Clamping force control and estimation strategy of electronic mechanical braking system

Abstract

The invention discloses a clamping force control and estimation strategy of an electronic mechanical braking system. The clamping force control and estimation strategy is used for calculating braking clamping force for wheel braking when a vehicle is braked. Wherein the slip rate compensation controller is used for monitoring the wheel slip rate of the braked wheel and compensating the driving current of the brake driving motor according to the monitored wheel slip rate; the sliding-mode observer is used for monitoring rotation interference electrical parameters of the brake driving motor and compensating driving current of the brake driving motor according to the rotation interference electrical parameters; and the backlash compensation controller is used for compensating the driving current of the brake driving motor according to the historical data of the rotation angle of the motor for eliminating the brake spacing of the disc brake. In the control and estimation of the braking clamping force, the influence of the vehicle running and braking parameters such as the slip rate, the rotation interference and the braking clearance on the vehicle braking process is considered, so that the generated braking clamping force better fits and meets the actual requirements of vehicle conditions, and the safety of the vehicle braking process is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automobile brake control, in particular to a clamping force control and estimation strategy of an electronic mechanical brake system. BACKGROUND

[0002] With the continuous development of automobile electrification and intelligence and the gradual popularization of advanced auxiliary driving systems, further requirements are put forward for the functions and performances of automobile brake control systems. On the one hand, it is hoped that the brake control system can realize decoupling between pedal force and wheel braking force, ensure good pedal feeling, realize brake energy recovery, achieve high-precision and rapid brake response speed, and realize independent adjustment of automobile four-wheel braking force. On the other hand, it is hoped that the brake control system has the function of active braking to meet the needs of intelligent auxiliary driving systems such as emergency braking. Since the electronic mechanical brake system (EMB) is completely controlled by electronics, it can well meet the above requirements.

[0003] The electronic mechanical brake system discards the hydraulic structure of the traditional brake system, and has a simple structure, is clean and environmentally friendly, and is convenient to arrange. Since there is no hydraulic brake, it also has the advantages of no brake medium leakage and rapid response. In addition, the electronic mechanical brake system can also independently allocate braking force to each wheel to realize independent braking of each wheel. Therefore, dynamically setting braking parameters according to the respective rotation parameters of each wheel is the main research direction of the electronic mechanical brake system at present. Among them, the core parameter of the braking parameter is the setting value of the braking clamping force required when braking the vehicle. SUMMARY

[0004] The technical problem solved by the present application is to accurately and effectively control the braking clamping force of each wheel when the electronic mechanical brake system brakes the vehicle.

[0005] According to a first aspect, in an embodiment, a clamping force control and estimation strategy of an electronic mechanical brake system is provided, comprising: The electronic mechanical brake system comprises a clamping force acquisition unit for calculating the braking clamping force of the wheel braking when the vehicle brakes. The clamping force acquisition unit comprises a slip rate compensation controller. The slip rate compensation controller is used to monitor the wheel slip rate of the braked wheel, and compensate the driving current of the brake driving motor according to the monitored wheel slip rate to compensate the braking clamping force.

[0006] In an embodiment, the clamping force control and estimation strategy further comprises: The clamping force acquisition unit further comprises a sliding mode observer; the sliding mode observer is used for monitoring a rotating disturbance electric parameter of the brake driving motor and compensating a driving current of the brake driving motor according to the rotating disturbance electric parameter, so as to anti-interference compensate the brake clamping force; wherein the rotating disturbance electric parameter comprises a dynamic change amount of a motor rotation angle and a dynamic change amount of a motor driving current.

[0007] In an embodiment, the clamping force control and estimation strategy further comprises: The clamping force acquisition unit further comprises a gap compensation controller; the gap compensation controller is used for compensating a driving current of the brake driving motor according to historical data of a motor rotation angle of the brake driving motor when a disc brake in the electromechanical brake system eliminates a brake gap, so as to gap compensate the brake clamping force, and further eliminate a change of the brake gap caused by brake wear; the brake gap is used for identifying a fitting distance of fitting the brake caliper with the brake disc.

