Electric brake device

Abstract

To provide an electric brake device which requires no prior measurement, supports a change over time, and is capable of calculating a thrust conversion ratio with respect to current, regardless of a mechanical structure.SOLUTION: An electric brake device includes: an electric motor 8; a piston 6 moving as the electric motor 8 rotates; brake pads 5a, 5b pressing a disc rotor 2 by thrust generated by movements of the piston 6; and a motor control device 11 for controlling rotation of the electric motor 8. The motor control device 11 is provided with an efficiency estimation unit 35 which estimates relations between current to be supplied to the electric motor 8 and the thrust on the basis of an increase in current value of the electric motor 8 with respect to an increase in position of the piston 6 and the current value of the electric motor 8.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electric brake device used for braking a vehicle. [Background technology]

[0002] In an electric brake device, it is necessary to estimate pad thrust to control braking force. Although it is possible to estimate pad thrust using a thrust sensor, this increases costs. If pad thrust could be estimated without using a thrust sensor, costs could be reduced. For example, technologies described in Patent Documents 1 and 2 have been proposed as technologies for estimating pad thrust without using a thrust sensor.

[0003] Patent Document 1 discloses a technique for estimating mechanical efficiency based on the motor current ratio during forward and reverse operation of a power transmission mechanism having a self-locking function part that is not prone to reverse operation.

[0004] Furthermore, Patent Document 2 discloses a technology in which the voltage and current values of an electric motor are measured multiple times during a current decrease section leading to a constant current section where the current becomes approximately constant, and calculations are performed from the multiple measured voltage and current values to estimate estimated parameters to be used in a cutoff current threshold calculation unit, and these estimated parameters are used to calculate a cutoff current threshold by the cutoff current threshold calculation unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-57065 A [Patent Document 2] Japanese Patent Application Publication No. 2018-118524 Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology described in Patent Document 1, the rotary / linear motion conversion mechanism uses a sliding screw and is limited to a configuration with a self-locking function. While it is possible to estimate the efficiency of this type of rotary / linear motion part, it is not possible to estimate the efficiency of the reducer part, etc., which can make it difficult to estimate the overall efficiency.

[0007] Furthermore, the technology described in Patent Document 2 has the problem that it is necessary to measure the characteristics of each individual device in advance, and that accuracy deteriorates when the brake pads change over time due to wear or other reasons.

[0008] An object of the present invention is to provide an electric brake device that can calculate the conversion ratio of thrust to current regardless of the mechanical configuration, without requiring prior measurement, and in response to changes over time. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides an electric brake device comprising an electric motor, a linear motion part that moves due to the rotation of the electric motor, brake pads that press a disc rotor that rotates together with a wheel with thrust generated by the movement of the linear motion part, and a motor control device that controls the rotation of the electric motor, wherein the motor control device comprises an efficiency estimation part that estimates the relationship between the current supplied to the electric motor and the thrust, based on the relationship between the increase in the current value of the electric motor in response to an increase in the position of the linear motion part and the current value of the electric motor. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an electric brake device that can calculate the conversion ratio of thrust to current regardless of the mechanical configuration, without requiring prior measurement, and in response to changes over time. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of an electric brake device according to a first embodiment of the present invention. [Figure 2]1 is a control block diagram of an electric brake device according to a first embodiment of the present invention. [Figure 3] 10 is a diagram showing the relationship between the motor current value I and the motor current value I differentiated with respect to the piston position x according to the first embodiment of the present invention. FIG. [Figure 4] FIG. 4 is a diagram showing the relationship between the piston position and the brake pad thrust force according to the first embodiment of the present invention. [Figure 5] FIG. 4 is a diagram showing the relationship between the brake pad thrust force and the position differential of the brake pad thrust force according to the first embodiment of the present invention. [Figure 6] FIG. 4 is a diagram showing the relationship between a current value from which a no-load current has been removed and a position derivative of the current according to the first embodiment of the present invention. [Figure 7] FIG. 6 is a control block diagram of an electric brake device according to a second embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing the relationship between the piston position and the motor current value required for the brake pad thrust force according to the second embodiment of the present invention. [Figure 9] FIG. 11 is a diagram showing the relationship between the brake pad thrust force and the position differential of the brake pad thrust force according to the third embodiment of the present invention. [Figure 10] FIG. 10 is a diagram showing the relationship between the brake pad thrust force and the position differential of the brake pad thrust force according to Example 4 of the present invention. [Figure 11] 10 is a diagram showing the relationship between the motor current value I minus the no-load current value I0 and its position derivative. FIG. [Figure 12] FIG. 10 is a control block diagram of an electric brake device according to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that substantially the same or similar components are designated by the same reference numerals, and where explanations are redundant, redundant explanations may be omitted. [Example]

[0013] First, an electric brake device according to a first embodiment will be described. Fig. 1 is a schematic diagram of the electric brake device according to the first embodiment of the present invention. Fig. 2 is a control block diagram of the electric brake device according to the first embodiment of the present invention.

