Electric braking device

Abstract

An electric braking device 10 comprises: a torque difference calculation unit 94 that calculates a pressurization / decompression torque difference that is a difference between a first command torque that is a command torque at a first timing at which a change trend of command torque to an electric motor 40 changes from an increase trend to a decrease trend and vice versa, and a second command torque that is a command torque at a second timing at which a pressing force applied to a rotor 110 starts to change by maintaining the change trend of the command torque from the first timing; and an efficiency estimation unit 95 that estimates the efficiency of the electric braking device 10 that is the ratio of the command torque to the difference between the command torque and the proportional loss torque, on the basis of the first command torque or the second command torque and the pressurization / decompression torque difference.

Description

electric braking device

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

[0002] Patent Document 1 describes an electric braking device that generates a braking force on a wheel by pressing a friction material against a rotating body that rotates together with the wheel. The electric braking device includes an electric motor and a linear motion conversion mechanism. The linear motion conversion mechanism has a rotating part that rotates in response to the rotational motion of the output shaft of the electric motor and a linear motion part that moves linearly in response to the rotational motion of the rotating part. The electric braking device presses the friction material against the rotating body using the linear motion part that moves linearly based on the power transmitted from the electric motor. In this way, the electric braking device generates a braking force on the wheel. In this way, in the electric braking device, the torque output by the electric motor is converted into a force that causes the friction material to press against the rotating body.

[0003] US Patent Application Publication No. 2014 / 0303865

[0004] Because electric braking systems include mechanical losses, not all of the torque output by the electric motor is converted into a pressing force on the friction material. If the efficiency of an electric braking system is defined as the proportion of the torque output by the electric motor that is converted into a pressing force on the friction material, the efficiency of the electric braking system may decrease as the characteristics of the system change over time. Therefore, if the efficiency of the electric braking system can be estimated, the electric braking system can correct values ​​related to the pressing force of the linear moving part. For example, the electric braking system can correct the torque command value for the electric motor or the estimated value of the pressing force of the linear moving part based on the efficiency of the electric braking system.

[0005] The electric braking device that solves the above problem is an electric braking device in which a rotating part of a linear motion conversion mechanism performs rotational motion in response to the rotational motion of an electric motor, and the rotational motion of the rotating part is converted into linear motion in a forward or backward direction of a linear motion part of the linear motion conversion mechanism, and the electric braking device is capable of applying a braking force to a wheel of a vehicle by pressing a friction material against a rotating body that rotates together with the wheel of the vehicle in response to the linear motion of the linear motion part. The electric braking device further comprises: a first command torque that is the command torque at a first time point when the change trend of the command torque, which is a command value of the torque for the electric motor, changes from one of an increasing trend and a decreasing trend to the other; and a pressing force applied to the rotating body as the change trend of the command torque is maintained from the first time point. and a second command torque which is the command torque at a second time point when the force starts to change. An efficiency estimation unit is configured to estimate, based on the first command torque or the second command torque and the acceleration / deceleration torque difference, an efficiency of the electric braking device which is the ratio between the command torque and a difference between the command torque and a proportional loss torque which increases as the command torque increases, and the command torque, wherein the proportional loss torque is the difference between the command torque in an ideal electric braking device with no mechanical loss and the command torque in the electric braking device with mechanical loss, of the torques output by the electric motor when applying the predetermined pressing force to the rotating body.

[0006] According to the electric braking device, it is possible to estimate the efficiency when generating braking force on the wheels.

[0007] Fig. 1 is a schematic diagram showing the general configuration of an electric braking device. Fig. 2 is a graph showing the relationship between command torque and pressing force. Fig. 3 is a graph showing the relationship between command torque and pressing force. Fig. 4 is a graph showing the relationship between command torque and a pressure-increasing / decreasing torque difference. Fig. 5(a) is a graph showing the relationship between command torque and pressing force, and Fig. 5(b) is a graph showing the relationship between command torque and a pressure-increasing / decreasing torque difference. Fig. 6(a) is a graph showing the relationship between command torque and pressing force, and Fig. 6(b) is a graph showing the relationship between command torque and a pressure-increasing / decreasing torque difference.

[0008] An embodiment of an electric braking device will be described with reference to the drawings. <Configuration of this embodiment> As shown in Fig. 1, the electric braking device 10 includes a caliper 20, a gearbox 30, an electric motor 40, a reduction mechanism 50, a linear motion conversion mechanism 60, a piston 70, a motor control device 80, and a braking control device 90. The electric braking device 10 is configured to apply a braking force to the wheel 100 by pressing a friction material 120 against a rotating body 110 that rotates together with the wheel 100. An example of the electric braking device 10 is a disc brake type braking device.

[0009] <Caliper and Gearbox> The caliper 20 has a cylinder body 21, a bridge 22, and an arm 23. The cylinder body 21 is connected to the arm 23 via the bridge 22. The cylinder body 21 has a cylinder 24 that includes a cylindrical space. The axis of the cylinder 24 extends in the same direction as the rotation axis of the wheel 100. The arm 23 is located in the 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, a 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.

[0010] The gearbox 30 houses the reduction gear 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 to the end where the friction material 120 is located in the front-rear direction. In the following description, the direction toward the friction material 120 in the front-rear direction is also referred to as the forward direction X1, and the direction toward the gearbox 30 is also referred to as the backward direction X2.

[0011] <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 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. The rotation angle sensor 42 is, for example, a magnetic sensor.

[0012] <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 To 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.

[0013] <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 power transmitted from the reduction gear mechanism 50, and a nut 62 that performs linear motion due to 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.

[0014] As shown in Figure 1, 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. In other words, the screw shaft 61 corresponds to the "rotating part of the linear motion conversion mechanism," and the nut 62 corresponds to the "linear motion part of the linear motion conversion mechanism."

