Rigidity updating method, device and equipment of actuator and braking system

Abstract

The invention provides a rigidity updating method of an actuator, and relates to the technical field of automobiles. The method comprises the steps that before an actuator is offline, current estimation clamping force and actual clamping force collected by a force sensor in the process that the actuator clamps and releases a brake disc for N times are obtained, and N is a positive integer; according to the current estimation clamping force and the actual clamping force, the friction coefficients of the actuator in different current segments in the clamping and releasing processes are estimated; in response to power-on recovery after the actuator is offline, target clamping force is determined according to motor current in the process that the actuator clamps and releases the brake disc M times and friction coefficients of the different current segments, and M is a positive integer; and according to the target clamping force, rigidity updating is conducted on the actuator. According to the method, the stiffness characteristic of the actuator can be accurately updated, and the control precision of the clamping force of the electronic mechanical brake is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of automobiles, and particularly relates to a method, device, equipment and braking system for updating the stiffness of an actuator. Background Art

[0002] An Electronic Mechanical Brake (EMB) uses an electronic controller and a mechanical actuator to directly apply a braking force to the wheel end, and it is necessary to accurately control the clamping force of the electronic mechanical brake during the braking process.

[0003] Currently, a pressure sensorless control scheme is used to accurately control the clamping force of the electronic mechanical brake, which mainly performs angle closed-loop control based on the stiffness characteristics updated regularly.

[0004] However, in the current pressure sensorless control scheme, the accuracy of updating the stiffness characteristics is poor, resulting in low control accuracy of the clamping force of the electronic mechanical brake. Summary of the Invention

[0005] The present invention provides a method, device, equipment and braking system for updating the stiffness of an actuator, which can accurately update the stiffness characteristics of the actuator and improve the control accuracy of the clamping force of the electronic mechanical brake.

[0006] In a first aspect, an embodiment of the present invention provides a method for updating the stiffness of an actuator, where the actuator is used to clamp or release a brake disc of a wheel, and the method includes:

[0007] Before the actuator is taken offline, obtain the current estimated clamping force during N clamping and releasing processes of the actuator on the brake disc and the actual clamping force collected by a force sensor, where N is a positive integer;

[0008] Estimate the friction coefficients of different current segments during the clamping and releasing processes of the actuator according to the current estimated clamping force and the actual clamping force;

[0009] In response to the actuator being powered on again after being taken offline, determine a target clamping force according to the motor current during M clamping and releasing processes of the actuator on the brake disc and the friction coefficients of different current segments, where M is a positive integer;

[0010] Update the stiffness of the actuator according to the target clamping force.

[0011] In a feasible embodiment, the step of determining a target clamping force according to the motor current during M clamping and releasing processes of the actuator on the brake disc and the friction coefficients of different current segments includes:

[0012] Obtain the motor currents at the same relative angular displacement with respect to the contact point during M clamping and releasing processes of the brake disc by the actuator.

[0013] Determine the target clamping force according to the motor currents at the same relative angular displacement with respect to the contact point during clamping and releasing, and the friction coefficients of different current segments.

[0014] In an implementable embodiment, the actuator includes a motor, a ball bearing, a planetary gear set, a thrust bearing, a ball screw, and a brake pad; wherein, the motor is connected to the ball bearing, the ball bearing is connected to the planetary gear set, the planetary gear set is connected to the thrust bearing, and the thrust bearing is connected to the ball screw; when the motor rotates, the ball screw drives the nut to move on the nut guide rail to drive the brake pad to clamp or release the brake disc.

[0015] The determining the target clamping force according to the motor currents at the same relative angular displacement with respect to the contact point during clamping and releasing, and the friction coefficients of different current segments includes:

[0016] Obtain the force conditions of the motor, ball bearing, planetary gear set, thrust bearing, ball screw, and brake pad during the clamping or releasing process of the actuator.

[0017] Analyze and model the frictional force of the ball screw during the forward clamping and reverse releasing processes according to the force conditions.

[0018] Determine the mapping relationship between the clamping force and the motor current through the established model.

[0019] Determine the first clamping force during forward clamping and the second clamping force during reverse releasing according to the mapping relationship and the motor currents at the same relative angular displacement with respect to the contact point during clamping and releasing.

[0020] Eliminate the frictional force of the ball screw during the clamping and releasing processes according to the first clamping force, the second clamping force, and the friction coefficient corresponding to the motor current to obtain the target clamping force.

[0021] In an implementable embodiment, the determining the target clamping force according to the motor currents at the same relative angular displacement with respect to the contact point during clamping and releasing, and the friction coefficients of different current segments includes:

[0022] Obtain the equivalent Coulomb friction coefficients during forward clamping and reverse releasing according to the friction coefficients of different current segments.

[0023] Obtain the total transmission ratio of the planetary gear set in the actuator, the gear transmission efficiency, the pitch radius of the lead screw, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during release.

[0024] Determine the target clamping force according to the equivalent Coulomb friction coefficient during forward clamping and reverse release, the total transmission ratio of the planetary gear set, the gear transmission efficiency, the pitch radius, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during release.

[0025] In an implementable embodiment, the determining the target clamping force according to the equivalent Coulomb friction coefficient during forward clamping and reverse release, the total transmission ratio of the planetary gear set, the gear transmission efficiency, the pitch radius, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during release includes:

[0026]

[0027] In the above formula, G t,A and G t,R are the equivalent Coulomb friction coefficients during clamping and release respectively, i g is the total transmission ratio of the planetary gear set, η g is the gear transmission efficiency, r s is the pitch radius of the lead screw, K m is the motor torque coefficient, i q，A is the q-axis current of the motor during clamping, i q，R is the q-axis current of the motor during release, F p,A is the clamping force during clamping, F p,B is the clamping force during release, F p is the target clamping force.

[0028] In an implementable embodiment, the updating the stiffness of the actuator according to the target clamping force includes:

[0029] Obtain the first stiffness curve of the actuator according to the target clamping force;

[0030] In response to the actuator being powered on again after the wheel has been braked L times, obtain the second stiffness curve of the actuator after being powered on again, where L is a positive integer;

[0031] If the deviation between the first stiffness curve and the second stiffness curve is greater than a set threshold, update the stiffness characteristics of the actuator according to the second stiffness curve.

