Electric braking device

Abstract

A processing circuit 90 of an electric braking device 10 functions as: a pressing force derivation unit that derives a pressing force estimation value based on the motor current value Imt; a filter unit that generates a post-filter pressing force-related value by attenuating signals of components with frequencies higher than a prescribed frequency among signals indicating pressing force-related values relating to the pressing force estimation value, while allowing signals of components with frequencies at or below the prescribed frequency to pass; and a motor control unit that controls an electric motor 40 on the basis of the post-filter pressing force-related value. By functioning as the filter unit, the processing circuit 90 sets the prescribed frequency such that the value decreases as the motor rotational speed decreases.

Description

electric braking device

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

[0002] Patent Document 1 discloses an electric braking system equipped with an electric motor as a power source. The control device of the electric braking system estimates wheel cylinder pressure, which corresponds to the force pressing a friction material against a rotating body that rotates integrally with the wheel, based on the magnitude of the motor current that flows through the electric motor.

[0003] The wheel cylinder pressure estimate derived as described above includes a periodically fluctuating error component. Therefore, the control device described above uses a low-pass filter to remove fluctuation components with frequencies higher than the cutoff frequency of the low-pass filter from the wheel cylinder pressure estimate. This allows the control device to improve the accuracy of deriving the wheel cylinder pressure estimate.

[0004] JP 2009-35031 A

[0005] In the electric braking device as described above, it is preferable to improve the accuracy of adjusting the pressing force by further increasing the accuracy of deriving an estimated value of the pressing force, which is the force pressing the friction material against the rotating body.

[0006] An electric braking device that solves the above problem is a device configured to adjust a pressing force, which is a force pressing a friction material against a rotating body that rotates integrally with a vehicle wheel, in accordance with the rotation of an electric motor. The electric braking device includes: a pressing force derivation unit that derives a pressing force estimation value that is an estimate of the pressing force based on a current flowing through the electric motor; a filter unit that generates a filtered pressing force-related value by attenuating signals that have frequency components higher than a predetermined frequency and passing signals that have frequency components equal to or lower than the predetermined frequency, among signals that indicate a pressing force-related value that is a value related to the pressing force estimation value; and a motor control unit that controls the electric motor based on the filtered pressing force-related value. The filter unit is configured to set the predetermined frequency so that the value decreases as the rotation speed of the electric motor decreases.

[0007] The above-described electric braking device has an advantage in that it is possible to increase the efficiency of removing error components contained in the estimated value of the pressing force.

[0008] Fig. 1 is a schematic diagram showing a general configuration of an electric braking system of a first embodiment. Fig. 2 is a block diagram showing the functional configuration of a processing circuit provided in the electric braking system of the first embodiment. Fig. 3 is a block diagram showing details of a filter unit shown in Fig. 2. Fig. 4 is a block diagram showing the functional configuration of a processing circuit provided in an electric braking system of a second embodiment.

[0009] First Embodiment Hereinafter, a first embodiment of an electric braking device provided in a vehicle will be described with reference to FIGS. 1 to 3. FIG.

[0010] 1, the electric braking device 10 includes a caliper 20, a gearbox 30, an electric motor 40, a 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 at a vehicle wheel 100 by pressing a friction material 120 against a rotating body 110 that rotates integrally with the wheel 100. An example of the electric braking device 10 is a disc-type braking device.

[0011] <Caliper and Gearbox> The caliper 20 has a cylinder body 21 , a bridge 22 , and an arm 23 .

[0012] The cylinder body 21 is connected to the arm 23 via a 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 extension direction of the axis of the cylinder 24. In the following description, the axial direction of the cylinder 24 will be referred to as the "front-rear direction." When the cylinder body 21 is assembled to the vehicle, the rotating body 110 is disposed between the cylinder body 21 and the arm 23. Two friction materials 120 are assembled to the cylinder body 21 and the arm 23, respectively. In other words, the two friction materials 120 are located on both sides of the rotating body 110 in the thickness direction.

[0013] The gearbox 30 houses the reduction mechanism 50. The gearbox 30 is attached to the cylinder body 21. The gearbox 30 is located at the end of the cylinder 24 opposite the end where the friction material 120 is located in the front-rear direction. Hereinafter, within the front-rear direction, the direction toward the friction material 120 is referred to as the "forward direction X1," and the direction toward the gearbox 30 is referred to as the "reverse direction X2."

