Electric braking device

Abstract

To provide an electric braking device capable of improving accuracy in estimating pressing force when estimating the pressing force on the basis of a motor current.SOLUTION: A processing circuit of an electric braking device functions as a pressing force estimation unit M11 for deriving a pressing force estimation value PE. The pressing force estimation unit M11 maintains the pressing force estimation value PE when a motor current Imt is a value in a dead zone range. When the motor current Imt is greater than an upper limit value of the dead zone, the pressing force estimation unit M11 derives the pressing force estimation value PE on the basis of a first relationship, and changes the upper limit value of a dead zone DZ. When the motor current Imt is less than a lower limit value of the dead zone, the pressing force estimation unit M11 derives the pressing force estimation value PE on the basis of a second relationship, and changes the lower limit value of the dead zone DZ.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 discloses an electric braking device that can apply a braking force to a wheel according to the rotation angle of an electric motor. In this electric braking device, by increasing the rotation angle of the electric motor, the pressing force that presses a friction material against a rotating body that rotates integrally with the vehicle wheel increases. The greater the pressing force, the greater the braking force applied to the wheel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6752668 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a correlation between the motor current, which is the current flowing through the electric motor, and the pressing force. Specifically, the larger the motor current, the larger the pressing force. Therefore, the control unit of the electric braking device as described above can estimate the pressing force based on the magnitude of the motor current.

[0005] However, in the above-described electric braking device, a power transmission path from the electric motor to the friction material is provided with a reduction mechanism, a linear motion conversion mechanism, and the like. Therefore, mechanical loss occurs due to friction in the power transmission path. The magnitude of this mechanical loss differs depending on whether the pressing force is increased or decreased. Therefore, in the electric braking device, when the pressing force is estimated based on the magnitude of the motor current, there is room for improvement in terms of improving the accuracy of the estimation of the pressing force. [Means for solving the problem]

[0006] An electric braking device for solving the above problems is a 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. The electric braking device includes a current acquisition unit that acquires a motor current, which is a current flowing through the electric motor, and a pressing force estimation unit that selects one of a first relationship, which is a relationship between 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, which is a relationship between the motor current and the pressing force when the electric motor is rotated in a direction that decreases the braking force, and derives a pressing force estimate value, which is an estimate of the pressing force, to a magnitude that corresponds to the motor current, based on the first relationship.When the motor current acquired by the current acquisition unit is within a value in a first dead band range having an upper limit value equal to the motor current at the time when the motor current transitions from an increasing state to a maintained or decreasing state, the pressure force estimation unit holds the pressure force estimated value at a value at the time when the upper limit value was set, when the motor current acquired by the current acquisition unit transitions from a value in the first dead band range to a value larger than the upper limit value of the first dead band, the pressure force estimation unit derives the pressure force estimated value to a magnitude corresponding to the motor current based on the first relationship, and when the motor current acquired by the current acquisition unit transitions from a value in the first dead band range to a value smaller than the lower limit value of the first dead band, the pressure force estimation unit derives the pressure force estimated value to a magnitude corresponding to the motor current based on the second relationship. and a second estimation process in which, if the motor current acquired by the current acquisition unit is within a value in a second dead band range whose lower limit value is the motor current at the time the motor current transitions from a decreasing state to a maintained or increasing state, the pressure estimation value is held at the value at the time the lower limit value is set, and, if the motor current acquired by the current acquisition unit transitions from a value in the second dead band range to a value smaller than the lower limit value of the second dead band, the pressure estimation value is derived to a magnitude corresponding to the motor current based on the second relationship, and, if the motor current transitions from a value in the second dead band range to a value larger than the upper limit value of the second dead band, the pressure estimation value is derived to a magnitude corresponding to the motor current based on the first relationship. [Effects of the Invention]

[0007] The electric braking device described above has the advantage that, when the pressing force is estimated based on the current flowing through the electric motor, the accuracy of estimating the pressing force can be increased. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of an electric braking device according to an embodiment. [Figure 2] FIG. 2 is a graph showing the first relationship and the second relationship. [Figure 3] FIG. 3 is a block diagram showing the functional configuration of a processing circuit included in the electric braking device shown in FIG. [Figure 4] FIG. 4 is a flowchart showing a series of processes executed by a processing circuit included in the electric braking device shown in FIG. [Figure 5] FIG. 5 is a schematic diagram showing how the upper and lower limits of the dead zone change. [Figure 6] FIG. 6 is a diagram showing the transition of the relationship between the motor current and the pressing force when the motor current is changed to vary the braking force. DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of an electric braking device will be described below with reference to FIGS. As shown in Fig. 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 so that, when the rotation angle of the electric motor 40 is increased, the pressing force P, which is the force pressing the friction material 120 against a rotating body 110 that rotates integrally with the vehicle wheel 100, increases, thereby increasing the braking force applied to the wheel 100. An example of the braking unit 11 is a disc-type braking device.