[0032] In an implementable embodiment, the method further includes:

[0033] Perform closed-loop control of the actuator's position without a pressure sensor according to the updated stiffness characteristics.

[0034] In a second aspect, an embodiment of the present invention provides a stiffness update device for an actuator, including:

[0035] An acquisition module, configured to acquire the current estimated clamping force and the actual clamping force collected by the force sensor during N clamping and releasing processes of the brake disc by the actuator before the actuator is taken offline, where N is a positive integer;

[0036] An estimation module, configured to estimate the friction coefficient of different current segments during the clamping and releasing processes of the actuator according to the current estimated clamping force and the actual clamping force;

[0037] A determination module, configured to determine a target clamping force according to the motor current and the friction coefficient of different current segments during M clamping and releasing processes of the brake disc by the actuator in response to the actuator being powered on again after being taken offline, where M is a positive integer;

[0038] An update module, configured to update the stiffness of the actuator according to the target clamping force.

[0039] In a third aspect, an embodiment of the present invention provides an electronic device, including: a processor and a memory storing computer program instructions, where when the processor executes the computer program instructions, the steps of the above method are implemented.

[0040] In a fourth aspect, an embodiment of the present invention provides a braking system, including the above electronic device.

[0041] The stiffness update method, device, equipment, and braking system for the actuator provided by the embodiments of the present invention can update the stiffness characteristics by acquiring the friction coefficients of different current segments, calibrating the change law of the asymmetry caused by the ball screw, and ensuring the accuracy of the clamping force control without a pressure sensor. Description of the Drawings

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0043] Figure 1 It is a schematic structural diagram of an actuator in an electromechanical braking system provided by an embodiment of the present application;

[0044] Figure 2 It is a working principle flowchart of a control system for stiffness characteristic update provided by an embodiment of the present application;

[0045] Figure 3A Schematic flowchart of the stiffness update method for the actuator provided by the embodiment of the present application;

[0046] Figure 3B Schematic diagram of the planar motion force analysis model of the ball screw provided by the embodiment of the present application;

[0047] Figure 4 Schematic flowchart of the friction coefficient estimation process provided by the embodiment of the present application;

[0048] Figure 5 Schematic flowchart of the process for the control system to implement the stiffness update function provided by the embodiment of the present application;

[0049] Figure 6 Schematic diagram of the structure of the stiffness update device for the actuator provided by the embodiment of the present application;

[0050] Figure 7 Schematic diagram of the hardware structure of the electronic device provided by the embodiment of the present invention. Detailed implementation manners

[0051] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present invention, rather than to limit the present invention. For those skilled in the art, the present invention can be implemented without some of these specific details. The following description of the embodiments is only intended to provide a better understanding of the present invention by showing examples of the present invention.

[0052] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, the elements defined by the statement "including..." do not exclude the existence of additional identical elements in the process, method, article or device including the elements.

[0053] The Electronic Mechanical Brake (EMB) is one of the research hotspots in the field of by-wire chassis. It uses an electronic controller and a mechanical actuator to directly apply braking force to the wheel end, significantly reducing system components. At the same time, it has a faster response speed and higher wheel-end execution flexibility, making it a highly integrated solution for braking systems. To achieve precise control of the clamping force of the electronic mechanical brake, a pressure sensor needs to be integrated in the limited space of the actuator. However, its single cost is relatively high, and it is easily affected by factors such as temperature, friction hysteresis, and assembly centering, resulting in poor reliability. Therefore, sensorless control is a key technology that urgently needs to be broken through. Currently, the mainstream solution for sensorless control is to perform angle closed-loop control based on the stiffness characteristics updated regularly. An accurate and robust stiffness characteristic update method is the prerequisite for achieving clamping force control. In related technologies, the stiffness characteristic update mainly includes the following methods: (1) Using the moment balance equation or state observer to estimate and update the stiffness characteristics in real time requires accurate calibration of the system friction characteristics, and the estimation noise is relatively large. (2) The estimation method of using a superimposed high-frequency signal to eliminate friction will generate relatively serious jitter and noise. (3) The estimation method of using forward and reverse clamping and releasing to eliminate friction does not consider the friction asymmetry caused by the ball screw. At the same time, the automatic calibration and update of the friction coefficient and stiffness are also key issues.

[0054] In view of the above problems, based on the estimation method of using forward and reverse clamping and releasing to eliminate friction, the embodiment of this application proposes a stiffness update method considering friction asymmetry and designs a stiffness update function module. The friction asymmetry caused by the actuator, especially the ball screw, is modeled, and its asymmetry change law is calibrated using endurance tests, improving the robustness of the algorithm throughout the entire life cycle of the actuator.

[0055] Next, the technical solution of this application will be described in detail through specific embodiments. It should be noted that these specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments.

[0056] In the electronic mechanical braking system, the motor drives a speed reduction and torque increasing mechanism (such as a planetary gear set), and the speed reduction and torque increasing mechanism drives a motion conversion mechanism (such as a ball screw). The lead screw nut moves linearly to push the brake pad and press the brake disc. Exemplarily, Figure 1 is a schematic structural diagram of the actuator in the electronic mechanical braking system provided by the embodiment of this application, as Figure 1As shown in the figure, it includes a motor, a ball bearing 11, a planetary gear set 12, a force sensor 13, a thrust bearing 14, a ball screw, a brake pad 15, and a caliper 17. Among them, the motor drives the ball bearing 11 to drive the planetary gear set 12 to move. The planetary gear set 12 drives the thrust bearing 14 to push the ball screw to move on the nut guide, so that the brake pad 15 clamps or releases the brake disc 16, thereby achieving braking.

[0057] In this embodiment, the stiffness update scheme of the actuator can run in the control system for stiffness characteristic update. Exemplarily, Figure 2 is the working principle flowchart of the control system for stiffness characteristic update provided by the embodiment of the present application. As Figure 2 shown, the control system for stiffness characteristic update mainly includes the following functional modules:

[0058] (1) Upper-level control system: It can determine whether to enable according to the friction coefficient calibration and stiffness curve update requirements and the current states of the vehicle and the actuator. When the function is enabled, it sends a clamping / releasing instruction to the execution control system.

