Electric braking system

Abstract

To provide an electric braking system that can suppress a decrease in braking performance of braking force while suppressing an increase in memory pressure.SOLUTION: A processing circuit of an electric braking system functions as a rotation angle detection unit M11 configured to derive a rotation angle detection value θS of an electric motor, a pressing force acquisition unit M13 configured to acquire a pressing force related value, a deviation amount derivation unit M17 configured to derive a related deviation amount that is an amount of deviation Δθ1 between a first rotation angle reference value θB1 corresponding to the pressing force related value defined from a reference relationship and a rotation angle detection value θS when the pressing force related value is acquired, a control amount derivation unit M21 configured to derive at least one of a first control amount C1 that is the intercept of an approximation line that linearly approximates the relationship between the pressing force related value and the amount of deviation Δθ1 and a second control amount C2 that is the slope of the approximation line, and a control unit M31 configured to control the electric motor on the basis of the at least one control amount.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an electric braking device provided in a vehicle.

Background Art

[0002] An electric braking device can adjust the pressing force, which is the force for pressing a friction material against a rotating body that rotates integrally with a wheel, by controlling the rotation angle of an electric motor. With such an electric braking device, the braking force generated by the wheel can be increased by increasing the pressing force. In such an electric braking device, when the rigidity of the friction material changes, the relationship between the rotation angle of the electric motor and the pressing force changes. When the relationship between the rotation angle and the pressing force changes in this way, there is a risk that the controllability of the braking force in the electric braking device will decrease.

[0003] Therefore, a plurality of reference rigidities are stored in advance in the memory of the electric braking device of Patent Document 1. The control unit of the electric braking device selects one reference rigidity from among the plurality of reference rigidities based on the estimation result of the rigidity of the friction material at that time. Then, the control unit controls the rotation angle of the electric motor using the reference rigidity. Thereby, a decrease in the controllability of the braking force due to a change in the rigidity of the friction material is suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above electric braking device, by controlling the rotation angle of the electric motor using a reference rigidity close to the rigidity of the friction material at that time, a decrease in the controllability of the braking force is suppressed. However, since a plurality of reference rigidities are stored in advance in the memory, the load on the memory becomes large.

Means for Solving the Problems

[0006] The electric braking device for solving the above problems is a device that generates a braking force on the wheels of a vehicle by adjusting the force pressing a friction material against a rotating body that rotates integrally with the wheels of the vehicle, wherein the rotating part of a linear motion conversion mechanism rotates in response to the rotational motion of an electric motor, the rotational motion of the rotating part is converted into a linear motion of a linear motion part of the linear motion conversion mechanism, and the linear motion of the linear motion part is adjusted. The electric braking device includes a rotation angle detection unit that derives a detected value of the rotation angle of the electric motor, a pressing force acquisition unit that acquires a pressing force related value that is a state quantity related to the pressing force that presses the friction material against the rotating body, a deviation amount derivation unit that derives a relationship deviation amount that is the deviation amount between the rotation angle corresponding to the pressing force related value determined from a reference relationship that is the relationship between the rotation angle and the pressing force, and the detected value of the rotation angle when the pressing force related value is acquired, a control amount derivation unit that derives at least one of a first control amount that is the relationship deviation amount when the pressing force related value is 0 (zero) on an approximate straight line that is a straight line obtained by linearly approximating the relationship between the pressing force related value and the relationship deviation amount, and a second control amount that is the change amount of the relationship deviation amount with respect to the change amount of the pressing force related value on the approximate straight line, and a control unit that controls the electric motor based on at least one of the first control amount and the second control amount.

Advantages of the Invention

[0007] The above electric braking device has an effect of suppressing a decrease in the controllability of the braking force while suppressing an increase in the load of the memory.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiment for Carrying Out the Invention

[0009] Hereinafter, an embodiment of an electric braking device provided in a vehicle will be described with reference to FIGS. 1 to 4. As shown in FIG. 1, the electric braking device 10 includes a caliper 20, a gearbox 30, an electric motor 40, a speed reduction mechanism 50, a linear motion conversion mechanism 60, a piston 70, and a motor control device 80. The electric braking device 10 is configured to generate a braking force on the wheel 100 by pressing a friction material 120 against a rotating body 110 that rotates integrally with the wheel 100 of the vehicle. An example of the electric braking device 10 is a disc-type braking device.

[0010] <Caliper and Gearbox> The caliper 20 has a cylinder body 21, a bridge 22, and an arm 23.