[0014] <Electric Motor> The electric motor 40 is mounted to the cylinder body 21. In this case, the axis of the output shaft 41 of the electric motor 40 is parallel to the axis of the cylinder 24. The output shaft 41 of the electric motor 40 also extends toward the inside of the gearbox 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. An example of the rotation angle sensor 42 is a magnetic sensor.

[0015] <Reduction Mechanism> The reduction mechanism 50 reduces the rotation speed of the output shaft 41 of the electric motor 40 and transmits the reduced rotation speed to the linear motion conversion mechanism 60. The reduction mechanism 50 has 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.

[0016] <Linear motion conversion mechanism> The linear motion conversion mechanism 60 converts the rotational motion of the third gear 53 into linear motion of the piston 70. The linear motion conversion mechanism 60 has a screw shaft 61 that performs rotational motion based on the power transmitted from the speed reduction mechanism 50, and a nut 62 that performs linear motion due to the power transmitted from the screw shaft 61. The linear motion conversion mechanism 60 is a so-called feed screw mechanism. In another embodiment, the linear motion conversion mechanism 60 may be a so-called ball screw mechanism.

[0017] 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 housed 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 of the screw shaft 61 is connected to the third gear 53. In this way, the screw shaft 61 can rotate integrally with the third gear 53.

[0018] <Piston> The piston 70 is housed in the cylinder 24 so as to be unable to rotate about an axis extending in the front-rear direction relative to the cylinder 24, but so as to be movable in the front-rear direction relative to the cylinder 24. The piston 70 faces the friction material 120 in the front-rear direction. The piston 70 is also integrated with the nut 62. Therefore, when the nut 62 moves in the forward direction X1, the piston 70 moves together with the nut 62 in the forward direction X1. On the other hand, when the nut 62 moves in the backward direction X2, the piston 70 moves together with the nut 62 in the backward direction X2.

[0019] <Operation of Electric Brake Device> In the electric brake device 10, when the electric motor 40 is driven, the rotational motion of the output shaft 41 of the electric motor 40 is reduced by the reduction mechanism 50. Subsequently, the rotational motion of the third gear 53 of the reduction mechanism 50 is transmitted to the threaded shaft 61 of the linear motion conversion mechanism 60. In the linear motion conversion mechanism 60, the rotational motion of the threaded shaft 61 is converted into 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. In this way, the piston 70 presses the friction material 120 against the rotating body 110, generating a braking force Fx on the wheel 100.

[0020] 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 against the rotating body 110 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." In this case, as the motor rotation angle θ increases, the pressing force P also increases. Therefore, the electric braking device 10 can adjust the pressing force P and the braking force Fx in accordance with the rotation of the electric motor 40.

[0021] <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 using power supplied from a power supply. The inverter circuit 81 generates signals for each phase of the electric motor 40 by turning the switching elements on and off based on commands from the processing circuit 90. The inverter circuit 81 then inputs the generated signals to each phase of the electric motor 40, thereby driving the electric motor 40.

[0022] An example of the processing circuit 90 is an electronic control device. 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 results of calculations by the CPU 91, etc. When the CPU 91 executes the control program in the first memory 92, the processing circuit 90 outputs the above-mentioned command to the inverter circuit 81.

[0023] <Functional Configuration of Processing Circuit> The functional configuration of the processing circuit 90 will be described with reference to Fig. 2. The CPU 91 executes the control program in the first memory 92, causing the processing circuit 90 to function as multiple functional units. The multiple functional units are functional units for controlling the electric motor 40. The multiple functional units include a pressing force derivation unit M11, a correction amount derivation unit M13, a filter unit M15, a pressing force target value setting unit M17, a reference rotation angle derivation unit M19, a rotation angle target value derivation unit M21, and a motor control unit M23.

[0024] <Pressing Force Derivation Unit> The pressing force derivation unit M11 derives a pressing force estimation value PE, which is an estimate of the pressing force P, for each predetermined control cycle based on the motor current value Imt. The motor current value Imt is the magnitude of the current flowing through the electric motor 40. In this case, the pressing force derivation unit M11 derives the pressing force estimation value PE so that the larger the motor current value Imt, the larger the pressing force estimation value PE.

[0025] The pressing force derivation unit M11 may derive the pressing force estimated value PE taking into account the motor inertia torque. Specifically, the pressing force derivation unit M11 differentiates the rotation angle detection value θS twice to convert it into angular acceleration, and then derives the pressing force estimated value PE taking into account the motor inertia torque obtained by unit conversion. The rotation angle detection value θS is the motor rotation angle θ based on the output signal of the rotation angle sensor 42.