[0059] (2) Piston position calculation: Calculate the current piston position according to the motor angle and the parameters of the brake actuator. Since the motor position sensor can sense the motor angle in real time, the piston position can be obtained by integrating according to the actuator parameters:

[0060]

[0061] In the above formula, S is the piston position, Θ is the mechanical angle of the motor rotation, K is the transmission ratio of the speed reduction and torque increase mechanism, p is the thread pitch, and r is the pitch circle radius.

[0062] (3) Contact point identification: Select to enable / disable the contact point identification function according to the clamping / releasing instruction of the upper-level control system. When the function is enabled, refresh the contact point according to the actuator current and the piston position.

[0063] (4) Clamping / releasing control: When the upper-level control system issues a clamping / releasing instruction, drive the motor to rotate forward / backward according to the piston position and the actuator clamping force to complete the clamping / releasing control of the actuator position closed-loop.

[0064] (5) Clamping force estimation: Estimate the motor torque according to the motor current, and estimate the clamping force from the gear set transmission ratio and the ball screw lead.

[0065] (6) Friction coefficient estimation: Before the actuator is taken offline, perform several clamping and releasing operations. Use the external force sensor to obtain the clamping force signal, estimate the friction coefficient from the current, the estimated clamping force, and the actual clamping force, and store the friction coefficients in different current segments during the clamping / releasing process respectively.

[0066] (7) Stiffness update: After the actuator is powered on, it performs several clamping and releasing operations, reads the friction coefficients in different current segments, superimposes the estimated clamping forces at the same piston displacement according to the asymmetric friction coefficients of clamping / releasing, eliminates the forward and reverse friction terms, obtains an accurate stiffness curve and stores it for subsequent closed-loop control without a pressure sensor.

[0067] In this embodiment, the stiffness update function is divided into three stages: ① Clamping and releasing; ② Data point storage; ③ Online fitting. First, perform a clamping and releasing operation according to the displacement ramp command and identify the contact point. Secondly, select several data points of the relative displacement according to the identified contact point. Finally, read the data points, eliminate the friction according to the calibrated asymmetric friction relationship to obtain the estimated clamping force, and perform an online fit to obtain the coefficients of the cubic curve of the stiffness characteristics. The following will be described in detail through some embodiments.

[0068] Exemplarily, Figure 3A is a schematic flowchart of the stiffness update method of the actuator provided by the embodiment of the present application. Combining the above Figure 1 , this actuator is mainly used to clamp or release the brake disc of the wheel. Among them, this actuator can be mounted on the braking system of the vehicle for braking the wheels on the vehicle. This method can be deployed on the electronic device of the vehicle and executed by the electronic device. As Figure 3A shown, this method specifically includes the following steps:

[0069] Step S310: Before the actuator is taken offline, obtain the current estimated clamping force and the actual clamping force collected by the force sensor during the N clamping and releasing operations of the brake disc by the actuator. Wherein, N is a positive integer.

[0070] In this embodiment, during the driving of the vehicle, when the actuator clamps the brake disc, the wheel speed slowly decreases, and when the actuator releases the brake disc, the wheel speed slowly recovers.

[0071] Among them, the actuator being taken offline may refer to the vehicle turning off the engine, etc., and the actuator enters the shutdown or standby state, so that the actuator is taken offline.

[0072] In this embodiment, the actuator can be controlled to clamp or release by a control command issued by the driver or the intelligent driving system. Among them, clamping and releasing are two relative states. After the clamping state is completed, it enters the release state, and after the release state is completed, it enters the clamping state.

[0073] In this embodiment, referring to the above Figure 1 , the force sensor can be arranged close to the thrust bearing. The electromechanical brake needs to adjust the pressing degree between the brake disc and the brake pads to achieve braking. At this time, the force sensor will display the braking force of the current wheel-end actuator, that is, the actual clamping force.

[0074] Among them, the current-estimated clamping force may refer to a clamping force estimated based on the current of the motor in the actuator during the clamping or releasing process of the actuator.

[0075] Step S320: Estimate the friction coefficients of different current segments of the actuator during the clamping and releasing processes according to the current-estimated clamping force and the actual clamping force.

[0076] In this embodiment, the friction coefficients of the ball screw of the actuator during the clamping and releasing processes are asymmetric, which affects the accuracy of the final clamping force control. Referring to the above Figure 1 , assume that the friction coefficient at a certain position point W1 where the thrust bearing pushes the ball screw to move forward horizontally to drive the brake pad to clamp the brake disc is A, and the friction coefficient at the same position point W1 where the thrust bearing drives the ball screw to move backward horizontally to drive the brake pad to release the brake disc is B, then A and B are asymmetric.

[0077] In this embodiment, after several automatic clamping and releasing operations, the friction coefficients can be estimated from the current-estimated clamping force and the actual clamping force and averaged, and the positive and negative asymmetric friction coefficients of different current segments are stored.

[0078] Exemplarily, the motor current of the actuator during the clamping and releasing processes can be obtained, and at the same time, the average value of the current-estimated clamping force and the actual clamping force is taken to obtain the average clamping force, and then the friction coefficient corresponding to this current is determined according to the mapping relationship between the clamping force and the current.

[0079] Step S330: In response to the actuator being powered on again after being powered off, determine the target clamping force according to the motor current and the friction coefficients of different current segments during M clamping and releasing processes of the actuator on the brake disc. Wherein, M is a positive integer.

[0080] Step S340: Update the stiffness of the actuator according to the target clamping force.

[0081] In this embodiment, after the actuator is powered on, the stiffness update is enabled, and the target clamping force is estimated using the motor current and the friction coefficient.

[0082] Among them, several clamping and releasing operations are automatically performed, the estimated clamping forces at the same piston position are superimposed according to the asymmetric friction coefficients, the positive and negative friction terms are eliminated and averaged to obtain a more accurate target clamping force at this angular displacement, and an accurate stiffness curve is obtained and stored based on this target clamping force.