[0011] The cylinder body 21 is connected to the arm 23 via the bridge 22. The cylinder body 21 has a cylinder 24 that includes a cylindrical space. The axis of the cylinder 24 extends in the same direction as the rotation axis of the wheel 100. The arm 23 is located in the direction extending the axis of the cylinder 24. In the following description, the axial direction of the cylinder 24 is referred to as the "front-rear direction". In a state where the cylinder body 21 is assembled to the vehicle, the rotating body 110 is disposed between the cylinder body 21 and the arm 23. The two friction materials 120 are respectively assembled to the cylinder body 21 and the arm 23. That is, the two friction materials 120 are located on both sides in the thickness direction of the rotating body 110.

[0012] The gear box 30 houses a speed reduction mechanism 50. The gear box 30 is assembled to the cylinder body 21. The gear box 30 is located at an end portion in the front-rear direction opposite to the end portion of the cylinder 24 where the friction material 120 is located. Hereinafter, in the front-rear direction, the direction toward the friction material 120 is referred to as "forward direction X1", and the direction toward the gear box 30 is referred to as "backward direction X2".

[0013] <Electric motor> The electric motor 40 is assembled to the cylinder body 21. At this time, the axis of the output shaft 41 of the electric motor 40 is parallel to the axis of the cylinder 24. Further, the output shaft 41 of the electric motor 40 extends toward the inside of the gear box 30. The electric motor 40 is provided with a rotation angle sensor 42 that outputs a signal corresponding to the rotation angle of the electric motor 40. The rotation angle sensor 42 may be, for example, a magnetic sensor.

[0014] <Speed reduction mechanism> The speed reduction mechanism 50 reduces the rotation of the output shaft 41 of the electric motor 40 and transmits it to the linear motion conversion mechanism 60. The speed reduction mechanism 50 includes a first gear 51 fixed to the output shaft 41 of the electric motor 40, a second gear 52 that rotates by the torque transmitted from the first gear 51, and a third gear 53 that rotates by the torque transmitted from the second gear 52. Therefore, the torque output by the electric motor 40 is transmitted to the linear motion conversion mechanism 60 via the first gear 51, the second gear 52, and the third gear 53.

[0015] <Linear motion conversion mechanism> The linear motion conversion mechanism 60 converts the rotational motion of the third gear 53 into the linear motion of the piston 70. The linear motion conversion mechanism 60 includes a screw shaft 61 that rotates based on the power transmitted from the speed reduction mechanism 50, and a nut 62 that linearly moves by the power transmitted from the screw shaft 61. The linear motion conversion mechanism 60 is a so-called feed screw mechanism. In other embodiments, the linear motion conversion mechanism 60 may be a so-called ball screw mechanism.

[0016] A thread groove is provided on the outer peripheral surface of the screw shaft 61. A thread groove corresponding to the screw shaft 61 is provided on the inner peripheral surface of the nut 62. In the linear motion conversion mechanism 60, the screw shaft 61 and the nut 62 are accommodated in the cylinder 24. At this time, the axial direction of the screw shaft 61 and the axial direction of the nut 62 coincide with the axial direction of the cylinder 24. The base end portion of the screw shaft 61 is connected to the third gear 53. Thus, the screw shaft 61 can rotate integrally with the third gear 53. That is, the screw shaft 61 corresponds to the "rotating part of the linear motion conversion mechanism", and the nut 62 corresponds to the "linear motion part of the linear motion conversion mechanism".

[0017] <Piston> The piston 70 is accommodated in the cylinder 24 so as not to be rotatable about an axis extending in the front-rear direction with respect to the cylinder 24 and to be movable in the front-rear direction with respect to the cylinder 24. The piston 70 faces the friction material 120 in the front-rear direction. Further, the piston 70 is integrated with the nut 62. For this reason, when the nut 62 moves in the forward direction X1, the piston 70 moves in the forward direction X1 together with the nut 62. On the other hand, when the nut 62 moves in the backward direction X2, the piston 70 moves in the backward direction X2 together with the nut 62.

[0018] <Operation of the Electric Braking Device> In the electric braking device 10, when the electric motor 40 is driven, the rotational motion of the output shaft 41 of the electric motor 40 is decelerated by the speed reduction mechanism 50. Subsequently, the rotational motion of the third gear 53 of the speed reduction mechanism 50 is transmitted to the screw shaft 61 of the linear motion conversion mechanism 60. In the linear motion conversion mechanism 60, the rotational motion of the screw shaft 61 is converted into a linear motion of the nut 62 in the forward direction X1. As a result, the piston 70 moves in the forward direction X1 together with the nut 62. Thus, when the piston 70 presses the friction material 120 against the rotating body 110, a braking force Fx is generated at the wheel 100.

