Electric braking device

Abstract

To increase opportunities of detecting a contact start position of a friction material with respect to a material to be rubbed.SOLUTION: The electric braking device (10) includes a function as a motor torque derivation unit that derives a motor torque corresponding to a current of the electric motor (18), a function as an inertia torque derivation unit that derives an inertia torque acting on a rotator 18A of the electric motor (18) in accordance with a change in a rotation speed of the electric motor (18), and an estimated load torque of the electric motor (18) obtained by subtracting the inertia torque from the motor torque. 11B 18A, the brake control device includes a control unit 30 having a function as an estimation part for estimating a contact start position of a brake pad 11B to a disc rotor 12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] There is known an electric braking device that generates a braking force on a vehicle by pressing a friction material against a friction object using torque generated by an electric motor. The electric braking device described in Patent Document 1 detects the contact start position of the friction material with the friction object by monitoring the current of the electric motor when the electric motor is driven at a constant speed until the friction material comes into contact with the friction object. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-81475 Summary of the Invention [Problem to be solved by the invention]

[0004] When braking a vehicle, it is sometimes necessary to adjust the rotation speed of the electric motor depending on the situation. In the conventional method for detecting the contact start position in the electric braking device described above, the electric motor needs to be driven at a constant speed, which limits the opportunities for detection. [Means for solving the problem]

[0005] The electric braking device that solves the above problem is an electric braking device that generates a braking force on a vehicle by pressing a friction material that moves linearly in accordance with the rotational movement of the rotor of an electric motor against a friction material, and is equipped with a motor torque derivation unit that derives a motor torque corresponding to the current value of the electric motor, an inertia torque derivation unit that derives an inertia torque acting on the rotor in accordance with changes in the rotational speed of the electric motor, and an estimation unit that estimates the contact start position of the friction material with the friction material based on an estimated load torque of the electric motor obtained by subtracting the inertia torque from the motor torque. [Effects of the Invention]

[0006] The electric braking device has the effect of increasing the chances of detecting the contact start position of the friction material with the friction target material. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram illustrating a schematic configuration of an embodiment of an electric braking device; [Figure 2] 4 is a flowchart of a process for estimating a contact start position, which is performed in the electric braking device of FIG. 1. [Figure 3] 2A is a time chart showing the transition of the piston stroke, the transition of the motor torque, the inertia torque, and the estimated load torque, and the transition of the pressing force of the friction material at the start of braking in the electric braking device of FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of an electric braking device will be described below with reference to FIGS. <Configuration of the electric braking system> First, the configuration of an electric braking device 10 of this embodiment will be described with reference to Fig. 1. The electric braking device 10 of this embodiment is configured as a caliper-type disc brake device that brakes the rotation of a disc rotor 12, which is a friction material, by clamping the disc rotor 12, which is a friction material, between two brake pads 11A and 11B.

[0009] The electric braking device 10 includes a caliper 13. The caliper 13 includes a cylinder body 14, a bridge portion 15, and claw portions 16. The cylinder body 14 and the claw portions 16 are arranged to sandwich the disc rotor 12 therebetween. The bridge portion 15 is a portion of the caliper 13 that connects the cylinder body 14 and the claw portions 16, and is arranged radially outward of the disc rotor 12. Of the two brake pads 11A, 11B, one (11A) is attached to the claw portion 16, and the other (11B) is attached to the cylinder body 14. The cylinder body 14 is also provided with a cylinder 17. The cylinder 17 is a cylindrical hole with a bottom that opens on the side of the cylinder body 14 where the disc rotor 12 is located.

[0010] The electric braking device 10 also includes an electric motor 18, a reduction gear mechanism 19, a linear motion conversion mechanism 20, and a piston 21. The reduction gear mechanism 19 is housed inside a gear box 19A that is assembled to the cylinder body 14. The electric motor 18 is assembled to the gear box 19A. The linear motion conversion mechanism 20 and the piston 21 are housed inside the cylinder 17 of the cylinder body 14.

[0011] The electric motor 18 includes a rotor 18A and a stator 18B. The electric motor 18 is configured to generate rotational motion of the rotor 18A in response to the application of current to the stator 18B. An example of the electric motor 18 is a brushless DC motor.

