Electric braking device

Abstract

An electric braking device 20 includes a control unit 123 that executes: processing for acquiring, on the basis of a reference characteristic, a reference rotation angle corresponding to a target pressing force; processing for specifying a time-of-parking characteristic when a vehicle is parking; processing for acquiring a provisional rotation angle on the basis of the time-of-parking characteristic; and processing for applying a parking braking force to a wheel on the basis of a rotation angle difference that is the difference between the reference rotation angle and the provisional rotation angle.

Description

Electric braking device

[0001] The present invention relates to an electric braking device.

[0002] Patent Document 1 describes an electric braking device that applies a braking force to a wheel by pressing a brake pad against a brake disk based on the power transmitted from an electric motor. When the vehicle is parked, the electric braking device executes an apply process that applies a parking braking force, which is a braking force for parking, to the wheel. In the apply process, the electric braking device maintains a state in which the brake pad is pressed against the brake disk. Thus, the electric braking device can maintain a state in which the parking braking force is applied to the wheel without continuously driving the electric motor.

[0003] International Publication No. 2020 / 158578

[0004] After the execution of the apply process, when the brake disk and the brake pad thermally contract as the temperatures of the brake disk and the brake pad decrease, the parking braking force may decrease. In this case, the electric braking device as described above executes the apply process again to compensate for the decrease in the parking braking force. In other words, when the parking braking force decreases as the brake disk and the brake pad thermally contract, the electric braking device as described above needs to execute the apply process again to maintain the parking of the vehicle.

[0005] An electric braking device that solves the above problems applies a braking force to the wheels by pressing a friction material against a rotating body that rotates together with the vehicle's wheels using the drive of an electric motor, the braking force being applied to the wheels in proportion to the pressing force which is the force pressing the friction material against the rotating body, the electric braking device comprising: a rotation angle acquisition unit that acquires the rotation angle of the electric motor; a pressing force acquisition unit that acquires a pressing force related value related to the pressing force; a reference rotation angle acquisition unit that acquires a reference rotation angle which is the rotation angle corresponding to a target pressing force related value which is the target pressing force related value when the vehicle is parked, based on a reference characteristic that shows a reference relationship between the pressing force related value and the rotation angle; and the pressing force acquisition unit that acquires the pressing force when the vehicle is parked. The system includes: a parking characteristic identification unit that identifies parking characteristics showing the relationship between the pressing force related value and the rotation angle when the vehicle is parked, based on the pressing force related value and the rotation angle acquired by the rotation angle acquisition unit; a provisional rotation angle acquisition unit that acquires a provisional rotation angle, which is the rotation angle corresponding to the target pressing force related value, based on the parking characteristics identified by the parking characteristic identification unit; and a parking braking control unit that performs parking control by controlling the electric motor based on a control amount which is the difference between the reference rotation angle acquired by the reference rotation angle acquisition unit and the provisional rotation angle acquired by the provisional rotation angle acquisition unit, thereby applying the braking force to the wheels to park the vehicle.

[0006] The electric braking system can suppress the need for reapplying after the temperature of the rotating body and friction material has decreased.

[0007] Figure 1 is a schematic diagram of a vehicle equipped with an electric braking system. Figure 2 is a graph showing the relationship between the rotation angle of the electric motor and the pressing force. Figure 3 is a graph showing the relationship between the difference in the rotation angle of the electric motor and the pressing force. Figure 4 is a flowchart showing the processing flow executed by the control device to apply parking braking force to the wheels. Figures 5(a) and 5(b) are timing charts showing the transition of the pressing force and the energization state of the solenoid when applying parking braking force to the wheels. Figure 6 is a flowchart showing the processing flow executed by a modified control device to apply parking braking force to the wheels.

[0008] The following describes one embodiment of a vehicle equipped with an electric braking system. <Configuration of this embodiment> As shown in Figure 1, the vehicle is equipped with a braking operating member 11, wheels 12, and an electric braking system 20.

[0009] The braking operation member 11 is a member operated by the driver when adjusting the deceleration of the vehicle. An example of the braking operation member 11 is the brake pedal. The wheels 12 have, for example, two front wheels and two rear wheels. In this case, the vehicle is a four-wheeled automobile.

[0010] <Electric Brake System 20> The electric brake system 20 includes a braking mechanism 30, a braking actuator 40, a plurality of sensors 51 to 54 and a switch 55, and a control device 100. The electric brake system 20 applies normal braking force to the wheels 12 to decelerate or stop the vehicle when it is in motion, and applies parking braking force to the wheels 12 to maintain the vehicle's parking position when it is parked.

[0011] <Braking Mechanism> A braking mechanism 30 is provided individually for each wheel 12. In other words, there are as many braking mechanisms 30 as there are wheels 12. Each braking mechanism 30 includes a rotating body 31 and a friction material 32. For example, the rotating body 31 is a brake disc, and the friction material 32 is a brake pad. The rotating body 31 rotates together with the wheel 12. Therefore, when the friction material 32 is pressed against the rotating body 31, a braking force is applied to the wheel 12. Hereafter, the force with which the friction material 32 is pressed against the rotating body 31 will be referred to as "pressing force F". Pressing force F corresponds to the "pressing force related value". In the braking mechanism 30, the higher the pressing force F, the greater the braking force applied to the wheel 12.