[0014] Generally, a vehicle such as an automobile is composed of four wheels, one each for the front and rear wheels, and a brake device is installed on each wheel. As shown in Fig. 1, the brake device 1 is composed of a housing 4 supported on a carrier (not shown) fixed to a non-rotating part of the vehicle located inside the vehicle of the disc rotor 2 (rotating member) so as to be able to float in the axial direction of the disc rotor 2, brake pads 5a, 5b (pressing members) arranged on both the left and right sides of the disc rotor 2, a piston 6 movable linearly within the housing 4, and an electric motor 8 that drives the piston 6. The electric motor 8 applies thrust to the brake pads 5a, 5b via a rotary-to-linear motion conversion mechanism 10 and the piston 6, and the brake pads 5a, 5b press the disc rotor 2, which rotates together with the wheel, from the left and right, applying a braking force by squeezing it together (pad thrust).

[0015] The output shaft of the electric motor 8 is connected to a reducer 9, and the output shaft of the reducer 9 is connected to a rotary-to-linear motion conversion mechanism 10, which enables the piston 6 to move in the linear motion direction.

[0016] In the first embodiment, the brake caliper 3 is made up of the disc rotor 2, the housing 4, the brake pads 5a, 5b, the piston 6, the electric motor 8, the reducer 9, and the rotary-to-linear motion conversion mechanism 10. The rotary-to-linear motion conversion mechanism 10 and the piston 6 make up a linear motion part.

[0017] The electric motor 8 is connected to a motor control device 11 (controller) by an electric wire 12. The rotation of the electric motor 8 is controlled by the motor control device 11. In FIG. 1, the electric motor 8 and the motor control device 11 are shown as separate entities, but they may also be configured as an integrated unit. As shown in FIG. 2, the electric motor 8 is also provided with a current detection unit 31 that detects the current when the motor is driven, and a motor position detection unit 32.

[0018] The motor control device 11 receives a braking force command Fr from a higher-level control device (vehicle control ECU) or the like, and provides a current command to the electric motor 8 based on a preset control program or the like, which is based on the detection value of the current detection unit 31 and the detection value of the motor position detection unit 32.

[0019] A control signal line 21 and communication lines 22 and 23 are connected to the motor control device 11. The control signal line 21 inputs control commands from a higher-level control device such as a vehicle control ECU (Electronic Control Unit) to the motor control device 11. The communication lines 22 and 23 communicate information other than the control commands with the higher-level control device. Note that although the higher-level control device and the motor control device 11 are shown here as being separately located, they may also be integrated into a single control device.

[0020] The calculation method of the motor control device 11 is shown in Figure 2. When a brake thrust command Fr (brake force) is given from a higher-level control device via control signal line 21, it is converted into a current command value by brake pad thrust-current command converter 34, and the current command value is output to current control unit 33. In current control unit 33, the motor current value of electric motor 8 detected by current detection unit 31 is fed back, a motor operation command value, which is a supply current value, is calculated, and a current based on the electric motor operation command value is supplied to electric motor 8. Here, brake pad thrust-current command converter 34 uses a value that is updated each time the brake pad thrust / current coefficient (current-thrust conversion ratio) estimated by efficiency estimator 35 is estimated.

[0021] Next, the method of calculating the current-thrust conversion ratio in the efficiency estimation unit 35 will be described below. This is calculated by performing a current-thrust conversion ratio calculation operation. The current-thrust conversion ratio calculation operation issues a command to the motor control device 11 in a direction to further increase the brake pad thrust when the brake pad thrust F is a sufficiently large value (a state estimated to be larger than the brake pad thrust F1 described below). For example, this operation is performed when the vehicle is parked and a sufficient brake pad thrust is being applied (brake pad thrust F2) and the force is to be further increased (at the time of application). As a result, the electric motor 8 operates in the force-increasing direction (apply direction), and the brake pad thrust and current value increase.

[0022] The current detection unit 31 detects a motor current value (for example, a current of the q-axis component corresponding to torque) that is a current that actually flows to the electric motor 8. When using the motor current value, it is desirable to use one that has been filtered to remove noise components.