[0012] The reduction mechanism 19 is a mechanism that reduces the rotation speed of the rotor 18A of the electric motor 18 and transmits the reduced speed to the linear motion conversion mechanism 20. In the present embodiment, a reduction gear mechanism having a plurality of gears is used as the reduction mechanism 19. The reduction mechanism 19 shown in FIG. 1 has a first gear 22 connected to the rotor 18A of the electric motor 18, a third gear 24 connected to the linear motion conversion mechanism 20, and a second gear 23 interposed between the first gear 22 and the third gear 24.

[0013] The linear motion conversion mechanism 20 is a mechanism that converts the rotation transmitted from the reduction mechanism 19 into linear motion. In this embodiment, a ball screw mechanism is used as the linear motion conversion mechanism 20. The linear motion conversion mechanism 20 includes a screw shaft 25 as a rotating member and a nut 26 as a linear motion member. The screw shaft 25 is connected to a third gear 24 of the reduction mechanism 19 so as to rotate integrally therewith. The linear motion conversion mechanism 20 is configured so that the nut 26 moves linearly in the axial direction of the cylinder 17 in response to the rotation of the screw shaft 25.

[0014] The piston 21 is installed in the cylinder 17 so as to be able to move linearly in the axial direction. In the following description, in the axial direction of the cylinder 17, the side on which the brake pad 11B is located as viewed from the piston 21 will be referred to as the forward direction F, and the opposite side will be referred to as the backward direction R. Furthermore, the direction of rotation of the rotor 18A of the electric motor 18 toward the side where the nut 26 moves in the forward direction F will be referred to as the forward direction, and the direction of rotation of the rotor 18A of the electric motor 18 toward the side where the nut 26 moves in the backward direction R will be referred to as the reverse direction.

[0015] When the rotor 18A of the electric motor 18 rotates, the rotation is slowed down by the reduction gear mechanism 19 and transmitted to the screw shaft 25 of the linear motion conversion mechanism 20. The linear motion conversion mechanism 20 converts the rotation of the screw shaft 25 into linear motion of the nut 26. The electric braking device 10 is configured to apply pressure to the piston 21 as the nut 26 moves in the forward direction F, and further transmit this pressure to the brake pad 11B via the piston 21, thereby braking the rotation of the disc rotor 12.

[0016] The electric braking device 10 further includes a control unit 30. The control unit 30 is composed of a CPU, a memory, a drive circuit for the electric motor 18, and the like. A detection signal from a rotation angle sensor 31 that detects the rotation angle θm of the rotor 18A of the electric motor 18 is input to the control unit 30. The control unit 30 controls the current value Im of the electric motor 18 to generate a braking force in response to a command. The control of the current value Im is performed, for example, based on the detection value of a current sensor (not shown).

[0017] The electric braking device 10 is configured so that when the nut 26 moves to a predetermined position in the reverse direction R, it comes into contact with another member and is restricted from moving further in the reverse direction R. In the following description, the position of the nut 26 at this time will be referred to as the most retracted position. Based on the detection result of the rotation angle sensor 31, the control unit 30 calculates the amount of rotation of the electric motor 18 in the forward direction from the most retracted position as the value of the piston stroke St.

[0018] <Estimating the contact start position S0> The electric braking device 10 configured as described above generates a braking force against the rotation of the disc rotor 12 when the brake pad 11B contacts and presses against the disc rotor 12. In the following description, the position of the nut 26 at which the brake pad 11B starts pressing against the disc rotor 12 is referred to as a contact start position S0. The contact start position S0 changes due to wear and thermal expansion of the brake pads 11A and 11B and the disc rotor 12. The control unit 30 estimates the contact start position S0 during braking. The control unit 30 then reflects the estimated contact start position S0 in the control of the electric braking device 10. For example, the control unit 30 sets the position of the nut 26, which has moved a predetermined amount from the contact start position S0 in the reverse direction R, as a standby position. When a braking request is released, the control unit 30 moves the nut 26 in the reverse direction R to the standby position. Therefore, when braking is not requested, the electric braking device 10 waits with the nut 26 located at the standby position.

[0019] Fig. 2 shows the processing procedure of the control unit 30 relating to estimation of the contact start position S0. After the control unit 30 has started up and completed preparations such as confirmation of the most retreated position, the control unit 30 starts the processing of Fig. 2.

[0020] 2, the control unit 30 waits until braking starts. The start of braking represents the time when the nut 26 starts moving in the forward direction F from the standby position in response to a braking request.