[0015] <Motor Control Device> The motor control device 80 controls the electric motor 40 based on the command torque T, which is a torque command value transmitted from the braking control device 90, and the detection signal from the rotation angle sensor 42. More specifically, the motor control device 80 controls the electric motor 40 so that the torque To output by the electric motor 40 becomes the command torque T. The motor control device 80 may be a motor driver that includes a drive circuit for the electric motor 40, etc.

[0016] <Piston> As shown in Fig. 1 , 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.

[0017] <Operation of Electric Brake Device> In the electric brake device 10, when the electric motor 40 is driven, the rotational motion of the output shaft 41 of the electric motor 40 is reduced by the reduction mechanism 50. Subsequently, the rotational motion of the third gear 53 of the reduction mechanism 50 is transmitted to the threaded shaft 61 of the linear motion conversion mechanism 60. In the linear motion conversion mechanism 60, the rotational motion of the threaded shaft 61 is converted into linear motion of the nut 62 in the forward direction X1. As a result, the piston 70 moves in the forward direction X1 together with the nut 62. In this way, the piston 70 presses the friction material 120 against the rotating body 110, generating a braking force on the wheel 100.

[0018] The magnitude of the braking force generated on the wheel 100 is proportional to the force with which the friction material 120 presses the rotating body 110 (hereinafter also referred to as "pressing force P"). Furthermore, the pressing force P of the friction material 120 is proportional to the magnitude of the torque To output by the electric motor 40. Therefore, when adjusting the braking force generated on the wheel 100, the command torque T for the electric motor 40 is adjusted. More specifically, when increasing the braking force generated on the wheel 100, the command torque T for the electric motor 40 is increased, and when decreasing the braking force generated on the wheel 100, the command torque T for the electric motor 40 is decreased.

[0019] <Characteristics of the Electric Brake Device> The torque To output by 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. For this reason, mechanical loss occurs in the power transmission path from the electric motor 40 to the friction material 120. In the following description, torque that is lost due to mechanical loss, of the torque To output by the electric motor 40, without being converted into the pressing force P of the friction material 120, is referred to as loss torque TL. The loss torque TL includes a proportional loss torque TLp that increases in proportion to the magnitude of the torque To output by the electric motor 40, and a constant loss torque TLc that is constant regardless of the magnitude of the torque To output by the electric motor 40.

[0020] 2 shows the relationship between the command torque T and the pressing force P of the electric braking device 10 when there is no mechanical loss and when there is mechanical loss. In either case, the larger the command torque T, the larger the pressing force P. In other words, the smaller the command torque T, the smaller the pressing force P.

[0021] It is assumed that there is no mechanical loss in the electric braking device 10. The relationship between the command torque T and the pressing force P in an ideal electric braking device 10 with no mechanical loss is shown by a solid line in Fig. 2. That is, the solid line shown in Fig. 2 is an ideal characteristic line Li that shows the relationship between the command torque T (Ti) and the pressing force P in an ideal electric braking device 10 with no mechanical loss. In this case, the magnitude of the pressing force P is uniquely determined by the magnitude of the command torque T. In other words, when the command torque T increases, the pressing force P increases along the ideal characteristic line Li, and when the command torque T decreases, the pressing force P decreases along the ideal characteristic line Li.

[0022] However, in reality, the electric braking device 10 has mechanical losses. The relationship between the command torque T and the pressing force P in the electric braking device 10 in this case is shown by the dashed line and the two-dot chain line in Figure 2. In the case of an electric braking device 10 with mechanical losses, the manner in which the pressing force P changes with respect to the command torque T is different from the case of an electric braking device 10 without mechanical losses.

[0023] When the command torque T increases, 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, as shown by the dashed dotted line in FIG. 2 , when the command torque T increases and there is a mechanical loss, the command torque T required to obtain the target pressing force P becomes larger. More specifically, the command torque Ta is larger than the command torque Ti. As a result, when the command torque T increases and there is a mechanical loss, the gradient of the change in pressing force P relative to the change in command torque T becomes gentler. In this respect, the gradient of the straight line indicated by the dashed dotted line is gentler than the gradient of the straight line indicated by the solid line.

[0024] When the command torque T is decreasing, 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 movement direction of the friction material 120. Therefore, as shown by the two-dot chain line in Figure 2, if there is a mechanical loss when the command torque T is decreasing, the command torque T required to output the target pressing force P becomes smaller. More specifically, the command torque Tr is smaller than the command torque Ti. As a result, if there is a mechanical loss when the command torque T is decreasing, the gradient of the change in pressing force P relative to the change in command torque T becomes steeper. In this respect, the gradient of the straight line indicated by the two-dot chain line is steeper than the gradient of the straight line indicated by the solid line.

[0025] In the following description, the line showing the relationship between the command torque T and the pressing force P when the command torque T is increasing will be referred to as the first pressurization line L1a, and the line showing the relationship between the command torque T and the pressing force P when the command torque T is decreasing will be referred to as the first depressurization line L1r. As described above, the gradient of the first pressurization line L1a is gentler than the gradient of the line shown by the solid line, and the gradient of the first depressurization line L1r is steeper than the gradient of the line shown by the solid line.

[0026] Furthermore, if the mechanical loss increases due to aging of the electric braking device 10, the gradient of the first pressure increase line L1a becomes gentler and the gradient of the first pressure decrease line L1r becomes steeper. In this way, if the electric braking device 10 includes mechanical loss, the target braking force cannot be applied to the wheels 100 unless the command torque T is corrected in accordance with the gradient of the first pressure increase line L1a or the gradient of the first pressure decrease line L1r.

[0027] 1, the braking control device 90 has a CPU 91 and a memory 92. The CPU 91 executes a program stored in the memory 92, causing the braking control device 90 to output a command value to the motor control device 80. In this way, the electric motor 40 is driven.