[0012] <Braking Actuator> Braking actuators 40 are provided individually for each wheel 12. In other words, there are as many braking actuators 40 as there are wheels 12. Braking actuators 40 include an electric motor 41, a reduction mechanism 42, a linear motion conversion mechanism 43, a piston 45, and a braking maintenance mechanism 46. Here, one of the braking actuators 40 for the front wheels and the braking actuators 40 for the rear wheels does not need to be equipped with a braking maintenance mechanism 46. Specifically, the braking actuator 40 for the front wheels does not need to be equipped with a braking maintenance mechanism 46.

[0013] The electric motor 41 has an output shaft 411 that rotates when power is supplied. The reduction mechanism 42 reduces the rotational motion of the output shaft 411 of the electric motor 41 and outputs it to the linear motion conversion mechanism 43. The reduction mechanism 42 has, for example, a plurality of gears that mesh with each other. The linear motion conversion mechanism 43 has a screw shaft 431 and a nut 432. The screw shaft 431 rotates based on the power transmitted from the reduction mechanism 42. The nut 432 is screwed onto the screw shaft 431. Thus, in the linear motion conversion mechanism 43, when the screw shaft 431 rotates, the nut 432 moves linearly in the axial direction of the screw shaft 431.

[0014] The piston 45 is connected to the nut 432. Therefore, when the nut 432 moves in a linear motion, the piston 45 moves in a linear motion in the same direction as the nut 432. When the piston 45 moves forward in the direction approaching the rotating body 31, the pressing force F increases. On the other hand, when the piston 45 moves backward in the direction away from the rotating body 31, the pressing force F decreases.

[0015] Thus, when the output shaft 411 of the electric motor 41 is rotated in one direction (hereinafter referred to as the "increasing direction"), the piston 45 moves forward, increasing the pressing force F. On the other hand, when the output shaft 411 of the electric motor 41 is rotated in the opposite direction to the increasing direction (hereinafter referred to as the "decreasing direction"), the piston 45 moves backward, decreasing the pressing force F. Therefore, the braking actuator 40 can adjust the pressing force F by driving the electric motor 41. In other words, the braking actuator 40 can adjust the braking force applied to the wheel 12 by driving the electric motor 41.

[0016] An example of a braking maintenance mechanism 46 includes a ratchet gear 461, a pawl member 462, and a solenoid 463. The ratchet gear 461 is fixed to the output shaft 411 of the electric motor 41 in a state that allows it to rotate integrally with the gear. The pawl member 462 is displaceable between a locked position in which it engages with the ratchet gear 461 and a retracted position in which it retracts from the ratchet gear 461. The pawl member 462 is biased in the direction from the locked position to the retracted position by a coil spring (not shown) or the like. When the pawl member 462 is in the locked position, the pawl member 462 restricts the rotation of the output shaft 411 and the ratchet gear 461 in the decreasing direction. On the other hand, when the pawl member 462 is in the locked position, the pawl member 462 does not restrict the rotation of the output shaft 411 and the ratchet gear 461 in the increasing direction. The solenoid 463 is a power source for displacing the pawl member 462 to the locked position. In other words, when power is supplied to the solenoid 463, the electromagnetic force generated by the solenoid 463 moves the pawl member 462 to the locked position. If the pawl member 462 is locked to the ratchet gear 461 in the locked position, the pawl member 462 will remain in the locked position even if the power supply to the solenoid 463 is stopped. In this way, the braking maintenance mechanism 46 can maintain a state in which a pressing force F is generated even when the power supply to the electric motor 41 is stopped.

[0017] <Sensors and Switches> As shown in Figure 1, the multiple sensors 51 to 54 output signals to the control device 100 according to the detection results. The brake sensor 51 outputs a detection signal according to the driver's operation of the braking operating member 11. An example of the brake sensor 51 is a stroke sensor that detects the amount of operation of the driver's braking operating member 11. The acceleration sensor 52 outputs a detection signal according to the acceleration in the longitudinal direction of the vehicle. The rotation angle sensor 53 outputs a detection signal according to the rotation angle θ of the electric motor 41. The pressing force sensor 54 outputs a signal according to the pressing force F. When a pressing force F is generated, an axial force acts on the screw shaft 431 of the braking actuator 40. In this respect, the pressing force sensor 54 can be any axial force sensor that detects the axial force acting on the screw shaft 431.

[0018] The parking brake switch 55 outputs a signal to the control device 100 according to the operation status of the switch. The parking brake switch 55 is operated by the driver to switch the parking brake on or off.

[0019] <Control device> As shown in Figure 1, the control device 100 includes a processing circuit 110 having a CPU 111 and a memory 112. The memory 112 stores control programs executed by the CPU 111 and various types of information. When the CPU 111 executes the control programs stored in the memory 112, the processing circuit 110 functions as an acquisition unit 121, a storage unit 122, and a control unit 123.

[0020] <Acquisition Unit> The acquisition unit 121 acquires the braking operation amount, which is the amount of operation of the braking operation member 11, based on the detection signal of the brake sensor 51. The acquisition unit 121 also acquires the longitudinal acceleration of the vehicle based on the detection signal of the acceleration sensor 52. Furthermore, the acquisition unit 121 acquires the road surface gradient G, which is the gradient of the road surface on which the vehicle is located, based on the longitudinal acceleration of the vehicle. The acquisition unit 121 also acquires the rotation angle θ of the electric motor 41 based on the detection signal of the rotation angle sensor 53. Hereafter, the rotation angle θ of the electric motor 41 when the piston 45 is positioned at an initial position away from the friction material 32 is defined as "0". In other words, if the rotation angle θ is greater than "0", it indicates that the piston 45 is moving forward from the initial position, and if the rotation angle θ is less than "0", it indicates that the piston 45 is moving backward from the initial position. Thus, the rotation angle θ does not indicate the increment of the amount of movement of the piston 45, but rather indicates the position of the piston 45. The acquisition unit 121 also acquires the pressing force F based on the detection signal of the pressing force sensor 54. In this respect, the acquisition unit 121 corresponds to the "rotation angle acquisition unit" and the "pressing force acquisition unit".