[0083] In this embodiment, the stiffness characteristic reflects the relationship between the force applied to the actuator and its deformation. By continuously updating the stiffness characteristic, the clamping force state can be indirectly understood. Combining with the angular position closed-loop control (i.e., adjusting the actuator's action according to the deviation between the set target angular position and the actual angular position), the control of the clamping force can be achieved. In an electromechanical brake, there is an inherent relationship between the stiffness characteristic of the actuator and the clamping force it outputs. For example, when a certain driving signal is input to the actuator, the relationship between the displacement generated and the corresponding clamping force reflects the stiffness situation. If the stiffness is large, a greater clamping force can be generated under the same displacement; conversely, the clamping force is smaller.

[0084] In this embodiment, since the electromechanical brake is affected by various factors during actual operation, such as the expansion or contraction of materials caused by changes in environmental temperature, the change in structure due to wear between components, and fatigue during long-term use, etc., these will all change the stiffness characteristic of the actuator. Therefore, it is necessary to update it regularly to ensure the accuracy and reliability of inferring the clamping force based on the stiffness characteristic. For example, when using an electromechanical brake in an environment with a large temperature difference, if the stiffness characteristic is not updated in time, there may be a large deviation when controlling the clamping force according to the initially set stiffness value, and precise control cannot be achieved.

[0085] In this embodiment, the angular position closed-loop control can be performed based on the regularly updated stiffness characteristic to achieve the braking of the wheel. Among them, the angular position closed-loop control is a control method that adjusts the actuator's action in real time by monitoring the rotation angle of the actuator to achieve precise control of the clamping force. Specifically, the angular position closed-loop control can set a target angular position, corresponding to the desired clamping force magnitude. During the execution process, the sensor will continuously feedback the actual angular position of the actuator, and the control system will compare the actual angular position with the target angular position and adjust the actuator's action according to the deviation between the two. For example, if the actual angular position is smaller than the target angular position, it means that the predetermined clamping degree has not been reached, and the control system will drive the actuator to continue rotating to increase the clamping force; conversely, if the actual angular position exceeds the target angular position, it means that the clamping force is too large, and the control system will correspondingly reduce the actuator's action to lower the clamping force.

[0086] Among them, the corner closed-loop control combined with stiffness characteristic update can closely relate the corner to the clamping force by using the stiffness characteristic. Through the accurate stiffness characteristic updated regularly, the corresponding clamping force can be calculated more precisely according to the current corner situation, and then the high-precision adjustment of the clamping force can be realized in the closed-loop control. For example, given the currently updated stiffness value and the angle of rotation of the actuator, the clamping force acting on the braking object at this time can be accurately determined according to the mathematical relationship between them (determined by the stiffness characteristic), and then the subsequent action of the actuator can be adjusted according to the difference between the target clamping force and the actually feedback clamping force (reflected by the corner), so as to achieve the purpose of accurately controlling the clamping force.

[0087] In addition, in some embodiments, the stiffness update after the actuator is powered on needs to judge the actuator, the brake disc and the vehicle state. In order to ensure the accuracy of the update, the stiffness update needs to be carried out when the actuator has no fault, the temperature of the brake disc is normal, and the vehicle is in a stationary state.

[0088] In the embodiments of the present application, by obtaining the friction coefficients of different current segments and calibrating the variation law of the asymmetry caused by the ball screw, the stiffness characteristic can be updated, ensuring the accuracy of the clamping force control without a pressure sensor.

[0089] The following provides a system overview through some embodiments to illustrate the stiffness update method considering the friction asymmetry caused by the ball screw.

[0090] First, in order to obtain the dynamic mapping relationship between the motor current and the clamping force in the forward and reverse directions, especially the friction asymmetry caused by the ball screw, it is necessary to perform a partial modeling of the actuator. Among them, the actuator includes a motor, a ball bearing, a planetary gear set, a thrust bearing, a ball screw and a brake pad; the motor is connected to the ball bearing, the ball bearing is connected to the planetary gear set, the planetary gear set is connected to the thrust bearing, and the thrust bearing is connected to the ball screw; when the motor rotates, the ball screw drives the nut to move on the nut guide rail to drive the brake pad to clamp or release the brake disc. Exemplarily, Figure 3B is a schematic diagram of the planar motion force analysis model of the ball screw provided in the embodiments of the present application, as Figure 3B shown, the ball 32 rolls in the nut guide rail 31, resulting in friction asymmetry of the ball screw.

[0091] Among them, except for the pad and the caliper stiffness, it is assumed that all mechanical components are rigid. The electrical equation and mechanical equation of the motor are as follows:

[0092]

[0093] In the above formula, u d and u qare the d-axis (excitation axis) and q-axis (torque axis) voltages of the motor, i d and i q are the d-axis and q-axis currents of the motor, L d and L q are the d-axis and q-axis inductances of the motor, R s is the stator resistance, K m is the motor torque coefficient, K m = 3 / 2P n Ψ f ,Ψ f is the permanent magnet flux linkage, θ e and θ m are the electrical angle and mechanical angle of the motor respectively, θ e = θ m P n ,P n is the number of pole pairs, J m is the moment of inertia of the motor, T mf and T L are the frictional torque and load torque of the motor respectively, B m and τ m are the viscous friction coefficient of the motor and the Coulomb friction torque independent of the load respectively.

[0094] Among them, the planetary gear set is modeled with an ideal transmission ratio including transmission efficiency as follows:

[0095] T s = i g η g T L

[0096]

[0097] In the above formula, T s is the driving torque of the lead screw, i g is the total transmission ratio of the planetary gear set, η g is the gear transmission efficiency, θ s is the rotation angle of the lead screw.

[0098] In some embodiments, Figure 4 is a schematic diagram of the friction coefficient estimation process provided by the embodiment of the present application. As Figure 4 shown, it includes the following steps:

[0099] Step S410: Obtain the first dynamic equation of the ball screw and nut during the clamping process and the second dynamic equation of the ball screw and nut during the release process.

[0100] In this embodiment, reference can be continued to the above Figure 3B to expand the ball screw as shown in Figure 3BThe force analysis model of planar motion shown converts the rotational motion of the ball screw into planar translation. When clamping forward and releasing backward, the external forces on the ball screw include the driving force F applied by the gear set s , the friction f of the thrust bearing b , the contact force N between the screw and the nut s , and the rolling friction f of the balls s . The external forces on the nut also include the clamping force F p and the friction force f between the nut and the housing guide rail n .

[0101] Among them, r s is the pitch radius of the ball screw, r s = L / 2π, where L is the lead of the ball screw.