[0021] When braking is started (S100: YES), in step S110, the control unit 30 acquires the current value Im and rotational angle θm of the electric motor 18. Next, in step S120, the control unit 30 calculates the current piston stroke St, the rotational speed ωm, and the angular acceleration αm of the electric motor 18 based on the rotational angle θm. For example, the control unit 30 calculates the time differential value of the rotational angle θm as the value of the rotational speed ωm. Furthermore, the control unit 30 calculates the time differential value of the rotational speed ωm as the value of the angular acceleration αm.

[0022] Next, in step S130, the control unit 30 determines whether the rotational speed ωm of the electric motor 18 is within a range greater than or equal to ω1 and less than or equal to ω2. If the absolute value of the rotational speed ωm is greater than or equal to a certain value or less than a certain value, the accuracy of calculating the angular acceleration αm based on the rotational angle θm decreases. In this embodiment, the lower limit of the range of the rotational speed ωm within which the accuracy of calculating the angular acceleration αm can be ensured is set to ω1, and the upper limit of the range is set to ω2. If the control unit 30 determines that the rotational speed ωm is less than ω1 or exceeds ω2, the control unit 30 returns to step S110 after a predetermined time has elapsed. On the other hand, if the control unit 30 determines that the rotational speed ωm is within a range greater than or equal to ω1 and less than or equal to ω2, the control unit 30 proceeds to step S140.

[0023] When the control unit 30 proceeds to step S140, it calculates the motor torque τm, which is the torque generated by the electric motor 18, based on the current value Im. Next, in step S150, the control unit 30 calculates the inertia torque τi based on the angular acceleration αm of the electric motor 18. The inertia torque τi represents the inertia torque acting on the rotor 18A in response to changes in the rotational speed ωm of the electric motor 18. In this embodiment, the control unit 30 calculates the value of the inertia torque τi by multiplying the inertia (moment of inertia) of the rotor 18A by the angular acceleration αm. Strictly speaking, when the rotational speed ωm of the electric motor 18 changes, the rotational speed of each rotating element arranged in the torque transmission path of the electric brake device 10 also changes, and inertia torque is also generated in these rotating elements. In this embodiment, as a result of deceleration by the reduction mechanism 19, the inertia torque of the rotating elements other than the rotor 18A becomes smaller than the inertia torque of the rotor 18A. Therefore, in this embodiment, the inertia torque τ of the rotor 18A itself is dominant in the inertia torque τ acting on the rotor 18A in response to changes in the rotational speed ωm of the electric motor 18. Therefore, the control unit 30 calculates the inertia torque of the rotor 18A itself as the inertia torque τ.

[0024] Thereafter, in step S160, the control unit 30 calculates the value obtained by subtracting the inertia torque τi from the motor torque τm as the value of the estimated load torque τl. Then, in the next step S170, the control unit 30 determines whether the estimated load torque τl is equal to or greater than a predetermined contact determination value τx. In this embodiment, the contact determination value τx is set to a value slightly greater than the mechanical loss torque, which is the torque mechanically lost in the torque transmission path from the electric motor 18 to the brake pad 11B. The mechanical loss torque includes torque loss due to friction in the rotary bearing of the rotor 18A, the thrust bearing of the nut 26, etc.

[0025] If the control unit 30 determines in step S170 that the estimated load torque τl is less than the contact determination value τx (NO), it performs the processes of steps S110 to S170 again after a predetermined time has elapsed. On the other hand, if the control unit 30 determines in step S170 that the estimated load torque τl is equal to or greater than the contact determination value τx (YES), it stores the current value of the piston stroke St as the contact start position S0 in step S180. Thereafter, the control unit 30 returns the process to step S100. Note that if the braking request is released after the start of braking but before performing the process of step S170, the control unit 30 returns the process to step S100.