[0023] The motor current value I detected by current detection unit 31 and the motor position detection value detected by motor position detection unit 32 are input to efficiency estimator 35 and stored in a buffer. From the data stored in this buffer, the motor current value I and the motor current value I differentiated with respect to the piston position x are shown in Figure 3.

[0024] FIG. 3 is a diagram showing the relationship between the motor current value I and the motor current value I differentiated with respect to the piston position x according to the first embodiment of the present invention.

[0025] 3, the horizontal axis represents motor current value I, and the vertical axis represents value ΔI / Δx obtained by differentiating motor current value I with respect to piston position. Note that piston position x can be calculated using the reduction ratio and rotation-to-linear ratio from the motor position obtained by motor position detection unit 32. Piston position x may also be detected directly using a sensor.

[0026] At this time, when the current-thrust conversion ratio is low, it is detected as shown by solid line 55, and when the current-thrust conversion ratio is high, it is detected as shown by solid line 56. From this, approximate lines shown by dotted lines 55A and 56A are calculated.

[0027] The approximate straight line can be expressed by the following formula.

[0028] dI / dx=A×I+C …(1) The slope A and intercept C can be determined from equation (1). Although the device was not operated in the low thrust range, when the current-to-thrust conversion ratio is low, the curve is indicated by a dotted line, such as dotted line 55B when the brake pads are new, and dotted line 55C when the brake pads are worn. Similarly, when the power-to-thrust conversion ratio is high, the curve is indicated by a dotted line, such as curve 56B when the brake pads are new, and dotted line 56C when the brake pads are worn.

[0029] The relationship (rigidity) between the piston position x and the brake pad thrust F varies depending on the wear state of the brake pad, but generally has the relationship shown in Figure 4.

[0030] 4 is a diagram showing the relationship between the piston position and the brake pad thrust force according to Example 1 of the present invention. In Fig. 4, the vertical axis represents the brake pad thrust force F, and the horizontal axis represents the piston position x.

[0031] In the low thrust region (F1 or less), when the brake pads are new 41, the brake pad thrust F increases slowly (low rigidity) relative to the motor rotation position at first, and then increases sharply (high rigidity) as the wear progresses to a state of wear 42 and a state of heavy wear 43.

[0032] However, in the high-thrust region (F1 or higher) of the brake pad thrust F, a range appears where the upward trend is almost constant. Note that the point where the piston position x on the horizontal axis is 0 indicates the point where the brake pad thrust F increases.

[0033] Based on this relationship, Figure 5 shows the brake pad thrust force F on the horizontal axis and the brake pad thrust force F differentiated with respect to the piston position x (thrust gradient) on the vertical axis. In Figure 5, 51 indicates a new brake pad, 52 indicates a brake pad in the middle of wear, and 53 indicates a brake pad with significant wear. Therefore, in the region where the brake pad thrust force F is F1 or greater, the relationship expressed by approximate line 54 of approximate equation (2) is expressed regardless of the state of wear.

[0034] dF / dx=a×F+b …(2) Here, F is the brake pad thrust, x is the piston stroke, a is the proportionality coefficient, and b is the intercept. This relationship can be determined in advance by measurement or calculation. Although not shown here, when the disc rotor 2 is tilted, the characteristics will similarly differ depending on the tilt of the disc rotor 2 in the low thrust range, but in the high thrust range, they will follow an approximation equation for the same thrust gradient.

[0035] Furthermore, when operating at a constant speed, the brake pad thrust force F and the motor current value I are generally related by equation (3).

[0036] F+F0=η×g×K×Kt×I …(3) Here, η is efficiency, g is reduction ratio, K is rotation-to-linear conversion ratio (for example, 2×π / L if the lead is L), and Kt is torque constant. Substituting this into equation (3), we get equation (4).

[0037] F+F0=α×I …(4) α is a current-thrust conversion ratio that includes factors such as reduction ratio, rotary-to-linear conversion ratio, efficiency, and torque constant.

[0038] Differentiating equation (4) gives equation (5).

[0039] dF / dx=α×dI / dx …(5) Substituting equations (5) and (4) into equation (2) gives equation (6).

[0040] α×dI / dx=a×(α×I-F0)+b …(6) Furthermore, equation (6) can be transformed to equation (7).

[0041] dI / dx=a×I+b / α-a×F0 / α …(7) If we ignore the friction F0, we get equation (8).

[0042] dI / dx=a×I+b / α …(8) Comparing the intercepts of equations (1) and (8) obtained in the current-thrust conversion ratio calculation operation results in equation (9), from which the current-thrust conversion ratio α can be found.