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

[0011] 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 mounted to the vehicle, the rotating body 110 is disposed between the cylinder body 21 and the arm 23. Two friction materials 120 are mounted 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.

[0012] The gearbox 30 houses the reduction mechanism 50. The gearbox 30 is assembled to the cylinder body 21. The gearbox 30 is located at the end of the cylinder 24 opposite to 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."

[0013] <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. In addition, the output shaft 41 of the electric motor 40 extends toward the inside of the gearbox 30.

[0014] <Deceleration 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.

[0015] <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 rotates based on the power transmitted from the reduction gear mechanism 50, and a nut 62 that linearly moves 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.

[0016] A screw groove is provided on the outer peripheral surface of the screw shaft 61. A screw 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.

[0017] <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 integral 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.

[0018] <Operation of the electric braking system> In the electric braking device 10, when the electric motor 40 is driven, the rotational motion of the output shaft 41 of the electric motor 40 is 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.

[0019] 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," as the motor rotation angle θ increases, the pressing force P increases. Therefore, the electric braking device 10 can adjust the pressing force P and the braking force Fx in accordance with the rotation of the electric motor 40.

[0020] 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 pressing force P and the braking force Fx is referred to as the "increasing rotation direction R1." The rotation direction of the electric motor 40 that decreases the pressing force P and the braking force Fx 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.

[0021] <Characteristics of the braking section> 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. Therefore, mechanical loss occurs in the power transmission path from the electric motor 40 to the friction material 120. The magnitude of the mechanical loss when the electric motor 40 rotates in the increasing rotation direction R1 is different from the magnitude of the mechanical loss 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 motor current Imt 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 motor current Imt and the pressing force P when the electric motor 40 rotates in the decreasing rotation direction R2. The motor current Imt is the current flowing through the electric motor 40.

[0022] 2 shows an example of the first relationship LR1 and the second relationship LR2. The output torque To is substantially correlated with the motor current Imt, and the larger the motor current Imt, the larger the output torque To. Therefore, the first relationship LR1 and the second relationship LR2 can also be said to be the relationship between the output torque To and the pressing force P.

[0023] In both the first relationship LR1 and the second relationship LR2, the pressing force P increases as the motor current Imt increases. 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 is the backward direction X2, which is the opposite direction to the moving direction of the friction material 120. Therefore, the motor current Imt required to obtain the target pressing force P increases. As a result, as indicated by the first relationship LR1, the gradient of change in the pressing force P relative to the change in the motor current Imt becomes gentler.

[0024] 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 motor current Imt 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 motor current Imt becomes steeper compared to when the pressing force P and the braking force Fx are increased.

[0025] In FIG. 2, the first reference relationship LRB1 and the second reference relationship LRB2 are indicated by dashed lines. When the electric motor 40 is driven, cogging torque and torque ripple are generated. Therefore, when the electric motor 40 is driven, a first fluctuation component, which is a fluctuation component caused by cogging torque, and a second fluctuation component, which is a fluctuation component caused by torque ripple, are superimposed on the motor current Imt. When the electric motor 40 is driven so that the pressing force P increases, the relationship between the motor current Imt and the pressing force P, assuming that the first fluctuation component and the second fluctuation component are not superimposed on the motor current Imt, is the first reference relationship LRB1. When the electric motor 40 is driven so that the pressing force P decreases, the relationship between the motor current Imt and the pressing force P, assuming that the first fluctuation component and the second fluctuation component are not superimposed on the motor current Imt, is the second reference relationship LRB2.

[0026] The larger the motor current Imt, the larger the motor rotation angle θ. Even as the motor rotation angle θ increases, the amplitude of the first fluctuation component changes very little. On the other hand, as the motor rotation angle θ increases, the amplitude of the second fluctuation component gradually increases. Therefore, the amplitude of the composite wave WC of the first fluctuation component and the second fluctuation component increases as the motor rotation angle θ increases.

