Brake system

Abstract

We provide highly practical vehicle-mounted electric braking systems. [Solution] A brake system comprising a pair of electric brake devices 12, each provided for each of the left and right wheels 10r, each having an electric motor as a drive source, which generates braking force by pressing the brake pads 36 against the disc rotor 34 with a pressing force dependent on the torque of the electric motors, and a controller 16 that performs service brake control for each of the pair of electric brake devices, which generates braking force in response to the operation of the brake operating member 14 by controlling the torque of the electric motors, wherein a characteristic learning process is performed for each of the pair of electric brake devices to learn the torque-pressing force characteristic, which is the characteristic of the pressing force in response to the torque of the electric motor. This makes it possible to generate accurate braking force in response to the operation of the brake operating member.

Description

[Technical Field]

[0001] The present invention relates to a braking system mounted on a vehicle, which includes an electric braking device. [Background technology]

[0002] Regarding brake systems equipped with an electric brake device (hereinafter sometimes referred to as "electric brake systems"), there exists a technology such as the one described in the following patent document. In this technology, the electric brake device generates braking force by using an electric motor to operate a piston, which in turn presses the brake pads against the disc rotor. In this technology, the electric motor is controlled based on rigidity characteristic data relating to the characteristics of the pressing force with respect to the rotational position of the electric motor, and this rigidity characteristic data is updated each time braking force is generated. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2011-213201 [Overview of the project] [Problems that the invention aims to solve]

[0004] The pressing force in an electric brake system depends on the mechanical efficiency of the brake system, and understanding this efficiency as some characteristic is meaningful for generating appropriate braking force. However, understanding this efficiency as the characteristic of the pressing force with respect to the rotational position of the electric motor (hereinafter sometimes referred to as "motor rotational position-pressing force characteristic") is not always sufficient, and it may be possible to understand it as a different characteristic. Furthermore, mechanical efficiency does not change each time braking force is generated, but can be assessed at a point after a certain amount of time has elapsed, in other words, after the electric brake system has been operated a certain number of times. In short, there is considerable room for improvement in electric brake systems, and it is possible to improve the practicality of electric brake systems by making some improvements. This invention has been made in view of such circumstances, and aims to provide a highly practical electric brake system. [Means for solving the problem]

[0005] To solve the above problems, the brake system of the present invention is A brake system installed in a vehicle, A brake operating member operated by the driver, A pair of electric brake devices are provided for each of the left and right wheels, each having an electric motor as a drive source, and generating braking force by pressing the brake pads against the disc rotor with a pressing force that relies on the torque of the electric motors. A controller that performs service brake control for each of the pair of electric brake devices, which generates a braking force corresponding to the operation of the brake operating member by controlling the torque of the electric motor. Equipped with, The controller is configured to perform a characteristic learning process for each of the pair of electric brake devices to learn the torque-pressure characteristic, which is the characteristic of the pressing force relative to the torque of the electric motor. [Effects of the Invention]

[0006] The torque-pressure characteristics described above depend on mechanical efficiency. More specifically, if the electric brake device includes a reduction mechanism that slows down the rotational motion of the electric motor, a motion conversion mechanism that converts the rotational motion of the electric motor into the movement of a piston, etc., then the characteristics depend on the efficiency of those mechanisms. Changes in that efficiency are mainly caused by changes in the performance of lubricants such as grease, wear in those mechanisms, etc. Therefore, by understanding the torque-pressure characteristics through the characteristic learning process described above, the electric brake device can generate accurate braking force in response to the operation of the brake operating member. Embodiment of the Invention

[0007] The brake system of the present invention, for example, is equipped with a pair of electric brake devices corresponding to one of the two front wheels or two rear wheels, but may also be equipped with a pair of electric brakes for the other side. Alternatively, the other side may be equipped with a so-called hydraulic brake device instead of an electric brake device. Incidentally, the brake operating member (hereinafter sometimes simply referred to as the "operating member") is generally a brake pedal, but may also be something like a steering stick or joystick. Furthermore, known forms of electric brake devices may be adopted.