[0028] The CPU 91 executes the program in the memory 92, causing the braking control device 90 to function as multiple functional units for generating command values ​​for the motor control device 80. The multiple functional units include a braking control unit 93, a torque difference calculation unit 94, an efficiency estimating unit 95, a constant loss calculation unit 96, and a correction unit 97.

[0029] <Braking Control Unit> The braking control unit 93 acquires a required braking force required for the vehicle. For example, when the driver is driving the vehicle, the braking control unit 93 calculates the required braking force according to the amount of operation of the brake pedal or the like. Furthermore, when the vehicle is being driven automatically, the braking control unit 93 acquires the required braking force transmitted from an automatic driving control device that controls the automatic driving of the vehicle. Next, the braking control unit 93 calculates a command torque T according to the required braking force. The required braking force and the pressing force P are correlated, and the pressing force P and the command torque T are correlated. Therefore, when the required braking force is large, the calculated command torque T also becomes large, and when the required braking force is small, the calculated command torque T also becomes small. The braking control unit 93 may calculate the command torque T by referring to a calculation formula that correlates the required braking force and the command torque T, or may acquire the command torque T by referring to a map that correlates the required braking force and the command torque T. Then, the braking control unit 93 transmits the command torque T to the motor control device 80.

[0030] <Torque Difference Calculation Unit> The torque difference calculation unit 94 acquires the command torque T at a time when the command torque T increases, in other words, when the required braking force increases, and the change trend of the command torque T changes from an increasing trend to a decreasing trend. That is, the torque difference calculation unit 94 acquires a first command torque T1, which is the command torque T at a first time point. Next, the torque difference calculation unit 94 acquires the command torque T at a time point when the change trend of the command torque T is maintained and the pressing force P begins to decrease. That is, the torque difference calculation unit 94 acquires a second command torque T2, which is the command torque T at a second time point. Then, the torque difference calculation unit 94 calculates a pressure increase / decrease torque difference ΔT, which is the difference between the first command torque T1 and the second command torque T2.

[0031] A case will be described in which the change trend of the command torque T changes from an increasing trend to a decreasing trend, as indicated by the first arrow V1 (V11, V12, V13) in FIG. 3 . As indicated by the first arrow V11, when the command torque T increases, the pressing force P increases along the first pressurizing line L1a. Thereafter, as indicated by the first arrow V12, when the change trend of the command torque T changes from an increasing trend to a decreasing trend, the command torque T begins to decrease. Here, the time when the change trend of the command torque T changes from an increasing trend to a decreasing trend is the first time point. In other words, the command torque T at the time when the change trend of the command torque T changes from an increasing trend to a decreasing trend is the first command torque T1 (T1a). As indicated by the first arrow V12, the pressing force P is maintained approximately constant for a while after the command torque T begins to decrease. In other words, even if the command torque T decreases, the pressing force P does not decrease. Thereafter, as indicated by the first arrow V13, when the decrease in the command torque T continues, the pressing force P begins to decrease along the first decompression line L1r. Here, the time when the pressing force P starts to decrease as the changing trend of the command torque T is maintained from the first time point is the second time point. That is, the command torque T at the time when the pressing force P starts to decrease as the changing trend of the command torque T is maintained from the first time point is the second command torque T2 (T2r). Thus, the difference between the first command torque T1 (T1a) and the second command torque T2 (T2r) is the compression / decompression torque difference ΔT (ΔT1).

[0032] Similarly, when the command torque T is decreasing, in other words, when the required braking force is decreasing, the torque difference calculation unit 94 acquires the command torque T at a time when the change trend of the command torque T changes from a decreasing trend to an increasing trend. That is, the torque difference calculation unit 94 acquires a first command torque T1, which is the command torque at a first time point. Next, the torque difference calculation unit 94 acquires the command torque T at a time when the pressing force P starts to increase under a situation where the change trend of the command torque T is maintained. That is, the torque difference calculation unit 94 acquires a second command torque T2, which is the command torque T at a second time point. Then, the torque difference calculation unit 94 calculates a pressure increase / decrease torque difference ΔT, which is the difference between the first command torque T1 and the second command torque T2.

[0033] A case will be described in which the change trend of the command torque T changes from a decreasing trend to an increasing trend, as indicated by the second arrow V2 (V21, V22, V23) in FIG. 3 . As indicated by the second arrow V21, when the command torque T decreases, the pressing force P decreases along the first pressure reduction line L1r. Thereafter, as indicated by the second arrow V22, when the change trend of the command torque T changes from a decreasing trend to an increasing trend, the command torque T begins to increase. Here, the time when the change trend of the command torque T changes from a decreasing trend to an increasing trend is the first time point. In other words, the command torque T at the time when the change trend of the command torque T changes from a decreasing trend to an increasing trend is the first command torque T1 (T1r). As indicated by the second arrow V22, the pressing force P is maintained approximately constant for a while after the command torque T begins to increase. In other words, even if the command torque T increases, the pressing force P does not increase. Thereafter, as indicated by the second arrow V23, when the command torque T continues to increase, the pressing force P begins to increase along the first pressure reduction line L1a. Here, the time when the pressing force P starts to increase as the changing trend of the command torque T is maintained from the first time point is the second time point. That is, the command torque T at the time when the pressing force P starts to increase as the changing trend of the command torque T is maintained from the first time point is the second command torque T2 (T2a). Thus, the difference between the first command torque T1 (T1r) and the second command torque T2 (T2a) is the compression / decompression torque difference ΔT (ΔT2).