[0021] The acquisition unit 121 acquires parking brake requests and parking brake release requests based on detection signals from the parking brake switch 55, etc. A parking brake request is a request to turn on the parking brake, and a parking brake release request is a request to turn off the parking brake. If the vehicle is equipped with a driving control device that controls the operation of the vehicle, the acquisition unit 121 may acquire parking brake requests and parking brake release requests transmitted from the driving control device.

[0022] <Control Unit> The control unit 123 adjusts the pressing force F by controlling the braking actuator 40. In other words, the control unit 123 adjusts the braking force applied to the wheel 12 by controlling the braking actuator 40.

[0023] <Normal Braking Process> When a normal braking request occurs, the control unit 123 controls the braking actuator 40 to perform a normal braking process that applies a normal braking force to the wheel 12. A normal braking request occurs when the driver operates the braking operating member 11 or when the vehicle's deceleration is requested by the vehicle's control device. When the control unit 123 performs a normal braking process, it calculates the required normal braking force according to the amount of braking operation. Next, the control unit 123 calculates the target pressing force Ft, which is the target value of the pressing force F, based on the required normal braking force. If the target pressing force Ft is high, the control unit 123 rotates the output shaft 411 of the electric motor 41 of the braking actuator 40 in the increasing direction. In this way, the control unit 123 increases the pressing force F by advancing the piston 45. On the other hand, if the target pressing force Ft is low, the control unit 123 rotates the output shaft 411 of the electric motor 41 of the braking actuator 40 in the decreasing direction. In this way, the control unit 123 reduces the pressing force F by retracting the piston 45.

[0024] <Apply Processing> When a parking brake request occurs, the control unit 123 controls the brake actuator 40 to perform an apply processing to apply parking braking force to the wheels 12. When performing the apply processing, the control unit 123 sets the requested pressing force Fr, which is the pressing force F corresponding to the requested parking braking force, to the target pressing force Ft. The requested parking braking force is set to be greater than or equal to the parking maintenance braking force required to maintain the vehicle's stop. Next, the control unit 123 rotates the output shaft 411 of the electric motor 41 of the brake actuator 40 in the increasing direction. In this way, the control unit 123 increases the pressing force F by advancing the piston 45. When the pressing force F increases to the target pressing force Ft, the control unit 123 stops the rotation of the output shaft 411 of the electric motor 41. In other words, the control unit 123 drives the electric motor 41 so that the rotation angle θ of the electric motor 41 is maintained. Next, the control unit 123 supplies power to the solenoid 463 of the brake maintenance mechanism 46, thereby displacing the claw member 462 to the locked position. After that, the control unit 123 stops supplying power to the electric motor 41 and the solenoid 463. In this way, the pressing force F is maintained at the target pressing force Ft, thereby maintaining the state in which the required parking braking force is applied to the wheel 12.

[0025] <Release Process> When a request to release the parking brake occurs, the control unit 123 controls the brake actuator 40 to perform a release process that releases the parking brake force applied to the wheel 12. When performing the release process, the control unit 123 slightly rotates the output shaft 411 of the electric motor 41 of the brake actuator 40 in the increasing direction. As a result, the claw member 462 separates from the ratchet gear 461, and the claw member 462 is displaced to the retracted position. Subsequently, the control unit 123 rotates the output shaft 411 of the electric motor 41 of the brake actuator 40 in the decreasing direction until the rotation angle θ becomes "0". When the rotation angle θ becomes "0", the control unit 123 stops supplying power to the electric motor 41. In this way, the pressing force F is released, and the requested parking brake force applied to the wheel 12 is released.

[0026] <Reclamping Process> When the driver is operating the vehicle, the parking brake switch 55 is operated after the vehicle has arrived at its destination. In other words, when a parking brake request is made, the rotating body 31 and friction material 32 in the braking mechanism 30 may be hot due to the vehicle's movement up to that point. Therefore, if the apply process is performed while the rotating body 31 and friction material 32 in the braking mechanism 30 are at a high temperature, the following problems may occur. Specifically, the rotating body 31 and friction material 32 in the braking mechanism 30 of the wheel 12 may contract due to thermal expansion as the temperature decreases, which can cause a decrease in the parking brake force applied to the wheel 12. In this case, in order to compensate for the decreased parking brake force, it becomes necessary to perform the apply process again (hereinafter also referred to as the "reclamping process") after some time has passed since the initial apply process.

[0027] When performing a reclamping process, the claw member 462 is in the locked position, while when performing an apply process, the claw member 462 is in the retracted position. Therefore, when performing a reclamping process, it is necessary to displace the claw member 462 to the retracted position, similar to when performing a release process. Subsequently, similar to the apply process, it is necessary to increase the pressing force F to the required pressing force Fr, and then displace the claw member 462 to the locked position.

