Electric braking device

Abstract

A processing circuit of this electric braking device functions as: a rotation angle detection unit M11 that acquires a detected rotation angle value θS that is a detected value of the rotation angle of an electric motor; and a pressing force estimation unit M21 that, on the basis of a relationship that corresponds to the rotation direction of the electric motor, among a first relationship between a motor current Imt and a pressing force when the electric motor is being rotated in an increasing rotation direction and a second relationship between the motor current Imt and the pressing force when the electric motor is being rotated in a decreasing rotation direction, derives an estimated pressing force value PE with a magnitude corresponding to the motor current Imt. If it is determined, on the basis of the detected rotation angle value θS and the motor current Imt, that the relationship between the motor current Imt and the pressing force deviates from both the first relationship and the second relationship, the pressing force estimation unit M21 derives, as the estimated pressing force value PE, an estimated pressing force value of immediately before the determination that the relationship deviates from both the first relationship and the second relationship .

Description

electric braking device

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

[0002] Patent Literature 1 discloses an electric braking device that can apply a braking force to a wheel according to the rotation angle of an electric motor. The electric braking device has a sensor that detects a pressing force, which is a force pressing a friction material against a rotating body that rotates integrally with the vehicle wheel. The control unit of the electric braking device selectively uses a direct estimation process that estimates the pressing force using the output of the sensor, and an indirect estimation process that estimates the pressing force without using the output of the sensor.

[0003] In the indirect estimation process, the control unit derives an estimated value of the pressing force based on the relationship between the rotation angle of the electric motor and the pressing force, with a magnitude corresponding to the rotation angle at that time.

[0004] Patent No. 6752668

[0005] In the electric braking device, the increasing rotation direction, which is the direction of rotation of the electric motor when increasing the braking force and the pressing force, and the decreasing rotation direction, which is the direction of rotation of the electric motor when decreasing the braking force and the pressing force, are different from each other. The decreasing rotation direction is the opposite direction of the increasing rotation direction.

[0006] Here, the relationship between the motor current and the pressing force when increasing the braking force is referred to as the "first relationship." The relationship between the motor current and the pressing force when decreasing the braking force is referred to as the "second relationship." It is known that the first relationship and the second relationship are different from each other. The motor current is the current that flows through the electric motor.

[0007] Therefore, we consider a method in which the first relationship is used to derive an estimated value of the pressing force when the electric motor is rotating in an increasing rotation direction, and the second relationship is used to derive an estimated value of the pressing force when the electric motor is rotating in a decreasing rotation direction. In this case, the control unit can accurately estimate the pressing force when the electric motor is rotating in an increasing rotation direction or a decreasing rotation direction to change the braking force. However, when the electric motor is stopped to maintain the braking force, the rotation direction of the electric motor is unknown, and the control unit cannot determine whether to select the first relationship or the second relationship.

[0008] As a method for estimating the pressing force when the electric motor is stopped, a method is considered in which an estimated pressing force is derived using one of the first and second relationships, which corresponds to the rotation direction of the electric motor immediately before the rotation is stopped. In this case, the control unit derives an estimated pressing force corresponding to the current motor current based on the relationship corresponding to the rotation direction of the electric motor immediately before the rotation is stopped. However, even if the motor current is the same, there is a large discrepancy between the estimated pressing force derived using the first relationship and the estimated pressing force derived using the second relationship. In other words, there is room for improvement in terms of improving the accuracy of estimating the pressing force when maintaining braking force.

[0009] An electric braking device for solving 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 rotation angle detection unit that detects a rotation angle of the electric motor, and a pressing force estimation unit that derives a pressing force estimate value that is a magnitude corresponding to the motor current based on one of the following relationships corresponding to the rotation direction of the electric motor: a first relationship that is a relationship between the pressing force and a motor current that is a current flowing through the electric motor or a correlation value of the motor current when the electric motor is rotated in a direction that increases the braking force, and a second relationship that is a relationship between the pressing force and the motor current or a correlation value of the motor current when the electric motor is rotated in a direction that decreases the braking force. When the pressure force estimation unit determines that the relationship between the motor current or the correlation value of the motor current and the pressure force deviates from both the first relationship and the second relationship based on a rotation angle detection value, which is the rotation angle detected by the rotation angle detection unit, and the motor current or the correlation value of the motor current, the pressure force estimation unit derives the pressure force estimation value immediately before it is determined that the relationship between the motor current or the correlation value of the motor current and the pressure force deviates from both the first relationship and the second relationship.

[0010] The electric braking device has an advantage that the accuracy of estimating the pressing force can be increased.

[0011] FIG. 1 is a schematic diagram showing the overall configuration of an electric braking device according to an embodiment. FIG. 2 is a graph showing a first relationship and a second relationship. FIG. 3 is a block diagram showing the functional configuration of a processing circuit included in the electric braking device shown in FIG. 1. FIG. 4 is a flowchart showing a series of processes executed by the processing circuit when deriving an estimated pressing force value. FIG. 5 is a flowchart showing in detail the processing content of step S11 shown in FIG. 4. FIG. 6 is a schematic diagram showing how the upper and lower limits of the dead band change. FIG. 7 is a diagram showing the transition of the relationship between the estimated load torque and the pressing force when the motor current is changed to vary the braking force. FIG. 8 is a flowchart showing in detail the processing content of step S11 shown in FIG. 4 in an electric braking device according to a first modified example. FIG. 9 is a flowchart showing in detail the processing content of step S11 shown in FIG. 4 in an electric braking device according to a second modified example.

[0012] An embodiment of an electric braking device provided in a vehicle will be described below with reference to Figures 1 to 7. As shown in Figure 1, the electric braking device 10 includes a braking unit 11 and a motor control device 80. The braking unit 11 includes a caliper 20, a gearbox 30, an electric motor 40, a reduction mechanism 50, a linear motion conversion mechanism 60, and a piston 70. The braking unit 11 is configured to apply a braking force to the wheel 100 by controlling the rotation angle of the electric motor 40 and adjusting a pressing force P that presses a friction material 120 against a rotating body 110 that rotates integrally with the wheel 100 of the vehicle. An example of the braking unit 11 is a disc-type braking device.