[0008] Regarding specific embodiments of service brake control, for example, in service brake control, the torque to be generated by the electric motor may be controlled based on a basic torque that includes a feedforward torque component and a feedback torque component. In this case, the feedforward torque component may be determined according to the torque-pressure characteristics described above, based on the actual pressing force, which is the pressing force actually generated, or the target pressing force, which is the pressing force that should be generated, and the feedback torque component may be determined according to a feedback control law, based on the motor rotation position deviation, which is the deviation of the actual motor rotation position, which is the deviation of the actual motor rotation position, from the target motor rotation position, which is the target motor rotation position, which is the motor rotation position, depending on the operation of the operating member.

[0009] In the above embodiment, if each of the pair of electric brake devices has a sensor for detecting the actual pressing force, the feedforward torque component may be determined based on the detected actual pressing force, which is the actual pressing force detected by the sensor. On the other hand, if the sensor is not present, the feedforward torque component may be determined based on the target pressing force. Note that if the electric brake device does not have the sensor, the cost of the electric brake device will be reduced.

[0010] The above characteristic learning process may be performed as an alternating characteristic learning process while the vehicle is stopped. The alternating characteristic learning process is a process in which the torque-pressure characteristics of one of a pair of electric brake devices are learned while maintaining the braking force of the other, and then the torque-pressure characteristics of the other are learned while maintaining the braking force of the other. By performing the alternating characteristic learning process, it is possible to prevent the vehicle from moving while it is stopped. If each of the pair of electric brake devices has a parking brake mechanism for generating parking brake force while the vehicle is stopped, the alternating characteristic learning process may be performed on the condition that both of the pair of electric brake devices are generating parking brake force. On the other hand, if neither of the pair of electric brake devices is generating parking brake force while the vehicle is stopped, a simultaneous characteristic learning process may be performed as a characteristic learning process, in which the torque-pressure characteristics of both of the pair of electric brake devices are learned simultaneously.

[0011] The characteristic learning process may be performed at predetermined intervals, more specifically, for example, each time the vehicle travels beyond a set distance. Furthermore, it may also be performed based on a predetermined command even if the vehicle has not traveled the set distance. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the overall configuration of the brake system of the embodiment, and the electric brake device that constitutes the brake system. [Figure 2]It is a cross-sectional view showing a brake actuator included in an electric brake device. [Figure 3] It is a functional block diagram of a controller related to service brake control. [Figure 4] It is a graph for explaining the significance of performing characteristic learning processing and the mode of characteristic learning processing. [Figure 5] It is a flowchart showing a process for performing characteristic learning processing.

Mode for Carrying Out the Invention

[0013] Hereinafter, as a mode for carrying out the present invention, a brake system which is an embodiment of the present invention will be described in detail while referring to the drawings. Note that the present invention can be implemented in various forms in which various changes and improvements are made based on the knowledge of those skilled in the art, in addition to the following embodiments and the forms described in the section of 〔Aspects of the Invention〕 above.

Embodiment

[0014] [A] Overall Configuration of Brake System As shown in Fig. 1(a), the brake system of the embodiment is mounted on a vehicle having left and right front wheels 10f and left and right rear wheels 10r. An electric brake device 12 is provided for each of the front wheels 10f, and an electric brake device 12 is provided for each of the rear wheels 10r. The brake system of the embodiment includes a pair of electric brake devices 12 provided on the rear wheels 10r, a brake pedal 14 as a brake operation member, and a brake electronic control unit (hereinafter sometimes simply referred to as "ECU") 16 as a controller for controlling the electric brake device 12. A pedal sensor 18 for detecting the operation amount (depression amount) δ of the brake pedal 14 is provided, and the detected operation amount δ is transmitted to the ECU 16. In addition, the vehicle is provided with a longitudinal acceleration sensor (hereinafter sometimes referred to as "longitudinal G sensor") 20, and the longitudinal acceleration Gx detected by this longitudinal G sensor 20 is also transmitted to the ECU 16.