[0102] In some embodiments, the driving force Fs applied by the planetary gear set to the ball screw, the friction force fb of the thrust bearing, the contact force Ns between the screw and the nut, the clamping force Fp, and the lead angle α of the screw can be analyzed. At the same time, further combined with the inertia J pg of the planet gear, the inertia J sg of the sun gear, the inertia J s of the screw, the total transmission ratio i g of the planetary gear set, the translational displacement of the ball screw and the nut along their axes, the total mass m p of the piston and the brake pad in the actuator, the mass m n of the nut, and the pitch radius r s of the ball screw, the first dynamic equation and the second dynamic equation are constructed.

[0103] Exemplarily, when clamping forward, the first dynamic equation of the ball screw and the nut is expressed as:

[0104]

[0105] When releasing backward, the second dynamic equations of the ball screw and the nut are respectively expressed as:

[0106]

[0107] In the above formula, J pg , J sg and J s are respectively the inertia of the planet gear, the inertia of the sun gear and the inertia of the screw, i g is the total transmission ratio of the planetary gear set, x s and y n are the translational displacements of the ball screw and the nut along their axes, α is the lead angle of the screw, m n is the mass of the nut, m p is the total mass of the piston and the brake pad, F sThe driving force applied by the planetary gear set to the ball screw, f b The frictional force of the thrust bearing, N s The contact force between the screw and the nut, f s The rolling frictional force of the ball, F p The clamping force, f n The frictional force between the nut and the housing guide rail.

[0108] Step S420: Obtain the relationship between the rotation angle of the ball screw and the displacement of the nut.

[0109] In this embodiment, the thrust bearing friction and the guide rail friction are respectively modeled (for example, using the Karnopp friction model):

[0110]

[0111] In the above formula, D b , C b and G b are respectively the viscous friction coefficient of the thrust bearing, the Coulomb friction torque independent of the load, and the Coulomb friction coefficient. D n , C n and G n are respectively the viscous friction coefficient of the guide rail, the Coulomb friction force independent of the load, and the Coulomb friction coefficient. T nb and F ns are the maximum static friction torque of the thrust bearing independent of the load and the maximum static friction of the guide rail. θ s is the rotation angle of the ball screw.

[0112] In some embodiments, the lead angle of the screw, the translational displacements of the ball screw and the nut along their axes can be obtained; then, based on the lead angle of the screw, the translational displacements of the ball screw and the nut along their axes, the relationship between the rotation angle of the ball screw and the displacement of the nut can be determined.

[0113] Exemplarily, the relationship between the screw rotation angle and the nut displacement:

[0114] y n =x s tanα = θ s r s tanα

[0115] In the above formula, θ s is the rotation angle of the ball screw, r s is the pitch radius of the ball screw, α is the lead angle of the screw, x s and y n are the translational displacements of the screw and the nut along their axes.

[0116] Step S430: Obtain the total frictional torque during the clamping and releasing processes.

[0117] Among them, the total frictional torque includes the equivalent frictional torque generated by the motor frictional torque, the thrust bearing frictional torque, the inclined plane friction of the ball screw ramp, the contact force separation, and the housing guide rail friction.

[0118] In this embodiment, the relationship between the screw rotation angle and the nut displacement is combined with the dynamic equations of the ball screw and the nut, the internal ball contact force and friction force are eliminated, and the dynamic mapping relationship between the motor current and the clamping force during forward clamping and reverse release is obtained after arrangement:

[0119]

[0120] In the above formula, i g is the total transmission ratio of the planetary gear set, η g is the gear transmission efficiency, r s is the pitch radius of the ball screw, K m is the motor torque coefficient, i q,A is the q-axis current of the motor during clamping, i q，R is the q-axis current of the motor during release, θ m，A is the mechanical angle of the motor during clamping, θ m，R is the mechanical angle of the motor during release, T f,A is the total frictional torque during forward clamping, T f，R is the total frictional torque during reverse release, J eq,A and J eq,R are the equivalent moments of inertia during forward clamping and reverse release respectively, F p,A and F p,R are the clamping forces during forward clamping and reverse release respectively.

[0121] Among them, the equivalent moment of inertia includes the motor moment of inertia, the planetary gear moment of inertia, the sun gear moment of inertia, the screw moment of inertia, and the equivalent moment of inertia of the translational masses of the nut, piston, and brake pads:

[0122]

[0123] In the above formula, J eq,A and J eq,R are the equivalent moments of inertia during forward clamping and reverse release respectively.

[0124] Exemplarily, the total frictional torque T f,A during the clamping process and the total frictional torque T f,R during the release process can be calculated by the following formula:

[0125]

[0126] Furthermore, by considering the entire ball screw along the x s , yn Perform a force analysis on the shaft. Since it is in an approximately constant low-speed motion state during the stiffness update process, the relatively small viscous friction and load-independent Coulomb friction are ignored:

[0127]

[0128] In this way, the friction torque of the thrust bearing and the friction force of the housing guide rail during forward clamping and reverse release can be sorted out:

[0129]

[0130] Further substitute it back into the total friction torque equation, and also ignore the relatively small viscous friction and load-independent Coulomb friction, and sort it out to get:

[0131]

[0132] Among them, the Coulomb friction consists of two parts: the item related to the motor output torque and the item related to the clamping force, and has strong asymmetry:

[0133]

[0134] Step S440: Determine the first mapping relationship between the motor current and the clamping force during the clamping process and the second mapping relationship between the motor current and the clamping force during the release process according to the relationship between the ball screw rotation angle and the nut displacement, the first dynamic equation, the second dynamic equation, and the total friction torque during the clamping and release processes.

[0135] In this embodiment, according to the relationship between the ball screw rotation angle and the nut displacement, the first dynamic equation, the second dynamic equation, and the total friction torque during the clamping and release processes, substitute them back into the dynamic mapping relationship formula between the motor current and the clamping force, and ignore the inertial force, then the first mapping relationship and the second mapping relationship can be obtained.

