motor current, motor position, and thrust, the electric brake ECU 53 controls the drive of the electric motor 39 so that the braking force generated by the electric brake 50 becomes the requested braking force specified in the braking command.

[0055] Incidentally, the electric brake 50 has a configuration in which at least one of the reduction mechanism (spur gear multi-stage reduction mechanism 35, planetary gear reduction mechanism 36) and the rotation-to-linear motion conversion mechanism (trapezoidal screw mechanism 52) cannot be operated by input on either the input side or the output side. In this case, as shown in Figure 8, there is a first region in which the braking force increases when the forward current (absolute value of the forward motor current) of the electric motor 39 increases, a second region in which the braking force is maintained until the forward current decreases from increasing to reaching a predetermined reverse current, and a third region in which the braking force decreases when the reverse current (absolute value of the reverse motor current) decreases from the predetermined current. This predetermined current is set to the current value at which the braking force switches from being maintained to decreasing. That is, in the second embodiment, the third region is in the second quadrant. For example, Figure 8 shows an example of the relationship between motor current and braking force when the braking force is increasing (increasing force) and decreasing (decreasing force). At this time, the braking force is approximately equal to the braking force obtained from the thrust detected by the thrust sensor 44.

[0056] The electric brake ECU 53 of the electric brake 50 controls the motor current supplied to the electric motor 39 so that, in the case of the electric brake 50 of a wheel for which a hold command has been received from the main ECU 9, which is a higher-level controller, the braking force generated along the third region is used for holding. This makes it possible to significantly reduce the motor current while reliably maintaining the braking force. Similar to the first embodiment, this control is applied to at least one wheel, such as constant braking, only the inner wheel during turning, or only the wheel with a higher ECU temperature than the other wheels. For this reason, if electric brakes 20 are applied to all four wheels, the above control may be applied only to the front or rear wheels. Furthermore, the decision to maintain the braking force may be based on a hold command from the higher-level controller, or it may be made by a control device (electric brake ECU 53) that controls the electric brake 50 based on a change in the braking command (braking force command) from the higher-level controller.

[0057] Next, the operation of the electric brake 50 will be explained using the timing chart in Figure 9. Figure 9 shows the time changes of the requested braking force, motor current, motor position (thrust), and braking force when a trapezoidal wave braking force is requested by the higher-level controller (main ECU 9). The solid line in Figure 9 shows the characteristics of the second embodiment, in which the motor current is controlled so that the braking force is maintained with the braking force generated along the third region when the braking force is maintained. The dashed line in Figure 9 shows the characteristics of a comparative example, in which the motor current is supplied in the first region when the braking force is maintained.

[0058] As shown by the solid line in Figure 9, when the braking force increases, the electric brake ECU 53 increases the forward motor current to satisfy the required braking force. When it recognizes the need to maintain the braking force, the electric brake ECU 53 switches from increasing to decreasing the absolute value of the forward motor current to zero, and then increases the absolute value of the reverse motor current. As a result, the electric motor 39 rotates in reverse, and the inner brake pad 22 and outer brake pad 23 are displaced away from the disc rotor D. When it detects that the motor position or thrust has decreased, the electric brake ECU 53 reduces the absolute value of the reverse motor current to zero and stops supplying motor current.

[0059] When the required braking force decreases, the electric brake ECU 11 increases the absolute value of the motor current in the reverse direction, and then decreases the absolute value of the motor current. At this time, the electric brake ECU 11 controls the motor current to compensate for the difference between the required braking force and the actual braking force when the current is zero, in accordance with the slope of the required braking force. However, when the required braking force decreases, the electric brake ECU 11 may compensate for the difference between the required braking force and the actual braking force, and then control the motor current in line with the required braking force. As a result, the braking force will be smaller than the required braking force, but this will be negligible, or it will be compensated for by other wheels so as not to affect the feeling.

[0060] Thus, in the second embodiment, substantially the same effects and advantages as in the first embodiment can be obtained. Furthermore, the electric brake 50 includes a spur gear multi-stage reduction mechanism 35 and a planetary gear reduction mechanism 36 as reduction mechanisms for reducing the rotational motion from the electric motor 39, and a trapezoidal screw mechanism 52 as a rotation-to-linear motion conversion mechanism that converts the rotational motion of the reduction mechanism into linear motion and pushes the inner brake pad 22 and outer brake pad 23 as braking members. At least one of the reduction mechanism and the rotation-to-linear motion conversion mechanism is configured so that it cannot be operated by input from either the input side (e.g., the electric motor 39 side) or the output side (e.g., the inner brake pad 22 and outer brake pad 23 side) (e.g., the output side). The braking force generated along the third region is controlled to be maintained by de-energizing the motor current of the electric motor 39. For this reason, for example, in the case of detection by motor position, detection can be performed only between the electric motor 39 and the non-operational location, more so than in the first embodiment, and it is possible to minimize changes in braking force. Furthermore, since braking force can be maintained even when the motor current is not flowing, further reductions in current consumption become possible.