[0028] <Parking Brake Control> In this embodiment, when a parking brake request occurs, the control unit 123 executes parking brake control so that re-clamping is unnecessary. The parking brake control includes a reference rotation angle acquisition process, a first apply process, a difference acquisition process, an added value acquisition process, and a second apply process.

[0029] Before explaining parking braking control, let's explain the relationship between the rotation angle θ of the electric motor 41 and the pressing force F. Figure 2 is a graph showing the relationship between the rotation angle θ and the pressing force F when the temperatures of the rotating body 31 and the friction material 32 in the braking mechanism 30 are different. In Figure 2, line Ls represents the case where the temperature of the rotating body 31 and the friction material 32 is at the reference temperature, line L1 represents the case where the temperature of the rotating body 31 and the friction material 32 is higher than the reference temperature, and line L2 represents the case where the temperature of the rotating body 31 and the friction material 32 is even higher than the reference temperature. In other words, line L1 represents the case where the rotating body 31 and the friction material 32 are more expanded than in the case shown by line Ls, and line L2 represents the case where the rotating body 31 and the friction material 32 are more expanded than in the case shown by line L1.

[0030] As shown in Figure 2, regardless of the temperature of the rotating body 31 and the friction material 32 in the braking mechanism 30, the pressing force F increases as the rotation angle θ increases. Specifically, except in the case of a very small rotation angle θ, the pressing force F increases linearly with increasing rotation angle θ. Also, line L1 when the temperature of the rotating body 31 and the friction material 32 is high is shifted to the left in the figure compared to line Ls when the temperature of the rotating body 31 and the friction material 32 is at the reference temperature. Similarly, line L2 when the temperature of the rotating body 31 and the friction material 32 is very high is shifted to the left in the figure compared to line L1 when the temperature of the rotating body 31 and the friction material 32 is high. In other words, under conditions where the pressing force F is equal, the higher the temperature of the rotating body 31 and the friction material 32, the smaller the rotation angle θ becomes. Specifically, comparing the rotation angle θ (θs, θ1, θ2) when the pressing force F is the required pressing force Fr, it is found that the higher the temperature of the rotating body 31 and the friction material 32, the smaller the rotation angle θ becomes.

[0031] Hereafter, the relationship between the rotation angle θ and the pressing force F when the temperature of the rotating body 31 and the friction material 32 in the braking mechanism 30 is the reference temperature, that is, the relationship shown by line Ls in Figure 2, will be referred to as the "reference characteristic." For example, the reference temperature can be between 10°C and 30°C. In other words, the reference temperature can be set to the average annual temperature in the vehicle's operating environment. Alternatively, the reference temperature may be set to the average temperature over a defined period such as a month or a week in the vehicle's operating environment. The reference characteristic is stored in the memory unit 122 of the control device 100. The reference characteristic may be a set of points showing the relationship between the rotation angle θ and the pressing force F, or it may be a relational expression.

[0032] <Reference Rotation Angle Acquisition Process> In the reference rotation angle acquisition process, the control unit 123 acquires the reference rotation angle θs, which is the rotation angle θ corresponding to the required pressing force Fr, based on the reference characteristics stored in the memory unit 122. The required pressing force Fr is the pressing force F corresponding to the required parking braking force. In other words, if the pressing force F is greater than or equal to the required pressing force Fr, the vehicle can be parked. In the example shown in Figure 2, the rotation angle θ when the pressing force F is the required pressing force Fr (= target pressing force Ft) on the line Ls corresponding to the reference characteristics is acquired as the reference rotation angle θs. If the required pressing force Fr is a variable value according to the gradient of the road surface on which the vehicle is parked, the reference rotation angle θs will also be a variable value. On the other hand, if the required pressing force Fr is a fixed value, the reference rotation angle θs will also be a fixed value. In this respect, the control unit 123 corresponds to the "reference rotation angle acquisition unit".

[0033] <First Apply Process> In the first apply process, the control unit 123 increases the pressing force F to the target pressing force Ft by controlling the electric motor 41 of the braking actuator 40. In the first apply process, the control unit 123 sets the target pressing force Ft to the requested pressing force Fr. On the other hand, in the first apply process, the control unit 123 does not control the solenoid 463 of the braking maintenance mechanism 46. In other words, in the first apply process, the control unit 123 maintains the pressing force F at the target pressing force Ft by continuing to control the electric motor 41 of the braking actuator 40. The target pressing force Ft corresponds to the "target pressing force related value".

[0034] <Difference Acquisition Process> In the difference acquisition process, the control unit 123 acquires the provisional rotation angle θp, which is the rotation angle θ after the execution of the first apply process. In other words, the control unit 123 acquires the provisional rotation angle θp, which is the rotation angle θ at the point when the pressing force F becomes the target pressing force Ft (= requested pressing force Fr). Subsequently, the control unit 123 acquires the rotation angle difference Δθ, which is the value obtained by subtracting the provisional rotation angle θp from the reference rotation angle θs. For example, when the first apply process is executed, if the rotation angle θ and the pressing force F change as shown by line L1 in Figure 2, the control unit 123 acquires line L1 as the "parking characteristics". Subsequently, the control unit 123 acquires the rotation angle θ1 corresponding to the requested pressing force Fr (= target pressing force Ft) on line L1 as the provisional rotation angle θp, and acquires the rotation angle difference Δθ1, which is the difference between the reference rotation angle θst and the provisional rotation angle θp, as the rotation angle difference Δθ. As shown in Figure 2, the higher the temperature of the rotating body 31 and the friction material 32, the smaller the provisional rotation angle θp becomes. Therefore, the higher the temperature of the rotating body 31 and the friction material 32, the larger the rotation angle difference Δθ becomes. In this respect, the control unit 123 corresponds to the "parking characteristic identification unit" and the "provisional rotation angle acquisition unit," and the rotation angle difference Δθ corresponds to the "control amount."