[0013] <Caliper and Gearbox> The caliper 20 has a cylinder body 21 , a bridge 22 , and an arm 23 .

[0014] 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.

[0015] 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."

[0016] <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.

[0017] <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.

[0018] <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.

[0019] 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.

[0020] <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.

[0021] <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, thereby applying a braking force Fx to the wheel 100.

[0022] The magnitude of the braking force Fx is substantially proportional to the magnitude of the pressing force P that presses the friction material 120 against the rotating body 110. When the rotation angle of the electric motor 40 is defined as the "motor rotation angle θ," increasing the motor rotation angle θ increases the pressing force P. 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.

[0023] When the rotation direction of the output shaft 41 of the electric motor 40 is defined as the "rotation direction of the electric motor 40," the rotation direction of the electric motor 40 that increases the motor rotation angle θ is referred to as the "increasing rotation direction R1." The rotation direction of the electric motor 40 that decreases the motor rotation angle θ is referred to as the "decreasing rotation direction R2." In this case, the decreasing rotation direction R2 is opposite to the increasing rotation direction R1.

[0024] <Characteristics of the Brake Unit> The output torque To of the electric motor 40 is converted into a pressing force P of the friction material 120 via the reduction gear mechanism 50, the linear motion conversion mechanism 60, and the piston 70. As a result, mechanical loss occurs in the power transmission path from the electric motor 40 to the friction material 120. The magnitude of the mechanical loss differs between when the electric motor 40 rotates in the increasing rotation direction R1 and when the electric motor 40 rotates in the decreasing rotation direction R2. Therefore, the first relationship LR1 and the second relationship LR2 are different from each other. The first relationship LR1 is the relationship between the load torque Tmt and the pressing force P when the electric motor 40 rotates in the increasing rotation direction R1. The second relationship LR2 is the relationship between the load torque Tmt and the pressing force P when the electric motor 40 rotates in the decreasing rotation direction R2. The load torque Tmt is a value obtained by subtracting the inertia torque TI of the electric motor 40 from the output torque To. The first and second relationships may be not only the relationship between the load torque Tmt and the pressing force P, but also the relationship between the output torque To and the pressing force P.

[0025] 2 illustrates an example of the first relationship LR1 and the second relationship LR2. The motor current Imt is the current flowing through the electric motor 40. The output torque To and the load torque Tmt are substantially correlated with the motor current Imt. In other words, the larger the motor current Imt, the larger the output torque To and the load torque Tmt. Therefore, the first relationship LR1 and the second relationship LR2 can also be said to be the relationship between the motor current Imt or the correlation value of the motor current Imt and the pressing force P.

[0026] In both the first relationship LR1 and the second relationship LR2, the larger the magnitude of the load torque Tmt, the larger the pressing force P. When the pressing force P and the braking force Fx are increased, the direction in which the resistance force corresponding to the mechanical loss acts can be said to be the backward direction X2, which is the opposite direction to the moving direction of the friction material 120. Therefore, the load torque Tmt required to obtain the target pressing force P increases. As a result, as shown in the first relationship LR1, the gradient of change in the pressing force P relative to the change in the load torque Tmt becomes gentler.

[0027] When the pressing force P and the braking force Fx are reduced, the direction in which the resistance force corresponding to the mechanical loss acts is the forward direction X1, which is the opposite direction to the moving direction of the friction material 120. Therefore, the load torque Tmt required to output the target pressing force P becomes smaller. As a result, as shown by the second relationship LR2, the gradient of change in the pressing force P relative to the change in the load torque Tmt becomes steeper compared to when the pressing force P and the braking force Fx are increased.

[0028] <Motor Control Device> As shown in FIG. 1 , the motor control device 80 includes an inverter circuit 81 and a processing circuit 90 .

[0029] 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 on / off the switching elements 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.

[0030] 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.

[0031] <Functional Configuration of Processing Circuit> The functional configuration of the processing circuit 90 will be described with reference to FIG. 3 . The CPU 91 executes the control program stored 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 rotation angle detection unit M11, a rotation direction determination unit M13, an inertia torque derivation unit M15, an output torque derivation unit M17, a load torque derivation unit M19, a pressing force estimation unit M21, and a rotation angle correction amount derivation unit M23. The multiple functional units further include a pressing force target value setting unit M31, a rotation angle reference value derivation unit M33, a rotation angle target value derivation unit M35, and a motor control unit M37.

[0032] <Rotation Angle Detection Unit> The rotation angle detection unit M11 detects the motor rotation angle θ for each predetermined calculation cycle. Specifically, the rotation angle detection unit M11 detects the motor rotation angle θ based on the output signal of the rotation angle sensor 42. The motor rotation angle θ detected by the rotation angle detection unit M11 is referred to as the "rotation angle detection value θS."

[0033] <Rotational Direction Determination Unit> The rotational direction determination unit M13 detects the rotational direction of the electric motor 40 for each predetermined calculation cycle. The rotational direction determination unit M13 determines whether the rotational direction of the electric motor 40 is an increasing rotational direction R1 or a decreasing rotational direction R2 based on the transition of the rotational angle detection value θS. For example, the rotational direction determination unit M13 determines that the rotational direction is the increasing rotational direction R1 when the rotational angle detection value θS is increasing. On the other hand, the rotational direction determination unit M13 determines that the rotational direction is the decreasing rotational direction R2 when the rotational angle detection value θS is decreasing.

[0034] <Inertia Torque Derivation Unit> The inertia torque derivation unit M15 derives the inertia torque TI of the electric motor 40 for each predetermined calculation cycle. The inertia torque derivation unit M15 time-differentiates the rotation angle detection value θS to derive a motor rotation speed dθS, which is the rotation speed of the electric motor 40. The inertia torque derivation unit M15 time-differentiates the motor rotation speed dθS to derive a motor rotation acceleration dDθ. The inertia torque derivation unit M15 then converts the motor rotation acceleration dDθ into torque and derives the value as the inertia torque TI.

[0035] <Output Torque Derivation Unit> The output torque derivation unit M17 estimates the output torque To of the electric motor 40 for each predetermined calculation cycle. For example, the output torque derivation unit M17 derives the output torque To so that the magnitude increases as the motor current Imt increases.