[0008] In an embodiment, the clamping force control and estimation strategy further comprises: When the slip rate compensation, the anti-interference compensation and the gap compensation are performed on the brake clamping force, different weight values are set for the driving current values of respective compensations.

[0009] In an embodiment, the gap compensation controller compensates the driving current of the brake driving motor according to the historical data of the motor rotation angle of the brake driving motor when the disc brake in the electromechanical brake system eliminates the brake gap, comprising: The gap compensation controller records the motor rotation angle of the brake driving motor when the disc brake in the electromechanical brake system eliminates the brake gap each time; According to the historically recorded motor rotation angle of eliminating the brake gap, a gap value caused by brake wear is obtained; When the gap value is greater than a preset gap threshold value, the brake gap is wear compensated according to the gap value.

[0010] In an embodiment, the slip rate compensation controller compensates the driving current of the brake driving motor according to the monitored and obtained wheel slip rate, comprising: A preset expected slip rate S hope is obtained, and a real-time slip rate S b of the wheel is monitored in real time; When the electromechanical brake system obtains a brake signal, the driving current of the brake driving motor is compensated according to a difference between the expected slip rate S hope and the real-time slip rate S b ; In the process of the same vehicle braking performed by the electromechanical brake system, when the real-time slip ratio S b is equal to the expected slip ratio S hope for the first time, the driving current of the brake driving motor is compensated according to the dynamic change range of the real-time slip ratio S b . The compensation of the driving current of the brake driving motor according to the dynamic change range of the real-time slip ratio S b includes: When the real-time slip ratio S b is less than a preset slip ratio minimum value S min or greater than a preset slip ratio maximum value S max , the driving current of the brake driving motor is positively compensated and negatively supplemented, respectively; otherwise, the driving current of the brake driving motor is not compensated.

[0011] In an embodiment, the slip observer compensates the driving current of the brake driving motor according to the rotational disturbance electrical parameter, including: real-time monitoring the driving current value of the brake driving motor; compensating the driving current of the brake driving motor according to the difference between the driving current value obtained by monitoring and the expected driving current value of the brake driving motor, so as to correct or compensate the brake clamping force.

[0012] In an embodiment, the slip observer compensates the driving current of the brake driving motor according to the rotational disturbance electrical parameter, including: real-time monitoring the motor angle value of the brake driving motor; compensating the driving current of the brake driving motor according to the difference between the motor angle value obtained by monitoring and the expected motor angle value, so as to correct or compensate the brake clamping force.

[0013] According to a second aspect, an embodiment provides a computer readable storage medium, wherein the medium stores a program, and the program can be executed by a processor to implement the clamping force control and estimation strategy according to the first aspect.

[0014] According to a third aspect, an embodiment provides a computer program product, including a computer program and / or instructions, and the computer program and / or instructions are executed by a processor to implement the clamping force control and estimation strategy according to the first aspect.

[0015] According to the clamping force control and estimation strategy of the above embodiment, since the influence of the vehicle running and braking parameters such as the slip rate, the rotation disturbance and the brake gap on the vehicle braking process is considered in the control and estimation of the braking clamping force, the generated braking clamping force is more suitable and meets the actual needs of the vehicle condition, thereby improving the safety of the vehicle braking process. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a structural block diagram of the electromechanical brake system in an embodiment; Figure 2 It is a mechanical structure section view of the mechanical execution module in an embodiment; Figure 3 It is an appearance structure view of the mechanical execution module in an embodiment; Figure 4 It is a flowchart of the electromechanical brake control strategy in an embodiment; Figure 5 It is a flowchart of the clamping force control and estimation strategy in an embodiment; Figure 6 It is a flowchart of the slip rate compensation in an embodiment; Figure 7 It is a current compensation flowchart of the slip rate compensation controller in an embodiment; Figure 8 It is a compensation diagram of the clamping force estimation in an embodiment. DETAILED DESCRIPTION

[0017] The application will be further described in detail through specific embodiments and the accompanying drawings. In different embodiments, similar elements are associated with similar element labels. In the following embodiments, many details are described in order to make the application better understood. However, those skilled in the art can easily recognize that some features can be omitted or replaced by other elements, materials or methods in different cases. In some cases, some operations related to the application are not shown or described in the specification in order to avoid the core part of the application being overwhelmed by too much description, and it is not necessary to describe these related operations in detail for those skilled in the art according to the description in the specification and the general technical knowledge in the art.