[0136] Exemplarily, the first mapping relationship is:

[0137]

[0138] In the above formula, F p,A is the clamping force during clamping, i g is the total transmission ratio of the planetary gear set, η g is the planetary gear transmission efficiency, r s is the pitch radius of the ball screw, K m is the motor torque coefficient, i q,A is the q-axis current of the motor during clamping, G t,A is the equivalent Coulomb friction coefficient during clamping;

[0139] The second mapping relationship is:

[0140]

[0141] In the above formula, F p,R is the clamping force at release, and G t,B is the equivalent Coulomb friction coefficient at release.

[0142] Step S450: Estimate the friction coefficient of different current segments during the clamping and release processes of the actuator according to the current, the estimated clamping force, the actual clamping force, the first mapping relationship, and the second mapping relationship.

[0143] Exemplarily, the friction coefficient is:

[0144]

[0145] In the above formula, G t,A and G t,B are the equivalent Coulomb friction coefficients during forward clamping and reverse release, respectively.

[0146] In some embodiments, when determining the target clamping force, the motor currents during M times of clamping and releasing the brake disc by the actuator can be used to obtain the motor currents at the same relative angular displacement relative to the contact point during clamping and release; then, according to the motor currents at the same relative angular displacement relative to the contact point during clamping and release, and the friction coefficients of different current segments, the target clamping force can be determined.

[0147] In this embodiment, when updating the stiffness, the currents at the same relative angular displacement relative to the contact point during forward clamping and reverse release are taken into account for the friction asymmetry.

[0148] In some embodiments, the equivalent Coulomb friction coefficients during forward clamping and reverse release can be obtained according to the friction coefficients of different current segments; then, the total transmission ratio of the planetary gear set in the actuator, the gear transmission efficiency, the pitch radius of the lead screw, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during release can be obtained. And according to the equivalent Coulomb friction coefficients during forward clamping and reverse release, the total transmission ratio of the planetary gear set, the gear transmission efficiency, the pitch radius, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during release, the target clamping force can be determined.

[0149] Exemplarily, the positive and negative frictions can be eliminated according to the following formula to obtain a more accurate clamping force at this angular displacement as the target clamping force:

[0150]

[0151] In the above formula, G t,A and G t,R are the equivalent Coulomb friction coefficients during clamping and release, respectively, and i gis the total transmission ratio of the planetary gear set, η g is the gear transmission efficiency, r s is the pitch radius of the lead screw, K m is the motor torque coefficient, i q，A is the q-axis current of the motor during clamping, i q，R is the q-axis current of the motor during release, F p,A is the clamping force during clamping, F p,B is the clamping force during release, F p is the target clamping force.

[0152] In some other embodiments, the actuator includes a motor, a ball bearing, a planetary gear set, a thrust bearing, a ball screw, and a brake pad; wherein, the motor is connected to the ball bearing, the ball bearing is connected to the planetary gear set, the planetary gear set is connected to the thrust bearing, and the thrust bearing is connected to the ball screw; when the motor rotates, the ball screw drives the nut to move on the nut guide rail to drive the brake pad to clamp or release the brake disc.

[0153] Among them, the friction coefficient corresponding to the motor current can be determined according to the q-axis current i q，R of the motor during release, the q-axis current i q，A of the motor during clamping, and the equivalent Coulomb friction coefficient during clamping and release. At the same time, F p,A can be used as the first clamping force during forward clamping, F p,B as the second clamping force during reverse release, and based on the first clamping force, the second clamping force, and the friction coefficient corresponding to the motor current, the friction force of the ball screw during clamping and release is eliminated to obtain the target clamping force. Among them, the first clamping force during forward clamping and the second clamping force during reverse release can be calculated based on the mapping relationship between the clamping force and the motor current.

[0154] In addition, the mapping relationship between the clamping force and the motor current can be analyzed and modeled through the force conditions of the motor, ball bearing, planetary gear set, thrust bearing, ball screw, and brake pad during the clamping or release process of the actuator. Through the established model, the mapping relationship between the clamping force and the motor current is determined, specifically including the first mapping relationship and the second mapping relationship above.

[0155] Furthermore, in some embodiments, the wear of the contact surface of mechanical parts is usually divided into three stages: running-in stage, stable wear stage, and severe wear stage. Under normal operating conditions, the actuator should work in the stable wear stage with a low and basically constant wear rate. Using bench durability tests to identify the friction parameters of each part of the actuator and calibrate its change law, there are:

[0156]

[0157] In the above formula, t m is the wear estimation time step, and G b0 , G n0 and μ s0 are respectively the thrust bearing, the housing guide rail and the ball Coulomb friction coefficients calibrated initially.

[0158] In some embodiments, after the vehicle has traveled a long distance, due to the wear of the spacer, the stiffness curve changes and the clamping force control has an error. Therefore, it is necessary to update the rigid characteristics. Among them, before the long-distance travel, the first stiffness curve of the actuator can be obtained according to the target clamping force, and then the position closed-loop control without a pressure sensor can be performed according to the first stiffness curve. After the long-distance travel, the actuator will first go offline, and then after being powered on again, the stiffness update can be enabled. At this time, the second stiffness curve of the actuator after being powered on again is obtained. If the deviation between the first stiffness curve and the second stiffness curve is greater than the set threshold, the stiffness characteristics of the actuator are updated according to the second stiffness curve.

[0159] Exemplarily, Figure 5 is a schematic flow chart of the control system provided by the embodiment of the present application to implement the stiffness update function. As Figure 5 shown, it includes the following steps:

[0160] Step S510: Enable the friction coefficient calibration before the actuator goes offline, and use an external force sensor to obtain the true clamping force signal.

[0161] Step S520: Automatically perform several clamping and releasing operations, estimate the friction coefficient from the current and the actual clamping force, take the average, and store the positive and negative asymmetric friction coefficients in different current segments.

[0162] Step S530: Enable the stiffness update after the actuator is powered on, and estimate the clamping force using the motor current and the friction coefficient.

[0163] Step S540: Automatically perform several clamping and releasing operations, superimpose the estimated clamping forces at the same piston position according to the asymmetric friction coefficient, eliminate the positive and negative friction terms, take the average, and obtain and store the accurate stiffness curve.

[0164] Step S550: Perform position closed-loop control without a pressure sensor according to the stiffness curve.

[0165] Step S560: After the long-distance travel, due to the wear of the spacer, the stiffness curve changes and the clamping force control has an error.