[0043] α=b / C …(9) In this study, friction F0 was ignored. However, if a certain value is set assuming that the frictional force does not change significantly, the current-thrust conversion ratio α can be calculated more accurately from equations (1) and (7) as equation (10).

[0044] α=(ba×F0) / C …(10) It should be noted that a no-load current estimation unit 46 may be provided to take friction F0 into consideration. The no-load current estimation unit 46 performs operation in the force increasing or decreasing direction when the brake pads 5a, 5b are not in contact with the disc rotor 2 and there is a gap, and the current that flows at this time is the no-load current value I0, which satisfies the relationship of the following equation (11).

[0045] F0=α×I0 …(11) Here, the friction F0 includes all friction that occurs between the electric motor 8 and the piston 6, and is converted into a value for the linear motion part. Since the friction F0 also includes a viscous term that is a function of speed, it is preferable to obtain this function in advance, or to operate the motor at multiple constant rotation speeds v and obtain it in advance as the no-load current value I0(v).

[0046] By using this no-load current value I0, the relationship shown in Figure 6 can be derived for the value obtained by subtracting the no-load current value I0 from the motor current value I and its position derivative in the current-thrust conversion ratio calculation operation. Accuracy can be further improved by using the no-load current value I0 as a value that takes into account the operating speed when calculating the current-thrust conversion ratio. When the current-thrust conversion ratio is low, it is detected as shown by the solid line 65, and when the current-thrust conversion ratio is high, it is detected as shown by the solid line 66. From this, the following approximate equation (12) can be obtained.

[0047] dI / dx=A×(I-I0)+C …(12) On the other hand, equation (4) is F = α × (I - I0) ... (13) and substituting equation (13) and the position differential of equation (13) into equation (2) and rearranging, we obtain equation (14).

[0048] dI / dx=a×(I-I0)+b / α …(14) From the above, by comparing equations (12) and (14), the current-thrust conversion ratio α can be obtained as equation (15).

[0049] α=b / C …(15) A similar operation may also be performed in the direction of reducing the thrust. For example, this operation is performed when the vehicle is parked and sufficient brake pad thrust is being applied (brake pad thrust F2) and the brake thrust is to be reduced (released). This causes the electric motor 8 to operate in the direction of reduction (release direction), reducing the brake pad thrust and current value. A similar relationship can be obtained, but since forward efficiency and reverse efficiency generally do not coincide, the current-thrust conversion ratio αr at the time of release is obtained.

[0050] Next, the thrust control method will be explained. When braking force is to be generated, the brake pad thrust-current command conversion unit 34 has calculated the current thrust conversion ratio α for the brake thrust command Fr, so by converting this into a current command Ir using equation (16) and providing the current command to the electric motor 8, thrust control becomes possible.

[0051] Ir = Fr / α + I0 …(16) The no-load current value I0 can be estimated by the no-load current estimation unit 46. In this case, the current control unit 33 can further improve accuracy by feeding back the detected motor current value I.

[0052] As described above, in the first embodiment, an efficiency estimation unit is provided that estimates the relationship between the current supplied to the electric motor and the thrust force based on the relationship between the increase in the current value of the electric motor in response to an increase in the position of the linear motion part and the current value of the electric motor.

[0053] According to the first embodiment, the brake pad thrust can be estimated without using a thrust sensor, and the brake pad thrust can be controlled at low cost and with high precision. [Example]

[0054] Next, a description will be given of a second embodiment of the present invention. Fig. 7 is a control block diagram of an electric brake device according to the second embodiment of the present invention.

[0055] In the second embodiment, a brake pad thrust-position command conversion unit 36 and a position current control unit 37 are provided, and the brake pad thrust-position command conversion unit 36 outputs a position command to the position current control unit 37 based on a signal from the stiffness table update unit 39.

[0056] The position current control unit 37 feeds back the position information obtained from the motor position detection unit 32 based on the position command and the current value of the electric motor 8 obtained from the current detection unit 31, and a current command is given to the electric motor 8.

[0057] Here, the stiffness table update unit 39 updates the stiffness table based on the current-position conversion processing unit 40 and the efficiency estimation unit 35 .

[0058] During braking, the current-position conversion processing unit 40 filters out noise components from the motor current value I detected by the current detection unit 31, and calculates the current required for the brake pad thrust, from which currents due to acceleration and friction have been removed, using the motor rotational position, motor speed, and motor acceleration obtained from the motor position detection unit 32. The relationship between this current and the motor position is tabulated as a stiffness table. The current due to friction is estimated by the no-load current estimation unit 46.