[0026] The correction amount derivation unit M13 derives a correction amount Δθ for the motor rotation angle θ based on the rotation angle detection value θS and the pressing force estimation value PE. In this embodiment, the correction amount Δθ corresponds to a "pressure-related value" that is a value related to the pressing force estimation value PE.

[0027] For example, the correction amount derivation unit M13 includes a rotation angle conversion unit M131 and a deviation amount derivation unit M133. When the pressing force derivation unit M11 acquires the pressing force estimated value PE, the rotation angle conversion unit M131 derives a first rotation angle reference value θB1, which is the motor rotation angle θ corresponding to the pressing force estimated value PE. The first rotation angle reference value θB1 is the motor rotation angle corresponding to the pressing force estimated value PE, which is determined from a reference relationship between the motor rotation angle θ and the pressing force P.

[0028] For example, the rotation angle conversion unit M131 derives the first rotation angle reference value θB1 using a reference map MP1, which is a map showing a 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 characteristics of the electric brake device 10.

[0029] When the first rotation angle reference value θB1 is derived by the rotation angle conversion unit M131, the deviation amount derivation unit M133 derives the difference between the rotation angle detection value θS and the first rotation angle reference value θB1 as the correction amount Δθ. For example, the deviation amount derivation unit M133 derives the correction amount Δθ by subtracting the first rotation angle reference value θB1 from the rotation angle detection value θS.

[0030] <Filter Unit> The filter unit M15 generates a filtered pressure-related value by filtering a signal indicating the pressure-related value. The signal indicating the pressure-related value is a signal indicating the transition of the pressure-related value. In this embodiment, a low-pass filter is used in the filtering. The cutoff frequency of the low-pass filter corresponds to the "predetermined frequency FRc."

[0031] The filter unit M15 attenuates the signal representing the correction amount Δθ having frequency components higher than a predetermined frequency FRc while passing the signal having frequency components equal to or lower than the predetermined frequency FRc, thereby generating a filtered correction amount ΔθF. In this embodiment, this filtered correction amount ΔθF corresponds to the "filtered pressure-related value." Furthermore, the signal representing the correction amount Δθ corresponds to the signal derived by the correction amount derivation unit M13.

[0032] The filter unit M15 is configured to vary the predetermined frequency FRc in accordance with the motor rotation speed Nmt. Furthermore, when the electric motor 40 is stopped, the filter unit M15 is configured to hold the filtered correction amount ΔθF at the value before the electric motor 40 stopped rotating.

[0033] An example of the configuration of the filter unit M15 will be described with reference to Fig. 3. The filter unit M15 includes, for example, a low-pass IIR digital filter. Fig. 3 shows a schematic configuration of such a filter unit M15.

[0034] The filter unit M15 includes a frequency setting unit M151, a removal processing unit M153, and a previous value acquisition unit M155. The frequency setting unit M151 derives the motor rotation speed Nmt based on the rotation angle detection value θS. For example, the frequency setting unit M151 derives the motor rotation speed Nmt by time-differentiating the rotation angle detection value θS. The frequency setting unit M151 sets the predetermined frequency FRc so that it increases as the motor rotation speed Nmt increases. For example, the frequency setting unit M151 may determine the predetermined frequency FRc using the following relational expression (D1). The proportionality constant K in the relational expression (D1) is a predetermined value. For example, the proportionality constant K is preferably set based on the rotational order of the cogging torque or torque ripple determined by the mechanical design of the electric motor 40.

[0035] FRc = K Nmt (D1) According to the relational expression (D1), when the electric motor 40 stops, the motor rotation speed Nmt becomes 0 (zero), and the predetermined frequency FRc also becomes 0 (zero). In other words, the filter unit M15 has a characteristic of passing only DC components, so the filtered correction amount ΔθF is held at the value before the electric motor 40 stopped rotating.

[0036] Here, the signal indicating the transition of the pressing force estimate value PE includes a periodically fluctuating error component. Examples of periodically fluctuating error components include an error component caused by cogging torque and an error component caused by torque ripple. These error components fluctuate with a longer period as the motor rotation speed Nmt decreases. The cogging torque does not depend on the magnitude of the load torque TQ of the electric motor 40. On the other hand, the torque ripple increases as the load torque TQ increases.