[0166] Step S570: Enable the stiffness update after the actuator is powered on again, automatically perform several clamping and releasing operations. If there is a large deviation between the average value of the stiffness curve and the stored value, update the stiffness characteristics.

[0167] Further, in some embodiments, after the stiffness characteristic update is completed, the actuator can be subjected to position closed-loop control without a pressure sensor according to the updated stiffness characteristic. Specifically, refer to the above Figure 5 In step S580, position closed-loop control without a pressure sensor is performed according to the updated stiffness curve.

[0168] The stiffness update method considering friction asymmetry provided by the embodiments of the present application models the friction asymmetry caused by the actuator, especially the ball screw, and calibrates the variation law of its asymmetry using durability tests, improving the robustness of the algorithm throughout the entire life cycle of the actuator. This patent designs a corresponding stiffness update function module, which can automatically update the stiffness characteristic when the vehicle is powered off, ensuring the accuracy of the clamping force control without a pressure sensor.

[0169] The following is an embodiment of the device of the present application, which can be used to execute the method embodiment of the present application. For details not disclosed in the device embodiment of the present application, please refer to the method embodiment of the present application.

[0170] Figure 6 It is a schematic structural diagram of a stiffness update device for an actuator provided by an embodiment of the present application. As Figure 6 shown, the stiffness update device 600 may include an acquisition module 610, an estimation module 620, a determination module 630, and an update module 640.

[0171] Among them, the acquisition module 610 is used to acquire the current estimated clamping force and the actual clamping force collected by the force sensor during N clamping and releasing processes of the brake disc by the actuator before the actuator is taken offline, where N is a positive integer. The estimation module 620 is used to estimate the friction coefficient of different current segments during the clamping and releasing processes of the actuator according to the current estimated clamping force and the actual clamping force. The determination module 630 is used to determine the target clamping force according to the motor current and the friction coefficient of different current segments during M clamping and releasing processes of the brake disc by the actuator in response to the actuator being powered on again after being taken offline, where M is a positive integer. The update module 640 updates the stiffness of the actuator according to the target clamping force.

[0172] The device provided by the embodiments of the present application can be used to execute the method in the above embodiments, and its implementation principle and technical effects are similar, which will not be elaborated here.

[0173] Figure 7 It is a schematic hardware structure diagram of an electronic device provided by an embodiment of the present invention. The electronic device can be integrated on a vehicle. As Figure 7 shown, the electronic device 700 may include a processor 701 and a memory 702 storing computer program instructions.

[0174] Specifically, the above-mentioned processor 701 may include a Central Processing Unit (CPU), or an Application Specific Integrated Circuit (ASIC), or may be configured as one or more integrated circuits for implementing the embodiments of the present invention.

[0175] The memory 702 may include a mass storage for data or instructions. By way of example and not limitation, the memory 702 may include a Hard Disk Drive (HDD), a floppy disk drive, a flash memory, an optical disc, a magneto-optical disc, a magnetic tape, or a Universal Serial Bus (USB) drive, or a combination of two or more of these. In one example, the memory 702 may include removable or non-removable (or fixed) media, or the memory 702 is a non-volatile solid-state memory. The memory 702 may be inside or outside the integrated gateway disaster recovery device.

[0176] In one example, the memory 702 may be a Read Only Memory (ROM). In one example, the ROM may be a mask-programmed ROM, a Programmable ROM (PROM), an Erasable PROM (EPROM), an Electrically Erasable PROM (EEPROM), an Electrically Alterable ROM (EAROM), or a flash memory, or a combination of two or more of these.

[0177] The memory 702 may include a Read Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk storage media device, an optical storage media device, a flash memory device, an electrical, optical, or other physical / tangible memory storage device. Thus, generally, the memory includes one or more tangible (non-transitory) computer-readable storage media (e.g., memory devices) encoded with software including computer-executable instructions, and when the software is executed (e.g., by one or more processors), it is operable to perform the operations described with reference to the method according to one aspect of the present disclosure.

[0178] The processor 701 realizes the method in the above embodiments by reading and executing the computer program instructions stored in the memory 702.

[0179] In one example, the electronic device 700 may further include a communication interface 703 and a bus 704. Among them, as Figure 7As shown, a processor 701, a memory 702, and a communication interface 703 are connected via a bus 704 to complete communication with each other. The communication interface 703 is mainly used to implement communication between various modules, devices, units, and / or equipment in the embodiments of the present invention. The bus 704 includes hardware, software, or both, and couples the components of the online data flow metering device to each other. By way of example and not limitation, the bus may include an Accelerated Graphics Port (AGP) or other graphics bus, an Extended Industry Standard Architecture (EISA) bus, a Front Side Bus (FSB), a Hyper Transport (HT) interconnect, an Industry Standard Architecture (ISA) bus, an InfiniBand interconnect, a Low Pin Count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a Serial Advanced Technology Attachment (SATA) bus, a Video Electronics Standards Association Local (VLB) bus, or other suitable buses or a combination of two or more of these. In a suitable case, the bus 704 may include one or more buses. Although the embodiments of the present invention describe and illustrate a specific bus, the present invention contemplates any suitable bus or interconnect.

[0180] In addition, in combination with the method in the above embodiments, an embodiment of the present invention may provide a braking system, which includes the above electronic device.

[0181] It should be clear that the present invention is not limited to the specific configurations and processes described above and illustrated in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and illustrated as examples. However, the method process of the present invention is not limited to the specific steps described and illustrated, and those skilled in the art can make various changes, modifications, and additions, or change the order between steps after understanding the spirit of the present invention.

[0182] The functional blocks shown in the above structural block diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a function card, and so on. When implemented in software, the elements of the present invention are programs or code segments for performing the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted via a data signal carried in a carrier wave over a transmission medium or a communication link. A "machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, read-only memory (ROM), flash memory, erasable read-only memory (EROM), floppy disks, compact disc read-only memory (CD-ROM), optical discs, hard disks, fiber optic media, radio frequency (RF) links, and so on. The code segment can be downloaded via a computer network such as the Internet, an intranet, and so on.

[0183] It should also be noted that the exemplary embodiments mentioned in the present invention describe some methods or systems based on a series of steps or devices. However, the present invention is not limited to the order of the above steps, that is, the steps can be executed in the order mentioned in the embodiments, can be different from the order in the embodiments, or several steps can be executed simultaneously.