[0059] From this result, the relationship shown in Figure 8 is obtained. Figure 8 is a diagram showing the relationship between piston position and motor current value required for brake pad thrust according to Example 2 of the present invention. The vertical axis represents motor current value I required for brake pad thrust, and the horizontal axis represents piston position x. Depending on the state of wear, the calculated relationship is 71 for new brake pads, 72 for moderately worn brake pads, and 73 for heavily worn brake pads.

[0060] Moreover, the efficiency estimation unit 35 calculates the current-thrust conversion ratio in the same manner as in the first embodiment.

[0061] Since the current-position relationship has been determined as a table by the current-position conversion processing unit 40, the rigidity table update unit 39 can calculate the relationship in the rigidity table (thrust-position) by multiplying the current by the current-thrust conversion ratio determined by the efficiency estimation unit, and updates the data in the rigidity table as needed.

[0062] When a brake pad thrust force-position command conversion unit 36 receives a brake thrust force command Fr (brake force), it converts it into a motor position command by referring to the stiffness table stored in a stiffness table update unit 39. A position current control unit 37 feeds back the motor current value I and the motor position (speed, acceleration) based on the motor position command, and outputs an operation command to the electric motor 8.

[0063] According to the second embodiment, by using the stiffness table without directly feeding back the current during thrust control, control can be performed using position detection values with less noise, and more accurate thrust control becomes possible. [Example]

[0064] Next, a third embodiment will be described with reference to Fig. 9. In the third embodiment, the efficiency calculation method in the efficiency estimating unit 35 is different from that in the first embodiment.

[0065] In the first embodiment, the relationship between the piston stroke and the brake pad thrust (rigidity) is a linear relationship regardless of wear, but the third embodiment shows a case where this relationship is different.

[0066] The rigidity of the brake caliper 3 is determined by the rigidity of the housing 4, the rotary-to-linear motion conversion mechanism 10, the brake pads 5a and 5b, etc. However, depending on the relationship between the rigidities, the brake pads 5a and 5b have an effect even in the high thrust region, and if the wear of the brake pads 5a and 5b is different, it may not be possible to assume that the approximate formula for rigidity does not change in the high thrust region.

[0067] For example, the relationship between the brake pad thrust force F and the position derivative ΔF / Δx of the brake pad thrust F may be as shown in Fig. 9. That is, unlike Example 1, in the high thrust region, the stiffness of a new brake pad is low (curve 63), and as wear progresses, the relationship becomes as shown in the curves of moderate wear (curve 62) and heavy wear (curve 61). In this case, it is assumed that a linear relationship is obtained in the high thrust region, and that these relationships are stored in advance for each amount of brake pad wear.

[0068] That is, it is assumed that the brake pad thrust F is equal to or greater than F1 and the relationship of equation (17) holds.

[0069] dF / dx=a(w)×F+b(w) …(17) w represents the amount of wear. For example, the greater the amount of wear, the greater the rigidity of both a(w) and b(w).

[0070] Except that a and b are functions of the amount of wear, the relationship of the following equation (18) is obtained, similar to that of Example 1.

[0071] dI / dx=a(w)×I+b(w) / α …(18) Furthermore, by using the no-load current value I0 as in the first embodiment, the current-to-thrust conversion ratio calculation operation can derive the relationship shown in FIG. 11 regarding the value obtained by subtracting the no-load current value I0 from the motor current value I and its position derivative. Accuracy can be further improved by using the no-load current value I0 as a value that takes into account the operating speed when calculating the current-to-thrust conversion ratio. When the current-to-thrust conversion ratio is low, it is detected as shown by the solid line 65, and when the current-to-thrust conversion ratio is high, it is detected as shown by the solid line 66. From this, the following approximate formula (19) can be obtained. dI / dx=A×(I-I0)+C …(19) Comparing equations (18) and (19) yields equation (20), which allows the amount of brake pad wear w to be determined.

[0072] a(w)=A …(20) Also, equation (21) b(w) / α=C …(21) By converting this, it is possible to derive the current thrust conversion ratio α as α=b(w) / C.

[0073] Although the equation (17) is a linear equation, it may be approximated by other functions. For example, it may be approximated by the equation (22).

[0074] dF / dx=a(w)×F^n+b(w) …(22) Here, when the position differential of equation (13) is substituted into equation (13), equation (23) is obtained.