[0037] In order to remove error components caused by cogging torque and torque ripple, it is advisable to change the predetermined frequency FRc according to the motor rotation speed Nmt. In this regard, the frequency setting unit M151 can set the predetermined frequency FRc so that the value decreases as the motor rotation speed Nmt decreases.

[0038] The elimination processing unit M153 prepares a low-pass filter whose cutoff frequency is the predetermined frequency FRc set by the frequency setting unit M151. Then, the elimination processing unit M153 passes the signal indicating the correction amount Δθ through a low-pass filter according to a relational expression (D2) described later, to derive the filtered correction amount ΔθF.

[0039] The previous value acquisition unit M155 acquires the filtered correction amount ΔθF derived by the removal processing unit M153 as the previous value ΔθFa of the filtered correction amount ΔθF. The removal processing unit M153 generates the filtered correction amount ΔθF based on the correction amount Δθ and the previous value ΔθFa. For example, the removal processing unit M153 generates a weighted average of the correction amount Δθ and the previous value ΔθFa as the filtered correction amount ΔθF. In this case, the removal processing unit M153 may use the following relational expression (D2):

[0040] ΔθF = (1 - α) Δθ + α ΔθFa (D2) In the relational expression (D2), "α" is a coefficient that varies between 0 (zero) and 1 depending on the predetermined frequency FRc. The elimination processor M153 sets the coefficient α to a larger value as the predetermined frequency FRc, i.e., the motor rotation speed Nmt, decreases. For example, the elimination processor M153 sets the coefficient α so that the coefficient α is 1 when the motor rotation speed Nmt is at a predetermined frequency FRc of 0 (zero). As a result, when the electric motor 40 is stopped from rotating, the elimination processor M153 can derive the previous value ΔθFa as the filtered correction amount ΔθF. In other words, when the electric motor 40 is stopped from rotating, the elimination processor M153 can hold the filtered correction amount ΔθF at the value before the electric motor 40 stopped from rotating.

[0041] 2, the pressure target value setting unit M17 sets a pressure target value PTr, which is a target value of the pressure P. For example, when the driver is operating the brake pedal, the pressure target value setting unit M17 derives a larger value as the pressure target value PTr as the brake pedal operation amount increases. Furthermore, when a deceleration request is received from another control device, the pressure target value setting unit M17 sets a value corresponding to the deceleration request as the pressure target value PTr.

[0042] <Reference Rotation Angle Derivation Unit> When the pressing force target value PTr is derived by the pressing force target value setting unit M17, the reference rotation angle derivation unit M19 derives a second rotation angle reference value θB2, which is a motor rotation angle corresponding to the pressing force target value PTr. For example, the reference rotation angle derivation unit M19 derives the motor rotation angle θ corresponding to the pressing force target value PTr as the second rotation angle reference value θB2 using the reference map MP1.

[0043] <Rotation Angle Target Value Derivation Unit> The rotation angle target value derivation unit M21 derives the sum of the filtered correction amount ΔθF and the second rotation angle reference value θB2 as the rotation angle target value θTr.

[0044] <Motor Control Unit> The motor control unit M23 controls the electric motor 40 based on the target rotation angle value θTr. For example, the motor control unit M23 derives a current command value based on the target rotation angle value θTr, and operates the inverter circuit 81 based on the current command value.

[0045] <Functions and Effects of the Present Embodiment> (1-1) The processing circuit 90 functions as a pressing force derivation unit M11 to derive a pressing force estimation value PE. The processing circuit 90 also functions as a correction amount derivation unit M13 to derive a motor rotation angle correction amount Δθ based on the rotation angle detection value θS and the pressing force estimation value PE.

[0046] The processing circuit 90 functions as the filter unit M15 to generate the filtered correction amount ΔθF as the filtered pressure-related value. Specifically, the processing circuit 90 attenuates the signal representing the correction amount Δθ, which has a frequency component higher than a predetermined frequency FRc, while passing the signal having a frequency component equal to or lower than the predetermined frequency FRc, thereby generating the filtered correction amount ΔθF.

[0047] Here, the processing circuit 90 derives the pressing force estimate PE based on the motor current value Imt. The motor current value Imt fluctuates due to the influence of cogging torque. Therefore, the pressing force estimate PE derived based on the motor current value Imt is also affected by the cogging torque. As described above, the cogging torque is an error component that depends on the motor rotation angle θ. Therefore, the frequency of the error component of the pressing force estimate PE that is caused by the cogging torque becomes lower as the motor rotation speed Nmt decreases.