[0026] The control unit 30 in the electric braking device 10 of this embodiment configured as described above derives the motor torque τm corresponding to the current value Im of the electric motor 18 in step S140 of FIG. 2. Furthermore, in step S150 of FIG. 2, the control unit 30 derives the inertia torque τi acting on the rotor 18A in accordance with changes in the rotational speed ωm of the electric motor 18, based on the angular acceleration αm of the electric motor 18. Furthermore, in step S160 of FIG. 2, the control unit 30 subtracts the inertia torque τi from the motor torque τm to derive the estimated load torque τl, which is an estimated value of the load torque of the electric motor 18. Then, in steps S170 and S180 of FIG. 2, the control unit 30 estimates the contact start position S0 of the brake pad 11B with the disc rotor 12 based on the estimated load torque τl. 2, the control unit 30 determines whether the estimated load torque τl is equal to or greater than the contact determination value τx. If the control unit 30 determines that the estimated load torque τl is equal to or greater than the contact determination value τx (S170: YES), the control unit 30 sets the piston stroke St at that time to the contact start position S0. The contact determination value τx is set based on the mechanical loss torque in the torque transmission path of the electric braking device 10. Therefore, the control unit 30 estimates the contact start position S0 based on the comparison result between the mechanical loss torque in the torque transmission path from the electric motor 18 to the brake pad 11B, which is a friction material, and the estimated load torque τl. In this embodiment, the control unit 30 corresponds to the motor torque derivation unit, the inertia torque derivation unit, and the estimation unit.

[0027] <Operation of the embodiment> Fig. 3 shows an example of the control mode at the start of braking of the electric braking device 10. Fig. 3(a) shows the transition of the piston stroke St, Fig. 3(b) shows the transition of the motor torque τm, the inertia torque τi, and the estimated load torque τl, and Fig. 3(c) shows the transition of the pressing force of the brake pad 11B against the disc rotor 12. In Fig. 3, the position of the nut 26 when the piston stroke St is "0" is set to the standby position.

[0028] When braking is not required, the electric braking device 10 waits with the nut 26 retracted to a standby position where the brake pads 11A, 11B are separated from the disc rotor 12. When braking is required, the control unit 30 rotates the electric motor 18 in the forward direction, which is the direction in which the nut 26 moves in the forward direction F. As the nut 26 moves in the forward direction F, it applies pressure to the piston 21 and, via the piston 21, to the brake pad 11B in the forward direction F. As the nut 26 moves in the forward direction F until the brake pad 11B comes into contact with and applies pressure to the disc rotor 12, braking of the disc rotor 12 begins.

[0029] In the case of FIG. 3 , at time t0, the nut 26 starts to move in the forward direction F in response to a braking request. Then, at a subsequent time t1, the brake pad 11B comes into contact with the disc rotor 12. During the period from time t0 to time t1, the mechanical loss torque in the torque transmission path from the electric motor 18 to the brake pad 11B acts as load torque on the electric motor 18. As described above, the control unit 30 derives the estimated load torque τl by subtracting the inertia torque τi from the motor torque τm corresponding to the current value Im of the electric motor 18. During the period from time t0 to time t1, the value of the estimated load torque τl does not greatly exceed the mechanical loss torque in the torque transmission path.

[0030] At time t1, when the brake pad 11B contacts and starts pressing against the disc rotor 12, in addition to the mechanical loss torque, a reaction torque to the pressing of the brake pad 11B against the disc rotor 12 acts as a load torque on the electric motor 18. Therefore, when the brake pad 11B contacts the disc rotor 12 at time t1, the value of the estimated load torque τl increases significantly, exceeding the mechanical loss torque. In the case of FIG. 3, the estimated load torque τl exceeds the contact determination value τx at time t1. The control unit 30 sets the piston stroke St at this time t1 to the contact start position S0.

[0031] <Effects of the embodiment> The electric braking device 10 of this embodiment has the following advantages. (1) To ensure that the braking force follows and responds to requests when braking the vehicle, it is difficult to drive the electric motor 18 at a constant speed. In response to this, the control unit 30 of the electric braking device 10 of this embodiment calculates the estimated load torque τl of the electric motor 18 used to estimate the contact start position S0 by subtracting the inertia torque τi from the motor torque τm. Therefore, the contact start position S0 can be estimated with high accuracy even if the electric motor 18 is not driven at a constant speed. Therefore, the electric braking device 10 of this embodiment has the effect of increasing the opportunities to detect the contact start position S0.

[0032] (2) The control unit 30 estimates the contact start position S0 based on the comparison result between the mechanical loss torque in the torque transmission path from the electric motor 18 to the brake pad 11B and the estimated load torque τl. Therefore, the contact start position S0 can be estimated with high accuracy.

[0033] (3) Since the contact start position S0 can be estimated each time braking is performed, changes in the contact start position S0 due to wear and thermal expansion of the brake pads 11A, 11B and the disc rotor 12 can be quickly reflected in the control of the electric braking device 10.