[0015] [B] Configuration of the electric brake system The electric brake device 12 has a general structure and, as shown in Figure 1(b), consists of a brake caliper 32 comprising a caliper body 28 and a brake actuator (hereinafter sometimes simply referred to as "actuator") 30 fixed thereto, a disc rotor 34 as a rotating body that rotates with the wheels 10f and 10r, and a pair of brake pads 36 (each having a friction member) held by the caliper body 28 so as to sandwich the disc rotor 34. The caliper body 32 is supported by a carrier or steering knuckle that rotatably holds the wheels 10f and 10r. The actuator 30 moves its piston 38 forward (to the left in the figure), pressing the pair of brake pads 36 against the disc rotor 34, thereby generating a braking force.

[0016] As shown in cross-section in Figure 2, the actuator 30 comprises a housing 42, a hollow electric motor 44 held in the housing 42 as a drive source, a hollow shaft 46 that functions as the motor shaft of the electric motor 44, a rotating shaft 48 that is rotated by the rotation of the hollow shaft 46, i.e., the rotation of the electric motor 44, a cycloidal reduction mechanism 50 (detailed explanation omitted) that reduces the rotation of the hollow shaft 46 and transmits it to the rotating shaft 48, a motion conversion mechanism 54 that converts the rotational motion of the rotating shaft 48 into the linear motion of the nut 52, and the aforementioned piston 38 held in the housing 42 and moved back and forth by the linear motion of the nut 52. More specifically, the motion conversion mechanism 54 is a ball screw mechanism in which the rotating shaft 48 and the nut 52 are screwed together via bearing balls 56. The rotating shaft 48 is held in the housing 42 so as to be immovable in the direction in which the axis L extends, i.e., the front-to-back direction (left-to-right direction in the figure, with left being the front direction), but rotatable around the axis L. The nut 52 is held in the housing 42 so as to be immovable around the axis L, but movable in the front-to-back direction. When the rotating shaft 48 is rotated in the forward direction by the electric motor 44, the nut 52 moves forward, and as the nut 52 moves forward, the nut 52 comes into contact with the piston 38 at its front end surface, causing the piston 38 to move forward. When the rotating shaft 48 is rotated in the reverse direction, the nut 52 moves backward, and the piston 38 moves backward in accordance with this backward movement.

[0017] The electric motor 44 is a three-phase brushless DC motor comprising coils 60 held in a housing 42 and magnets 62 attached to the outer circumference of a hollow shaft 46 facing the coils 60. By supplying current to the electric motor 44 to rotate in the forward direction, the piston 38 moves forward, and a pair of brake pads 36 are pressed against the disc rotor 34. The magnitude of the pressing force depends on the magnitude of the supplied current, and the brake device 12 generates a braking force corresponding to that pressing force. The actuator 30 is equipped with a motor rotation angle sensor (resolver; see Figure 1(a)) 66 that detects the rotation angle (rotation phase) of the hollow shaft 46, which is the motor shaft, i.e., the motor rotation position, which is the motor rotation angle θ, in order to switch the energizing phase in the current supply to the electric motor 44. It is also equipped with a current sensor 68 for detecting the current I supplied to the electric motor 44 (see Figure 1(a)). Incidentally, to put it simply, the pressing force also depends on the amount of forward movement of the piston 38, that is, the angle of rotation (amount of rotation) of the electric motor 44 in the forward direction from the reference rotation angle.

[0018] The rotating shaft 48 is rotatably supported on the support plate 72 via a thrust bearing 70. More specifically, an axial force sensor (which is a load cell) 78 is positioned between the thrust bearing 70 and the support plate 72. The aforementioned pressing force acts as a reaction force, specifically as an axial force (thrust force) on the rotating shaft 48. This force can be called an axial force, and for convenience, in the following explanation, the pressing force will be referred to as the axial force F. The axial force sensor 78 detects this axial force F. Note that the axial force sensor 78 can be omitted to reduce the cost of the actuator 30, i.e., the electric brake device 12. As will be explained in detail later, in that case, the axial force F can be estimated from the current I supplied to the electric motor 44.