[0036] <Load Torque Derivation Unit> The load torque derivation unit M19 estimates the load torque Tmt of the electric motor 40 for each predetermined calculation cycle based on the output torque To and the inertia torque T1. For example, the load torque derivation unit M19 derives the load torque Tmt by subtracting the inertia torque T1 from the output torque To. The output torque To is a torque derived based on the motor current Imt. Therefore, the load torque Tmt derived using the output torque To can be said to be a correlation value of the motor current Imt.

[0037] <Pressure Force Estimation Unit> The pressure force estimation unit M21 derives a pressure force estimation value PE, which is an estimate of the pressure force P, for each predetermined calculation cycle. The pressure force estimation unit M21 derives the pressure force estimation value PE based on the rotation angle detection value θS, the rotation direction of the electric motor 40, and the motor current Imt or the load torque Tmt, which is a correlation value of the motor current Imt.

[0038] The pressing force estimator M21 derives the pressing force estimated value PE to a magnitude corresponding to the motor current Imt based on the relationship between the first relationship LR1 and the second relationship LR2 that corresponds to the rotation direction of the electric motor 40 at that time. For example, the pressing force estimator M21 selects the first relationship LR1 when the rotation direction of the electric motor 40 is the increasing rotation direction R1. Then, when it is determined that the relationship between the load torque Tmt and the pressing force P is the first relationship LR1 based on the rotation angle detected value θS and the load torque Tmt, the pressing force estimator M21 derives the pressing force estimated value PE to a magnitude corresponding to the load torque Tmt based on the first relationship LR1.

[0039] Furthermore, for example, when the rotation direction of the electric motor 40 is the decreasing rotation direction R2, the pressing force estimating unit M21 selects the second relationship LR2. Then, when it is determined that the relationship between the load torque Tmt and the pressing force P satisfies the second relationship LR2 based on the rotation angle detection value θS and the load torque Tmt, the pressing force estimating unit M21 derives the pressing force estimated value PE to a magnitude corresponding to the load torque Tmt based on the second relationship LR2.

[0040] On the other hand, the pressing force estimation unit M21 may determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. In this case, the pressing force estimation unit M21 derives, as the pressing force estimated value PE, the pressing force estimated value immediately before it is determined that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2.

[0041] Here, when the motor current Imt increases and the electric motor 40 rotates in the increasing rotation direction R1, the detected rotation angle value θS increases. When the detected rotation angle value θS increases in this manner, the pressing force P increases substantially in accordance with the first relationship LR1 shown in FIG. 2 . When the state in which the detected rotation angle value θS increases transitions from a state in which the detected rotation angle value θS is maintained or decreased, the motor current Imt may decrease. When the motor current Imt decreases, the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. When the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2, the pressing force P is essentially maintained. If the motor current Imt continues to decrease and the relationship between the load torque Tmt and the pressing force P conforms to the second relationship LR2, the pressing force P decreases in accordance with the decrease in the motor current Imt.

[0042] Furthermore, when the motor current Imt decreases and the electric motor 40 rotates in the decreasing rotation direction R2, the detected rotation angle value θS decreases. When the detected rotation angle value θS decreases in this manner, the pressing force P decreases substantially in accordance with the second relationship LR2. When the state in which the detected rotation angle value θS decreases transitions to a state in which the detected rotation angle value θS is maintained or increased, the motor current Imt may increase. When the motor current Imt increases, the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. When the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2, the pressing force P is essentially maintained. If the motor current Imt continues to increase and the relationship between the load torque Tmt and the pressing force P conforms to the first relationship LR1, the pressing force P increases in accordance with the increase in the motor current Imt.

[0043] Therefore, the pressing force estimation unit M21 determines whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2. If the pressing force estimation unit M21 determines that the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2, the pressing force estimation unit M21 retains the detected rotation angle θS at the time when the detected rotation angle θS transitioned from an increasing state to a maintained or decreasing state. If the pressing force estimation unit M21 determines that the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2, the pressing force estimation unit M21 retains the detected rotation angle θS at the time when the detected rotation angle θS transitioned from a decreasing state to a maintained or increasing state.

[0044] The rotation angle correction amount derivation unit M23 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. For example, the rotation angle correction amount derivation unit M23 includes a rotation angle conversion unit M25 and a deviation amount derivation unit M27.

[0045] When the pressure estimation unit M21 derives the pressure estimation value PE, the rotation angle conversion unit M25 derives a first rotation angle reference value θB1, which is the motor rotation angle θ corresponding to the pressure estimation value PE. The first rotation angle reference value θB1 is the motor rotation angle corresponding to the pressure estimation value PE, which is determined from the reference relationship between the motor rotation angle θ and the pressure P.

[0046] For example, the rotation angle conversion unit M25 derives the first rotation angle reference value θB1 using a reference map MP1, which is a map showing a reference relationship. One example of 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 braking unit 11 at that time.

[0047] When the first rotation angle reference value θB1 is derived by the rotation angle conversion unit M25, the deviation amount derivation unit M27 derives a value corresponding to 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 M27 derives a value corresponding to the difference between the rotation angle detection value θS and the first rotation angle reference value θB1 as the correction amount Δθ.

[0048] <Pressure force target value setting unit> The pressure force target value setting unit M31 sets a pressure force target value PTr, which is a target value of the pressure force P, for each predetermined calculation cycle. For example, when the driver is operating the brake pedal, the pressure force target value setting unit M31 derives a larger value as the pressure force target value PTr as the brake pedal operation amount increases. Furthermore, when a deceleration request is received from another control device, the pressure force target value setting unit M31 sets a value corresponding to the deceleration request as the pressure force target value PTr.

[0049] <Rotation Angle Reference Value Derivation Unit> When the pressing force target value PTr is set by the pressing force target value setting unit M31, the rotation angle reference value derivation unit M33 derives a second rotation angle reference value θB2, which is the motor rotation angle corresponding to the pressing force target value PTr. For example, the rotation angle reference value derivation unit M33 uses the reference map MP1 described above to derive the motor rotation angle θ corresponding to the pressing force target value PTr as the second rotation angle reference value θB2.