[0019] The magnitude of the braking force Fx is substantially proportional to the magnitude of the force pressing the friction material 120 against the rotating body 110. The force pressing the friction material 120 is referred to as the "pressing force P". The rotation angle of the electric motor 40 is referred to as the "motor rotation angle θ". At this time, as the motor rotation angle θ increases, the pressing force P increases. Therefore, the electric braking device 10 can adjust the pressing force P and the braking force Fx by controlling the motor rotation angle θ.

[0020] <Motor control device> The motor control device 80 includes an inverter circuit 81 and a processing circuit 90. The inverter circuit 81 has a plurality of switching elements that operate by the power supplied from the power source. The inverter circuit 81 generates signals for each phase of the electric motor 40 by the on / off operation of the switching elements based on commands from the processing circuit 90. Then, the inverter circuit 81 drives the electric motor 40 by inputting the generated signals to each phase of the electric motor 40.

[0021] An example of the processing circuit 90 is an electronic control unit. In this case, the processing circuit 90 has a CPU 91, a first memory 92, and a second memory 93. The first memory 92 stores a control program executed by the CPU 91. The second memory 93 stores the calculation results of the CPU 91 and the like. By the CPU 91 executing the control program in the first memory 92, the processing circuit 90 outputs the above commands to the inverter circuit 81.

[0022] <Functional configuration of the processing circuit> Referring to FIG. 2, the functional configuration of the processing circuit 90 will be described. By the CPU 91 executing the control program in the first memory 92, the processing circuit 90 functions as a plurality of functional units. The plurality of functional units are functional units for controlling the electric motor 40. The plurality of functional units include a rotation angle detection unit M11, a pressing force acquisition unit M13, a first reference rotation angle derivation unit M15, a deviation amount derivation unit M17, a determination unit M19, a control amount derivation unit M21, a control amount storage unit M23, a target value setting unit M25, a second reference rotation angle derivation unit M27, a target value correction unit M29, and a control unit M31.

[0023] <Rotation angle detection unit> Based on the detection signal of the rotation angle sensor 42, the rotation angle detection unit M11 derives a detected value θS of the motor rotation angle θ. Hereinafter, the detected value θS is referred to as the "rotation angle detected value θS". The rotation angle detection unit M11 derives the rotation angle detected value θS every predetermined control cycle.

[0024] <Pressing force acquisition unit> The pressing force acquisition unit acquires a pressing force related value, which is a state quantity related to the pressing force P, every predetermined control cycle. In the present embodiment, the pressing force acquisition unit M13 acquires a pressing force estimated value PE, which is an estimated value of the pressing force P, as the pressing force related value. For example, the pressing force acquisition unit M13 derives the pressing force estimated value PE based on the motor current value Imt, which is the magnitude of the current flowing through the electric motor 40.

[0025] There is a correlation between the load torque of the electric motor 40 and the pressing force P. The larger the load torque, the larger the motor current value Imt. Therefore, the pressing force acquisition unit M13 may derive the pressing force estimated value PE so that the value increases as the motor current value Imt increases.

[0026] <First reference rotation angle derivation unit> When the pressing force acquisition unit M13 acquires the pressing force estimated value PE, the first reference rotation angle derivation unit M15 derives a first rotation angle reference value θB1, which is a motor rotation angle θ corresponding to the pressing force estimated value PE. The first rotation angle reference value θB1 is a motor rotation angle corresponding to the pressing force estimated value PE determined from a reference relationship, which is the relationship between the motor rotation angle θ and the pressing force P.

[0027] For example, the first reference rotation angle derivation unit M15 derives the first rotation angle reference value θB1 using a reference map MP1, which is a map showing the reference relationship. The reference map MP1 is a map showing the relationship between the motor rotation angle θ and the pressing force P based on the initial characteristics of the electric braking device 10.

[0028] <Deviation amount derivation unit> When the first reference rotation angle derivation unit M15 derives the first rotation angle reference value θB1, the deviation amount derivation unit M17 derives the relationship deviation amount Δθ1, which is the deviation amount between the rotation angle detection value θS and the first rotation angle reference value θB1. For example, the deviation amount derivation unit M17 derives, as the relationship deviation amount Δθ1, a value obtained by subtracting the first rotation angle reference value θB1 from the rotation angle detection value θS.