[0034] As shown in FIG. 3 , of the first command torques T1a and T1r, the first command torque T1a is the command torque T corresponding to the first pressurizing line L1a, and the first command torque T1r is the command torque T corresponding to the first depressurizing line L1r. Similarly, of the second command torques T2a and T2r, the second command torque T2a is the command torque T corresponding to the first pressurizing line L1a, and the second command torque T2r is the command torque T corresponding to the first depressurizing line L1r. Therefore, the first command torque T1a at a first time point when the command torque T changes from an increasing trend to a decreasing trend is referred to as the pressurizing-side first command torque T1a. The second command torque T2r at a second time point when the pressing force P begins to change as the command torque T continues to decrease from the first time point is referred to as the depressurizing-side second command torque T2r. Furthermore, the first command torque T1r at the first time point when the command torque T changes from a decreasing trend to an increasing trend is referred to as the depressurizing-side first command torque T1r. The second command torque T2a at the second time point when the pressing force P starts to change as the increasing trend of the command torque T is maintained from the first time point is referred to as the pressure-side second command torque T2a.

[0035] Then, every time the torque difference calculation unit 94 calculates the acceleration / decrease pressure torque difference ΔT, the torque difference calculation unit 94 associates the first command torque T1 and the second command torque T2 used in calculating the acceleration / decrease pressure torque difference ΔT with the acceleration / decrease pressure torque difference ΔT and stores them in the memory 92. For example, in the example shown in Fig. 3 , the compression-side first command torque T1a and the compression-side second command torque T2r with the compression / decrease pressure torque difference ΔT1 and are stored in the memory 92 in an associated state. Also, the compression-side first command torque T1r and the compression-side second command torque T2a with the compression / decrease pressure torque difference ΔT2 and are stored in the memory 92 in an associated state.

[0036] When the pressing force P changes, the friction material 120 moves in the forward direction X1 or the backward direction X2. In other words, when the pressing force P changes, the rotation angle of the electric motor 40 changes. Therefore, the torque difference calculation unit 94 determines that the pressing force P has changed when the rotation angle of the electric motor 40 fluctuates under conditions in which the command torque T is maintained to change. Therefore, the torque difference calculation unit 94 determines the second period based on the fluctuation in the rotation angle of the electric motor 40 under conditions in which the command torque T is maintained to change. As described above, the rotation angle of the electric motor 40 changes under the second period, and therefore a back electromotive force is generated under the second period. Therefore, the electric brake device 10 may determine the second period based on the back electromotive force under conditions in which the command torque T is maintained to change.

[0037] <Efficiency Estimation Unit> The efficiency estimation unit 95 estimates the efficiencies Ea and Er of the electric brake device 10 based on the relationship between the first command torque T1 or the second command torque T2 and the pressure increase / decrease torque difference ΔT.

[0038] Fig. 4 is a graph showing the relationship between the first command torque T1 and the second command torque T2 obtained by the torque difference calculation unit 94 and the compression / decompression torque difference ΔT. In Fig. 4, the line showing the relationship between the compression-side first command torque T1a and the compression-side second command torque T2a and the compression / decompression torque difference ΔT is referred to as a second compression line L2a. Also, the line showing the relationship between the compression-side first command torque T1r and the compression-side second command torque T2r and the compression / decompression torque difference ΔT is referred to as a second decompression line L2r.

[0039] The second pressurization line L2a is a straight line obtained by linearly approximating a plurality of plot data pieces showing the relationship between the first pressurization-side command torque T1a and the pressurization / depressurization torque difference ΔT1 and a plurality of plot data pieces showing the relationship between the second pressurization-side command torque T2a and the pressurization / depressurization torque difference ΔT2. The second pressurization line L2a can also be obtained from only the plurality of plot data pieces showing the relationship between the first pressurization-side command torque T1a and the pressurization / depressurization torque difference ΔT1. Similarly, the second pressurization line L2a can also be obtained from only the plurality of plot data pieces showing the relationship between the second pressurization-side command torque T2a and the pressurization / depressurization torque difference ΔT2.

[0040] The second pressure reduction line L2r is a straight line obtained by linearly approximating a plurality of plot data pieces showing the relationship between the pressure reduction-side first command torque T1r and the acceleration / deceleration torque difference ΔT2 and a plurality of plot data pieces showing the relationship between the pressure reduction-side second command torque T2r and the acceleration / deceleration torque difference ΔT1. The second pressure reduction line L2r can also be obtained from only the plurality of plot data pieces showing the relationship between the pressure reduction-side first command torque T1r and the acceleration / deceleration torque difference ΔT2. Similarly, the second pressure reduction line L2r can also be obtained from only the plurality of plot data pieces showing the relationship between the pressure reduction-side second command torque T2r and the acceleration / deceleration torque difference ΔT1.

[0041] In the following description, the gradient of the second pressurization line L2a is referred to as a pressurization gradient α, and the gradient of the second depressurization line L2r is referred to as a depressurization gradient β. The second pressurization line L2a and the second depressurization line L2r can be approximated by, for example, the least squares method.

[0042] 4, for the sake of simplicity, only one plot data showing the relationship between the first pressurizing-side command torque T1a and the pressurizing / depressurizing torque difference ΔT1 and one plot data showing the relationship between the second pressurizing-side command torque T2a and the pressurizing / depressurizing torque difference ΔT2 are shown. Similarly, only one plot data showing the relationship between the first pressure reduction-side command torque T1r and the pressurizing / depressurizing torque difference ΔT2 and one plot data showing the relationship between the second pressure reduction-side command torque T2r and the pressurizing / depressurizing torque difference ΔT1 are shown. Furthermore, since the multiple plot data actually obtained contain errors, it is highly unlikely that the multiple plot data will be aligned on a straight line without deviation.