[0050] <Rotation Angle Target Value Derivation Unit> The rotation angle target value derivation unit M35 derives the rotation angle target value θTr by correcting the second rotation angle reference value θB2 with the correction amount Δθ. For example, the rotation angle target value derivation unit M35 derives the rotation angle target value θTr as the sum of the correction amount Δθ and the second rotation angle reference value θB2.

[0051] <Motor Control Unit> The motor control unit M37 controls the electric motor 40 based on the target rotation angle value θTr. For example, the motor control unit M37 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.

[0052] <Pressure Force Estimation Process> Referring to Fig. 4, the pressure force estimation process, which is a series of processes executed by the processing circuit 90 when deriving the pressure force estimation value PE, will be described. The processing circuit 90 repeatedly executes the pressure force estimation process for each predetermined calculation cycle. The processing circuit 90 functions as a pressure force estimation unit M21, thereby executing the processes of multiple steps S11 to S21.

[0053] In step S11, the processing circuit 90 determines whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2. If the processing circuit 90 determines that the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2 (S11: YES), the processing circuit 90 proceeds to step S21. On the other hand, if the processing circuit 90 determines that the relationship between the load torque Tmt and the pressing force P is either the first relationship LR1 or the second relationship LR2 (S11: NO), the processing circuit 90 proceeds to step S13. Details of step S11 will be described later using FIGS. 5, 8, and 9.

[0054] It is assumed that the first relationship and the second relationship are relationships between the output torque To and the pressing force P. In this case, in step S11, the processing circuit 90 may determine whether the relationship between the output torque To and the pressing force P deviates from either the first relationship or the second relationship.

[0055] In step S13, the processing circuit 90 selects from the first relationship LR1 and the second relationship LR2 the relationship that corresponds to the rotation direction of the electric motor 40. For example, if the processing circuit 90 determines that the rotation direction is an increasing rotation direction R1, it selects the first relationship LR1. If the processing circuit 90 determines that the rotation direction is a decreasing rotation direction R2, it selects the second relationship LR2.

[0056] In the following step S15, the processing circuit 90 derives the pressure P corresponding to the load torque Tmt as the pressure force estimated value PE based on the relationship selected in step S13. Thereafter, the processing circuit 90 ends the pressure force estimation process.

[0057] In step S21, the processing circuit 90 holds the pressing force estimated value PE immediately before it is determined that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Then, the processing circuit 90 ends the pressing force estimation process.

[0058] <Dead Zone Setting Process> Fig. 5 is a flowchart showing the dead zone setting process, which is a detailed example of step S11 shown in Fig. 4. The processing circuit 90 functions as the pressure force estimation unit M21, thereby executing the processes of a plurality of steps S111 to S116 included in the dead zone setting process.

[0059] In step S111, the processing circuit 90 determines whether the rotation angle detection value θS is within the range of the dead zone DZ. If the rotation angle detection value θS is equal to or greater than the lower limit θL1 and equal to or less than the upper limit θL2 of the dead zone DZ, the processing circuit 90 determines that the rotation angle detection value θS is within the range of the dead zone DZ (S111: YES). Then, the processing circuit 90 proceeds to step S21 shown in FIG. 4.

[0060] That is, when the detected rotation angle value θS is within the range of the dead zone DZ, it can be determined that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, the processing circuit 90 holds the pressing force estimated value PE immediately before it is determined that the relationship deviates from both the first relationship LR1 and the second relationship LR2. More specifically, the pressing force estimator M21 sets a first dead zone DZ1 in which the detected rotation angle value θS at the time when the detected rotation angle value θS transitions from an increasing state to a maintained or decreasing state is set as the upper limit value θL2 of the dead zone DZ. When the rotation angle detection value θS is within the range of the first dead zone DZ1, the pressure force estimation unit M21 executes a first estimation process to derive the pressure force estimation value PE at the time when the upper limit value θL2 of the first dead zone DZ1 is set, and thereby retains the pressure force estimation value PE immediately before it is determined to be outside both the first relationship LR1 and the second relationship LR2.

[0061] Furthermore, the pressure force estimating unit M21 sets a second dead zone DZ2 in which the detected rotation angle θS at the time when the detected rotation angle θS transitions from a decreasing state to a maintained or increasing state is set as the lower limit value θL1 of the dead zone DZ. When the detected rotation angle θS is within the range of the second dead zone DZ2, the pressure force estimating unit M21 executes a second estimation process to derive the pressure force estimated value PE at the time when the lower limit value θL1 of the second dead zone DZ2 is set as the pressure force estimated value PE, thereby holding the pressure force estimated value PE immediately before it is determined to be outside both the first relationship LR1 and the second relationship LR2.

[0062] On the other hand, if the detected rotation angle θS is less than the lower limit θL1 of the dead zone DZ or greater than the upper limit θL2 of the dead zone DZ, the processing circuit 90 determines that the detected rotation angle θS is outside the range of the dead zone DZ (S111: NO), and proceeds to step S112.

[0063] In step S112, the processing circuit 90 determines whether the detected rotation angle value θS is increasing. For example, if the detected rotation angle value θS is greater than the upper limit value θL2, it can be considered that the detected rotation angle value θS is increasing. If the detected rotation angle value θS is smaller than the lower limit value θL1, it can be considered that the detected rotation angle value θS is decreasing. If the processing circuit 90 determines that the detected rotation angle value θS is increasing (S112: YES), it proceeds to step S115. On the other hand, if the processing circuit 90 determines that the detected rotation angle value θS is decreasing (S112: NO), it proceeds to step S113.

[0064] In step S115, the processing circuit 90 sets the current rotation angle detection value θS as the upper limit value θL2. In the following step S116, the processing circuit 90 sets the lower limit value θL1 so that the range of the dead zone DZ becomes wider as the current motor current Imt increases. For example, the processing circuit 90 sets the lower limit value θL1 so that the magnitude of the difference between the upper limit value θL2 and the lower limit value θL1 corresponds to the magnitude of the difference between the motor current Imt estimated from the first relationship LR1 and the motor current Imt estimated from the second relationship LR2, which are based on the current pressing force estimation value PE. The processing circuit 90 then proceeds to step S13 shown in FIG. 4.