[0029] <Determination unit> The determination unit M19 determines whether the reliability of the pressing force estimated value PE acquired by the pressing force acquisition unit M13 is high.

[0030] Here, when the temperature of the electric braking device 10 is low, the viscosity of the grease used for lubricating the components of the electric braking device increases, resulting in an increase in viscous resistance. As a result, the load torque of the electric motor 40 may become larger compared to when the temperature of the electric braking device 10 is high. The change in load torque due to the increase in viscous resistance reduces the accuracy of the pressing force estimated value PE. Also, when the change amount of the pressing force P with respect to the change amount of the load torque of the electric motor 40 is defined as the "mechanical efficiency of the electric braking device 10", the mechanical efficiency may decrease with the aging of the electric braking device 10.

[0031] Therefore, for example, when at least one of the following conditions (A1) and (A2) is satisfied, the determination unit M19 determines that the reliability of the pressing force estimated value PE is not high. When neither of the following conditions (A1) and (A2) is satisfied, the determination unit M19 determines that the reliability of the pressing force estimated value PE is high.

[0032] (A1) The temperature of the electric braking device 10 is equal to or lower than the low temperature determination value. (A2) The number of operating times of the electric braking device 10 after the estimation of the mechanical efficiency is performed is equal to or more than the deterioration determination number threshold.

[0033] A temperature serving as a criterion for determining whether the temperature of the electric braking device 10 is too low is set as a low-temperature determination value. The temperature of the electric braking device 10 can be estimated based on the operating time of the electric braking device 10, the outside air temperature, and the like. Of course, when a sensor for detecting the temperature of the electric braking device 10 is provided, the detected value of the sensor may be adopted as the temperature of the electric braking device 10.

[0034] When the mechanical efficiency is estimated, according to the usage situation of the electric braking device 10, the mechanical efficiency is estimated when data necessary for the estimation of the efficiency can be collected. The number of operating times at which a decrease in the mechanical efficiency is expected due to the use of the electric braking device 10 is set as a deterioration determination number threshold.

[0035] <Control quantity derivation unit> When the pressing force estimated value PE is acquired by the pressing force acquisition unit M13, the control quantity derivation unit M21 derives a first control quantity C1 and a second control quantity C2 based on the pressing force estimated value PE and the relationship deviation amount Δθ1. In the present embodiment, the control quantity derivation unit M21 executes the derivation process of the first control quantity C1 and the second control quantity C2 on the condition that the determination unit M19 determines that the reliability of the pressing force estimated value PE is high. That is, the control quantity derivation unit M21 does not execute the derivation process when the determination unit M19 determines that the reliability of the pressing force estimated value PE is not high.

[0036] Referring to FIG. 3, the derivation process of the first control quantity C1 and the second control quantity C2 will be described. A plurality of relationship points Z1 shown in FIG. 3 are points indicating the relationship between the relationship deviation amount Δθ1 and the pressing force estimated value PE.

[0037] When the friction material 120 wears, the change amount of the pressing force P with respect to the change amount of the rotation angle θ becomes larger than when the friction material 120 does not wear. That is, the rigidity of the friction material 120 increases. Therefore, when the relationship between the rotation angle θ and the pressing force P when the friction material 120 does not wear is set as a reference relationship, when the friction material 120 wears, as shown in FIG. 3, the relationship deviation amount Δθ1 tends to decrease as the rotation angle detection value θS increases. However, the pressing force estimated value PE includes various error components.

[0038] Therefore, the control quantity derivation unit M21 derives an approximate straight line L1, which is a straight line obtained by linearly approximating the relationship between the pressing force estimated value PE and the deviation amount Δθ1. For example, the control quantity derivation unit M21 derives the approximate straight line L1 using the least squares method. At this time, the control quantity derivation unit M21 derives the intercept of the approximate straight line L1 as the first control quantity C1. The control quantity derivation unit M21 derives the slope of the approximate straight line L1 as the second control quantity C2. That is, the first control quantity C1 is the deviation amount Δθ1 when the pressing force estimated value PE is 0 (zero) on the approximate straight line L1. The second control quantity C2 is the change amount of the deviation amount Δθ1 with respect to the change amount of the pressing force estimated value PE on the approximate straight line L1.