[0075] dI / dx=a(w)×α^(n-1)×(I-I0)^n+b(w) / α …(23) On the other hand, in the current thrust conversion ratio calculation operation, the relationship of equation (24) is obtained.

[0076] dI / dx=A×(I-I0)^n+C …(24) Comparing the coefficients, we obtain equations (25) and (26).

[0077] A = a(w) × α^(n-1) …(25) C=b(w) / α …(26) The current-thrust conversion ratio α and the wear amount w can be calculated from equations (25), (26), and the fact that a(w) and b(w) are functions of the wear amount w.

[0078] Although an example using an exponential function is shown here, there is no limitation to the form of the function, and in some cases, it is also possible to grasp the relationship between dF / dx and F in a table.

[0079] This embodiment relates to a method for calculating the efficiency of the efficiency estimating unit 35, and the control method using the efficiency estimating unit 35 is the same as in the first and second embodiments.

[0080] According to this embodiment, even in an electric brake in which the amount of stiffness change varies depending on the amount of wear of the brake pads in the high thrust range, it is possible to derive the current-thrust conversion ratio without a thrust sensor, and it is also possible to perform high-precision thrust control taking into account the amount of wear of the brake pads.

[0081] In addition, in this embodiment, since the wear state of the brake pads can also be estimated, it is also possible to provide information such as when to replace the brake pads. [Example]

[0082] Next, a fourth embodiment will be described with reference to Fig. 10. In the fourth embodiment, the efficiency estimation method in the efficiency estimation unit 35 is different from that in the first embodiment.

[0083] In the fourth embodiment, as shown in FIG. 10, an example is shown in which the relationship between dF / dx and F has more generalized characteristics in which the slope changes depending on F.

[0084] In this case too, it is assumed that the relationship between dF / dx and F is known in advance. This gives the relationship ΔF / Δx=a(w)×F+b(w) at a specific brake pad thrust Fa (dotted line in FIG. 10).

[0085] In this case, the relationship of the following equation (27) is obtained at a specific brake pad thrust force Fa, as in the first embodiment.

[0086] dI / dx=a(w)×I+b(w) / α …(27) Furthermore, by performing the same current-thrust conversion ratio calculation operation as in the first embodiment, the relationship in equation (28) is obtained at a certain motor current value I (dotted line in FIG. 11).

[0087] dI / dx=A×(I-I0)+C …(28) At this time, it is sufficient to know the current value I of the brake pad thrust force Fa, but since it is unknown at this point, from the provisional conversion ratio αT (for example, using the nominal value or the α calculated previously), I=Fa / αT Find A and C in this case.

[0088] From the above, by comparing equations (27) and (28), the amount of brake pad wear w can be determined from equation (29).

[0089] a(w)=A …(29) Also, equation (30) b(w) / α=C …(30) is converted to α=b(w) / C, and the current-thrust conversion ratio α can be derived.

[0090] Here, this value may be set as the current thrust conversion ratio α, but this estimated value is set as αb, and furthermore, the motor current value I at Fa is again found by equation (31).

[0091] I=Fa / αb …(31) Equation (28) is recalculated using the motor current value I calculated here.

[0092] dI / dx=A×(I-I0)+C …(32) By comparing the coefficients again, the following equation can be obtained, similar to equations (29) and (30).

[0093] a(w)=A …(33) b(w) / α=C …(34) Then, by converting equation (34) to α=b(w) / C, the current-thrust conversion ratio α can be derived.

[0094] By repeating this once or several times, α can be converged, making it possible to calculate the current-thrust conversion ratio α.

[0095] In the fourth embodiment, the efficiency estimation unit estimates the relationship between the current supplied to the electric motor 8 and the thrust force based on the relationship between the increase in the electric motor current value I in response to an increase in the position of the linear motion part at the expected current value that generates a specific thrust force (a current value calculated from a specific thrust force using a value that estimates or assumes the relationship between the current and thrust force in advance) and the electric motor current value I.

[0096] By performing the calculation as described above, it is possible to convert the current-thrust conversion ratio α even for stiffness with characteristics in which ΔF / Δx changes depending on the thrust. [Example]

[0097] Next, a fifth embodiment will be described. In the fifth embodiment, an example will be described in which the temperature of the brake device 1 is used when the efficiency estimation unit 35 estimates the efficiency. When the temperature of the brake pads 5a and 5b changes, the stiffness of the brake pads changes.

[0098] Therefore, if there is a linear relationship above brake pad thrust F1, as in Example 1, the relationship between brake pad thrust F and the position derivative obtained by differentiating the brake pad thrust with respect to the piston position can be expressed as shown in Equation (35), where the slope a and intercept b are functions of temperature.