[0027] The first relationship LR1 is set based on the first reference relationship LRB1 and the composite wave WC. On the graph shown in FIG. 2, the first relationship LR1 is set so that the line representing the first relationship LR1 is positioned on the side where the motor current Imt is increased by the amplitude of the composite wave WC relative to the line representing the first reference relationship LRB1. Furthermore, the increase gradient of the pressing force P, which is the amount of increase in the pressing force P with respect to an increase in the motor current Imt in the first relationship LR1, is smaller than the increase gradient of the pressing force P, which is the amount of increase in the pressing force P with respect to an increase in the motor current Imt, in the first reference relationship LRB1. On the graph shown in FIG. 2, the second relationship LR2 is set so that the line representing the second relationship LR2 is positioned on the side where the motor current Imt is decreased by the amplitude of the composite wave WC relative to the line representing the second reference relationship LRB2. Furthermore, the decrease gradient of the pressing force P, which is the amount of decrease in the pressing force P with respect to a decrease in the motor current Imt in the second relationship LR2, is larger than the decrease gradient of the pressing force P, which is the amount of decrease in the pressing force P with respect to a decrease in the motor current Imt, in the second reference relationship LRB2.

[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 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.

[0030] The inverter circuit 81 has a current sensor 82 that acquires the motor current Imt. The current sensor 82 corresponds to the "current acquisition unit." 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 calculation results of the CPU 91. 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 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 estimation unit M11, a pressing force target value setting unit M13, and a motor control unit M15.

[0032] <Pushing force estimation section> The pressure estimator M11 derives a pressure estimated value PE, which is an estimate of the pressure, for each predetermined calculation cycle. The pressure estimator M11 selects one of the first relationship LR1 and the second relationship LR2. Then, based on the selected relationship, the pressure estimator M11 derives the pressure estimated value PE to a magnitude corresponding to the motor current Imt.

[0033] Here, when the motor current Imt increases, the electric motor 40 rotates in the increasing rotation direction R1, and the pressing force P increases substantially in accordance with the first relationship LR1 shown in FIG. 2. When the motor current Imt transitions from an increasing state to a decreasing state, the relationship between the motor current Imt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. When the relationship between the motor current Imt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2, the pressing force P is essentially maintained. As the motor current Imt continues to decrease, the relationship between the motor current Imt and the pressing force P becomes the second relationship LR2. Therefore, the electric motor 40 rotates in the decreasing rotation direction R2 in response to the decrease in the motor current Imt, and the pressing force P decreases. When the electric motor 40 rotates in the decreasing rotation direction R2 in response to the decrease in the motor current Imt, the pressing force P decreases substantially in accordance with the second relationship LR2. When the motor current Imt transitions from a state in which it decreases to a state in which it increases, the relationship between the motor current Imt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. When the relationship between the motor current Imt 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 thereafter and the relationship between the motor current Imt and the pressing force P becomes the first relationship LR1, the pressing force P increases in accordance with the increase in the motor current Imt.

[0034] Therefore, the pressing force estimation unit M11 sets a dead zone DZ for the motor current Imt. If the motor current Imt is within the range of the dead zone DZ, it can be considered that the relationship between the motor current Imt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2.

[0035] For example, the pressure estimator M11 sets a first dead zone DZ1 as the dead zone DZ, in which the motor current Imt at the time when the motor current Imt transitions from an increasing state to a maintained or decreasing state is set as an upper limit value ImtL2. When the motor current Imt is within the range of the first dead zone DZ1, the pressure estimator M11 executes a first estimation process to hold the estimated pressure value PE at the value at the time when the upper limit value ImtL2 was set.

[0036] In the first estimation process, when the motor current Imt transitions from a value within the range of the first dead zone DZ1 to a value greater than the upper limit of the first dead zone DZ1, the pressure estimator M11 selects the first relationship LR1 from the first relationship LR1 and the second relationship LR2, and derives the pressure estimated value PE based on the first relationship LR1 to a magnitude corresponding to the motor current Imt.

[0037] In the first estimation process, when the motor current Imt transitions from a value within the range of the first dead zone DZ1 to a value smaller than the lower limit of the first dead zone DZ1, the pressure estimation unit M11 selects the second relationship LR2 from the first relationship LR1 and the second relationship LR2, and derives the pressure estimation value PE based on the second relationship LR2 to a magnitude corresponding to the motor current Imt.

[0038] 2, the distance between the line indicating the first relationship LR1 and the line indicating the second relationship LR2 becomes wider as the motor current Imt becomes larger. Therefore, in the first estimation process, the pressing force estimation unit M11 sets the lower limit value of the first dead zone DZ1 so that the range of the first dead zone DZ1 becomes wider as the upper limit value ImtL2 becomes larger, that is, as the motor current Imt becomes larger at the time when the motor current Imt transitions from an increasing state to a maintained or decreasing state. This allows the pressing force estimation unit M11 to set the width of the range of the first dead zone DZ1 to a width corresponding to the distance between the line indicating the first relationship LR1 and the line indicating the second relationship LR2.