[0048] If the pressure force estimate PE contains an error, an error occurs in the correction amount Δθ, resulting in a large rotation angle target value error θTr_error, which is the difference between the ideal rotation angle θtruth, which is the rotation angle at which the pressure force target value PTr is generated, and the rotation angle target value θTr.

[0049] Therefore, the processing circuit 90 functions as a filter unit M15 and sets the predetermined frequency FRc so that the value decreases as the motor rotation speed Nmt decreases. Therefore, even if the frequency of the error component caused by the cogging torque becomes lower because the motor rotation speed Nmt is low, the processing circuit 90 can remove the error component caused by the cogging torque from the correction amount Δθ.

[0050] Therefore, the electric braking device 10 can increase the efficiency of removing the error component contained in the pressing force estimate value PE. As a result, even when the motor rotation speed Nmt is low, the electric braking device 10 can reduce the error component of the correction amount Δθ, and ultimately reduce the rotation angle target value error θTr_error. In other words, the electric braking device 10 can improve the accuracy of adjusting the pressing force.

[0051] Additionally, in the electric braking device 10, the higher the motor rotation speed Nmt, the higher the predetermined frequency FRc, and therefore the higher the frequency component of the pressing force-related value, i.e., the correction amount Δθ, that passes through the filter unit M15. This allows the electric braking device 10 to suppress the effect of a response delay in the pressing force-related value, i.e., the correction amount Δθ, when the motor rotation speed Nmt is high.

[0052] (1-2) As described above, the pressing force estimate PE includes an error component due to torque ripple. The lower the motor rotation speed Nmt, the lower the frequency of the error component due to torque ripple. In this regard, the processing circuit 90 sets the predetermined frequency FRc so that the value becomes smaller the lower the motor rotation speed Nmt. Therefore, by performing the above-described filtering process on the correction amount Δθ, the electric braking device 10 can remove the error component due to torque ripple from the correction amount Δθ even when the motor rotation speed Nmt is low.

[0053] (1-3) When the electric motor 40 is rotating, the magnitude of the error component due to cogging torque fluctuates periodically. Therefore, by performing the above-described filtering process, the processing circuit 90 can remove the error component due to cogging torque from the correction amount Δθ. On the other hand, when the electric motor 40 is stopped, the magnitude of the error component due to cogging torque is maintained at the value it had immediately before the electric motor 40 stopped rotating.

[0054] Therefore, in this embodiment, when the rotation of the electric motor 40 is stopped, the processing circuit 90 holds the filtered correction amount ΔθF at the value before the rotation of the electric motor 40 was stopped. Therefore, even when the rotation of the electric motor 40 is stopped, the processing circuit 90 can derive the filtered correction amount ΔθF as a value from which the error component caused by the cogging torque has been removed. Then, the processing circuit 90 controls the electric motor 40 based on the rotation angle target value θTr derived using this filtered correction amount ΔθF. Therefore, even when the rotation of the electric motor 40 is stopped, the processing circuit 90 can reduce the rotation angle target value error θTr_error, thereby improving the adjustment accuracy of the pressing force.

[0055] (1-4) Consider a case where the pressure force estimate PE is filtered to remove error components caused by cogging torque, and the resulting pressure force estimate PE is derived as a filtered pressure force estimate PEF. In this case, the processing circuit uses the filtered pressure force estimate PEF to derive a correction amount for the motor rotation angle θ, and then uses the correction amount to derive the rotation angle target value θTr.

[0056] However, when filtering is performed on the pressure force estimate PE in this manner, a response delay component resulting from the filtering process is superimposed on the filtered pressure force estimate PEF. The effect of the response delay is superimposed on the correction amount Δθ derived using this filtered pressure force estimate PEF. As a result, when the rotation angle target value θTr is derived based on the correction amount Δθ, the rotation angle target value error θTr_error may become large.

[0057] In this regard, in this embodiment, the processing circuit 90 performs filtering on the correction amount Δθ derived based on the pressing force estimate value PE. Fluctuations in the correction amount Δθ are smaller than fluctuations in the pressing force estimate value PE. Therefore, the processing circuit 90 can prevent response delay components resulting from filtering from being superimposed on the correction amount Δθ. Therefore, the electric brake device 10 can reduce the rotation angle target value error θTr_error and improve the pressing force adjustment accuracy.