[0019] The electric brake system 12 shown in Figures 1(b) and 2 is an electric brake system 12 provided for the rear wheel 10r and functions not only as a service brake but also as a parking brake. In order to function as a parking brake, the actuator 30 is equipped with a piston retraction prevention mechanism, i.e., a so-called locking mechanism 80, to prevent the piston 38 from retracting. The locking mechanism 80 consists of a ratchet gear 84 that rotates integrally with the hollow shaft 46 and has multiple teeth 82 formed on its outer circumference, a locking pin 86 that acts as a stopper to engage with one of the multiple teeth 82 to lock the ratchet gear 84, and a solenoid 88 that acts as a stopper moving device to move the locking pin 86. Since the locking mechanism 80 has a general structure, a detailed explanation of its structure and operation will be omitted, but the locking mechanism 80 locks the electric brake system 12 that generates the braking force, thereby maintaining the parking brake force. Incidentally, the electric brake system 12 provided for the front wheel 10f does not have a locking mechanism 80.

[0020] [C] Service Brake Control The ECU 16, which is the controller, consists of a computer as its main component and an inverter, which is the drive circuit (driver) for the electric motor 44. More specifically, the ECU 16's computer performs service brake control for each of the electric brake devices 12 by controlling the torque generated by the electric motor 44, thereby generating a braking force corresponding to the operation of the brake pedal 14. Referring to the functional block diagram of the ECU 16 shown in Figure 3(a), the service brake control for each of the electric brake devices 12 will be described below.

[0021] Although not shown in the functional block diagram, the ECU 16 determines the target pressing force, which is the pressing force that the electric brake device 12 should generate, based on the amount δ of operation of the brake pedal 14, and the target axial force F that should be generated. * This is determined according to equation (1) below. F *=α·δ ···(1) α: Coefficient of determination of axial force

[0022] Furthermore, the ECU 16 receives the detected actual axial force F from the axial force sensor 78, which is the actual axial force generated by the electric brake device 12, as the detected actual axial force, and the target axial force F * However, the axial force-motor rotation angle conversion unit (hereinafter sometimes referred to as the "F-θ conversion unit") 100 converts the target motor rotation angle θ accordingly. * The estimated motor rotation angle θe, which is estimated from the actual axial force F, is determined. The F-θ conversion unit 100 refers to the F-θ map shown graphically in Figure 3(b) and determines the target motor rotation angle θ * The estimated motor rotation angle θe is determined. The solid line in the graph is the characteristic curve stored in the F-θ conversion unit 100. The ECU 16 constantly recognizes the motor rotation angle θ when the piston 38 retracts and the braking force becomes 0, that is, when the axial force F, which is the pressing force, decreases to 0, as the reference motor rotation angle θ0, and the motor rotation angle θ is considered to be the cumulative rotation angle based on this reference motor rotation angle θ0. Incidentally, in the graph, the axial force F is represented as pressure obtained by dividing it by the pressure-receiving area.

[0023] The ECU 16 determines the motor torque T that the electric motor 44 should generate and controls the electric motor 44 based on that motor torque T. The ECU 16 determines the feedforward component (hereinafter sometimes referred to as the "FF torque component") Tff, which is a component of the motor torque T, based on the actual axial force F. This determination is performed by the FF torque component determination unit 102. Specifically, the FF torque component Tff is determined according to the following equation (2). Tff = F / Kft ... (2) Kft: Axial force-torque conversion coefficient Incidentally, the axial force-torque conversion coefficient Kft represents the torque-compression force characteristic and is expressed by the following equation (3). Kft=Rg·(2π / Ls)·ε···(3) Rg: Gear ratio of cycloidal reduction mechanism 50 Ls: Screw lead (the amount of movement of the piston 38 per rotation of the rotating shaft 48) ε: Mechanical efficiency Note that, as will be described later, when the electric brake device 12 does not include the axial force sensor 78, as shown by the broken line in the block diagram of Fig. 3(a), instead of the actual axial force F, the target axial force F * Based on this, the FF torque component Tff is determined according to the following formula (2)'. Tff = F * / Kft ···(2)