[0039] <Control quantity storage unit> As shown in FIG. 2, the control quantity storage unit M23 stores the first control quantity C1 and the second control quantity C2, which are the control quantities derived by the control quantity derivation unit M21. In the present embodiment, the control quantity storage unit M23 executes the storage process of the first control quantity C1 and the second control quantity C2 on the condition that the determination unit M19 determines that the reliability of the pressing force estimated value PE is high. That is, the control quantity derivation unit M21 does not execute the storage process when the determination unit M19 determines that the reliability of the pressing force estimated value PE is not high.

[0040] <Target value setting unit> The target value setting unit M25 derives a pressing force target value PTr, which is the target value of the pressing force P. For example, when the driver operates the brake pedal, the target value setting unit M25 derives a larger value as the pressing force target value PTr as the operation amount of the brake pedal increases. Further, when there is a deceleration request from another control device, the target value setting unit M25 sets a value corresponding to the deceleration request as the pressing force target value PTr.

[0041] <Second reference rotation angle derivation unit> When the pressing force target value PTr is derived by the target value setting unit M25, the second reference rotation angle derivation unit M27 derives a second rotation angle reference value θB2, which is the motor rotation angle corresponding to the pressing force target value PTr. The second rotation angle reference value θB2 is the motor rotation angle corresponding to the pressing force target value PTr determined from the above reference relationship. For example, the second reference rotation angle derivation unit M27 derives the second rotation angle reference value θB2 using the above reference map MP1. The second rotation angle reference value θB2 can also be said to be the target value of the motor rotation angle θ before correction.

[0042] <Target value correction unit> The target value correction unit M29 derives a rotation angle target value θTr, which is the target value of the motor rotation angle θ, by correcting the second rotation angle reference value θB2 based on the control amount stored by the control amount storage unit M23.

[0043] The target value correction unit M29 derives a rotation angle correction amount Δθ2, which is the correction amount of the motor rotation angle θ, using the first control amount C1 and the second control amount C2 stored by the control amount storage unit M23. For example, the target value correction unit M29 derives the sum of the product of the second control amount C2 and the pressing force target value PTr and the first control amount C1 as the rotation angle correction amount Δθ2.

[0044] Then, the target value correction unit M29 derives the sum of the rotation angle correction amount Δθ2 and the second rotation angle reference value θB2 as the rotation angle target value θTr. <Control unit> The control unit M31 controls the electric motor 40 based on the control amount derived by the control amount derivation unit M21. For example, the control unit M31 controls the rotational movement of the electric motor 40 based on the rotation angle target value θTr. At this time, the control unit M31 derives a current command value based on the rotation angle target value θTr and operates the inverter circuit 81 based on the current command value.

[0045] <Operations and effects of this embodiment> With reference to FIG. 4, the operations and effects of this embodiment will be described. When not braking, the friction material 120 is separated from the rotating body 110. When a braking requirement occurs in this state and the electric motor 40 starts to drive, since the motor rotation angle θ increases, the friction material 120 approaches the rotating body 110. When the friction material 120 contacts the rotating body 110, the pressing force P becomes greater than 0 (zero). As a result, a braking force Fx is generated in the wheel 100. When the motor rotation angle θ at the time when the friction material 120 contacts the rotating body 110 is defined as the "rotation angle at braking start θF", when the motor rotation angle θ becomes greater than the rotation angle at braking start θF, the pressing force P and the braking force Fx also become greater.

[0046] When the electric braking device 10 is used, the wear of the friction material 120 progresses. That is, the thickness of the friction material 120 gradually becomes thinner. Then, since the relationship between the motor rotation angle θ and the pressing force P changes, as indicated by the arrow Y1 in FIG. 4, the rotation angle at braking start θF becomes larger.

[0047] Note that the line L2 in FIG. 4 shows the above reference relationship. The line L3 in FIG. 4 shows an example of the relationship between the motor rotation angle θ and the pressing force P when the wear of the friction material 120 progresses.

[0048] In the present embodiment, when driving the electric motor 40 to adjust the braking force Fx as described above, the processing circuit 90 functions as a rotation angle detection unit M11 to derive a rotation angle detection value θS. Further, the processing circuit 90 functions as a pressing force acquisition unit M13 to derive a pressing force estimation value PE. The processing circuit 90 derives a first rotation angle reference value θB1 as the motor rotation angle corresponding to the pressing force estimation value PE determined from the above reference relationship. For example, the processing circuit 90 derives the first rotation angle reference value θB1 by referring to the above reference map MP1. Further, the processing circuit 90 functions as a deviation amount derivation unit M17 to derive a relationship deviation amount Δθ1, which is the deviation amount between the first rotation angle reference value θB1 and the rotation angle detection value θS.