[0058] Second Embodiment A second embodiment of the electric braking device will be described with reference to Fig. 4. The second embodiment differs from the first embodiment in that filtering is performed on the pressing force estimated value. In the following description, differences from the first embodiment will be mainly described, and the same reference numerals will be used to designate the same components as those in the first embodiment, and redundant description will be omitted.

[0059] 4 illustrates the functional configuration of the processing circuit 90 in this embodiment. The processing circuit 90 includes a pressing force derivation unit M11, a filter unit M12A, a correction amount derivation unit M13A, a pressing force target value setting unit M17, a reference rotation angle derivation unit M19, a rotation angle target value derivation unit M21, and a motor control unit M23. The configurations of the pressing force derivation unit M11, the pressing force target value setting unit M17, the reference rotation angle derivation unit M19, the rotation angle target value derivation unit M21, and the motor control unit M23 are the same as those in the first embodiment. Therefore, detailed descriptions of these functional units will be omitted.

[0060] <Filter Unit> The filter unit M12A generates a filtered pressure force estimated value PEF by performing a filter process on the pressure force estimated value PE. In this embodiment, the pressure force estimated value PE corresponds to the "pressure-related value." The filtered pressure force estimated value PEF corresponds to the "filtered pressure-related value."

[0061] Specifically, the filter unit M12A generates a filtered pressure estimate value PEF by filtering a signal indicating the pressure estimate value PE. The signal indicating the pressure estimate value PE is a signal that indicates the transition of the pressure estimate value PE. In this embodiment, a low-pass filter is used in the filtering process. The cutoff frequency of the low-pass filter corresponds to the "predetermined frequency FRc."

[0062] The filter unit M12A attenuates the signal components of the signal indicating the pressure force estimate value PE that are higher in frequency than a predetermined frequency FRc, while passing the signal components that are lower in frequency than the predetermined frequency FRc, thereby generating a filtered pressure force estimate value PEF.

[0063] The filter unit M12A is configured to vary the predetermined frequency FRc in accordance with the motor rotation speed Nmt. Furthermore, when the rotation of the electric motor 40 is stopped, the filter unit M12A is configured to hold the filtered pressure estimate value PEF at the value before the rotation of the electric motor 40 was stopped.

[0064] For example, the filter unit M12A includes a frequency setting unit that sets the predetermined frequency FRc so that the value decreases as the motor rotation speed Nmt decreases. The setting of the predetermined frequency FRc is the same as in the first embodiment.

[0065] The filter unit M12A is provided with a low-pass filter whose cutoff frequency is the set predetermined frequency FRc, and derives a filtered pressure estimate value PEF by passing the signal indicating the pressure estimate value PE through the low-pass filter.

[0066] The filter unit M12A includes a previous value acquisition unit that acquires the filtered pressure estimate value PEF as a previous value PEFa of the filtered pressure estimate value PEF. The filter unit M12A generates the filtered pressure estimate value PEF based on the pressure estimate value PE and the previous value PEFa. For example, the filter unit M12A generates a weighted average of the pressure estimate value PE and the previous value PEFa as the filtered pressure estimate value PEF. In this case, the filter unit M12A may use the following relational expression (D3):

[0067] PEF = (1 - β) PE + β PEFa (D3) In relational expression (D3), "β" is a coefficient that varies between 0 (zero) and 1 depending on the motor rotation speed Nmt. The filter unit M12A sets the coefficient β to a larger value the lower the motor rotation speed Nmt. For example, the filter unit M12A sets the coefficient β so that when the motor rotation speed Nmt is 0 (zero), the coefficient β is 1. In this way, when the rotation of the electric motor 40 is stopped, the filter unit M12A can hold the filtered pressure estimate value PEF at the value before the rotation of the electric motor 40 was stopped.

[0068] <Correction Amount Derivation Unit> The correction amount derivation unit M13A derives a correction amount Δθ for the motor rotation angle θ based on the rotation angle detection value θS and the filtered pressing force estimate value PEF.

[0069] When the correction amount derivation unit M13A acquires the filtered pressure estimate value PEF from the filter unit M12A, it derives a first rotation angle reference value θB11, which is the motor rotation angle θ corresponding to the filtered pressure estimate value PEF. The first rotation angle reference value θB11 is the motor rotation angle corresponding to the filtered pressure estimate value PEF, which is determined from the reference relationship between the motor rotation angle θ and the pressure P.