[0035] Furthermore, if the rotation angle difference Δθ is large, that is, if the temperature of the rotating body 31 and the friction material 32 is high, the control unit 123 may notify the driver that the temperature of the rotating body 31 and the friction material 32 is high using an in-vehicle display or warning lights. In addition, if the rotation angle difference Δθ is very large, that is, if the temperature of the rotating body 31 and the friction material 32 is very high, the control unit 123 may cancel the parking brake request. In this case, it is preferable for the control unit 123 to notify the driver that parking brake force cannot be applied to the wheels 12. The control unit 123 may also notify the driver to wait for a while until the temperature of the rotating body 31 and the friction material 32 decreases.

[0036] <Addition Value Acquisition Process> When the temperature of the rotating body 31 and the friction material 32 is high at the time the parking brake request is generated, the pressing force F decreases more easily with respect to the passage of time after the application process is executed than when the temperature is low. Also, the amount of temperature decrease of the rotating body 31 and the friction material 32 after the application process is executed correlates with the amount of decrease of the pressing force F. Therefore, if the application process is executed with a target value obtained by adding an addition value Fa corresponding to the temperature of the rotating body 31 and the friction material 32 at the time of the execution of the first application process to the requested pressing force Fr, the pressing force F when thermal loosening occurs will become the requested pressing force Fr. Accordingly, in the addition value acquisition process, the control unit 123 acquires an addition value Fa based on the rotation angle difference Δθ. In this embodiment, the control unit 123 acquires an addition value Fa corresponding to the rotation angle difference Δθ by referring to the map shown in Figure 3.

[0037] Figure 3 is a map showing the relationship between the rotation angle difference Δθ and the added value Fa. As shown in Figure 3, the added value Fa increases as the rotation angle difference Δθ increases. Therefore, in the process of acquiring the added value, the added value Fa becomes small when the rotation angle difference Δθ is small, and large when the rotation angle difference Δθ is large. In the example shown in Figure 2, the pressing force F changes linearly with respect to the change in rotation angle θ, except when the pressing force F is low. This trend is generally the same whether the temperature of the rotating body 31 and the friction material 32 is at the reference temperature or higher than the reference temperature. Therefore, in Figure 3, the added value Fa changes linearly with respect to the rotation angle difference Δθ.

[0038] The addition value acquisition process may also be performed by acquiring the addition value Fa based on a relationship formula and table equivalent to the map shown in Figure 3. Furthermore, the relationship between the rotation angle θ and the pressing force F shown in Figure 2 is just one example. Depending on the characteristics of the braking mechanism 30, the relationship between the rotation angle θ and the pressing force F may not be linear.

[0039] <Second Apply Process> In the second apply process, the control unit 123 controls the electric motor 41 of the braking actuator 40 to increase the pressing force F to the target pressing force Ft. In the second apply process, the control unit 123 sets the target pressing force Ft to the value obtained by adding the added value Fa obtained in the added value acquisition process to the requested pressing force Fr. However, if the added value Fa is a very large value, the target pressing force Ft will be set to a very large value, which may place a large load on the electric braking device 20 when the second apply process is executed. Therefore, if the added value Fa is less than the upper limit value FaTh, the control unit 123 sets the target pressing force Ft to the value obtained by adding the added value Fa to the requested pressing force Fr. On the other hand, if the added value Fa is equal to or greater than the upper limit value FaTh, the control unit 123 sets the target pressing force Ft to the value obtained by adding the upper limit value FaTh to the requested pressing force Fr. The upper limit value FaTh is set in advance based on, for example, the specifications of the braking actuator 40 of the electric braking system 20.

[0040] In the second apply process, when the pressing force F increases to the required pressing force Fr corresponding to the required parking braking force, the control unit 123 stops the rotation of the output shaft 411 of the electric motor 41. In other words, the control unit 123 drives the electric motor 41 so that the rotation angle θ of the electric motor 41 is maintained. Subsequently, the control unit 123 supplies power to the solenoid 463 of the braking maintenance mechanism 46, thereby displacing the claw member 462 to the locked position. As a result, even if the power supply to the electric motor 41 and the solenoid 463 is stopped, the braking force applied to the wheel 12 is maintained. After that, the control unit 123 stops the power supply to the electric motor 41 and the solenoid 463. In this respect, the control unit 123 corresponds to the "parking braking control unit," and the second apply process corresponds to "parking control." Furthermore, in "parking control," the control unit 123 imposes a restriction on the control of the electric motor 41 based on the "control amount" by comparing the added value Fa with the upper limit value FaTh.

[0041] <Processing flow executed by the control device> Referring to the flowchart shown in Figure 4, the processing flow executed by the control device 100 when applying parking braking force to the wheels 12 based on a parking braking request will be explained.