[0039] Furthermore, for example, the pressure estimator M11 sets a second dead zone DZ2 as the dead zone DZ, in which the motor current Imt at the time when the motor current Imt transitions from a decreasing state to a maintained or increasing state is set to a lower limit value ImtL1. Then, when the motor current Imt is within the range of the second dead zone DZ2, the pressure estimator M11 executes a second estimation process to hold the estimated pressure value PE at the value at the time when the lower limit value ImtL1 was set.

[0040] In the second estimation process, when the motor current Imt transitions from a value within the range of the second dead zone DZ2 to a value smaller than the lower limit of the second dead zone DZ2, the pressure estimation unit M11 selects the second relationship LR2 from the first relationship LR1 and the second relationship LR2, and derives the pressure estimation value PE based on the second relationship LR2 to a magnitude corresponding to the motor current Imt.

[0041] In the second estimation process, when the motor current Imt transitions from a value within the range of the second dead zone DZ2 to a value greater than the upper limit of the second dead zone DZ2, the pressure estimation unit M11 selects the first relationship LR1 from the first relationship LR1 and the second relationship LR2. Then, the pressure estimation unit M11 derives the pressure estimated value PE based on the first relationship LR1 to a magnitude corresponding to the motor current Imt.

[0042] 2, the distance between the line indicating the first relationship LR1 and the line indicating the second relationship LR2 becomes wider as the motor current Imt becomes larger. Therefore, in the second estimation process, the pressing force estimation unit M11 sets an upper limit value of the second dead zone DZ2 so that the range of the second dead zone DZ2 becomes wider as the lower limit value ImtL1 becomes larger, that is, as the motor current Imt becomes larger at the time when the motor current Imt transitions from a decreasing state to a maintained or increasing state. This allows the pressing force estimation unit M11 to set the width of the range of the second dead zone DZ2 to a width corresponding to the distance between the line indicating the first relationship LR1 and the line indicating the second relationship LR2.

[0043] <Pressure target value setting section> The pressing force target value setting unit M13 sets a pressing force target value PTr, which is a target value of the pressing force P, for each predetermined calculation cycle. For example, when the driver is operating the brake pedal, the pressing force target value setting unit M13 derives a larger value as the pressing force target value PTr as the brake pedal operation amount increases. Furthermore, when a deceleration request is received from another control device, the pressing force target value setting unit M13 sets a value corresponding to the deceleration request as the pressing force target value PTr.

[0044] <Motor control unit> The motor control unit M15 controls the electric motor 40 based on the pressure force estimate value PE and the pressure force target value PTr. Specifically, the motor control unit M15 sets at least one of a current command value and a voltage command value so that the pressure force estimate value PE becomes the pressure force target value PTr. Then, the motor control unit M15 operates the inverter circuit 81 based on at least one of the current command value and the voltage command value.

[0045] 4 and 5, a series of processes executed by the processing circuit 90 will be described. The processing circuit 90 repeatedly executes the series of processes for each predetermined calculation cycle. The processing circuit 90 functions as a pressing force estimation unit M11, thereby executing a plurality of processes from steps S11 to S29.

[0046] In step S11, the processing circuit 90 determines whether the motor current Imt is within the range of the dead zone DZ. If the motor current Imt is equal to or greater than the lower limit value ImtL1 and equal to or less than the upper limit value ImtL2 of the dead zone DZ, the processing circuit 90 determines that the motor current Imt is within the range of the dead zone DZ (S11: YES). Then, the processing circuit 90 proceeds to step S29. On the other hand, if the motor current Imt is less than the lower limit value ImtL1 of the dead zone DZ or is greater than the upper limit value ImtL2, the processing circuit 90 determines that the motor current Imt is outside the range of the dead zone DZ (S11: NO). Then, the processing circuit 90 proceeds to step S13.

[0047] In step S13, the processing circuit 90 determines whether the motor current Imt is increasing. For example, if the motor current Imt is greater than the upper limit value ImtL2, the motor current Imt can be considered to be increasing. If the motor current Imt is smaller than the lower limit value ImtL1, the motor current Imt can be considered to be decreasing. If the processing circuit 90 determines that the motor current Imt is increasing (S13: YES), the processing circuit 90 proceeds to step S15. On the other hand, if the processing circuit 90 determines that the motor current Imt is decreasing (S13: NO), the processing circuit 90 proceeds to step S21.