[0065] Here, referring to FIG. 6 , a description will be given of how the range of the dead zone DZ changes as the detected rotation angle θS increases. When the detected rotation angle θS is within the range of the dead zone DZ as shown in FIG. 6A, the processing circuit 90 maintains the range of the dead zone DZ. When the detected rotation angle θS increases from the state shown in FIG. 6A and reaches the upper limit θL2 of the dead zone DZ as shown in FIG. 6B, the upper limit θL2 of the dead zone DZ increases in response to the increase in the detected rotation angle θS as shown in FIG. 6C. Furthermore, in this embodiment, when the upper limit θL2 is increased, the processing circuit 90 also changes the lower limit θL1 so that the range of the dead zone DZ becomes wider.

[0066] Returning to FIG. 5 , in step S113, the processing circuit 90 sets the current rotation angle detection value θS as the lower limit value θL1. In the following step S114, the processing circuit 90 sets the upper limit value θL2 so that the range of the dead zone DZ becomes wider as the current motor current Imt increases. For example, the processing circuit 90 sets the upper limit value θL2 so that the magnitude of the difference between the upper limit value θL2 and the lower limit value θL1 corresponds to the magnitude of the difference between the motor current Imt estimated from the first relationship LR1 and the motor current Imt estimated from the second relationship LR2, which are based on the current pressing force estimation value PE. Then, the processing circuit 90 proceeds to step S13 shown in FIG. 4 .

[0067] Here, we will explain how the range of the dead zone DZ changes when the detected rotation angle θS decreases. When the detected rotation angle θS decreases while it is within the range of the dead zone DZ and reaches the lower limit θL1 of the dead zone DZ, the lower limit θL1 of the dead zone DZ decreases as the detected rotation angle θS decreases. Furthermore, in this embodiment, when the processing circuit 90 decreases the lower limit θL1, it also changes the upper limit θL2 so that the range of the dead zone DZ narrows.

[0068] There is a reference correspondence relationship determined by the gear ratio of the reduction mechanism 50 between the motor rotation angle θ, which is the rotation angle of the output shaft 41 of the electric motor 40, and the rotation angle of the input part of the linear motion conversion mechanism 60. For example, if the gear ratio of the reduction mechanism 50 is 3, the motor rotation angle θ is three times the rotation angle of the input part of the linear motion conversion mechanism 60.

[0069] However, when the load torque Tmt is large, due to deformation of the components constituting the output shaft 41 and the reduction gear mechanism 50, the motor rotation angle θ deviates more from the reference correspondence relationship as the load torque Tmt increases, compared to when the load torque Tmt is small. This characteristic is called a "torsional rigidity characteristic." Due to the torsional rigidity characteristic, the motor rotation angle θ may change depending on the magnitude of the load torque Tmt even if the pressing force P is constant.

[0070] Taking this torsional rigidity characteristic into consideration, the dead zone DZ of the rotation angle detection value θS is set to be wider as the magnitude of the load torque Tmt or the motor current Imt increases.

[0071] <Functions and Effects of the Present Embodiment> The functions and effects of the present embodiment will be described with reference to FIG. 7 . When the pressing force P, i.e., the braking force Fx, is increased, the relationship between the load torque Tmt and the pressing force P is generally maintained at the first relationship LR1. When the pressing force P increases as the motor current Imt increases, the rotation direction of the electric motor 40 is the increasing rotation direction R1. Furthermore, while the rotation angle detection value θS is increasing, the upper limit value θL2 and the lower limit value θL1 of the dead zone DZ are continuously updated. As a result, the processing circuit 90 determines that the relationship between the load torque Tmt and the pressing force P is the first relationship LR1. Then, the processing circuit 90 derives the pressing force P corresponding to the load torque Tmt as the pressing force estimated value PE based on the first relationship LR1.

[0072] In the example shown in Figure 7, when the load torque Tmt reaches the first torque Tmt1, the increase in the detected rotation angle θS is stopped and the detected rotation angle θS is maintained or begins to decrease. For example, if the detected rotation angle θS decreases due to a decrease in the motor current Imt, the operating point representing the load torque Tmt and the pressing force P in Figure 7 moves along the first hysteresis line HS1 in a direction that reduces the load torque Tmt. In this case, the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Furthermore, even if the detected rotation angle θS decreases due to the influence of the torsional rigidity characteristics in response to a decrease in the motor current Imt, the pressing force P is maintained.

[0073] Here, consider a case where the pressing force P is estimated based on either the first relationship LR1 or the second relationship LR2 under the condition that the operating point indicating the load torque Tmt and the pressing force P is point Z on the first hysteresis line HS1. The actual pressing force P when the relationship between the load torque Tmt and the pressing force P is point Z on the first hysteresis line HS1 is defined as pressing force P1. When the pressing force P is estimated based on the first relationship LR1, pressing force P2 is derived as the pressing force estimated value PE. The pressing force P2 is smaller than the pressing force P1. Conversely, when the pressing force P is estimated based on the second relationship LR2, pressing force P3 is derived as the pressing force estimated value PE. The pressing force P3 is larger than the pressing force P1. In other words, when the operating point indicating the load torque Tmt and the pressing force P is point Z on the first hysteresis line HS1, it is difficult to say that the estimation accuracy of the pressing force P is high.

[0074] Therefore, when the processing circuit 90 determines that the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2, the processing circuit 90 derives, as the pressing force estimated value PE, the value immediately before it is determined that the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2. As a result, the electric brake device 10 can accurately estimate the pressing force P even when, while the braking force Fx is being applied to the wheel 100, the rotation angle detected value θS transitions from an increasing state to a maintained or decreasing state.

[0075] If the detected rotation angle θS continues to decrease due to the decrease in the motor current Imt beyond the influence of the torsional rigidity characteristic, the relationship between the load torque Tmt and the pressing force P becomes the second relationship LR2. If the motor current Imt and the detected rotation angle θS continue to decrease even in this state, the relationship between the load torque Tmt and the pressing force P is generally maintained according to the second relationship LR2. As a result, the pressing force P, i.e., the braking force Fx, decreases. If the pressing force P decreases as the motor current Imt decreases, the rotation direction of the electric motor 40 is the decreasing rotation direction R2. Furthermore, while the detected rotation angle θS is decreasing, the upper limit θL2 and lower limit θL1 of the dead zone DZ continue to be updated. As a result, the processing circuit 90 determines that the relationship between the load torque Tmt and the pressing force P is the second relationship LR2. The processing circuit 90 then derives the pressing force P corresponding to the load torque Tmt as the pressing force estimated value PE based on the second relationship LR2.