[0042] As shown in FIG. 4, the control device 100 sets the required pressing force Fr to the target pressing force Ft (S11). Subsequently, the control device 100 executes a first application process based on the target pressing force Ft set in step S11 (S12). Thereafter, the control device 100 acquires a provisional rotation angle θp which is the rotation angle θ at the completion time of the first application process (S13). Subsequently, the control device 100 acquires a reference rotation angle θs based on the reference characteristics stored in the storage unit 122 (S14). Then, the control device 100 obtains a rotation angle difference Δθ by subtracting the provisional rotation angle θp obtained in step S13 from the reference rotation angle θs obtained in step S14 (S15).

[0043] The control device 100 refers to the map shown in FIG. 3 and acquires an addition value Fa corresponding to the rotation angle difference Δθ obtained in step S15 (S16). Subsequently, the control device 100 determines whether or not the addition value Fa is less than a predetermined upper limit value FaTh (S17). When the addition value Fa is less than the upper limit value FaTh (S17: YES), the control device 100 sets the target pressing force Ft to the sum of the required pressing force Fr and the addition value Fa (S18). On the other hand, when the addition value Fa is greater than or equal to the upper limit value FaTh (S17: NO), the control device 100 sets the target pressing force Ft to the sum of the required pressing force Fr and the upper limit value FaTh (S19). In steps S18 and S19, when the setting of the target pressing force Ft is completed, the control device 100 executes a second application process based on the target pressing force Ft (S20). Thereafter, the control device 100 ends this process.

[0044] <Operation and Effect of the Present Embodiment> The operation of the electric braking device 20 will be described with reference to FIGS. 5(a) and 5(b). FIG. 5(a) shows the transition of the pressing force F, and FIG. 5(b) shows the transition of the power supply state to the solenoid 463 of the braking maintenance mechanism 46. In FIG. 5, the change in the state of the comparative example is indicated by a dashed-dotted line, and the change in the state of the present embodiment is indicated by a solid line.

[0045] As shown by the dashed lines in Figures 5(a) and (b), in the comparative example, when a parking brake request occurs at timing t11, the apply process is executed. Therefore, at timing t11, after the pressing force F increases to the requested pressing force Fr, power is supplied to the solenoid 463 of the brake maintenance mechanism 46. As a result, the state in which the pressing force F (= requested pressing force Fr) is generated is maintained. In other words, the state in which parking brake force is applied to the wheel 12 is maintained.

[0046] From timing t11 onward, the temperature of the rotating body 31 and the friction material 32 decreases over time. As a result, the pressing force F gradually decreases due to thermal relaxation. At timing t13, when the elapsed time since the apply process reaches the determination time, the reclamp process is executed. In other words, at timing t13, after the pressing force F increases again to the required pressing force Fr, power is supplied again to the solenoid 463 of the braking maintenance mechanism 46. As a result, the state in which the pressing force F (= required pressing force Fr) is generated is maintained. In other words, the state in which parking braking force is applied to the wheel 12 is maintained. From timing t13 onward, the pressing force F does not decrease as easily because the temperature of the rotating body 31 and the friction material 32 decreases less easily.

[0047] As shown by the solid lines in Figures 5(a) and (b), in this embodiment, when a parking brake request occurs at timing t11, a first apply process is executed to set the target pressing force Ft to the requested pressing force Fr. As a result, at timing t11, the pressing force F increases to the requested pressing force Fr. After the pressing force F reaches the requested pressing force Fr, an added value Fa corresponding to the decrease in pressing force F due to thermal relaxation is calculated. Subsequently, at timing t12, immediately following timing t11, a second apply process is executed to set the target pressing force Ft to the sum of the requested pressing force Fr and the added value Fa. As a result, after the pressing force F increases to the sum of the requested pressing force Fr and the added value Fa, power is supplied to the solenoid 463 of the braking maintenance mechanism 46. As a result, the state in which a pressing force F (= requested pressing force Fr + added value Fa) is generated is maintained. In reality, the period from timing t11 to timing t12 is a very short period.

[0048] That is, when the first apply process and the second apply process are continuously executed, the pressing force F instantaneously increases to the sum of the required pressing force Fr and the addition value Fa at the timing t11.

[0049] After the timing t12, as time passes, the temperatures of the rotating body 31 and the friction material 32 decrease. Therefore, due to thermal relaxation, the pressing force F gradually decreases. When the timing t13 is reached at which the temperatures of the rotating body 31 and the friction material 32 have sufficiently decreased, the pressing force F decreases to the required pressing force Fr. As described above, in this embodiment, the electric braking device 20 can determine the target pressing force Ft in the second apply process in consideration of the degree of expansion of the rotating body 31 and the friction material 32 when a parking brake request occurs. Therefore, the electric braking device 20 can ensure the parking braking force after thermal relaxation has occurred. Accordingly, the electric braking device 20 does not need to execute the reclamp process. In other words, when applying the parking braking force to the wheel 12, the electric braking device 20 can suppress the number of power supply times to the solenoid 463 to one time.

[0050] Further, when the addition value Fa is greater than or equal to the upper limit value FaTh, the electric braking device 20 limits the target pressing force Ft in the second apply process to a value obtained by adding the upper limit value FaTh to the required pressing force Fr. Therefore, the electric braking device 20 can suppress a load from being applied to the electric braking device 20. In other words, the electric braking device 20 can enhance durability.

[0051] Note that when the vehicle is parked on a slope or the like, there is a possibility that the pressing force F decreases due to reasons other than thermal relaxation after the timing t13 in FIG. 5, resulting in the vehicle slipping down. In this embodiment, the electric braking device 20 may suppress the vehicle from slipping down by increasing the pressing force F by means of the reclamp process.