[0043] As shown in Figure 5(a), in an electric braking device 10 with no mechanical loss, the command torque T required to obtain a predetermined pressing force P is defined as "Ti". On the other hand, in an electric braking device 10 with mechanical loss, the command torque T required to obtain a predetermined pressing force P when the command torque T increases is defined as "Ta", and the command torque T required to obtain a predetermined pressing force P when the command torque T decreases is defined as "Tr". Furthermore, the pressurization efficiency, which is the efficiency of the electric braking device 10 when the command torque T increases, is defined as "Ea", and the pressure reduction efficiency, which is the efficiency of the electric braking device 10 when the command torque T decreases, is defined as "Er". In this case, the pressurization efficiency Ea and the pressure reduction efficiency Er are defined as follows:

[0044] When the command torque T increases, the command torque Ta becomes larger than the command torque Ti in that it is necessary to increase the command torque T by an amount corresponding to the resistance force corresponding to the mechanical loss. At this point, the pressurization efficiency Ea becomes less than "1". The smaller the difference between the command torque Ta and the command torque Ti, that is, the smaller the command torque Ta, the higher the pressurization efficiency Ea. On the other hand, when the command torque T decreases, the command torque Tr becomes smaller than the command torque Ti in that it is necessary to decrease the command torque T by an amount corresponding to the resistance force corresponding to the mechanical loss. At this point, the pressure reduction efficiency Er becomes less than "1". The smaller the difference between the command torque Tr and the command torque Ti, that is, the larger the command torque Tr, the higher the pressure reduction efficiency Er.

[0045] As shown in FIG. 5A, when the command torque T is increasing, the proportional loss torque TLp proportional to the command torque T is the difference between the command torque Ti and the command torque Ta. Therefore, the pressurization efficiency Ea in (Equation 1) is the ratio of the command torque T (= Ta) to the difference (= Ti) between the command torque T (= Ta) and the proportional loss torque TLp (= Ta - Ti). Also, when the command torque T is decreasing, the proportional loss torque TLp proportional to the command torque T is the difference between the command torque Ti and the command torque Tr. Therefore, the pressure reduction efficiency Er in (Equation 2) is the ratio of the command torque T (= Tr) to the difference (= Ti) between the command torque T (= Tr) and the proportional loss torque TLp (= Ti - Tr).

[0046] In this respect, the proportional loss torque TLp can be said to be the difference between the command torque T in an ideal electric braking device 10 with no mechanical loss and the command torque T in an electric braking device 10 with mechanical loss, among the torques output by the electric motor 40 when a predetermined pressing force P is applied to the rotating body 110.

[0047] By multiplying the left sides of (Equation 1) and (Equation 2) together and multiplying the right sides together with an equal sign, the following equation can be obtained.

[0048] ​​As shown in Figure 5(b), the pressurization gradient α of the second pressurization line L2a is ΔT / Ta, the pressure reduction gradient β of the second pressure reduction line L2r is ΔT / Tr, and the pressurization / pressurization torque difference ΔT is Ta - Tr. Therefore, the pressurization gradient α and the pressure reduction gradient β can be expressed by the following equations.

[0049] Here, the pressurization efficiency Ea of a new electric braking device 10 is "Ean", the pressure reduction efficiency Er of a new electric braking device 10 is "Ern", and the coefficient of variation indicating the degree of aging for a new electric braking device 10 is "K". The coefficient of variation K of a new electric braking device 10 is "1", and the coefficient of variation K of the electric braking device 10 gradually decreases with age. The pressurization efficiency Ean and the pressure reduction efficiency Ern should be set based on the measured value of the pressing force P when the electric braking device 10 is manufactured. The pressurization efficiency Ea and the pressure reduction efficiency Er of the current electric braking device 10 can be expressed by the following equations.

[0050] By multiplying the left sides of (Equation 6) and (Equation 7) together and multiplying the right sides together with an equal sign, the following equation can be obtained.

[0051] By moving the coefficient of variation K of equation (8) to the left side, the following equation can be obtained.

[0052] By substituting the modified (Equation 4) or (Equation 5) into the numerator on the right side of (Equation 9), the following equation can be obtained.

[0053] As shown in (Equation 10), the coefficient of variation K is calculated from the pressurization efficiency Ean and pressure reduction efficiency Ern of a new electric braking device 10 and the pressurization gradient α. Also, as shown in (Equation 11), the coefficient of variation K is calculated from the pressurization efficiency Ean and pressure reduction efficiency Ern of a new electric braking device 10 and the pressure reduction gradient β.

[0054] ​​​​​Substituting (Equation 10) or (Equation 11) into (Equation 6) gives a formula for calculating the pressurization efficiency Ea of the electric braking device 10, based on the pressurization gradient α of the second pressurization line L2a and the pressurization efficiency Ean and pressure reduction efficiency Ern of a new electric braking device 10. Substituting (Equation 10) or (Equation 11) into (Equation 7) gives a formula for calculating the pressurization efficiency Ea of the electric braking device 10, based on the pressure reduction gradient β of the second pressure reduction line L2r and the pressurization efficiency Ean and pressure reduction efficiency Ern of a new electric braking device 10.

[0055] In this way, the efficiency estimator 95 estimates the coefficient of variation K of the electric brake device 10 based on the pressurization gradient α of the second pressurization line L2a and the pressurization efficiency Ean and pressure reduction efficiency Ern of a brand new electric brake device 10. Here, the efficiency estimator 95 calculates the pressurization gradient α based on the relationship between at least one of the first pressurization-side command torque T1a and the second pressurization-side command torque T2a and the pressurization / pressurization torque difference ΔT. More specifically, the efficiency estimator 95 calculates the pressurization gradient α based on at least one of the relationship between the first command torque T1a and the pressurization / pressurization torque difference ΔT1 when the change trend of the command torque T changes from an increasing trend to a decreasing trend, and the relationship between the second command torque T2a and the pressurization / pressurization torque difference ΔT2 when the change trend of the command torque T changes from a decreasing trend to an increasing trend.