[0049] By functioning as the control quantity derivation unit M21, the processing circuit 90 derives a first control quantity C1, which is the intercept of an approximate straight line L1 obtained by linearly approximating the relationship between the pressing force estimated value PE and the deviation amount Δθ1, and a second control quantity C2, which is the slope of the approximate straight line L1.

[0050] As described above, as the wear of the friction material 120 progresses, the rotation angle θF at the start of braking increases, so the first control quantity C1, which is the intercept of the approximate straight line L1, increases. The processing circuit 90 derives the rotation angle target value θTr based on such a first control quantity C1. Then, by functioning as the control unit M31, the processing circuit 90 controls the rotational movement of the electric motor 40 based on such a rotation angle target value θTr. Therefore, the electric braking device 10 can suppress a decrease in the controllability of the braking force Fx due to the progress of wear of the friction material 120. In particular, the electric braking device 10 can suppress a decrease in the controllability of the timing of generation of the braking force Fx.

[0051] Further, as the wear of the friction material 120 progresses further, the rigidity of the friction material 120 may increase. In this case, the slope of the characteristic line when the motor rotation angle θ is larger than the rotation angle θF at the start of braking changes. Then, the second control quantity C2 corresponding to the slope of the approximate straight line L1 changes. That is, the second control quantity C2 corresponds to the change amount of the slope of the characteristic line.

[0052] In the present embodiment, the processing circuit 90 derives the rotation angle target value θTr based on such a second control quantity C2. Then, by functioning as the control unit M31, the processing circuit 90 controls the rotational movement of the electric motor 40 based on such a rotation angle target value θTr. Thereby, the electric braking device 10 can suppress a decrease in the controllability of the braking force Fx due to an increase in the rigidity of the friction material 120. In particular, the electric braking device 10 can suppress a decrease in the controllability of the magnitude of the braking force Fx from the point in time when the braking force Fx is generated.

[0053] Note that if the processing circuit 90 has the reference map MP1 indicating the above reference relationship, the braking force Fx can be appropriately controlled by using the approximate straight line L1. That is, it is not necessary to previously store a plurality of maps in the memory of the processing circuit 90. Therefore, the electric braking device 10 can improve the control accuracy of the braking force Fx while suppressing an increase in the memory load.

[0054] Furthermore, the load of the process of deriving the approximate straight line L1 by linear approximation is not so high. Therefore, an increase in the arithmetic load of the processing circuit 90 can be suppressed as compared with the case where the processing circuit 90 is caused to execute the process of deriving an Nth-order function (N is an integer of 2 or more).

[0055] Here, a comparative example will be described. In the comparative example, a pressing force deviation amount, which is the deviation amount between a pressing force reference value that is a pressing force corresponding to the rotation angle detection value θS determined from the above reference relationship and a pressing force estimated value PE when the rotation angle detection value θS is derived, is derived. Further, an approximate straight line L11 is derived as a straight line obtained by linearly approximating the relationship between the motor rotation angle θ and the pressing force deviation amount. A first control amount C11, which is the pressing force deviation amount when the motor rotation angle θ is 0 (zero) in the approximate straight line L11, and a second control amount C21, which is the slope of the approximate straight line L11, are derived. The pressing force target value PTr is corrected by using the first control amount C11 and the second control amount C21. A motor rotation angle θ corresponding to the corrected pressing force target value PTr is derived as a rotation angle target value. Then, the rotational movement of the electric motor 40 is controlled based on the rotation angle target value. Even in the case of this comparative example, similarly to the present embodiment, a decrease in the controllability of the braking force Fx is suppressed even if the wear of the friction material 120 slightly progresses.

[0056] As shown in FIG. 4, the friction material 120 may be significantly worn. Specifically, the friction material 120 may be worn until the rotation angle θF at the start of braking after the wear of the friction material 120 progresses becomes larger than the upper limit of the motor rotation angle θ indicated by the line L2 when the friction material 120 is not worn. In this case, in the comparative example, since the pressing force deviation amount cannot be derived, a straight line obtained by linearly approximating the relationship between the motor rotation angle θ and the pressing force deviation amount cannot be derived. As a result, since the first control amount C11 and the second control amount C21 cannot be derived, the rotation angle target value cannot be set.