[0018] In addition, features described in the specification, operation or characteristics can be combined in any appropriate manner in various embodiments. At the same time, the steps or actions in the method description can also be sequentially exchanged or adjusted in a manner obvious to those skilled in the art. Therefore, the various sequences in the specification and drawings are only for the purpose of clearly describing a certain embodiment, and do not mean that the sequence is necessary, unless otherwise stated that a certain sequence must be followed.

[0019] The serial numbers of components in this paper, such as "first", "second", etc., are only used to distinguish the described objects, and have no technical meaning. The "connection" and "coupling" in this application include direct and indirect connection (coupling) unless otherwise specified.

[0020] Embodiment one:

[0021] When the vehicle is driving in an automatic driving or intelligent assisted driving manner, if driving intervention is needed, only driving direction intervention control and vehicle brake intervention control can be used. One way of vehicle brake intervention control is to control the stroke depth of the brake pedal. In the prior art, the control mechanism of the brake pedal is that as long as the brake pedal has a stroke, the brake caliper is attached to the brake disc, and then the brake caliper applies a brake clamping force to the brake disc for vehicle braking. The brake clamping force is directly related to the stroke depth of the brake pedal. During the entire braking operation, one brake action (implementing a stepping action on the brake pedal) of the driver, the electronic mechanical brake system needs to eliminate the brake clearance of the disc brake first, and then apply the brake clamping force to the brake disc. This process of eliminating the brake clearance will prolong the time of vehicle braking. Another way of vehicle brake intervention control is to set through function software (for example, when the vehicle speed control is performed according to the preset driving mode, the vehicle needs to be accelerated and decelerated), and the process of eliminating the brake clearance will also affect the accuracy of the vehicle speed control. In addition, when the vehicle is driven in a defensive manner, it is difficult for the driver to determine how much stepping force to apply to the brake pedal to achieve the effective braking force on the vehicle in the shortest time. Too much force will generate a large braking force, and too little force will also affect the realization time of rapid braking.

[0022] In an embodiment of the present application, the working state of the electromechanical brake system includes three working stages, i.e. a building stage, a following stage and an eliminating stage. In the building stage, the brake caliper is pre-applied to the brake disc (without applying brake force to the brake disc), so that the brake gap of the disc brake can be eliminated in advance, and the timeliness and reliability of the vehicle brake intervention control can be improved. Especially when the vehicle is driven defensively (after the brake pedal is stepped on), the driver can be informed subjectively whether the current stepping force and / or depth has eliminated the brake gap in advance (i.e. whether the current electromechanical brake system is working in the building stage).

[0023] Please refer to Figure 1 , a structural block diagram of the electromechanical brake system in an embodiment is shown, which includes an electronic control module 100 and a mechanical execution module 200. The electronic control module 100 includes a brake signal acquisition unit 101, a clamping force acquisition unit 102 and a brake driving unit 103. The brake signal acquisition unit 101 is configured to acquire a stroke depth signal of a brake pedal or a preset automatic emergency brake system issued brake instruction signal. The clamping force acquisition unit 102 is configured to calculate a brake clamping force for braking the vehicle according to the stroke depth signal or the brake instruction signal. The brake driving unit 103 is configured to switch the working state of the electromechanical brake system according to the stroke depth signal, the brake instruction signal or the brake clamping force. The mechanical execution module 200 includes a brake driver 201, a brake actuator 202 and a disc brake 203.