[0056] On the other hand, the efficiency estimator 95 can also calculate the coefficient of variation K of the electric brake device 10 based on the pressure reduction gradient β of the second pressure reduction line L2a and the pressure increase efficiency Ean and pressure reduction efficiency Ern of a brand new electric brake device 10. Here, the efficiency estimator 95 calculates the pressure reduction gradient β based on the relationship between at least one of the pressure reduction-side first command torque T1r and the pressure reduction-side second command torque T2r and the pressure increase / decrease torque difference ΔT. More specifically, the efficiency estimator 95 calculates the pressure reduction gradient β based on at least one of the relationship between the first command torque T1r and the pressure increase / decrease torque difference ΔT2 when the change trend of the command torque T changes from a decreasing trend to an increasing trend, and the relationship between the second command torque T2r and the pressure increase / decrease torque difference ΔT1 when the change trend of the command torque T changes from an increasing trend to a decreasing trend.

[0057] In this way, the efficiency estimation unit 95 estimates at least one of the pressurization efficiency Ea and pressure reduction efficiency Er of the electric braking device 10 based on the estimated coefficient of variation K and at least one of the pressurization efficiency Ean and pressure reduction efficiency Ern of a new electric braking device 10.

[0058] <Constant Loss Calculation Section> The constant loss calculation section 96 calculates the constant loss torque TLc based on the first command torque T1 or the second command torque T2 and the pressure increase / decrease torque difference ΔT.

[0059] As described above, the loss torque TL includes the constant loss torque TLc that is not proportional to the magnitude of the torque To output by the electric motor 40. Therefore, as shown by the dashed-dotted line in FIG. 6A , when the command torque T is increased from "0," if the command torque T is less than the constant loss torque TLc, the friction material 120 does not move in the forward direction X1. In other words, if the command torque T is less than the constant loss torque TLc, the pressing force P becomes "0." If the command torque T becomes equal to or greater than the constant loss torque TLc, the friction material 120 moves in the forward direction X1. In other words, if the command torque T becomes equal to or greater than the constant loss torque TLc, the pressing force P increases as the command torque T increases.

[0060] On the other hand, as shown by the two-dot chain line in FIG. 6A , when the command torque T is decreased toward "0," the friction material 120 does not return to its initial position even when the command torque T becomes "0." In other words, even when the command torque T becomes "0," the pressing force P does not become "0." In this case, if the command torque T is decreased to a value having the same magnitude as the constant loss torque TLc but with a different positive and negative sign, the pressing force P becomes "0." In this embodiment, the constant loss torque TLc acts equally when the command torque T increases and decreases. In other words, the command torque T (= TLca) corresponding to the intercept of the horizontal axis of the first pressure increase line L1a in FIG. 6A is equal in magnitude to the constant loss torque TLc and is also equal in sign to the constant loss torque TLc. On the other hand, the command torque T (= TLcr) corresponding to the intercept of the horizontal axis of the first pressure decrease line L1r in FIG. 6A is equal in magnitude to the constant loss torque TLc but is also equal in sign to the constant loss torque TLc.

[0061] 6(b) shows the second pressurization line L2a and the second depressurization line L2r. The gradient of the second pressurization line L2a and its intercepts on the horizontal and vertical axes can be obtained simultaneously when determining the linear approximation of the second pressurization line L2a. Similarly, the gradient of the second depressurization line L2r and its intercepts on the horizontal and vertical axes can be obtained simultaneously when determining the linear approximation of the second depressurization line L2r.

[0062] If the command torque T corresponding to the intercept of the second pressurization line L2a and the second depressurization line L2r on the horizontal axis is defined as TLc0, the constant loss torque TLc can be expressed by the following equation. Note that (Equation 12) is a relational equation for the y coordinate at point Qa, and (Equation 13) is a relational equation for the y coordinate at point Qr. Also, as shown in FIG. 6(b), the torque TLc0 is the command torque T when the pressurization / depressurization torque difference ΔT becomes "0".

[0063] Since TLca = TLc, by replacing TLca with TLc in (Equation 12) and then rearranging the equation, we can obtain (Equation 14). Similarly, since TLcr = -TLc, by replacing TLcr with -TLc in (Equation 13) and then rearranging the equation, we can obtain (Equation 15).

[0064] In this way, the efficiency estimator 95 calculates the constant loss torque TLc based on the pressurization gradient α of the second pressurization line L2a and the torque TLc0 that is the intercept of the second pressurization line L2a on the horizontal axis. That is, the efficiency estimator 95 calculates the constant loss torque TLc based on the relationship between at least one of the pressurization-side first command torque T1a and the pressurization-side second command torque T2a and the pressurization / depressurization torque difference ΔT, and the torque TLc0. On the other hand, the efficiency estimator 95 calculates the constant loss torque TLc based on the pressure reduction gradient β of the second pressure reduction line L2r and the torque TLc0 that is the intercept of the second pressure reduction line L2r on the horizontal axis. That is, the efficiency estimator 95 calculates the constant loss torque TLc based on the relationship between at least one of the pressure reduction-side first command torque T1r and the pressure reduction-side second command torque T2r and the pressurization / depressurization torque difference ΔT, and the torque TLc0.

[0065] ​​The efficiency estimator 95 can also calculate the constant loss torque TLc based on the pressurization gradient α of the second pressurization line L2a and the intercept of the second pressurization line L2a on the vertical axis. Similarly, the efficiency estimator 95 can also calculate the constant loss torque TLc based on the pressure reduction gradient β of the second pressure reduction line L2r and the intercept of the second pressure reduction line L2r on the vertical axis.

[0066] <Correction Unit> The correction unit 97 corrects a pressing force-related value related to the pressing force P based on the efficiencies Ea, Er and the constant loss torque TLc of the electric brake device 10. For example, the correction unit 97 corrects the command torque T as an example of a pressing force-related value. Here, the command torque T calculated by the braking control unit 93 is referred to as the pre-correction command torque, and the command torque T corrected by the correction unit 97 is referred to as the post-correction command torque.