[0076] In the example shown in Figure 7, when the load torque Tmt reaches the second torque Tmt2, the decrease in the detected rotation angle value θS stops and the detected rotation angle value θS begins to be maintained or increase. For example, if the detected rotation angle value θS increases due to an increase in the motor current Imt, the operating point representing the load torque Tmt and the pressing force P moves along the second hysteresis line HS2 in a direction that increases the load torque Tmt. In this case, the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Furthermore, even if the detected rotation angle value θS increases due to the influence of the torsional rigidity characteristics in response to an increase in the motor current Imt, the pressing force P is maintained.

[0077] In this case, the processing circuit 90 can determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, the processing circuit 90 derives, as the pressing force estimated value PE, the value immediately before it is determined that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. This allows the electric brake device 10 to accurately estimate the pressing force P even when the rotation angle detected value θS transitions from a decreasing state to a maintained or increasing state while the braking force Fx is being applied to the wheel 100.

[0078] If the increase in the motor current Imt continues thereafter, exceeding the influence of the torsional rigidity characteristic and continuing to increase the detected rotation angle θS, the relationship between the load torque Tmt and the pressing force P becomes the first relationship LR1. If the motor current Imt and the detected rotation angle θS continue to increase even in this state, the relationship between the load torque Tmt and the pressing force P is generally maintained at the first relationship LR1. As a result, the pressing force P, i.e., the braking force Fx, increases.

[0079] The present embodiment can further achieve the following effects. (1) When the detected rotation angle θS is greater than the upper limit θL2 of the dead zone DZ, the processing circuit 90 can determine that the relationship between the load torque Tmt and the pressing force P satisfies the first relationship LR1. Therefore, the processing circuit 90 derives the pressing force estimate PE based on the first relationship LR1. When the detected rotation angle θS transitions from an increasing state to a maintained or decreasing state, the detected rotation angle θS falls within the range of the dead zone DZ. When the detected rotation angle θS falls within the range of the dead zone DZ in this manner, the processing circuit 90 can determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, the processing circuit 90 sets the detected rotation angle θS at the time when the detected rotation angle θS transitions from an increasing state to a maintained or decreasing state as the upper limit θL2 of the dead zone DZ. The processing circuit 90 then executes a first estimation process to derive the estimated pressing force PE at the time when the upper limit value θL2 is set as the estimated pressing force PE. As a result, the processing circuit 90 can maintain the load torque Tmt when the detected rotation angle θS is within the dead zone DZ (i.e., the first dead zone DZ1).

[0080] Consider the case where the detected rotation angle θS transitions from an increasing state to a maintained state. When the electric motor 40 is generating torque, the torsional rigidity characteristics affect the motor rotation angle θ, which deviates by the amount of torsion from the reference correspondence relationship determined by the rotation angle of the input part of the linear motion conversion mechanism 60 and the gear ratio of the reduction gear mechanism 50. When attempting to maintain the pressing force, i.e., to maintain the rotation angle of the input part of the linear motion conversion mechanism 60, reducing the torque of the electric motor 40 maintains the rotation angle of the input part of the linear motion conversion mechanism 60, but the amount of torsion decreases, which may result in a decrease in the motor rotation angle θ, i.e., the detected rotation angle θS. In this case, the detected rotation angle θS falls within the dead zone DZ.

[0081] In this embodiment, in such a case, the processing circuit 90 can determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, the processing circuit 90 can maintain the pressing force estimation value PE at the magnitude at the time when the rotation angle detection value θS transitions from an increasing state to a maintaining state.

[0082] (2) As shown in FIG. 7, the length of the first hysteresis line HS1 increases as the motor current Imt increases at the time when the rotation angle detection value θS transitions from an increasing state to a maintained or decreasing state.

[0083] Therefore, when the rotation angle detection value θS transitions from an increasing state to a maintained or decreasing state, the processing circuit 90 sets the lower limit θL1 of the dead zone DZ in the first estimation process so that the range of the dead zone DZ becomes wider as the load torque Tmt at the time of the transition increases. By using such a dead zone DZ, the processing circuit 90 can accurately determine whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2. Therefore, the processing circuit 90 can accurately estimate the pressing force P.

[0084] (3) When the detected rotation angle θS is smaller than the lower limit θL1 of the dead zone DZ, the processing circuit 90 determines that the relationship between the load torque Tmt and the pressing force P is the second relationship LR2. The processing circuit 90 then derives the pressing force estimate PE based on the second relationship LR2. When the detected rotation angle θS transitions from a decreasing state to a maintained or increasing state, the detected rotation angle θS falls within the range of the dead zone DZ. When the detected rotation angle θS falls within the range of the dead zone DZ in this manner, the processing circuit 90 determines that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, the processing circuit 90 sets the detected rotation angle θS at the time when the detected rotation angle θS transitions from a decreasing state to a maintained or increasing state as the lower limit θL1 of the dead zone DZ. The processing circuit 90 then executes a second estimation process to derive the estimated pressing force PE at the time when the lower limit value θL1 is set as the estimated pressing force PE. As a result, the processing circuit 90 can maintain the load torque Tmt when the detected rotation angle θS is within the dead zone DZ (i.e., the second dead zone DZ2).

[0085] Now consider the case where the detected rotation angle θS transitions from a decreasing state to a maintaining state. When the electric motor 40 is generating torque, the torsional rigidity characteristics affect the motor rotation angle θ, which deviates by the amount of torsion from the reference correspondence relationship determined by the rotation angle of the input part of the linear motion conversion mechanism 60 and the gear ratio of the reduction gear mechanism 50. When attempting to maintain the pressing force, i.e., to maintain the rotation angle of the input part of the linear motion conversion mechanism 60, increasing the torque of the electric motor 40 maintains the rotation angle of the input part of the linear motion conversion mechanism 60, but the amount of torsion increases, which may increase the motor rotation angle θ, i.e., the detected rotation angle θS. In this case, the detected rotation angle θS falls within the dead zone DZ.