[0099] dF / dx=a(T)×F+b(T) …(35) On the other hand, the brake pad temperature in the current-thrust conversion ratio calculation operation is set to Tp1. This Tp1 is assumed to be estimated or measured in advance. In the current-thrust conversion ratio calculation operation, the relationship in equation (36) can be obtained, similar to equation (12) in the first embodiment.

[0100] dI / dx=A×(I-I0)+C …(36) On the other hand, the current-to-thrust conversion ratio α includes the efficiency η, the reduction ratio g, the rotary-to-linear conversion K, and the torque constant Kt. Among these, the torque constant of the electric motor 8 is particularly susceptible to the influence of temperature. Therefore, if the motor temperature during the current-to-thrust conversion ratio calculation operation is Tm1, α is expressed as a function of the motor temperature Tm1.

[0101] From these relationships, the current-thrust conversion ratio α can be calculated as equation (37).

[0102] α(Tm1)=b(Tp1) / C …(37) If it is known in advance that the torque constant at this temperature T is β(T) times the torque constant Kt0 at the reference temperature (T0), the relationship in equation (38) can be obtained.

[0103] Kt(T) = Kt0 × β(T) …(38) Therefore, the current-thrust conversion ratio α(T0) at the reference temperature T0 can be calculated as equation (39).

[0104] α(T0)=α / β(Tm1) …(39) This embodiment relates to a method for calculating the efficiency of the efficiency estimating unit 35, and the control method using the efficiency estimating unit 35 is the same as in the first and second embodiments.

[0105] For example, when it is desired to generate a certain braking force as in the first embodiment, the brake pad thrust force-current command conversion unit 34 determines the thrust current conversion ratio α(T0) at the reference temperature T0 for the brake thrust force command Fr, and if the temperature when it is desired to actually generate a braking force is (Tm2), then by converting this into a current command Ir using equation (40), it is possible to give a command to the electric motor to obtain the commanded thrust.

[0106] Ir = Fr / β(Tm2) + I0 … (40) Furthermore, as in the second embodiment, the current-position relationship is obtained as a table by the current-position conversion processing unit 40, and therefore the stiffness table update unit 39 can calculate the stiffness table (thrust-position) relationship by multiplying the current by the current-thrust conversion ratio obtained by the efficiency estimation unit 35, and updates the stiffness table as needed.

[0107] In this embodiment, the relationship dF / dx=a(T)×F+B(T) is described as a function of temperature only, but as shown in embodiment 3, a function of the amount of brake pad wear may be further added.

[0108] That is, equation (41) is used.

[0109] dF / dx=a(T,w)×F+b(T,w) …(41) From this, it is possible to obtain the current-thrust conversion ratio and the amount of wear in the same manner as in the third embodiment, and it is also possible to obtain the amount of wear taking the temperature into consideration.

[0110] The efficiency estimation unit 35 of this embodiment estimates the relationship between current and thrust force from the difference in temperature based on the temperature when the relationship between current and thrust force is estimated.

[0111] According to this embodiment, by incorporating temperature conversion, it is possible to obtain the current-thrust conversion ratio regardless of the temperature at the time of the current-thrust conversion ratio calculation operation or the amount of wear on the brake pads. [Example]

[0112] Next, a sixth embodiment will be described with reference to Fig. 12. Fig. 12 is a control block diagram of an electric brake device according to the sixth embodiment of the present invention.

[0113] In this embodiment, the electric brake device shown in the first embodiment is further provided with a thrust detector 44 for detecting the thrust of the brake pad.

[0114] As shown in Fig. 12, a thrust current control unit 47 is provided which performs feedback control of the motor current value and the detected value of the brake pad thrust in response to a brake thrust command Fr from a higher level. In addition to the current detection unit 31 and the motor position detection unit 32, a thrust detection unit 44 is also provided. An abnormality detection unit 45 is also provided which detects an abnormality in the thrust detection unit 44.

[0115] In the abnormality detection unit 45, when the current-thrust conversion ratio α is obtained by the efficiency estimation unit as shown in the first to fourth embodiments, the brake pad thrust F can be estimated by the formula (42).

[0116] F = α × (I - I0) … (42) Here, the brake pad thrust Fs obtained from the thrust detection unit 44 is also obtained. These values are compared to detect an abnormality in the thrust detection unit 44. If an abnormality is detected, a signal informing the host control device of the abnormality is sent, and the control method is changed. The control method is changed, for example, to a control method that does not require the thrust detection unit 44, as shown in the first to fourth embodiments.