[0070] For example, the correction amount derivation unit M13A uses the reference map MP1 to derive the motor rotation angle θ corresponding to the filtered pressing force estimate value PEF as the first rotation angle reference value θB11. After deriving the first rotation angle reference value θB11, the correction amount derivation unit M13A derives the difference between the rotation angle detected value θS and the first rotation angle reference value θB11 as the correction amount Δθ. For example, the correction amount derivation unit M13A derives the value obtained by subtracting the first rotation angle reference value θB11 from the rotation angle detected value θS as the correction amount Δθ.

[0071] <Functions and Effects of the Present Embodiment> (2-1) The processing circuit 90 functions as the pressure derivation unit M11 to derive the pressure estimate value PE. Then, the processing circuit 90 functions as the filter unit M12A to perform the above-described filtering process on the pressure estimate value PE. As a result, the processing circuit 90 generates a filtered pressure estimate value PEF.

[0072] Here, the motor current value Imt used by the processing circuit 90 to derive the pressing force estimate value PE fluctuates due to the influence of cogging torque. Therefore, the pressing force estimate value PE is also affected by the cogging torque. As described above, the cogging torque is an error component that depends on the motor rotation angle θ. Therefore, the frequency of the error component of the pressing force estimate value PE that is caused by the cogging torque becomes lower as the motor rotation speed Nmt becomes lower.

[0073] Therefore, the processing circuit 90 functions as a filter unit M12A and sets the predetermined frequency FRc so that the value decreases as the motor rotation speed Nmt decreases. Therefore, even if the frequency of the error component caused by the cogging torque becomes lower because the motor rotation speed Nmt is low, the processing circuit 90 can remove the error component caused by the cogging torque from the pressing force estimate value PE. The processing circuit 90 can also remove the error component caused by the torque ripple from the pressing force estimate value PE.

[0074] Therefore, the electric braking device 10 can increase the efficiency of removing the error component contained in the pressing force estimate value PE. As a result, the electric braking device 10 can reduce the rotation angle target value error θTr_error even when the motor rotation speed Nmt is low, thereby improving the accuracy of adjusting the pressing force.

[0075] (2-2) When the rotation of the electric motor 40 is stopped, the processing circuit 90 can hold the filtered pressure estimate value PEF at the value before the rotation of the electric motor 40 was stopped. Therefore, even when the rotation of the electric motor 40 is stopped, the processing circuit 90 can derive the filtered pressure estimate value PEF as a value from which error components due to cogging torque have been removed. The processing circuit 90 then controls the electric motor 40 based on the rotation angle target value θTr derived using this filtered pressure estimate value PEF. Therefore, even when the rotation of the electric motor 40 is stopped, the processing circuit 90 can reduce the rotation angle target value error θTr_error and improve the adjustment accuracy of the pressure.

[0076] (Modifications) The above-described embodiments can be modified as follows: The above-described embodiments and the following modifications can be combined with each other within the scope of technical compatibility.

[0077] When the rotation of the electric motor 40 is stopped, the filter unit M15 may employ a method different from the method described in the first embodiment as long as it can hold the filtered correction amount ΔθF at the value before the rotation of the electric motor 40 was stopped. For example, the filter unit M15 determines whether the rotation of the electric motor 40 is stopped based on the transition of the rotation angle detected value θS. If the filter unit M15 determines that the rotation of the electric motor 40 is not stopped, the filter unit M15 derives the value after the correction amount Δθ has passed through a low-pass filter with a predetermined cutoff frequency as the filtered correction amount ΔθF. On the other hand, if the filter unit M15 determines that the rotation of the electric motor 40 is stopped, the filter unit M15 derives the previous value ΔθFa as the filtered correction amount ΔθF.

[0078] When the rotation of the electric motor 40 is stopped, the filter unit M12A may employ a method different from the method described in the second embodiment, as long as it can retain the filtered pressure estimate value PEF at the value before the rotation of the electric motor 40 was stopped. For example, the filter unit M12A determines whether the rotation of the electric motor 40 is stopped based on the transition of the rotation angle detected value θS. If the filter unit M12A determines that the rotation of the electric motor 40 is not stopped, it derives the value of the pressure estimate value PE after passing it through a low-pass filter with a predetermined cutoff frequency as the filtered pressure estimate value PEF. On the other hand, if the filter unit M12A determines that the rotation of the electric motor 40 is stopped, it derives the previous value PEFa as the filtered pressure estimate value PEF.