[0086] In this embodiment, in such a case, the processing circuit 90 can determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, the processing circuit 90 can maintain the pressing force estimation value PE at the magnitude at the time when the rotation angle detection value θS transitions from a state in which it is decreasing to a state in which it is being maintained.

[0087] (4) As shown in FIG. 7, the length of the second hysteresis line HS2 becomes shorter as the motor current Imt decreases when the detected rotation angle value θS changes from a decreasing state to a maintained or increasing state.

[0088] Therefore, when the rotation angle detection value θS transitions from a decreasing state to a maintained or increasing state, the processing circuit 90 sets the upper limit θL2 of the dead zone DZ in the second estimation process so that the range of the dead zone DZ narrows as the load torque Tmt at the time of the transition decreases. By using this dead zone DZ, the processing circuit 90 can accurately determine whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2. Therefore, the processing circuit 90 can accurately estimate the pressing force P.

[0089] <Modifications> The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0090] In the above embodiment, the processing circuit 90 continues to update the range of the dead zone DZ when the detected rotation angle θS continues to increase. However, this is not limited to this. For example, the processing circuit 90 may set a first dead zone DZ1 as the dead zone DZ at a first transition point, which is the point when the detected rotation angle θS transitions from an increasing state to a maintained or decreasing state. In this case, the processing circuit 90 sets the first dead zone DZ1 with the detected rotation angle θS at the first transition point as its upper limit θL2. Furthermore, the processing circuit 90 may set a lower limit θL1 of the first dead zone DZ1 so that the range of the first dead zone DZ1 widens as the motor current Imt increases. Then, when the detected rotation angle θS is within the range of the first dead zone DZ1, the processing circuit 90 derives the pressing force estimate value at the first transition point as the current pressing force estimate value PE.

[0091] In the above embodiment, the processing circuit 90 continues to update the range of the dead zone DZ when the detected rotation angle θS continues to decrease. However, this is not limited to this. For example, the processing circuit 90 may set a second dead zone DZ2 as the dead zone DZ at a second transition point, which is the point when the detected rotation angle θS transitions from a decreasing state to a maintained or increasing state. In this case, the processing circuit 90 sets the second dead zone DZ2 such that the detected rotation angle θS at the second transition point is set to a lower limit θL1. Furthermore, the processing circuit 90 may set an upper limit θL2 of the second dead zone DZ2 so that the range of the second dead zone DZ2 widens as the motor current Imt increases. Then, when the detected rotation angle θS is within the range of the second dead zone DZ2, the processing circuit 90 derives the pressing force estimate value at the second transition point as the current pressing force estimate value PE.

[0092] In the electric braking device of the first modified example, the processing circuit 90 may determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2 when the following condition (A1) is met:

[0093] (A1) The change gradient, which is the amount of change in the detected rotation angle value θS relative to a change in the motor current Imt, is less than a change gradient judgment value. If the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2, the change in the pressing force P relative to a change in the load torque Tmt will be small, and therefore the change in the detected rotation angle value θS relative to a change in the load torque Tmt will be small. Therefore, if the above condition (A1) is established, it can be considered that the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2.

[0094] FIG. 8 illustrates an example of the details of step S11 shown in FIG. 4 . In step S117, the processing circuit 90 derives a change gradient ΔθS of the detected rotation angle value θS. The processing circuit 90 may derive the change gradient ΔθS by dividing the amount of change in the detected rotation angle value θS by the amount of change in the motor current Imt. In the following step S118, the processing circuit 90 determines whether the change gradient ΔθS is less than a change gradient determination value ΔθSth. The change gradient determination value ΔθSth is set as a criterion for determining whether the amount of change in the detected rotation angle value θS relative to a change in the motor current Imt is extremely small. If the change gradient ΔθS is less than the change gradient determination value ΔθSth (S118: YES), the processing circuit 90 proceeds to step S21 shown in FIG. 4 . On the other hand, if the change gradient ΔθS is equal to or greater than the change gradient determination value ΔθSth (S118: NO), the processing circuit 90 proceeds to step S13 shown in FIG. 4 .

[0095] The process shown in Fig. 8 may be combined with the process shown in Fig. 5. In this case, the processing circuit 90 does not need to change the width of the range of the dead zone DZ depending on the magnitude of the motor current Imt.

[0096] In the electric braking device of the second modified example, the processing circuit 90 may determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2 if the following condition (B1) is met:

[0097] (B1) The absolute value of the motor rotation speed dθS is less than the rotation speed judgment value. When the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2, the change in the pressing force P relative to the change in the load torque Tmt is small, and therefore the change in the rotation angle detected value θS relative to the change in the load torque Tmt is small. Therefore, when the above condition (B1) is established, it can be considered that the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2.

[0098] FIG. 9 illustrates an example of details of step S11 shown in FIG. 4 . The process shown in FIG. 9 is a modified example of the process shown in FIG. 5 or 8 . In step S119, the processing circuit 90 determines whether the absolute value |dθS| of the motor rotation speed is less than the rotation speed determination value dθSth. The rotation speed determination value dθSth is set as a criterion for determining whether the absolute value |dθS| of the motor rotation speed is extremely small. If the absolute value |dθS| of the motor rotation speed is less than the rotation speed determination value dθSth (S119: YES), the processing circuit 90 proceeds to step S21 shown in FIG. 4 . On the other hand, if the absolute value |dθS| of the motor rotation speed is equal to or greater than the rotation speed determination value dθSth (S119: NO), the processing circuit 90 proceeds to step S13 shown in FIG. 4 .

[0099] The pressure estimation process shown in Fig. 9 may be combined with the processes shown in Fig. 5 or 8. In this case, the processing circuit 90 does not need to change the width of the dead zone DZ depending on the magnitude of the motor current Imt.

[0100] 5 and the processing shown in FIG. 8 or 9, the processing circuit 90 does not need to set the detected rotation angle θS at the time when the detected rotation angle θS transitions from an increasing state to a maintained or decreasing state as the upper limit θL2 of the dead zone DZ. This is because the processing shown in FIG. 8 or 9 allows the processing circuit 90 to determine that the relationship between the load torque Tmt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2, and therefore can hold the pressing force estimated value PE immediately before it is determined that the relationship deviates from both the first relationship LR1 and the second relationship LR2. Similarly to the above, the processing circuit 90 does not need to set the detected rotation angle θS at the time when the detected rotation angle θS transitions from a decreasing state to a maintained or increasing state as the lower limit θL1 of the dead zone DZ.