[0024] On the other hand, the actual motor rotation angle θ, which is the actual motor rotation angle, is input from the motor rotation angle sensor 66. The ECU 16 determines the feedback component (hereinafter sometimes referred to as the "FB torque component") Tfb, which is another component of the motor torque T. Specifically, the motor rotation angle correction value θc, which is the difference between the actual motor rotation angle θ and the estimated motor rotation angle θe, is calculated by the subtraction unit 104, and the addition unit 106 corrects the target motor rotation angle θ based on the motor rotation angle correction value θc * . Then, the motor rotation angle deviation Δθ, which is the deviation of the actual motor rotation angle θ with respect to the corrected target motor rotation angle θ, is calculated by the subtraction unit 108, and in the FB torque component determination unit 110, based on the calculated motor rotation angle deviation Δθ, the FB torque component Tfb is determined according to the following formula (4) for the feedback control law * Tfb = Gp·Δθ + Gi·∫Δθdt + Gd·dΔθ / dt ···(4) Gp: Proportional term gain, Gi: Integral term gain, Gd: Differential term gain Gp: Proportional term gain, Gi: Integral term gain, Gd: Differential term gain

[0025] Note that the actual motor rotation angle θ is the actual forward position of the actual piston 38, and the target motor rotation angle θ * can be considered as the target forward position where the piston 38 should advance. Therefore, it can be considered that the above FB torque component Tfb is a component based on the deviation of the actual forward position with respect to the target forward position of the piston 38.

[0026] As described above, the FF torque component Tff and the FB torque component Tfb are added together in the addition unit 112 to determine the basic torque Tb. As will be explained later, the torque-axial force characteristics of the actuator 30 differ depending on whether the piston 38 is moving forward or backward, in other words, whether the electric motor 44 is rotating in the forward or reverse direction, depending on the forward and reverse efficiency of the actuator 30. Therefore, the ECU 16 determines the motor torque T that the electric motor 44 should generate by correcting the basic torque Tb in the direction-aware unit 116, based on the change in the actual rotation angle θ in the direction-aware unit 114. Although not shown in the figure, the ECU 16 determines the current I to be supplied to the electric motor 44 according to the following equation (5) based on the motor torque T, and supplies that current I to the electric motor 44. I = T / Kt ... (5) Kt: Motor torque constant

[0027] The above explanation describes the case where the actuator 30 is equipped with an axial force sensor 78. However, if the actuator 30 is not equipped with an axial force sensor 78, the estimated actual axial force Fe is used instead of the actual axial force (detected axial force) F. The estimated actual axial force Fe is determined based on the actual motor rotation angle θ of the electric motor 44 and the actual current I supplied to the electric motor 44 detected by the current sensor 68, as shown in the functional block diagram in Figure 3(c). More specifically, the ECU 16 determines the estimated motor torque Te based on the actual current I in the torque estimation unit 118 according to the following equation (6). Te=Kt·I ···(6) On the other hand, in the motor rotation angular acceleration determination unit 120, the motor rotation angular acceleration θ'' is determined based on the actual motor rotation angle θ, and in the inertial torque determination unit 122, the inertial torque Ti is determined based on the motor rotation angular acceleration θ'' according to the following equation (7). Ti = Mi·θ” ···(7) Mi: moment of inertia Then, in the subtraction unit 124, the estimated motor torque Te is corrected based on the inertial torque Ti.

[0028] Based on the estimated motor torque Te calculated as described above, the estimated actual axial force Fe is determined in the estimated actual axial force determination unit 126. While a detailed explanation is omitted, the estimated actual axial force determination unit 126 makes the determination according to the following equation (8). Fe = Kft·Te ···(8) As explained earlier, the torque-axial force characteristics of the actuator 30 differ depending on the rotation direction of the electric motor 44. Therefore, in addition to the above determination, the estimated actual axial force determination unit 126 makes corrections based on the rotation direction of the electric motor 44 as determined by the direction grasping unit 128, and the estimated actual axial force Fe is determined.

[0029] In addition to the service brake control described above, the ECU 16 also performs parking brake control on the electric brake devices 12 located on the rear wheels 10r. Since parking brake control is a common type of control, a detailed explanation will be omitted, but in this control, parking brake force is applied to the left and right rear wheels 10r by the driver operating the parking brake switch. The ECU 16 can independently apply or release parking brake force to each of the pair of electric brake devices 12 located on the left and right rear wheels 10r, without any operation by the driver.