[0079] When the rotation of the electric motor 40 is stopped, the filter unit does not need to hold the filtered pressure-related value at the value before the rotation of the electric motor 40 was stopped. The filter unit may employ a filter other than a low-pass filter. For example, the filter unit may use a rate limiter. A rate limiter limits the gradient of change in the pressure-related value. Even when the filter unit performs filtering using a rate limiter, it is possible to attenuate signal components of the signal indicating the pressure-related value that have frequencies higher than a predetermined frequency FRc, while passing signal components of frequencies equal to or lower than the predetermined frequency FRc.

[0080] In the second embodiment, the filter unit M12A may derive a delay amount of the pressure estimated value PE due to filtering, and the correction amount derivation unit M13A may correct the correction amount Δθ based on the delay amount. The filter unit M12A may derive a delay time, which is a time delay due to filtering, as the delay amount based on a predetermined frequency FRc. It is desirable that the correction amount derivation unit M13A derives the correction amount Δθ after performing a delay process corresponding to the delay time on the rotation angle detected value θS.

[0081] Alternatively, the filter unit M12A may derive a delay angle resulting from filtering based on the predetermined frequency FRc and the motor rotation speed Nmt as the delay amount. In this case, the correction amount derivation unit M13A preferably corrects the detected rotation angle θS in the delay direction before deriving the correction amount Δθ.

[0082] The electric braking device may be a drum-type braking device. The electric braking device may be a wet-type electric braking device including an electric cylinder powered by an electric motor.

[0083] The processing circuit may 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 that executes at least some of the various processes, or a combination thereof. Dedicated hardware can include, for example, an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, which stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0084] <Other Technical Ideas> The following describes technical ideas that can be understood from the above-described multiple embodiments and modified examples. [Supplementary Note 1] It is preferable that the estimated pressing force-related value is the pressing force estimated value, the filter unit attenuates signals of frequency components higher than a predetermined frequency among signals indicating the pressing force estimated value while passing signals of frequency components equal to or lower than the predetermined frequency, thereby generating a filtered pressing force estimated value as the filtered pressing force-related value, the electric braking device includes: a reference rotation angle derivation unit that derives a rotation angle of the electric motor corresponding to a target value of the pressing force as a rotation angle reference value, and a correction amount derivation unit that derives a correction amount for the rotation angle based on the rotation angle of the electric motor and the filtered pressing force estimated value, and the motor control unit controls the electric motor based on a target value of the rotation angle of the electric motor that is the sum of the rotation angle reference value and the correction amount for the rotation angle.

[0085] It should be noted that the expression "at least one" used in this specification means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" 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.

Claims

1. An electric braking device configured to be able to adjust a pressing force, which is a force pressing a friction material against a rotating body that rotates integrally with a vehicle wheel, in accordance with the rotation of an electric motor, comprising: a pressing force derivation unit that derives a pressing force estimation value, which is an estimate of the pressing force, based on the current flowing through the electric motor; a filter unit that generates a filtered pressing force related value by attenuating signals of frequency components higher than a predetermined frequency among signals indicating a pressing force related value, which is a value related to the pressing force estimation value, while passing signals of frequency components equal to or lower than the predetermined frequency; and a motor control unit that controls the electric motor based on the filtered pressing force related value, wherein the filter unit is configured to set the predetermined frequency so that the value becomes smaller the lower the rotation speed of the electric motor.

2. The electric braking device according to claim 1, wherein, when the rotation of the electric motor is stopped, the filter unit holds the filtered pressing force-related value at the value before the rotation of the electric motor was stopped.

3. An electric braking device according to claim 1 or claim 2, comprising: a reference rotation angle derivation unit that derives the rotation angle of the electric motor corresponding to the target value of the pressing force as a rotation angle reference value; and a correction amount derivation unit that derives a correction amount for the rotation angle based on the rotation angle of the electric motor and the pressing force estimated value as the pressing force related value, wherein the filter unit attenuates signals of frequency components higher than the predetermined frequency out of the signals derived by the correction amount derivation unit, while passing signals of frequency components equal to or lower than the predetermined frequency, thereby generating a filtered correction amount as the filtered pressing force related value, and the motor control unit controls the electric motor based on the target value of the rotation angle of the electric motor, which is the sum of the rotation angle reference value and the filtered correction amount.

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