[0101] The processing circuit 90 does not need to execute the second estimation process as long as it executes the first estimation process. If the second estimation process is not executed, the processing circuit 90 can determine whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2 by executing the determination process of step S118 shown in FIG. 8 when the rotation angle detected value θS transitions from a decreasing state to a maintained or increasing state. Alternatively, the processing circuit 90 can determine whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2 by executing the determination process of step S119 shown in FIG. 9 when the rotation angle detected value θS transitions from a decreasing state to a maintained or increasing state.

[0102] The processing circuit 90 does not need to execute the first estimation process as long as it executes the second estimation process. If the first estimation process is not executed, the processing circuit 90 can determine whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2 by executing the determination process of step S118 shown in FIG. 8 when the rotation angle detected value θS transitions from an increasing state to a maintained or decreased state. Alternatively, the processing circuit 90 can determine whether the relationship between the load torque Tmt and the pressing force P deviates from either the first relationship LR1 or the second relationship LR2 by executing the determination process of step S119 shown in FIG. 9 when the rotation angle detected value θS transitions from an increasing state to a maintained or decreased state.

[0103] 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.

[0104] The processing circuitry 90 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 for performing at least some of the various processes, or a combination thereof. Dedicated hardware may include, for example, an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, which store program code or instructions configured to cause the CPU to perform processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0105] <Other Technical Ideas> The technical ideas that can be understood from the above-described embodiment and modified examples will be described. [Supplementary Note 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 rotation angle detection unit that detects a rotation angle of the electric motor; and a pressing force estimation unit that derives a pressing force estimate value, which is an estimate of the pressing force, to a magnitude corresponding to the motor current, based on one of a first relationship that is a relationship between a motor current that is a current flowing through the electric motor or a correlation value of the motor current and the pressing force when the electric motor is rotated in a direction that increases the braking force, and a second relationship that is a relationship between the motor current or a correlation value of the motor current and the pressing force when the electric motor is rotated in a direction that decreases the braking force, wherein the pressing force estimation unit: when the rotation angle detection value is a value outside a dead band, derives the pressing force estimate value to a magnitude corresponding to the motor current based on the relationship between the first relationship and the second relationship that is corresponding to the rotation direction of the electric motor, an electric braking device, characterized in that, when the rotation angle detection value is larger than an upper limit value of the dead zone, the range of the dead zone is updated so that the rotation angle detection value becomes the upper limit value; and, when the rotation angle detection value is smaller than a lower limit value of the dead zone, the range of the dead zone is updated so that the rotation angle detection value becomes the lower limit value.

[0106] [Supplementary Note 2] When the range of the dead zone is updated because the rotation angle detection value becomes a value outside the range of the dead zone, it is preferable that the pressing force estimation unit sets a lower limit value and an upper limit value of the dead zone so that the range of the dead zone becomes wider as the motor current increases.

[0107] [Supplementary Note 3] It is preferable to include a motor control unit that controls the electric motor based on the difference between the rotation angle of the electric motor corresponding to the pressing force estimated value and the rotation angle detection value. Note 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 rotation angle detection unit that detects the rotation angle of the electric motor; and a pressing force estimation unit that derives a pressing force estimate value, which is an estimate of the pressing force, to a magnitude corresponding to the motor current, based on one of the following relationships corresponding to the rotation direction of the electric motor: a first relationship, which is the relationship between the pressing force and a motor current, which is the current flowing through the electric motor, or a correlation value of the motor current, when the electric motor is rotated in a direction that increases the braking force; and a second relationship, which is the relationship between the pressing force and the motor current, or a correlation value of the motor current, when the electric motor is rotated in a direction that decreases the braking force; an electric braking device, characterized in that, when it is determined that the relationship between the motor current or the correlation value of the motor current and the pressing force deviates from both the first relationship and the second relationship based on a rotation angle detection value, which is the rotation angle detected by the rotation angle detection unit, and the motor current or the correlation value of the motor current, the pressing force estimation unit derives, as the pressing force estimated value, the pressing force estimated value immediately before it is determined that the relationship between the motor current or the correlation value of the motor current and the pressing force deviates from both the first relationship and the second relationship.

2. The electric braking device according to claim 1, wherein the pressing force estimation unit determines that the relationship between the motor current or the correlation value of the motor current and the pressing force deviates from either the first relationship or the second relationship when a change gradient, which is the amount of change in the rotation angle detection value relative to a change in the motor current, is less than a change gradient determination value.

3. The electric braking device according to claim 1, wherein the pressing force estimation unit determines that the relationship between the motor current or the correlation value of the motor current and the pressing force deviates from either the first relationship or the second relationship when the absolute value of the rotational speed of the electric motor is less than a rotational speed determination value.

4. An electric braking device according to any one of claims 1 to 3, wherein the pressing force estimation unit executes at least one of a first estimation process in which, when the rotation angle detection value detected by the rotation angle detection unit is within a value range of a first dead band whose upper limit is the rotation angle detection value at the time the rotation angle detection value transitions from an increasing state to a maintained or decreasing state, the pressing force estimation unit derives the pressing force estimation value at the time the upper limit is set, and a second estimation process in which, when the rotation angle detection value detected by the rotation angle detection unit is within a value range of a second dead band whose lower limit is the rotation angle detection value at the time the rotation angle detection value transitions from a decreasing state to a maintained or increasing state, the pressing force estimation unit derives the pressing force estimation value at the time the lower limit is set.

5. An electric braking device according to claim 4, wherein the pressing force estimation unit is configured to execute the first estimation process, and in the first estimation process, the pressing force estimation unit sets a lower limit value of the first dead zone so that the range of the first dead zone becomes wider as the motor current becomes larger.

6. An electric braking device according to claim 4, wherein the pressing force estimation unit is configured to execute the second estimation process, and in the second estimation process, the pressing force estimation unit sets an upper limit value of the second dead zone so that the range of the second dead zone becomes wider as the motor current increases.

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