[0052] <Modification Example> This embodiment can be implemented by making the following modifications. This embodiment and the following modification examples can be implemented in combination with each other as long as they do not technically conflict with each other.

[0053] - When a vehicle is parked on a flat road surface, it may be possible to maintain the vehicle's parking position even if the parking braking force decreases due to thermal relaxation. Therefore, the control device 100 should prohibit parking braking control based on the rotation angle difference Δθ if the magnitude of the road surface gradient G while the vehicle is stopped is less than a predetermined gradient determination value GTh. The following describes the processing flow executed by the control device 100 in this case.

[0054] As shown in Figure 6, after executing the process in step S11, the control device 100 determines whether the magnitude of the road surface gradient G while the vehicle is stopped is greater than or equal to the gradient determination value GTh (S31). If the magnitude of the road surface gradient G is greater than or equal to the gradient determination value GTh (S31: YES), the control device 100 proceeds to step S12. The flow of processing from step S12 onward is the same as in the above embodiment. On the other hand, if the magnitude of the road surface gradient G is less than the gradient determination value GTh (S31: NO), the control device 100 performs the normal apply process (S32). After that, the control device 100 terminates this process.

[0055] This modification example involves performing a second apply process that targets a pressing force F greater than the required pressing force Fr, only when there is a high need to suppress the decrease in parking braking force due to thermal loosening when applying parking braking force to the wheel 12. As a result, the electric braking device 20 can have a higher durability.

[0056] - In step S16 of Figure 4, the control device 100 may set the added value Fa to "0" if the magnitude of the road surface gradient G is less than the gradient determination value GTh. In other words, the control device 100 may execute a second apply process in which the added value Fa is set to "0" if the magnitude of the road surface gradient G is less than the gradient determination value GTh. This modified example can obtain the same effects as the modified example described above.

[0057] The control device 100 may correct the added value Fa according to various conditions. For example, if there is variation in the time from the start of parking brake control to the execution of the second apply process, the control device 100 may reduce the added value Fa the longer the time. This is because the longer the time from the start of parking brake control to the execution of the second apply process, the greater the temperature decrease between the rotating body 31 and the friction material 32.

[0058] - When parking a vehicle, a normal braking force is applied to decelerate the vehicle. The control device 100 may calculate an added value Fa based on the relationship between the rotation angle θ and the pressing force F when a normal braking force is applied to the wheels 12 immediately before a parking braking request is generated. In this case, when a parking braking request is generated, the control device 100 may execute the second apply process without executing the first apply process.

[0059] - The control device 100 does not need to set an upper limit on the added value Fa. In this case, the control device 100 may limit the target pressing force Ft by setting an upper limit on the calculated rotation angle difference Δθ. - When the control device 100 makes the target pressing force Ft a variable value according to the gradient, the upper limit value FaTh may be made smaller as the target pressing force Ft increases. This allows the control device 100 to suppress the generation of large pressing forces F, thereby further increasing the durability of the electric braking device 20.

[0060] As shown in Figure 3, the rotation angle difference Δθ as a "controlled amount" and the added value Fa are correlated. Therefore, in the second apply processing based on the rotation angle difference Δθ, the control device 100 may limit the rotation angle difference Δθ to be less than or equal to a predetermined upper limit of the controlled amount. Specifically, the control device 100 determines whether the rotation angle difference Δθ is greater than or equal to a predetermined upper limit of the controlled amount. If the rotation angle difference Δθ is less than or equal to the upper limit of the controlled amount, the control device 100 obtains an added value Fa corresponding to the acquired rotation angle difference Δθ. On the other hand, if the rotation angle difference Δθ is greater than the upper limit of the controlled amount, the control device 100 obtains an added value Fa corresponding to the upper limit of the controlled amount. In this way, the control device 100 can suppress the load on the electric brake device 20 in the second apply processing by setting a limit on the rotation angle difference Δθ. Furthermore, the control device 100 may reduce the upper limit of the controlled amount as the target pressing force Ft increases. In this way, the load on the electric brake device 20 in the second apply processing can be further suppressed. As described above, the rotation angle difference Δθ and the added value Fa are correlated, so setting a limit on the added value Fa is equivalent to setting a limit on the rotation angle difference Δθ, and varying the upper limit FaTh is equivalent to varying the upper limit of the controlled variable. In other words, the upper limit of the controlled variable can be said to be the value obtained by converting the upper limit FaTh in the above embodiment to the rotation angle difference Δθ.

[0061] In the above embodiment, the control device 100 acquired the parking characteristics after the execution of the first apply process, and then acquired the provisional rotation angle θp, but it is not limited to this. For example, the control device 100 may acquire the parking characteristics during the execution of the first apply process, that is, before the pressing force F reaches the target pressing force Ft. For example, the control device 100 may acquire the parking characteristics based on the gradient of change of the pressing force F with respect to the rotation angle θ during the execution of the first apply process. In this case, the control device 100 can acquire the provisional rotation angle θp based on the parking characteristics before the end of the first apply process. Furthermore, the control device 100 can execute the second apply process immediately following the first apply process. In other words, the control device 100 can complete the second apply process without stopping the driving of the electric motor 41 which was started by the first apply process.