[0024] Please refer to Figure 2 and Figure 3Fig. 1 and Fig. 2 are respectively a schematic diagram of a mechanical structure section and a schematic diagram of an external structure of a mechanical execution module in an embodiment, the brake driver 201 comprises a brake driver motor 1, a motor output shaft 2 and a motor controller assembly 3. The brake execution mechanism 202 can comprise a nut 4, a roller 5, a lead screw 6, a guide 7, a housing 8, a brake push rod 10, a front end cover 11, a brake lever 14, a hinge 13 and a push disc 15. Among them, the brake lever first state 12 and the brake lever 14 are used to identify the working stroke of the brake lever. The disc brake 203 comprises a brake caliper 16 and a brake disc 17. The output shaft of the brake driver motor 1 is internally hollow, used to accommodate part of the lead screw 6. The nut 4 is connected with the motor output shaft 2, and the axial position of the nut 4 is fixed by a bearing, so that the nut 4 rotates with the rotation of the motor output shaft 2. The nut 4 is internally provided with a threaded raceway, and the roller 5 rolls in the threaded raceway, used to transmit the torque output by the brake driver motor 1 to the lead screw 6 via the nut 4 and the roller 5, so that the lead screw 6 moves axially. One end of the lead screw 6 is provided with a hexagonal boss, and the axial displacement of the hexagonal boss in the hexagonal guide restricts the lead screw 6 to only axial movement. The lead screw 6 guide end is processed with a guide 7, and the translation of the lead screw 6 is transmitted to the brake push rod 10 via the guide 7, and the brake push rod 10 is used to act on the brake caliper 16 by pushing the brake lever to rotate around the fixed hinge 13. The housing in the arrangement area of the brake push rod 10 is provided with a pull-back spring 9, used to store energy when the brake caliper 16 is in contact with the brake disc 17, and release energy when the electronic mechanical brake system works in the elimination stage, so as to quickly separate and reset the brake caliper 16 and the brake disc 17.

[0025] The electronic mechanical brake system disclosed in an embodiment of the present application adopts a computer to control the brake control motor and the brake execution mechanism, and is used for implementing the brake of a disc brake or a drum brake. Compared with the traditional brake device, the electronic control module replaces part of the mechanical and hydraulic elements with electronic elements and more compact mechanical devices, and is an electromechanical integrated system. When the vehicle brake is executed, each controller calculates the required brake clamping force of the brake disc according to the vehicle state and external environment information collected by the wheel speed sensor, brake pedal position sensor and the like, and controls the brake control motor to output the corresponding torque according to the calculated expected brake clamping force, so as to control the brake push rod to implement the brake. Compared with the traditional air pressure type and hydraulic type brake device, the electronic control module has faster brake response, higher safety and more compact structure, and can be better combined with ABS, ESP and the like, and greatly improves the reliability and stability of the vehicle.

[0026] In Figure 2The motor output shaft 2 connected with the brake driving motor 1 is internally machined as hollow, which can be used to accommodate part of the volume of the lead screw 6 to reduce the axial size of the electromechanical brake system. The motor output shaft 2 is connected with the nut 4, and the power of the motor is transmitted to the nut 4 through the spline, so that the nut 4 rotates with the motor output shaft 2. The axial position of the nut 4 is fixed by the bearing, which restricts the axial displacement of the nut 4 and only allows rotation around the axis. The nut 4 is internally provided with a threaded raceway, so that the roller 5 rolls in the threaded raceway. The rotation of the nut 4 is transmitted to the lead screw 6 through the roller 5, so that the lead screw 6 moves axially. One end of the lead screw 6 is received in the motor output shaft 2, and the other end is machined with a hexagonal boss. On the one hand, it can constrain the rotation freedom of the lead screw 6 while the housing 8 is machined as a hexagonal internal passage that can move axially, so that the lead screw 6 does not rotate around the axis; on the other hand, it increases the contact area of the lead screw 6 and the guide 7, so that the power of the lead screw 6 is more smoothly transmitted to the guide 7. The connection process of the guide 7 and the brake push rod 10 allows the guide 7 to rotate at a small angle around the connection between them, so as to reduce the axial force borne by the brake push rod 10 due to the height difference between the connection end of the brake lever and the brake push rod 10 during the rotation of the brake lever around the hinge 13 during braking. The front end cover 11 (the housing in the brake push rod arrangement area) is provided with a return spring 9, which can store energy during braking and release energy during release, for rapid return after braking.

[0027] The brake lever rotates around the hinge 13 after receiving the action of the brake push rod 10, transmits power to the push plate 15, so that the push plate 15 pushes the brake calipers 16 on both sides of the brake disc to displace, and then clamps the brake disc 17 to brake.