[0030] [D] Changes in Torque-Pressure Characteristics and Learning The characteristics of the electric brake device 12 change depending on the number of times the brake device 12 is operated, etc. For example, the axial force-motor rotation angle characteristics represented by the F-θ map in Figure 3(b) change due to changes in the elastic modulus caused by wear of the brake pads 36, etc. This change can be addressed by determining the FB torque component Tfb based on the above method without changing the F-θ map stored in the ECU 16. Specifically, if the actual characteristic line shown by the dashed line in Figure 3(b) deviates from the stored solid line characteristic line, the target axial force F * Actual axial force F, target motor rotation angle θ *The estimated motor rotation angle θe and the motor rotation angle correction value θc are the values ​​shown in parentheses in the functional block diagram of Figure 3(a), and can accommodate changes in the axial force-motor rotation angle characteristics.

[0031] However, the above method for determining the FB torque component Tfb cannot adequately address the changes in torque-pressure characteristics related to the characteristics of the electric brake device 12, i.e., the changes in torque-axial force characteristics. The torque-axial force characteristics depend on the mechanical efficiency ε of the actuator 30, and this mechanical efficiency ε changes significantly due to the lubrication performance (e.g., grease performance) of the cycloidal reduction mechanism 50 and the motion conversion mechanism 54, as well as the wear (including peeling wear) and dimensional changes of their components. Specifically, as schematically shown in the graph of Figure 4(a), the mechanical efficiency ε decreases with increasing number of operations of the electric brake device 12. Furthermore, as schematically shown in the graph of Figure 4(b), the torque-axial force characteristics change depending on the mechanical efficiency ε. The dashed-dotted characteristic line in the graph represents the characteristic line when the mechanical efficiency ε is 100%, the solid characteristic line represents the characteristic line when the mechanical efficiency ε is 75%, and the dashed characteristic line represents the characteristic line when the mechanical efficiency ε is 50%. Incidentally, as explained earlier, the torque-axial force characteristics when the mechanical efficiency ε decreases differ between the forward rotation and reverse rotation of the electric motor 44, that is, when the piston 38 moves forward and when it moves backward (when the axial force F increases and when it decreases).

[0032] Figure 4(c) shows the graph of the target axial force F in service brake control. * A schematic example of the actual change in axial force F in response to a change in [the target axial force] is shown. Incidentally, this graph shows the change when the actuator 30 is equipped with an axial force sensor 78. The dashed line in the graph represents the target axial force F. *The solid line shows the change in actual axial force F when the mechanical efficiency ε perceived by the ECU16 is appropriate (when the stored mechanical efficiency ε matches the actual mechanical efficiency ε), and the dashed line shows the change in actual axial force F when the mechanical efficiency ε perceived by the ECU16 is inappropriate (when the stored mechanical efficiency ε does not match the actual mechanical efficiency ε). As mentioned above, in service brake control, the axial force-torque conversion coefficient Kft, which includes the mechanical efficiency ε, is used in determining the FF torque component Tff. Therefore, in the transient region where the gradient of axial force F changes, as indicated by the circle in the graph, the actual axial force F is equal to the target axial force F * This will result in a discrepancy. Conversely, by understanding the appropriate mechanical efficiency ε, that is, by learning the torque-axial force characteristics, which are the torque-compression force characteristics, the change in the actual axial force F will be equal to the target axial force F. * This will be in line with the changes.

[0033] If the actuator 30 is not equipped with an axial force sensor 78, as described above, the axial force-torque conversion coefficient Kft is used not only for determining the FF torque component Tff but also for estimating the estimated actual axial force Fe. Therefore, as shown in the graph in Figure 4(d) as an example, the actual axial force F is equal to the target axial force F not only in the transient region but also in the steady-state region where the gradient of the axial force F does not change. * This results in a deviation. In other words, a steady-state deviation β exists in the steady-state region. That is, even in an electric brake device 12 that does not have an axial force sensor 78, by learning the mechanical efficiency ε, the change in the actual axial force F becomes the target axial force F * This will be in line with the changes. Furthermore, in service brake control based on estimated actual axial force Fe, learning the mechanical efficiency ε, that is, the torque-axial force characteristic which is the torque-pressure characteristic, is more significant than in service brake control based on detected actual axial force F.