[0117] In the sixth embodiment, an abnormality detection unit 45 is provided that detects an abnormality in the thrust detection unit 44 from the output value of the thrust detection unit 44 and the output value of the efficiency estimation unit 35 .

[0118] According to the sixth embodiment, it becomes possible to detect an abnormality in the thrust detector 44, thereby improving the reliability of the system.

[0119] In each embodiment, an electric brake using a disc brake has been described as an example, but various types of brakes, such as drum brakes, may be configured to generate braking force by operating a piston using an electric motor or the like to press the brake lining against a brake drum, which is a rotating body.

[0120] It may also be used to estimate thrust in an electric parking brake. In a control block configuration such as that shown in FIG. 1, when a parking brake command is given from a higher level, motor current is supplied, the point in time when the required thrust for the parking brake is reached is detected by the current value, and the motor current is stopped at that point. [Explanation of symbols]

[0121] 1...brake device, 2...disc rotor, 3...brake caliper, 4...housing, 5a, 5b...brake pad, 6...piston, 8...electric motor, 9...reduction gear, 10...rotation-to-linear motion conversion mechanism, 11...motor control device, 31...current detection unit, 32...motor position detection unit, 33...current control unit, 34...brake pad thrust-to-current command conversion unit, 35...efficiency estimation unit, 36...brake pad thrust-to-position command conversion unit, 37...position current control unit, 39...stiffness table update unit, 40...current-to-position conversion processing unit, 44...thrust detection unit, 45...abnormality detection unit, 46...no-load current estimation unit, 47...thrust current control unit

Claims

1. An electric brake device comprising: an electric motor; a linear motion part that moves due to rotation of the electric motor; brake pads that press a disc rotor that rotates together with a wheel by thrust generated by the movement of the linear motion part; and a motor control device that controls rotation of the electric motor, the motor control device further comprises an efficiency estimation unit that estimates the relationship between the current supplied to the electric motor and the thrust force, based on the relationship between an increase in a current value of the electric motor in response to an increase in the position of the linear motion part and the current value of the electric motor.

2. In claim 1, The electric brake device according to claim 1, wherein the efficiency estimation unit estimates the relationship between the current and the thrust force at the time of application by causing the electric motor to operate in the application direction when the vehicle is in a parked state.

3. In claim 1, an efficiency estimation unit that estimates the relationship between the current and the thrust force at the time of release by issuing a command to the electric motor to operate in the release direction when the vehicle is in a parked state;

4. In claim 1, the motor control device includes a current control unit that supplies current to the electric motor based on the relationship between the current and the thrust obtained by the efficiency estimator and a brake thrust command from a higher-level control device.

5. In claim 4, The motor control device is characterized in that it includes a brake pad thrust-current command conversion unit that outputs a current command value to the current control unit based on the relationship between the current and the thrust obtained by the efficiency estimator and a brake thrust command from a higher-level control device.

6. In claim 1, The motor control device is characterized in that it includes a current-position conversion processing unit that converts the relationship between the current value of the electric motor and the position of the linear motion part during braking into a stiffness table, and a stiffness table update unit that updates the data in the stiffness table based on the current-position conversion processing unit and the efficiency estimating unit.

7. In claim 1, The electric brake device, wherein the efficiency estimation unit estimates the amount of wear of the brake pads from a motor current value and a no-load current value.

8. In any one of claims 1 to 7, The electric brake device according to claim 1, wherein the efficiency estimation unit estimates the relationship between the current and the thrust force from a difference in temperature based on the temperature at which the relationship between the current and the thrust force is estimated.

9. In claim 1, the motor control device is an electric brake device characterized in that it includes a thrust detection unit that detects the thrust of the brake pad, and an abnormality detection unit that detects an abnormality in the thrust detection unit based on an output value of the thrust detection unit and an output value of the efficiency estimator.

10. An electric brake device comprising: an electric motor; a linear motion part that moves due to rotation of the electric motor; brake pads that press a disc rotor that rotates together with a wheel by thrust generated by the movement of the linear motion part; and a motor control device that controls rotation of the electric motor, the motor control device includes an efficiency estimating unit that estimates a relationship between the current supplied to the electric motor and the thrust force, based on a relationship between an increase in a current value of the electric motor in response to an increase in a position of the linear motion part at an expected current value that generates a specific thrust force, and the current value of the electric motor; An electric brake device characterized in that the expected current value is a current value calculated from a specific thrust using a value that is estimated or assumed in advance as a relationship between current and thrust.

Images