[0028] Please refer to Figure 4 As a flowchart of the electronic mechanical brake control strategy in an embodiment, the application also discloses an electronic mechanical brake control strategy applied to the electronic mechanical brake system as described above, which specifically comprises: The working states of the electromechanical brake system include a building-up phase, a following phase and a releasing phase. In the building-up phase, the brake caliper is attached to the brake disc to eliminate the brake gap of the disc brake of the electromechanical brake system. The disc brake includes the brake caliper and the brake disc. In the following phase, the brake caliper applies a brake clamping force to the brake disc for braking the vehicle. In the releasing phase, the brake caliper is detached from the brake disc. When the electromechanical brake system does not acquire a brake signal, the electromechanical brake system works in the releasing phase or normal driving. When the electromechanical brake system acquires a first brake signal, the electromechanical brake system works in the building-up phase. When the electromechanical brake system acquires a second brake signal, the electromechanical brake system works in the following phase. The first brake signal and the second brake signal correspond to different stroke depth ranges of a brake pedal respectively.

[0029] In an embodiment, the electromechanical brake control strategy further includes: First, the motor angle of the brake gap after each execution of the releasing phase is recorded. Then, the gap value caused by brake wear is obtained according to the recorded motor angle of the brake gap. Finally, when the gap value is greater than a preset gap threshold, the brake gap is compensated for wear according to the gap value.

[0030] In an embodiment, the magnitude of the brake clamping force is related to the stroke depth of the brake pedal, the wheel slip rate and / or the wheel speed. In an embodiment, the brake clamping force is provided by a brake drive motor.

[0031] In an embodiment, the drive current of the brake drive motor is positively related to the magnitude of the brake clamping force. The electromechanical brake control strategy further includes: First, the drive current value of the brake drive motor is monitored in real time. Then, the drive current of the brake drive motor is compensated for according to the difference between the monitored drive current value and the expected drive current value of the brake drive motor, so as to correct or compensate for the brake clamping force.

[0032] In an embodiment of the present application, the electronic mechanical brake control strategy takes the brake clamping force as the control target, the brake clamping force calculated by the brake clamping force estimation algorithm as the feedback input, and uses it to correct the actual tracking of the brake clamping force. The target of the pressure building stage (brake clamping force is zero) is to quickly eliminate the brake gap of the electronic mechanical brake system actuator and the brake inside. At this time, the brake clamping force is not used as the control input, and the maximum speed of the brake drive motor is set as the tracking target to achieve the purpose of quickly eliminating the brake gap. In an embodiment, the brake gap is controlled by a gap compensation controller, which records the brake drive motor angle at the moment of each gap elimination and builds pressure, and calculates the gap value caused by brake wear according to the difference between the brake drive motor angle at this moment and the theoretical pressure building moment. When the gap value is less than the threshold value, no compensation is performed; when the gap value is greater than the threshold value, the corresponding compensation current is calculated, and the brake drive motor is blocked after rotating through the corresponding angle after the vehicle's current braking is completed to the next braking, thereby achieving compensation for the gap. The target of the brake clamping force following stage (brake clamping force is a preset expected value) is to accurately follow the expected brake clamping force input by the upper layer. At this time, the control target is switched from the expected speed to the expected brake clamping force, and all controllers work normally. Based on the brake clamping force pressure building stage, the slip rate controller judges the actual braking condition of the vehicle according to the vehicle's braking parameters such as vehicle speed, slip rate, etc., and outputs the corresponding compensation current to further correct the brake clamping force control condition; in addition, the sliding mode observer observes the disturbance and unmodeled uncertainties of the electronic mechanical brake system during braking, calculates the corresponding compensation current, and inputs it to the current controller to correct the brake clamping force. In addition, the brake clamping force estimator calculates the brake clamping force estimation value according to the actual angle and actual output torque of the brake drive motor, and inputs it to the brake clamping force controller to achieve closed-loop control of the brake clamping force, and finally achieve accurate tracking of the brake clamping force. The control target of the elimination stage (to recover the brake gap) is switched to quickly eliminate the brake force and quickly return the actuator, thereby reducing the negative effects such as energy loss, mechanism wear caused by incomplete brake separation and untimely brake separation. First, the control target is switched from the expected brake clamping force to the expected speed (maximum reverse speed of the brake drive motor), at which time the position controller, speed controller and current controller are in working condition, and the brake drive motor is controlled to track the target speed to quickly return the actuator. Then, when the brake clamping force estimation value is less than the contact threshold, the brake drive motor is switched to position closed-loop control, so that the brake caliper and brake disc are completely separated, and the brake mechanism returns to zero position. Similarly, springs are arranged on the brake push rod area shell and the brake lever area shell to store energy during the pressure building and following stages, and release energy to quickly return the mechanism during the elimination stage.