[0034] [E] Characteristic learning process In light of the above, this braking system performs a characteristic learning process when the vehicle is stopped to learn the torque-pressure characteristic, i.e., the torque-axial force characteristic, which is the characteristic of the pressing force relative to the torque T of the electric motor 44. Incidentally, the characteristic learning process can also be described as a process for learning the above-mentioned mechanical efficiency ε.

[0035] To explain the characteristics learning process, for example, as shown in the graph in Figure 4(e), the ECU 16 increases the axial force F from 0 to a set axial force Fs, and then decreases the axial force F from the set axial force Fs back to 0. This process is repeated multiple times (for example, four times), and during these repetitions, the torque-axial force characteristics are grasped and the grasped characteristics are stored. In other words, the ECU 16 stores the axial force-torque conversion coefficient Kft through this process. If the electric brake device 12 has an axial force sensor 78, the axial force F can be obtained by detection by the axial force sensor 78. If the electric brake device 12 does not have an axial force sensor 78, the axial force F can be obtained by estimation based on the supply current I to the electric motor 44 as described above.

[0036] The process for executing the characteristic learning process, that is, the initiation of the characteristic learning process, is carried out by the characteristic learning process execution program, as shown in the flowchart in Figure 5. The ECU16 computer executes this program while the vehicle is stationary.

[0037] In the process according to the above program, first, in step 1 (hereinafter sometimes abbreviated as "S1"; the same applies to other steps), it is determined whether the start conditions are met. The start conditions are either (i) the vehicle has traveled a set distance or more since the last learning was performed, and a set time has elapsed since the brake system entered a self-holding state, or (ii) a learning command has been issued. The set distance is set to a distance at which changes in mechanical efficiency ε can be grasped (for example, several to several tens of kilometers). Even if the ignition switch of the vehicle is turned OFF, the ECU16 does not stop immediately, and the self-holding state refers to the state until the ECU16 stops. The set time is set to, for example, 30 seconds to 1 minute. The learning command is a command to execute the characteristic learning process even if the vehicle has not traveled the above set distance. The learning command may be issued, for example, by the driver operating a predetermined switch, or it may be issued based on the operation of a predetermined operating terminal by a dealer's service technician. Furthermore, the command may be issued, for example, by the vehicle receiving a wireless communication from a management center (a so-called OTA (on-the-air) command). If the start conditions are not met, the characteristic learning process will not be performed.

[0038] If the starting conditions are met, in the following S2, it is determined whether or not the tolerance conditions are met. The tolerance conditions are that the gradient of the road surface on which the vehicle is stopped is less than or equal to the set gradient, the shift lever is in the parking position, and all electric brake devices 12 of the brake system are functioning correctly. The road surface gradient is estimated based on the longitudinal acceleration detected by the longitudinal acceleration sensor 20. The set gradient is set to a value at which it can be determined that the vehicle will not start moving even if braking force is not applied to all wheels. Incidentally, if the tolerance conditions are not met, and the above learning command has been issued, in S3, the reason why the characteristic learning process cannot be executed is notified to the driver via a monitor such as the car navigation display, voice, etc. If the tolerance conditions are not met, the characteristic learning process is not performed.

[0039] If the permissible conditions are met, in S4, it is determined whether or not parking brake force is applied to the left and right rear wheels 10r by the electric brake device 12. If parking brake force is applied, in S5, alternating characteristic learning processing is performed; if parking brake force is not applied, in S6, simultaneous characteristic learning processing is performed.

[0040] The alternating characteristic learning process is a process that learns the torque-pressure characteristics of one of the two electric brake devices 12 on the rear wheels 10r while maintaining the braking force of the other, and then learns the torque-pressure characteristics of the other while maintaining the braking force of the other. In other words, it is a process for learning the characteristics of each electric brake device 12 while taking measures to prevent the vehicle from moving. Specifically, first, the electric brake devices 12 on the left and right front wheels 10f apply a set amount of braking force to those front wheels 10f. Then, the parking brake force of one of the left and right rear wheels 10r is released, the characteristic learning process for that electric brake device 12 is executed, and then the application of the parking brake force is restored. Next, the parking brake force of the other left and right rear wheel 10r is released, the characteristic learning process for the other electric brake device 12 is executed, and then the application of the parking brake force is restored. Furthermore, the braking force applied to the left and right front wheels 10f is released, and the characteristic learning process for each of the electric brake devices 12 of the left and right front wheels 10f is performed simultaneously.