[0048] In step S15, the processing circuit 90 sets the current motor current Imt as the upper limit value ImtL2. In the following step S17, the processing circuit 90 sets the lower limit value ImtL1 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 ImtL1 so that the difference between the upper limit value ImtL2 and the lower limit value ImtL1 is equal to 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 estimate PE. Then, the processing circuit 90 proceeds to step S25.

[0049] Here, referring to FIG. 5, a change in the range of the dead zone DZ when the motor current Imt increases will be described. When the motor current Imt is within the range of the dead zone DZ as shown in FIG. 5A, the processing circuit 90 maintains the range of the dead zone DZ. When the motor current Imt increases from the state shown in FIG. 5A and reaches the upper limit value ImtL2 of the dead zone DZ as shown in FIG. 5B, the upper limit value ImtL2 increases in accordance with the increase in the motor current Imt as shown in FIG. 5C. Furthermore, in this embodiment, when the upper limit value ImtL2 is increased, the processing circuit 90 also changes the lower limit value ImtL1 so that the range of the dead zone DZ widens.

[0050] Returning to FIG. 4, in step S21, the processing circuit 90 sets the current motor current Imt as the lower limit value ImtL1. In the following step S23, the processing circuit 90 sets the upper limit value ImtL2 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 ImtL2 so that the difference between the upper limit value ImtL2 and the lower limit value ImtL1 is equal to 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 estimate PE. Then, the processing circuit 90 proceeds to step S25.

[0051] Here, we will explain how the range of the dead zone DZ changes when the motor current Imt decreases. When the motor current Imt decreases while it is within the range of the dead zone DZ and reaches the lower limit value ImtL1 of the dead zone DZ, the lower limit value ImtL1 decreases as the motor current Imt decreases. Furthermore, in this embodiment, when the processing circuit 90 decreases the lower limit value ImtL1, it also changes the upper limit value ImtL2 so that the range of the dead zone DZ narrows.

[0052] In step S25, the processing circuit 90 selects one of the first relationship LR1 and the second relationship LR2. For example, when the motor current Imt is greater than the upper limit value ImtL2, the processing circuit 90 selects the first relationship LR1. When the motor current Imt is smaller than the lower limit value ImtL1, the processing circuit 90 selects the second relationship LR2.

[0053] In the following step S27, the processing circuit 90 derives the pressing force P corresponding to the motor current Imt as the pressing force estimated value PE based on the relationship selected in step S25. After that, the processing circuit 90 temporarily ends the series of processes.

[0054] In step S29, the processing circuit 90 holds the pressing force estimated value PE immediately before it is determined that the motor current Imt is within the range of the dead zone DZ, and then the processing circuit 90 temporarily ends the series of processes.

[0055] <Actions and Effects of This Embodiment> The operation and effects of this embodiment will be described with reference to FIG. When the pressing force P, i.e., the braking force Fx, is increased, the relationship between the motor current Imt 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 motor current Imt is increasing, the motor current Imt is greater than the upper limit value ImtL2 of the dead zone DZ, and therefore the upper limit value ImtL2 and the lower limit value ImtL1 of the dead zone DZ are continuously updated. As a result, the processing circuit 90 selects the first relationship LR1 from the first relationship LR1 and the second relationship LR2. Based on the first relationship LR1, the processing circuit 90 derives the pressing force P corresponding to the motor current Imt as the pressing force estimated value PE.

[0056] In the example shown in Figure 6, when the motor current Imt reaches the first motor current Imt1, the increase in the motor current Imt stops and the motor current Imt is maintained or begins to decrease. For example, when the motor current Imt begins to decrease, the operating point representing the motor current Imt and the pressing force P in Figure 6 moves along the first hysteresis line HS1 in a direction that decreases the motor current Imt. In this case, the relationship between the motor current Imt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, even if the motor current Imt decreases, the pressing force P is maintained.

[0057] Here, consider a case where the pressure P is estimated based on either the first relationship LR1 or the second relationship LR2 under the condition that the operating point representing the motor current Imt and the pressure P is point Z on the first hysteresis line HS1. The actual pressure P when the relationship between the motor current Imt and the pressure P is point Z on the first hysteresis line HS1 is defined as pressure P1. When the pressure P is estimated based on the first relationship LR1, a pressure P2 is derived as the pressure estimated value PE. The pressure P2 is smaller than the pressure P1. Conversely, when the pressure P is estimated based on the second relationship LR2, a pressure P3 is derived as the pressure estimated value PE. The pressure P3 is larger than the pressure P1. In other words, when the operating point representing the motor current Imt and the pressure P is point Z on the first hysteresis line HS1, it is difficult to say that the estimation accuracy of the pressure P is high.