[0184] Aspects of the present disclosure have been described above with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present disclosure. It should be understood that each block in the flowcharts and / or block diagrams, and the combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device to produce a machine, such that the instructions executed by the processor of the computer or other programmable data processing device enable the implementation of the functions / actions specified in one or more blocks of the flowchart and / or block diagram. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor, or a field programmable logic circuit. It should also be understood that each block in the block diagram and / or flowchart, and the combinations of blocks in the block diagram and / or flowchart, can also be implemented by dedicated hardware for performing the specified functions or actions, or by a combination of dedicated hardware and computer instructions.

[0185] The above are only specific embodiments of the present invention. Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, modules, and units can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for updating the stiffness of an actuator, characterized in that, The actuator is used to clamp or release the brake disc of a wheel, and the method includes: Before the actuator comes off the production line, obtain the current estimated clamping force during N clamping and releasing processes of the actuator on the brake disc and the actual clamping force collected by a force sensor, where N is a positive integer; Estimate the friction coefficients of different current segments during the clamping and releasing processes of the actuator based on the current estimated clamping force and the actual clamping force; In response to the actuator being powered on again after coming off the production line, determine a target clamping force based on the motor current during M clamping and releasing processes of the actuator on the brake disc and the friction coefficients of different current segments, where M is a positive integer; Update the stiffness of the actuator according to the target clamping force.

2. The method according to claim 1, characterized in that, The step of determining the target clamping force based on the motor current during M clamping and releasing processes of the actuator on the brake disc and the friction coefficients of different current segments includes: Based on the motor current during M clamping and releasing processes of the actuator on the brake disc, obtain the motor current at the same relative angular displacement relative to the contact point during clamping and releasing; Determine the target clamping force based on the motor current at the same relative angular displacement relative to the contact point during clamping and releasing and the friction coefficients of different current segments.

3. The method according to claim 2, wherein The actuator includes a motor, a ball bearing, a planetary gear set, a thrust bearing, a ball screw, and a brake pad; wherein, the motor is connected to the ball bearing, the ball bearing is connected to the planetary gear set, the planetary gear set is connected to the thrust bearing, and the thrust bearing is connected to the ball screw; when the motor rotates, the ball screw drives a nut to move on a nut guide rail to drive the brake pad to clamp or release the brake disc; The step of determining the target clamping force based on the motor current at the same relative angular displacement relative to the contact point during clamping and releasing and the friction coefficients of different current segments includes: Obtain the force conditions of the motor, ball bearing, planetary gear set, thrust bearing, ball screw, and brake pad during the clamping or releasing process of the actuator; Analyze and model the friction force of the ball screw during the forward clamping and reverse releasing processes based on the force conditions; Determine the mapping relationship between the clamping force and the motor current through the established model; Determine a first clamping force during forward clamping and a second clamping force during reverse releasing based on the mapping relationship and the motor current at the same relative angular displacement relative to the contact point during clamping and releasing; Eliminate the friction force of the ball screw during the clamping and releasing processes based on the first clamping force, the second clamping force, and the friction coefficient corresponding to the motor current to obtain the target clamping force.

4. The method according to claim 2, wherein The step of determining the target clamping force based on the motor current at the same relative angular displacement relative to the contact point during clamping and releasing and the friction coefficients of different current segments includes: Obtain the equivalent Coulomb friction coefficients during forward clamping and reverse releasing based on the friction coefficients of different current segments; Obtain the total transmission ratio of the planetary gear set, the gear transmission efficiency, the pitch radius of the screw, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during releasing in the actuator. Determine the target clamping force according to the equivalent Coulomb friction coefficient during forward clamping and reverse release, the total transmission ratio of the planetary gear set, the gear transmission efficiency, the pitch radius, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during release.

5. The method according to claim 4, wherein The determining of the target clamping force according to the equivalent Coulomb friction coefficient during forward clamping and reverse release, the total transmission ratio of the planetary gear set, the gear transmission efficiency, the pitch radius, the motor torque coefficient, the q-axis current of the motor during clamping, and the q-axis current of the motor during release includes: In the above formula, G t,A and G t,R are the equivalent Coulomb friction coefficients during clamping and releasing respectively, i g is the total transmission ratio of the planetary gear set, η g is the gear transmission efficiency, r s is the pitch radius of the lead screw, K m is the motor torque coefficient, i q，A is the q-axis current of the motor during clamping, i q，R is the q-axis current of the motor during releasing, F p,A is the clamping force during clamping, F p,B is the clamping force during releasing, F p is the target clamping force.

6. The method according to any one of claims 1-5, characterized in that, The stiffness update of the actuator according to the target clamping force includes: Obtain the first stiffness curve of the actuator according to the target clamping force; In response to the actuator being powered on again after the wheel has been braked L times, obtain the second stiffness curve of the actuator after being powered on again, where L is a positive integer; If the deviation between the first stiffness curve and the second stiffness curve is greater than a set threshold, update the stiffness characteristic of the actuator according to the second stiffness curve.

7. The method according to claim 1, characterized in that The method further includes: Perform position closed-loop control of the actuator without a pressure sensor according to the updated stiffness characteristic.

8. A stiffness updating device for an actuator, characterized in that Includes: An acquisition module, configured to acquire the current estimated clamping force and the actual clamping force collected by the force sensor during N clamping and releasing processes of the brake disc by the actuator before the actuator is taken offline, where N is a positive integer; An estimation module, configured to estimate the friction coefficient of different current segments during the clamping and releasing processes of the actuator according to the current estimated clamping force and the actual clamping force; A determination module, configured to determine the target clamping force according to the motor current and the friction coefficient of different current segments during M clamping and releasing processes of the brake disc by the actuator in response to the actuator being powered on again after being taken offline, where M is a positive integer; An update module, configured to perform stiffness update on the actuator according to the target clamping force.

9. An electronic device, characterized in that, Includes: A processor and a memory storing computer program instructions, and when the processor executes the computer program instructions, the steps of the method according to any one of claims 1-7 are implemented.

10. A braking system, characterized in that, An electronic device including the electronic device according to claim 9 above.

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