[0033] In an embodiment, the switching logic from the normal driving stage to the pressure building stage of the electromechanical brake system is designed according to the upper layer brake instruction or the driver's depression of the brake pedal. When the upper layer input brake instruction or the driver steps on the brake pedal (a first brake signal is obtained), the brake clamping force building stage is entered. In this stage, the maximum speed of the brake driving motor is first taken as a tracking target to achieve rapid pressure building to generate brake force, and then when the brake clamping force estimate exceeds the contact threshold instantaneously, it is considered that the brake gap is completely eliminated, at which time the motor angle of the current state is kept unchanged and further brake instruction is waited.

[0034] In an embodiment, the switching logic from the pressure building stage to the following stage of the electromechanical brake system is designed according to the estimate of the clamping force. When the expected brake clamping force input by the upper layer is not zero (a second brake signal is obtained) and the brake clamping force estimate at the current time exceeds the contact threshold, the switching from the pressure building stage to the following stage is performed, and the switching of the control target from the speed to the brake clamping force is realized, and the brake driving motor outputs the corresponding brake torque to realize the tracking of the target brake clamping force.

[0035] In an embodiment, the switching logic from the brake clamping force following stage to the brake clamping force elimination stage is designed according to the input of the upper layer clamping force and the estimate of the actual clamping force. When the expected brake clamping force input by the upper layer is zero and the clamping force estimate is not zero, the switching from the brake clamping force following stage to the brake clamping force elimination stage is performed, and the switching of the control target from the brake clamping force to the speed is realized, and the brake driving motor is controlled to reverse. When the clamping force estimate is further reduced and is less than the contact threshold, the switching of the control target from the speed to the position is performed, so that each mechanism is quickly returned and the brake is completely separated.

[0036] In an embodiment, the switching logic from the elimination stage to the normal driving stage is designed according to the output of the brake driving motor speed. When there is no brake instruction input by the upper layer, the clamping force estimate is less than the contact threshold, and the speed of the brake driving motor is zero, it is indicated that each mechanism has been completely separated, the brake process is ended, and the vehicle returns to the normal driving.

[0037] The electronic mechanical brake control strategy disclosed in the embodiment comprises: when the electronic mechanical brake system obtains a first brake signal and a second brake signal, the electronic mechanical brake system works in a building pressure stage and a following stage respectively, and when the electronic mechanical brake system does not obtain a brake signal, the electronic mechanical brake system works in an eliminating stage. In the building pressure stage, the brake caliper is attached to the brake disc, in the following stage, the brake caliper applies brake clamping force for vehicle braking to the brake disc, and in the eliminating stage, the brake caliper is separated from the brake disc. Since the electronic mechanical brake system is set to work in the building pressure stage within a preset brake pedal stroke depth range, the brake interval is preferentially eliminated, so that the brake efficiency of the electronic mechanical brake system is faster, more reliable and safer.

[0038] Embodiment two

[0039] To accurately and effectively control the brake clamping force of each wheel, it is necessary to accurately control the brake driving motor and the actuator (mechanical execution module) according to the input brake instruction to control the brake driving motor and the actuator to move, so that the brake caliper clamps the brake disc to output corresponding clamping force. In actual application, the clamping force of the brake caliper clamping the brake disc is taken as the control input of the brake driving motor in the electronic mechanical brake system, and the accuracy directly affects the control accuracy of the electronic mechanical brake system. In engineering implementation, it is hoped to realize accurate measurement and high-performance clamping force control of the caliper clamping force by directly installing a clamping force sensor measurement element. However, due to the high price of the clamping force sensor meeting the accuracy requirement, the difficulty in installation and arrangement, and the poor working conditions making it difficult to maintain and easy to damage (poor reliability), the monitoring mode of the clamping force sensor cannot meet the actual application requirements of the electronic mechanical brake system.