[0058] Therefore, when the motor current Imt transitions from an increasing state to a maintained or decreasing state, the processing circuit 90 sets a dead zone DZ in which the first motor current Imt1, which is the motor current at that time, is set as an upper limit value ImtL2. Then, when the motor current Imt is within the range of the dead zone DZ, the processing circuit 90 holds the pressing force estimate PE at the value at the time when the upper limit value ImtL2 was set. This allows the electric braking device 10 to improve the accuracy of estimating the pressing force P when estimating the pressing force P based on the motor current Imt under conditions in which a braking force Fx is being applied to the wheel 100. Furthermore, the electric braking device 10 can estimate the pressing force P without using detection signals from a sensor that detects the pressing force or its correlation value and a sensor that detects the motor rotation angle θ.

[0059] In the example shown in Figure 6, when the motor current Imt, which has been decreasing, reaches the second motor current Imt2, the decrease in the motor current Imt stops and the motor current Imt begins to be maintained or increased. For example, when the motor current Imt increases, the operating point representing the motor current Imt and the pressing force P in Figure 6 moves along the second hysteresis line HS2 in the direction that increases the motor current Imt. In this case, the relationship between the motor current Imt and the pressing force P deviates from both the first relationship LR1 and the second relationship LR2. Therefore, even if the motor current Imt increases, the pressing force P is maintained.

[0060] Therefore, when the motor current Imt transitions from a decreasing state to a maintained or increasing state, the processing circuit 90 sets a dead zone DZ in which the second motor current Imt2, which is the motor current at that time, is set to a lower limit value ImtL1. Then, when the motor current Imt is within the value of the dead zone DZ, the processing circuit 90 holds the pressing force estimate PE at the value at the time when the lower limit value ImtL1 was set. This allows the electric brake device 10 to improve the accuracy of estimating the pressing force P when estimating the pressing force P based on the motor current Imt while a braking force Fx is being applied to the wheel 100.

[0061] If the motor current Imt continues to increase thereafter, the motor current Imt becomes larger than the upper limit value ImtL2 of the dead zone DZ, and the relationship between the motor current Imt and the pressing force P becomes the first relationship LR1. Then, as described above, the processing circuit 90 derives the pressing force estimated value PE based on the first relationship LR1, and updates the upper limit value ImtL2 and the lower limit value ImtL1 of the dead zone DZ.

[0062] In this embodiment, the following effects can be further obtained. (1) As shown in FIG. 6, the length of the first hysteresis line HS1 increases as the motor current Imt increases at the time when the motor current Imt transitions from an increasing state to a maintained or decreasing state.

[0063] Therefore, when the motor current Imt transitions from an increasing state to a maintained or decreasing state, the processing circuit 90 sets a lower limit ImtL1 of the dead zone DZ in the first estimation process so that the range of the dead zone DZ becomes wider as the motor current Imt 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 motor current Imt 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.

[0064] (2) As shown in FIG. 6, the length of the second hysteresis line HS2 becomes shorter as the motor current Imt decreases at the time when the motor current Imt changes from a decreasing state to a maintained or increasing state.

[0065] Therefore, when the motor current Imt transitions from a decreasing state to a maintained or increasing state, the processing circuit 90 sets an upper limit value ImtL2 of the dead zone DZ in the second estimation process so that the range of the dead zone DZ becomes wider as the motor current Imt at the time of transition increases. By using such a dead zone DZ, the processing circuit 90 can accurately determine whether the relationship between the motor current Imt 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.

[0066] (3) The processing circuit 90 uses the first relationship LR1 that is set by taking into consideration the magnitude of the amplitude of the composite wave WC of the first fluctuation component due to the cogging torque and the second fluctuation component due to the torque ripple. As a result, when the motor current Imt is greater than the upper limit value ImtL2 of the dead zone DZ, the processing circuit 90 can accurately estimate the pressing force P by using the first relationship LR1.

[0067] (4) The processing circuit 90 uses the second relationship LR2 that is set by taking into consideration the magnitude of the amplitude of the composite wave WC of the first fluctuation component due to the cogging torque and the second fluctuation component due to the torque ripple. As a result, when the motor current Imt is smaller than the lower limit value ImtL1 of the dead zone DZ, the processing circuit 90 can accurately estimate the pressing force P by using the second relationship LR2.