[0061] As shown in Figure 9, in the second embodiment, the electric brake ECU 53 of the electric brake 50 reduces the motor current from the moment it recognizes that the main ECU 9, which is a higher-level controller, has requested that the braking force be maintained, and maintains the braking force in the third region. The present invention is not limited to this, and as shown in the third modified example in Figure 10, when the electric brake ECU 53 recognizes that the main ECU 9 has requested that the braking force be maintained, it may increase the forward motor current by the amount detected, taking into consideration that the braking force will decrease in order to detect the transition to the third region, and then decrease the motor current.

[0062] Furthermore, in the third modified example, when increasing the braking force, the braking force generated by the brake mechanism 51 is increased in accordance with the increase in the required braking force, similar to the first embodiment. The present invention is not limited to this, and as shown in the fourth modified example in Figure 11, when increasing the braking force, a motor current that has been pre-added (increased) by the amount necessary for detecting the third region may be supplied. Subsequently, when the main ECU 9 recognizes that it has requested that the braking force be maintained, the electric brake ECU 53 reduces the motor current to detect the transition to the third region. After detecting the third region, the electric brake ECU 53 de-energizes the motor current and maintains the braking force in the third region.

[0063] Furthermore, in the above embodiments, the electric brakes 20 are applied to the rear wheels 5L and 5R, but the electric brakes 20 may also be applied to the front wheels 3L and 3R, or to all four wheels. In addition, the electric brakes may be electric disc brakes or electric drum brakes.

[0064] In the embodiments described above, electric brakes 20 and 50 used in four-wheeled vehicles were used as examples. However, the invention is not limited to these, and can also be applied to two-wheeled and three-wheeled vehicles, or to work vehicles, transport vehicles such as trucks and buses.

[0065] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Also, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations.

[0066] This application claims priority under Japanese Patent Application No. 2023-017512, filed on 8 February 2023. The entire disclosure of Japanese Patent Application No. 2023-017512, filed on 8 February 2023, including the specification, claims, drawings, and abstract, is incorporated into this application by reference. [Explanation of symbols]

[0067] 11, 53: ECU (control unit) for electric brakes, 20, 50: electric brake (electric brake device), 21, 51: brake mechanism (braking mechanism), 22: inner brake pad (braking member), 23: outer brake pad (braking member), 32: piston, 35: spur gear multi-stage reduction mechanism (reduction mechanism), 36: planetary gear reduction mechanism (reduction mechanism), 39: electric motor, 41: ball screw mechanism (rotation-to-linear motion conversion mechanism), 44: thrust sensor (thrust detection unit), 46: rotation angle sensor (electric motor position detection unit), 49: current sensor, 52: trapezoidal screw mechanism (rotation-to-linear motion conversion mechanism), D: disc rotor (braked member)

Claims

1. An electric brake device, wherein the electric brake device is A braking mechanism that presses a braking member against a member being braked, An electric motor that drives the braking mechanism, Equipped with, The electric brake device has a first region in which the braking force increases when the current of the electric motor increases, a second region in which the braking force is maintained until the current switches from increasing to decreasing and reaches a predetermined current, and a third region in which the braking force decreases when the current decreases from the predetermined current. An electric brake device characterized in that the braking force of at least one wheel is increased in advance in the first region by an amount necessary to detect the transition to the third region, and is controlled to be maintained by the braking force generated along the third region.

2. In the electric brake device according to claim 1, A reduction mechanism for reducing the rotational motion from the aforementioned electric motor, A rotation-to-linear motion conversion mechanism that converts the rotational motion of the reduction mechanism into linear motion and pushes the braking member, Equipped with, The reduction mechanism and the rotary-to-linear motion conversion mechanism are configured to operate with input from either the input side or the output side. An electric brake device characterized in that the braking force generated along the third region is controlled to be maintained by maintaining the current of the electric motor.

3. In the electric brake device according to claim 1, A reduction mechanism for reducing the rotational motion from the aforementioned electric motor, A rotation-to-linear motion conversion mechanism that converts the rotational motion of the reduction mechanism into linear motion and pushes the braking member, Equipped with At least one of the reduction mechanism and the rotary-to-linear motion conversion mechanism is configured in such a way that it cannot be operated by an input on either the input side or the output side. An electric brake device characterized in that the braking force generated along the third region is controlled to be maintained by de-energizing the electric motor.

4. In the electric brake device according to any one of claims 1 to 3, The electric brake device includes an electric motor position detection unit that detects the rotational position of the electric motor, An electric brake device characterized in that the electric motor position detection unit determines that the braking force is generated along the third region.

5. In the electric brake device according to any one of claims 1 to 3, The electric brake device includes a thrust detection unit that detects the thrust generated in the braking mechanism, An electric brake device characterized in that the thrust detection unit determines that the braking force is generated along the third region.

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