[0041] The simultaneous characteristic learning process is executed when the vehicle does not start moving even without applying braking force to all wheels 10f and 10r. The characteristic learning process is executed simultaneously for each electric brake device 12 of all wheels 10f and 10r. [Explanation of Symbols]

[0042] 10f: Front wheel 10r: Rear wheel 12: Electric brake device 14: Brake pedal [operating element] 16: Brake ECU [controller] 28: Caliper body 30: Brake actuator 32: Brake caliper 34: Disc rotor 36: Brake pad 44: Electric motor [drive source] 48: Rotating shaft 50: Cycloid reduction mechanism 54: Motion conversion mechanism 78: Axial force sensor δ: Amount of operation (of brake pedal) F: Axial force (pressing force) F * :Target axial force θ:Motor rotation angle θ * :Target motor rotation angle T:Motor torque Tff:Feedforward component Tfb:Feedback component Tb:Basic torque I:Current (current supplied to electric motor) Kft:Axial force-torque conversion coefficient Kt:Motor torque constant ε:Mechanical efficiency

Claims

1. A brake system installed in a vehicle, A brake operating member operated by the driver, A pair of electric brake devices are provided for each of the left and right wheels, each having an electric motor as a drive source, and generating braking force by pressing the brake pads against the disc rotor with a pressing force that relies on the torque of the electric motors. A controller is provided for each of the pair of electric brake devices to perform service brake control, which generates a braking force corresponding to the operation of the brake operating member by controlling the torque of the electric motor. Equipped with, A brake system in which the controller is configured to perform a characteristic learning process for each of the pair of electric brake devices to learn the torque-pressure characteristic, which is the characteristic of the pressing force relative to the torque of the electric motor.

2. The brake system according to claim 1, wherein the service brake control is a control that controls the torque to be generated by the electric motor based on a basic torque including a feedforward torque component and a feedback torque component, and the controller is configured to determine the feedforward torque component in the service brake control according to the torque-pressure characteristic based on the actual pressing force which is the pressing force actually generated, or the target pressing force which is the pressing force which should be generated, and to determine the feedback torque component according to the feedback control law based on the motor rotation position deviation which is the deviation of the actual motor rotation position which is the actual motor rotation position relative to the target motor rotation position which is the target motor rotation position which depends on the operation of the brake operating member.

3. The brake system according to claim 2, wherein each of the pair of electric brake devices has a sensor for detecting the actual pressing force, and the controller is configured to determine the feedforward torque component based on the detected actual pressing force, which is the actual pressing force detected by the sensor.

4. The brake system according to claim 2, wherein each of the pair of electric brake devices does not have a sensor for detecting the actual pressing force, and the controller is configured to determine the feedforward torque component based on the target pressing force.

5. The brake system according to claim 1, wherein the controller is configured to perform an alternating characteristic learning process, which, as the characteristic learning process, learns the torque-pressure characteristics of one of the pair of electric brake devices while maintaining the braking force of the other while the vehicle is stopped, and then learns the torque-pressure characteristics of the other while maintaining the braking force of the other.

6. Each of the aforementioned pair of electric brake devices has a parking brake mechanism for generating parking brake force while the vehicle is stopped. The brake system according to claim 5, wherein the controller is configured to perform the alternating characteristic learning process when both of the pair of electric brake devices are generating a parking brake force.

7. The brake system according to claim 6, wherein the controller is configured to perform a simultaneous characteristic learning process as the characteristic learning process, in which, when neither of the pair of electric brake devices is generating a parking brake force while the vehicle is stopped, the controller simultaneously learns the torque-pressure characteristics of both of the pair of electric brake devices at the same time.

8. The brake system according to claim 1, wherein the controller is configured to perform the characteristic learning process each time the vehicle travels a set distance or more, and also to perform the process based on a predetermined command even when the vehicle has not traveled the set distance.

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