[0068] <Example of change> 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.

[0069] If the first relationship LR1 is set taking into consideration the magnitude of the amplitude of the composite wave WC, the second relationship LR2 may be set without taking into consideration the magnitude of the amplitude of the composite wave WC. For example, the second relationship LR2 may be the second reference relationship LRB2 shown in FIG. 2.

[0070] If the second relationship LR2 is set taking into consideration the magnitude of the amplitude of the composite wave WC, the first relationship LR1 may be set without taking into consideration the magnitude of the amplitude of the composite wave WC. For example, the first relationship LR1 may be the first reference relationship LRB1 shown in FIG. 2.

[0071] The first relationship LR1 may take into account only one of the first fluctuation component due to cogging torque and the second fluctuation component due to torque ripple. The second relationship LR2 may take into account only one of the first fluctuation component due to cogging torque and the second fluctuation component due to torque ripple.

[0072] If the processing circuit 90 sets the range of the first dead zone DZ1 in accordance with the upper limit value ImtL2, it is not necessary for the processing circuit 90 to vary the range of the second dead zone DZ2 in accordance with the lower limit value ImtL1.

[0073] The processing circuit 90 does not need to vary the range of the first dead zone DZ1 depending on the upper limit value ImtL2, as long as the range of the second dead zone DZ2 is set depending on the lower limit value ImtL1.

[0074] In the above embodiment, the processing circuit 90 continues to update the range of the dead zone DZ while the motor current Imt continues to increase. However, this is not limited to this. For example, the processing circuit 90 may set the dead zone DZ as a first dead zone DZ1 at a first transition point, which is the point at which the motor current Imt transitions from an increasing state to a maintained or decreasing state. In this case, the processing circuit 90 sets the first dead zone DZ1 such that the motor current Imt at the first transition point is set as an upper limit value ImtL2. Furthermore, the processing circuit 90 may set a lower limit value ImtL1 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 motor current Imt is within the range of the first dead zone DZ1, the processing circuit 90 sets the current pressure force estimate PE to the pressure force estimate value at the first transition point.

[0075] In the above embodiment, the processing circuit 90 continues to update the range of the dead zone DZ while the motor current Imt 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 at which the motor current Imt 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 motor current Imt at the second transition point is equal to the lower limit value ImtL1. Furthermore, the processing circuit 90 may set an upper limit value ImtL2 of the second dead zone DZ2 so that the range of the second dead zone DZ2 becomes wider as the motor current Imt increases. Then, when the motor current Imt is within the range of the second dead zone DZ2, the processing circuit 90 sets the current pressure force estimate PE to the pressure force estimate at the second transition point.

[0076] The processing circuit 90 may not necessarily execute the second estimation process as long as it executes the first estimation process. In this case, the processing circuit 90 may derive the pressing force estimation value PE based on the first relationship LR1 when the motor current Imt transitions from a decreasing state to a maintaining or increasing state.

[0077] The processing circuit 90 may not necessarily execute the first estimation process if it executes the second estimation process. In this case, the processing circuit 90 may derive the pressing force estimation value PE based on the second relationship LR2 when the motor current Imt transitions from an increasing state to a maintained or decreasing state.

[0078] The braking unit may be equipped with a rotation angle sensor that detects the motor rotation angle θ. Even in this case, if an abnormality occurs in the rotation angle sensor, the processing circuit 90 may estimate the pressing force P using the method described in the above embodiment.

[0079] The processing circuit 90 may use the pressing force estimate value PE derived by the method described in the above embodiment to determine whether or not there is an abnormality in other components such as a rotation angle sensor. During antilock brake control, the processing circuit 90 may estimate the pressing force when the wheel locks using the pressing force estimation value PE derived using the method described in the above embodiment and the detection value of the wheel speed sensor.

[0080] The braking unit may be a drum-type braking device. The electric braking device may be a wet-type electric braking device having an electric cylinder powered by an electric motor.