[0057] On the other hand, in the present embodiment, different from the comparative example, a relationship deviation amount Δθ1, which is the deviation amount between a first rotation angle reference value θB1 corresponding to the pressing force estimated value PE determined from the above reference relationship and the rotation angle detection value θS when the pressing force estimated value PE is obtained, is derived. Thereby, even if the friction material 120 is significantly worn as described above, the first control amount C1 and the second control amount C2 can be derived, and thus the rotation angle detection value θS can be derived.

[0058] Therefore, in the present embodiment, even if the friction material 120 is significantly worn, the braking force Fx can be appropriately controlled. In addition, in the present embodiment, the following effects can be further obtained.

[0059] The processing circuit 90 functions as a determination unit M19 to determine whether the reliability of the acquired pressing force estimated value PE is high. Then, the processing circuit 90 derives the first control amount C1 and the second control amount C2 on the condition that it is determined that the reliability of the pressing force estimated value PE is high. Specifically, the processing circuit 90 stores the first control amount C1 and the second control amount C2 derived when it is determined that the reliability of the pressing force estimated value PE is high. Then, the processing circuit 90 derives a rotation angle target value θTr using the first control amount C1 and the second control amount C2 derived when it is determined that the reliability of the pressing force estimated value PE is high, and controls the rotational movement of the electric motor 40 based on the rotation angle target value θTr. Thereby, the electric braking device 10 can suppress a decrease in the derivation accuracy of the rotation angle target value θTr.

[0060] <Modification example> The above-described embodiment can be implemented with the following modifications. The above-described 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.

[0061] · When the above condition (A1) is satisfied, the determination unit M19 may determine that the reliability of the pressing force estimated value PE is high regardless of whether the condition (A2) is satisfied. Further, when the above condition (A2) is satisfied, the determination unit M19 may determine that the reliability of the pressing force estimated value PE is high regardless of whether the condition (A1) is satisfied.

[0062] · On the condition that it is determined that the relationship between the rotation angle and the pressing force is broken, the control amount derivation unit M21 may stop deriving at least one of the first control amount C1 and the second control amount C2.

[0063] For example, when the temperature of the friction material 120 temporarily rises due to the generation of the braking force accompanying the operation of the electric braking device 10, the pressing force for a predetermined rotation angle increases as compared with when the temperature of the friction material 120 is not rising. Thereby, the determination unit can determine that the relationship between the rotation angle and the pressing force is broken. This is because the friction material 120 expands due to the temperature rise of the friction material 120, and as a result, the values of the first control amount C1 and the second control amount C2 change as compared with the case where the relationship between the rotation angle and the pressing force is not broken. When the temperature of the raised friction material 120 returns, the broken relationship between the rotation angle and the pressing force returns to its original state, so the values of the first control amount C1 and the second control amount C2 return to their original values. Thus, on the condition that it is determined that the relationship between the rotation angle and the pressing force is broken, the control amount derivation unit can suppress deriving the rotation angle target value θTr based on the changed first control amount C1 and second control amount C2 by stopping deriving at least one of the first control amount C1 and the second control amount C2, and consequently can suppress the derivation accuracy of the rotation angle target value θTr from becoming low.

[0064] As another example, when the vehicle is parked and the moisture adhering to the rotating body 110 freezes, ice may be interposed between the rotating body 110 and the friction material 120, so that the relationship between the rotation angle and the pressing force is disrupted, and the values of the first control amount C1 and the second control amount C2 may change. In this case as well, when the ice melts, the disrupted relationship between the rotation angle and the pressing force and the values of the first control amount C1 and the second control amount C2 return to their original states.

[0065] · The determination unit M19 may be omitted. · When the electric braking device 10 includes a sensor for detecting the pressing force P, the pressing force acquisition unit may acquire the detected value of the pressing force P as the pressing force-related value.

[0066] · If the control amount derivation unit is to derive the first control amount C1, it does not necessarily have to derive the second control amount C2. In this case, the target value correction unit M29 derives the rotation angle correction amount Δθ2 using only the first control amount C1 among the first control amount C1 and the second control amount C2.

[0067] · If the control amount derivation unit is to derive the second control amount C2, it does not necessarily have to derive the first control amount C1. In this case, the target value correction unit M29 derives the rotation angle correction amount Δθ2 using only the second control amount C2 among the first control amount C1 and the second control amount C2.