[0067] When the command torque T is on an increasing trend, the corrector 97 corrects the pre-correction command torque so that the post-correction command torque becomes larger as the pressure increase efficiency Ea of the electric brake device 10 becomes lower. Furthermore, the corrector 97 corrects the pre-correction command torque so that the post-correction command torque becomes larger as the constant loss torque TLc becomes larger. On the other hand, when the command torque T is on a decreasing trend, the corrector 97 corrects the pre-correction command torque so that the post-correction command torque becomes smaller as the pressure reduction efficiency Er of the electric brake device 10 becomes lower. Furthermore, the corrector 97 corrects the pre-correction command torque so that the post-correction command torque becomes smaller as the constant loss torque TLc becomes larger. Note that the corrector 97 may correct the command torque T using a predetermined map or a predetermined correction formula.

[0068] <Actions and Effects of the Present Embodiment> When a braking request is made for the vehicle, the electric braking device 10 is controlled based on the requested braking force. More specifically, the electric motor 40 of the electric braking device 10 is controlled based on a command torque T corresponding to the requested braking force. Then, the torque To output from the electric motor 40 is converted into a pressing force P of the friction material 120. In this way, the friction material 120 presses against the rotating body 110, generating a braking force on the wheel 100.

[0069] Because the electric braking device 10 has mechanical losses, when the torque To output by the electric motor 40 is converted into the pressing force P of the friction material 120, not all of the torque To output by the electric motor 40 is converted into the pressing force P of the friction material 120. Specifically, the electric motor 40 includes a proportional loss torque TLp and a constant loss torque TLc as the loss torque TL. In this regard, in the present embodiment, the electric braking device 10 corrects the command torque T calculated in accordance with the required braking force based on the efficiencies Ea and Er of the electric braking device 10 and the constant loss torque TLc. Therefore, the electric braking device 10 can prevent the braking force generated at the wheel 100 from being excessive or insufficient with respect to the required braking force. Furthermore, the electric braking device 10 can reduce the discrepancy between the braking force generated at the wheel 100 and the required braking force, compared to when the command torque T is corrected based on only one of the efficiencies Ea and Er of the electric braking device 10 or the constant loss torque TLc.

[0070] The electric braking device 10 estimates the current efficiencies Ea, Er of the electric braking device 10 based on the first command torque T1 or the second command torque T2 and the acceleration / deceleration torque difference ΔT. In other words, the electric braking device 10 can estimate the current efficiencies Ea, Er of the electric braking device 10 even without a sensor that detects the pressing force P of the friction material 120. Therefore, it is possible to inexpensively configure the electric braking device 10 that is capable of estimating the efficiencies Ea, Er.

[0071] The electric braking device 10 can achieve the following operational effects. (1) The second command torque T2 is the command torque T at the second time point when the pressing force P begins to change as the changing trend of the command torque T from the first time point is maintained. The electric braking device 10 determines the second time point based on fluctuations in the rotation angle of the electric motor 40. When the pressing force P is constant, the rotation angle of the electric motor 40 is constant, and when the pressing force P fluctuates, the rotation angle of the electric motor 40 fluctuates. Therefore, the electric braking device 10 can accurately determine the second time point after the changing trend of the command torque T from the first time point is maintained.

[0072] <Modifications> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0073] When the vehicle is stopped, the braking control device 90 may obtain the first command torque T1 and the second command torque T2 by increasing or decreasing the command torque T. In this case, the braking control device 90 can obtain the first command torque T1, the second command torque T2, and the acceleration / deceleration torque difference ΔT in a situation where the influence of external disturbances is small.

[0074] If the characteristics of the electric braking device 10 change excessively over time, the pressurization efficiency Ea or the pressure reduction efficiency Er may decrease excessively. Therefore, if the pressurization efficiency Ea or the pressure reduction efficiency Er decreases below a predetermined efficiency determination value, the brake control device 90 may issue a notification to the vehicle user or the like to urge the user to repair or replace the electric braking device 10. Here, the efficiency determination value to be compared with the pressurization efficiency Ea and the efficiency determination value to be compared with the pressure reduction efficiency Er may be different values.

[0075] When the command torque T is small, the proportion of the constant loss torque TLc in the loss torque TL is more likely to be higher than the proportion of the proportional loss torque TLp in the loss torque TL than when the command torque T is large. Therefore, when the command torque T is less than a predetermined torque determination value, the braking control device 90 may correct the pressing force-related value by taking into account only the constant loss torque TLc of the loss torque TL.

[0076] Similarly, when the command torque T is large, the proportion of the proportional loss torque TLp in the loss torque TL is more likely to be higher than the proportion of the constant loss torque TLc in the loss torque TL than when the command torque T is small. Therefore, when the command torque T is equal to or greater than a predetermined torque determination value, the brake control device 90 may correct the pressing force-related value based only on the proportional loss torque TLp of the loss torque TL. In other words, when the command torque T is equal to or greater than the predetermined torque determination value, the brake control device 90 may correct the pressing force-related value based only on the efficiencies Ea and Er of the electric brake device 10.

[0077] The braking control device 90 may correct the command torque T without taking the constant loss torque TLc into consideration. In other words, the braking control device 90 may include a correction unit 97 that corrects the pressing force-related value, which is a value related to the pressing force, based only on the efficiencies Ea and Er of the electric braking device 10.

[0078] As shown in (Equation 10) and (Equation 11), the coefficient of variation K can be calculated using the pressurization gradient α or the depressurization gradient β. As shown in (Equation 14) and (Equation 15), the constant loss torque TLc can be calculated using the pressurization gradient α or the depressurization gradient β. Therefore, the brake control device 90 can correct the pressing force-related value if it can obtain the pressurization gradient α or the depressurization gradient β. Here, as shown in FIG. 4 , the pressurization-side command torque T (T1a, T2a) corresponding to the same magnitude of the pressurization / depressurization torque difference ΔT is larger than the depressurization-side command torque T (T1r, T2r). The larger the value of the command torque T, the larger the ratio of the magnitude of the command torque T to the disturbance. Therefore, the brake control device 90 can more accurately correct the pressing force-related value by using the pressurization gradient α.