[0081] The processing circuitry 90 may be configured as 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. Examples of dedicated hardware include 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 perform the processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0082] <Other technical ideas> The technical concepts that can be understood from the above-described embodiments and modifications will be described below. [Appendix 1] In an electric braking device configured to be able to adjust the pressing force, which is the force that presses a friction material against a rotating body that rotates integrally with a vehicle wheel, in accordance with the rotation of an electric motor, a current acquisition unit that acquires a motor current that is a current flowing through the electric motor; a pressing force estimating unit that selects one of a first relationship that is a relationship between 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 and the pressing force when the electric motor is rotated in a direction that decreases the braking force, and derives a pressing force estimated value that is an estimate of the pressing force based on the first relationship, the magnitude of which corresponds to the motor current; The pressing force estimation unit When the motor current is greater than an upper limit value of a predetermined dead zone, the first relationship is selected from the first relationship and the second relationship, and the pressing force estimated value is derived to a magnitude corresponding to the motor current based on the first relationship; When the motor current is smaller than a lower limit value of the dead zone, the second relationship is selected from the first relationship and the second relationship, and the pressing force estimated value is derived to a magnitude corresponding to the motor current based on the second relationship; When the motor current is within the dead band, the estimated pressing force value is held. If the motor current is greater than an upper limit value of the dead band, the range of the dead band is updated so that the motor current becomes the upper limit value; An electric braking device, comprising: when the motor current is smaller than a lower limit value of the dead zone, the range of the dead zone is updated so that the motor current becomes the lower limit value.

[0083] [Appendix 2] When the pressure estimation unit updates the range of the dead zone because the motor current has become a value outside the range of the dead zone, it is preferable that the pressure estimation unit sets lower and upper limits of the dead zone so that the range of the dead zone becomes wider as the motor current becomes larger.

[0084] [Supplementary Note 3] It is preferable to include a motor control unit that controls the electric motor so that the estimated pressing force value becomes the target value of the pressing force. The expression "at least one" used herein means "one or more" of the desired options. As an example, the expression "at least one" used herein 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 herein means "only one option" or "any combination of two or more options" if the number of options is three or more. [Explanation of symbols]

[0085] 10…Electric braking device 11...Brake part 40...Electric motor 80...Motor control device 82...Current sensor (an example of a current acquisition unit) 90...Processing circuit 100...wheel 110...rotating body 120...Friction material M11…Pushing force estimation part M15: Motor control unit

Claims

1. An electric braking 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, a current acquisition unit that acquires a motor current that is a current flowing through the electric motor; a pressing force estimating unit that selects one of a first relationship that is a relationship between 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 and the pressing force when the electric motor is rotated in a direction that decreases the braking force, and derives a pressing force estimated value that is an estimate of the pressing force based on the first relationship, the magnitude of which corresponds to the motor current; The pressing force estimation unit a first estimation process for holding the pressure estimated value at a value at the time when the upper limit value is set, when the motor current acquired by the current acquisition unit is within a value of a first dead band whose upper limit value is the motor current at the time when the motor current transitions from an increasing state to a maintained or decreasing state; deriving the pressure estimated value to a magnitude corresponding to the motor current based on the first relationship, when the motor current acquired by the current acquisition unit transitions from a value within the first dead band to a value larger than the upper limit value of the first dead band; and deriving the pressure estimated value to a magnitude corresponding to the motor current based on the second relationship, when the motor current acquired by the current acquisition unit transitions from a value within the first dead band to a value smaller than the lower limit value of the first dead band; a second estimation process for holding the pressure estimated value at a value at the time the lower limit value was set when the motor current acquired by the current acquisition unit is within a value in a second dead band range having a lower limit value as the motor current at the time the motor current transitioned from a decreasing state to a maintained or increasing state, deriving the pressure estimated value to a magnitude corresponding to the motor current based on the second relationship when the motor current acquired by the current acquisition unit transitioned from a value in the second dead band range to a value smaller than the lower limit value of the second dead band, and deriving the pressure estimated value to a magnitude corresponding to the motor current based on the first relationship when the motor current transitioned from a value in the second dead band range to a value larger than an upper limit value of the second dead band. An electric braking device characterized by:

2. the pressing force estimation unit is configured to execute the first estimation process, In the first estimation process, the pressing force estimating unit sets a lower limit value of the first dead zone such that the range of the first dead zone becomes wider as the upper limit value of the first dead zone increases. The electric braking device according to claim 1 .

3. the pressing force estimation unit is configured to execute the second estimation process, In the second estimation process, the pressing force estimating unit sets an upper limit value of the second dead zone such that the range of the second dead zone becomes wider as the lower limit value of the second dead zone increases. The electric braking device according to claim 1 .

4. At least one of the first relationship and the second relationship is set taking into consideration the magnitude of the amplitude of a composite wave of a fluctuation component due to cogging torque superimposed on the motor current and a fluctuation component due to torque ripple superimposed on the motor current. The electric braking device according to any one of claims 1 to 3.

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