[0034] (4) When the rotational speed ωm of the electric motor 18 is higher or lower than a certain level, the calculation accuracy of the angular acceleration αm based on the rotational angle θm decreases. In the electric braking device 10 of this embodiment, when the rotational speed ωm of the electric motor 18 is not within a predetermined range, estimation of the contact start position S0 based on the estimated load torque τl is stopped. Therefore, the estimation accuracy of the contact start position S0 can be ensured.

[0035] (Other embodiments) This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0036] The contact determination value τx used in the determination in step S170 of FIG. 2 may be a variable value. Because the viscosity of grease applied to bearings and the like increases at low temperatures, the mechanical loss torque in the torque transmission path may increase at low temperatures. Furthermore, the mechanical loss torque in the torque transmission path may change due to the deterioration of components over time. Therefore, by variably setting the contact determination value τx depending on the outside air temperature, the number of years the electric braking device 10 has been in use, and the like, the accuracy of estimating the contact start position S0 may be improved.

[0037] The electric braking device 10 may be provided with a mechanical return mechanism so that the braking force can be removed in the event of a power failure. In this case, it is desirable to set the contact determination value τx taking into account the mechanical torque loss caused by the return mechanism.

[0038] In the above embodiment, if the rotational speed ωm of the electric motor 18 is not within the range of not less than "ω1" and not more than "ω2", the estimation of the contact start position S0 based on the estimated load torque τl is stopped. However, only a lower limit or only an upper limit may be set for the range of the rotational speed ωm for which the estimation of the contact start position S0 based on the estimated load torque τl is performed.

[0039] If the rotational speed ωm of the electric motor 18 is not within a predetermined range, the rotational speed ωm may be controlled so as to be within the range. For example, during the period from the start of braking to the completion of estimation of the contact start position S0, the following control of the rotational speed ωm of the electric motor 18 is performed. If the rotational speed ωm of the electric motor 18 is less than "ω1", the rotational speed ωm of the electric motor 18 is increased until it becomes equal to or greater than "ω1", and if the rotational speed ωm exceeds "ω2", the rotational speed ωm of the electric motor 18 is decreased until it becomes equal to or less than "ω2".

[0040] When the estimation of the contact start position S0 based on the estimated load torque τl is stopped, the contact start position S0 may be estimated using another method. The determination process of step S130 in FIG. 2 may be omitted, and the contact start position S0 may be estimated based on the estimated load torque τl regardless of the rotation speed ωm of the electric motor 18.

[0041] The logic for estimating the contact start position S0 in the above embodiment can also be applied to an electric braking device 10 having a configuration different from that shown in Fig. 1. For example, the logic for estimating the contact start position S0 in the above embodiment may be applied to an electric braking device configured to transmit torque from the electric motor 18 to a friction material via a hydraulic circuit. Furthermore, the logic for estimating the contact start position S0 in the above embodiment may be applied to a drum-type electric braking device in which a brake shoe is used as the friction material and a brake drum is used as the friction-bearing material.

[0042] The control unit 30 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware for performing at least some of the various processes, or a combination thereof. Dedicated hardware may include, for example, an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, which stores program code or instructions configured to cause the CPU to perform processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer. [Explanation of symbols]

[0043] 10…Electric braking device 11A, 11B...Brake pads (friction material) 12...Disc rotor (friction material) 18...Electric motor 18A...Rotor 18B…Stator 19...Reduction mechanism 20...Linear motion conversion mechanism 30...Control unit (motor torque derivation unit, inertia torque derivation unit, estimation unit).

Claims

1. An electric braking device that generates a braking force on a vehicle by pressing a friction material that moves linearly in response to the rotational movement of a rotor of an electric motor against a friction target material, a motor torque derivation unit that derives a motor torque corresponding to a current value of the electric motor; an inertia torque derivation unit that derives an inertia torque acting on the rotor in accordance with a change in the rotational speed of the electric motor; an estimation unit that estimates a contact start position of the friction material with the friction target material based on an estimated load torque of the electric motor obtained by subtracting the inertia torque from the motor torque; An electric braking device comprising:

2. 2. The electric braking device according to claim 1, wherein the estimation unit estimates the contact start position based on a comparison result between a mechanical loss torque, which is torque mechanically lost in a torque transmission path from the electric motor to the friction material, and the estimated load torque.

3. The electric braking device according to claim 1 , wherein the estimation unit stops estimating the contact start position based on the estimated load torque when the rotation speed of the electric motor is not within a predetermined range.

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