[0068] · The control unit may perform an abnormality determination using the control amount as control of the electric motor 40 based on the control amount derived by the control amount derivation unit. For example, when the first control amount C1 is outside a predetermined range, the control unit may determine that the approximate straight line L1 has not been appropriately created and determine that there is an abnormality. For example, when the second control amount C2 is outside a predetermined range, the control unit may determine that the approximate straight line L1 has not been appropriately created and determine that there is an abnormality. Here, the predetermined range may be set such that it is outside the predetermined range when exceeding the range determined from the mechanical characteristics of the friction material 120.

[0069] · As the electric braking device, it may be embodied as a drum-type braking device. · The electric braking device may be a wet electric braking device including an electric cylinder using an electric motor as a power source.

[0070] · As the linear motion conversion mechanism, a mechanism in which the nut functions as the "rotating part" while the screw shaft functions as the "linear motion part" may be adopted. · The processing circuit 90 can be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware for executing at least a part of various processes, or a combination thereof. Examples of the dedicated hardware include, for example, an ASIC which is an integrated circuit for a specific use. The processor includes a CPU and memories such as a RAM and a ROM, and the memories store program codes or instructions configured to cause the CPU to execute processes. The memory, that is, the storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0071] <Other technical ideas> The technical ideas understandable from the above-described embodiments and modification examples will be described. [Appendix 1] It is preferable that the pressing force acquisition unit acquires, as the pressing force-related value, an estimated value of the pressing force based on the current flowing through the electric motor.

[0072] [Appendix 2] It is preferable to provide a determination unit that determines reliability based on the temperature of the electric braking device, the mechanical efficiency of the electric braking device, and the like. [Appendix 3] It is preferable that the control unit performs abnormality diagnosis using the control amount derived by the control amount derivation unit as the control of the electric motor.

[0073] Note that, as used in this specification, the expression "at least one" means "one or more" of the desired options. As an example, the expression "at least one" as used in this specification means "only one option" or "both of the two options" if the number of options is two. As another example, the expression "at least one" as used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

Explanation of Signs

[0074] 10…Electric braking device 40…Electric motor 60…Linear motion conversion mechanism 61…Screw shaft (an example of a rotating part) 62…Nut (an example of a linear motion part) 80…Motor control device 90…Processing circuit 100…Wheel 110…Rotating body 120…Friction material M11…Rotation angle detection unit M13…Pressing force acquisition unit M15…First reference rotation angle derivation unit M17…Deviation amount derivation unit M19…Judgment unit M21…Control amount derivation unit M25…Target value setting unit M27…Second reference rotation angle derivation unit M29…Target value correction unit M31…Control unit

Claims

1. An electric braking device in which a rotating part of a linear motion conversion mechanism rotates in response to the rotational motion of an electric motor, the rotational motion of the rotating part is converted into linear motion of a linear motion part of the linear motion conversion mechanism, and a braking force is generated at a wheel of a vehicle by adjusting a force pressing a friction material against a rotating body that rotates integrally with the wheel in response to the linear motion of the linear motion part, a rotation angle detection unit that detects a rotation angle of the electric motor; a pressing force acquisition unit that acquires a pressing force-related value that is a state quantity related to a pressing force that is a force pressing the friction material against the rotating body; a deviation amount deriving unit that derives a relationship deviation amount that is a deviation amount between the rotation angle corresponding to the pressure-related value determined from a reference relationship that is a relationship between the rotation angle and the pressure, and a detection value of the rotation angle when the pressure-related value is acquired; a control amount derivation unit that derives at least one of a first control amount, which is the relationship deviation amount when the pressing force-related value is 0 (zero) on an approximation line that is a straight line that linearly approximates the relationship between the pressing force-related value and the relationship deviation amount, and a second control amount, which is a change amount of the relationship deviation amount with respect to a change amount of the pressing force-related value on the approximation line; a control unit that controls the electric motor based on at least one of the first control amount and the second control amount. Electric braking device.

2. The control amount derivation unit derives at least one of the first control amount and the second control amount on condition that the reliability of the pressure-related value acquired by the pressure acquisition unit is determined to be high.

2. The electric braking device according to claim 1.

3. The control amount derivation unit stops derivation of at least one of the first control amount and the second control amount on condition that it is determined that the relationship between the rotation angle and the pressing force is lost.

2. The electric braking device according to claim 1.

4. a target value correcting unit that corrects a target value of the rotation angle corresponding to a target value of the pressing force based on at least one of the first control amount and the second control amount derived by the control amount derivation unit, The control unit controls the rotational motion of the electric motor based on the target value corrected by the target value correction unit. The electric braking device according to any one of claims 1 to 3.

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