[0062] The rotation angle θ of the electric motor 41 is correlated with the stroke amount of the piston 45. For this reason, the electric braking device 20 may be equipped with a stroke sensor that detects the stroke amount of the piston 45 instead of the rotation angle sensor 53. In other words, the control device 100 may use a rotation angle-related value corresponding to the rotation angle θ instead of the rotation angle θ.

[0063] The braking mechanism 30 may have a wheel cylinder that presses the friction material 32 against the rotating body 31 with a force corresponding to the hydraulic pressure. In this case, it is preferable that the braking actuator 40 is configured to adjust the hydraulic pressure of the wheel cylinder in accordance with the linear motion of the piston 45. In this case, the hydraulic pressure of the wheel cylinder corresponds to the "pressing force related value".

[0064] When the braking actuator 40 increases the braking force applied to the wheel 12, not only does the pressing force F increase, but the load on the electric motor 41 also increases. For this reason, the control device 100 may use the current value of the electric motor 41 instead of the pressing force F. In this case, the current value of the electric motor 41 corresponds to the "pressing force related value".

[0065] - A parking brake request is not necessarily triggered by the driver operating the parking brake switch 55. For example, a parking brake request may be triggered when the vehicle door is opened to exit the vehicle or when the ignition power is turned off.

[0066] - When a parking brake request is generated based on the driver's operation of the parking brake switch 55, the driver is likely to be able to respond even if heat loosening occurs due to the execution of the normal apply process, since the driver is in the vehicle. On the other hand, when a parking brake request is generated that is unrelated to the driver's intention, the driver is not necessarily in the vehicle, so even if heat loosening occurs due to the execution of the normal apply process, the driver is unlikely to be able to respond. Therefore, the control device 100 may execute the normal apply process when a parking brake request is generated based on the driver's operation of the parking brake switch 55. On the other hand, the control device 100 may execute the parking brake control of the above embodiment when a parking brake request is generated that is unrelated to the driver's intention. This modification can increase the durability of the electric brake device 20 by reducing the frequency of execution of the parking brake control.

[0067] The electric braking device 20 may include a normal braking actuator for applying normal braking force to the wheels 12 and a parking braking actuator for applying parking braking force to the wheels 12. In this case, it is preferable that the parking braking actuator includes an electric motor and a conversion mechanism for converting the rotational motion of the output shaft of the electric motor into the linear motion of the friction material 32. Furthermore, it is preferable that the parking braking actuator is configured to maintain a state in which the friction material 32 is pressed against the rotating body 31 even when power is not supplied, through a self-locking function.

[0068] The control device 100 is not limited to a processing circuit 110 that includes a CPU 111 and a memory 112 and executes software processing. For example, the control device 100 may include a dedicated hardware circuit that executes at least a part of the various processes performed in the above embodiment. An example of a dedicated hardware circuit is an ASIC. ASIC is an abbreviation for "Application Specific Integrated Circuit". In other words, the control device 100 may have any of the following configurations (a) to (c).

[0069] (a) A processing circuit comprising a processing unit that executes all of the above processes according to a program, and a program storage device such as memory for storing the program. (b) A processing circuit comprising a processing unit and a program storage device that execute a part of the above processes according to a program, and a dedicated hardware circuit that executes the remaining processes.

[0070] (c) A processing circuit equipped with dedicated hardware circuits to perform all of the above processing. Here, there may be multiple software execution devices equipped with processing units and program storage devices, and dedicated hardware circuits.

[0071] As used herein, the expression "at least one" means "one or more" of the desired options. For example, as used herein, if there are two options, the expression "at least one" means "only one option" or "both of the two options." As another example, as used herein, the expression "at least one" means "only one option" or "any combination of two or more options" if there are three or more options.

Claims

1. An electric braking device that applies a braking force to a wheel corresponding to a pressing force, which is the force pressing the friction material against the rotating body, by driving an electric motor, wherein the device comprises: a rotation angle acquisition unit that acquires the rotation angle of the electric motor; a pressing force acquisition unit that acquires a pressing force related value related to the pressing force; a reference rotation angle acquisition unit that acquires a reference rotation angle, which is the rotation angle corresponding to a target pressing force related value, which is the pressing force related value, when the vehicle is parked, based on a reference characteristic that shows a reference relationship between the pressing force related value and the rotation angle; a parking characteristic identification unit that identifies parking characteristics showing the relationship between the pressing force related value and the rotation angle when the vehicle is parked, based on the pressing force related value acquired by the pressing force acquisition unit and the rotation angle acquired by the rotation angle acquisition unit; and a provisional rotation angle acquisition unit that acquires a provisional rotation angle, which is the rotation angle corresponding to the target pressing force related value, based on the parking characteristics identified by the parking characteristic identification unit. An electric braking device comprising: a parking braking control unit that performs parking control by controlling the electric motor based on a control amount which is the difference between the reference rotation angle acquired by the reference rotation angle acquisition unit and the provisional rotation angle acquired by the provisional rotation angle acquisition unit, thereby applying the braking force to the wheels for parking the vehicle.

2. The electric braking device according to claim 1, wherein the parking braking control unit prohibits the execution of the parking control based on the control amount when the magnitude of the road surface gradient is less than the gradient determination value.

3. The electric braking device according to claim 1 or 2, wherein the parking braking control unit, in controlling the electric motor based on the control amount of the parking control, limits the control amount to be less than or equal to a predetermined upper limit of the control amount, and the upper limit of the control amount is smaller as the target pressing force related value increases.

Images