[0079] A change in the pressing force P applied to the rotating body 110 causes a change in the acceleration of the vehicle. Therefore, while the vehicle is traveling, the electric brake device 10 may determine, based on the acceleration of the vehicle, a second time point at which the pressing force P applied to the rotating body 110 begins to change as a result of the command torque T maintaining its tendency of change from the first time point.

[0080] The pressing force-related value may be a value related to the pressing force P separate from the command torque T. For example, the pressing force-related value may be an estimated value of the pressing force P. In this case, the brake control device 90 may estimate the estimated value of the pressing force P of the current electric braking device 10 based on the estimated value of the pressing force P of a new electric braking device 10 and the efficiencies Ea and Er of the electric braking device 10.

[0081] The linear motion conversion mechanism can be replaced with a mechanism in which the nut 62 functions as the "rotating part" and the screw shaft 61 functions as the "linear motion part." The electric braking device 10 may be equipped with an axial force sensor that can detect the pressing force P. The braking control device 90 may then calculate the efficiencies Ea, Er of the electric braking device 10 based on the command torque T and the detection results of the axial force sensor. In this case, the electric braking device 10 may determine whether the efficiencies Ea, Er based on the detection results of the axial force sensor are appropriate by comparing the efficiencies Ea, Er based on the detection results of the axial force sensor with the efficiencies Ea, Er based on the compression / decompression torque difference ΔT.

[0082] The electric braking device 10 may be a wet-type electric braking device that generates a braking force on the wheel 100 by supplying brake fluid to a wheel cylinder in accordance with the forward movement of the piston 70 .

[0083] The electric braking device 10 does not have to be a caliper-type disc brake device as long as it is equipped with the linear motion conversion mechanism 60 having the nut 62 and the screw shaft 61. For example, the electric braking device 10 may be a drum-type electric braking device.

[0084] The braking control device 90 is not limited to a processing circuit that includes a CPU 91 and a memory 92 and executes software processing. For example, the braking control device 90 may include a dedicated hardware circuit that executes at least some of the various processes executed in the above-described embodiment. An example of a dedicated hardware circuit is an ASIC. ASIC is an abbreviation for "Application Specific Integrated Circuit." In other words, the braking control device 90 may have any one of the following configurations (a) to (c):

[0085] (a) A processing circuit comprising a processing device that executes all of the above processes according to a program and a program storage device such as memory 92 that stores the program. (b) A processing circuit comprising a processing device and program storage device that executes part of the above processes according to a program, and a dedicated hardware circuit that executes the remaining processes.

[0086] (c) A processing circuit comprising dedicated hardware circuits for executing all of the above processes, wherein the software execution device comprising a processing device and a program storage device, and the dedicated hardware circuits may be plural.

Claims

1. An electric braking device in which a rotating part of a linear motion conversion mechanism rotates in response to the rotational motion of an electric motor, the rotational motion of the rotating part is converted into linear motion in a forward or backward direction of a linear motion part of the linear motion conversion mechanism, and a braking force can be applied to a vehicle wheel by pressing a friction material against a rotating body that rotates together with the wheel in response to the linear motion of the linear motion part, the electric braking device comprising: a torque difference calculation unit that calculates a compression / decompression torque difference that is the difference between a first command torque, which is a command value of torque for the electric motor, at a first time point when the change trend of the command torque changes from one of an increasing trend and a decreasing trend to the other, and a second command torque, which is the command torque at a second time point when the change trend of the command torque from the first time point is maintained and the pressing force applied to the rotating body begins to change; and an efficiency estimation unit that estimates the efficiency of the electric braking device, which is the ratio between the command torque and a difference between the command torque and a proportional loss torque that increases as the command torque increases, based on the first command torque or the second command torque and the compression / decompression torque difference, The proportional loss torque is a difference between the command torque in an ideal electric braking device with no mechanical loss and the command torque in the electric braking device with mechanical loss, among the torque output by the electric motor when a predetermined pressing force is applied to the rotating body.

2. The electric braking device according to claim 1, wherein the torque difference calculation unit determines the second time period based on a fluctuation in the rotation angle of the electric motor.

3. The electric braking device according to claim 1, wherein the efficiency estimation unit estimates the efficiency of the electric braking device based on at least one of: a pressurization gradient, which is the gradient of a linear approximation calculated from at least one of the relationship between the first command torque and the pressurization / depressurization torque difference when the change trend of the command torque changes from an increasing trend to a decreasing trend, and the relationship between the second command torque and the pressurization / depressurization torque difference when the change trend of the command torque changes from a decreasing trend to an increasing trend; and a depressurization gradient, which is the gradient of a linear approximation calculated from at least one of the relationship between the first command torque and the pressurization / depressurization torque difference when the change trend of the command torque changes from a decreasing trend to an increasing trend, and the relationship between the second command torque and the pressurization / depressurization torque difference when the change trend of the command torque changes from an increasing trend to a decreasing trend.

4. An electric braking device as claimed in any one of claims 1 to 3, further comprising a constant loss calculation unit that calculates the constant loss torque based on the first command torque or the second command torque and the acceleration / depressurization torque difference, and further comprising: a constant loss calculation unit that calculates the constant loss torque based on the first command torque or the second command torque and the acceleration / depressurization torque difference.

5. The electric braking device according to claim 4, further comprising a correction unit that corrects a pressing force related value, which is a value related to the pressing force, based on at least one of the efficiency of the electric braking device and the constant torque loss.

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