[0040] Please refer to Figure 5 , a flowchart of a clamping force control and estimation strategy in an embodiment, a clamping force control and estimation strategy is disclosed in an embodiment of the present application, which calculates the brake clamping force for wheel braking through a clamping force acquisition unit of an electronic mechanical brake system, and improves the clamping force estimation accuracy of the electronic mechanical brake system. The clamping force control and estimation strategy comprises: Step 101, slip rate compensation.

[0041] The clamping force acquisition unit comprises a slip rate compensation controller, which is used for monitoring the wheel slip rate of the braked wheel, and compensating the driving current of the brake driving motor according to the monitored wheel slip rate, so as to compensate the brake clamping force.

[0042] Step 102, anti-interference compensation.

[0043] ​The clamping force acquisition unit further comprises a sliding mode observer, which is used for monitoring a rotating disturbance electric parameter of the brake driving motor and compensating the driving current of the brake driving motor according to the rotating disturbance electric parameter, so as to anti-interference compensate the brake clamping force. The rotating disturbance electric parameter comprises a dynamic change amount of the motor angle and a dynamic change amount of the motor driving current.

[0044] In step 103, gap compensation is performed.

[0045] The clamping force acquisition unit further comprises a gap compensation controller, which is used for compensating the driving current of the brake driving motor according to historical data of the motor angle of the brake driving motor when the disc brake eliminates the brake gap in the electromechanical brake system, so as to gap compensate the brake clamping force, and further eliminate the change of the brake gap caused by brake action wear. The brake gap is used for identifying the fitting distance of fitting the brake caliper with the brake disc.

[0046] In step 104, a weight value is set.

[0047] When the slip rate compensation, the anti-interference compensation and the gap compensation are performed on the brake clamping force, different weight values are set for the driving current values of respective compensations, so as to realize the optimal brake current compensation effect of the brake driving motor.

[0048] Please refer to Figure 6 FIG. 1 is a flowchart of a process for realizing the slip rate compensation in an embodiment. In an embodiment, the slip rate compensation controller compensates the driving current of the brake driving motor according to the monitored and acquired wheel slip rate, which comprises the following steps. In step 201, a real-time slip rate is acquired.

[0049] A preset expected slip rate S hope is acquired, and a real-time slip rate S b of the wheel is monitored in real time.

[0050] In step 202, compensation is performed according to the difference.

[0051] When the electromechanical brake system acquires a brake signal, the driving current of the brake driving motor is compensated according to the difference between the expected slip rate S hope and the real-time slip rate S b .

[0052] In step 203, dynamic compensation is performed.

[0053] In the process of performing the same vehicle brake by the electromechanical brake system, when the real-time slip rate S b is equal to the expected slip rate S hope for the first time, the driving current of the brake driving motor is compensated according to the real-time slip rate S bThe dynamic variation range of the slip rate S b The dynamic variation range of the slip rate S When the real-time slip rate S b is less than a preset slip rate minimum value S min or greater than a preset slip rate maximum value S max , the driving current of the brake driving motor is positively compensated and negatively compensated, respectively; otherwise, the driving current of the brake driving motor is not compensated.

[0054] In an embodiment, the sliding mode observer monitors the dynamic variation of the motor angle and the dynamic variation of the motor driving current, and the compensation for the dynamic variation is to compensate for the disturbance caused by complex and difficult-to-model disturbance items to the system, so as to improve the tracking accuracy of the brake clamping force.

[0055] In an embodiment, the method for anti-interference compensation of the sliding mode observer for the dynamic variation of the motor angle includes: First, the motor angle value of the brake driving motor is monitored in real time, and then the driving current of the brake driving motor is compensated according to the difference between the monitored motor angle value and the expected motor angle value, so as to correct or compensate the brake clamping force.

[0056] In an embodiment, the method for anti-interference compensation of the sliding mode observer for the dynamic variation of the motor driving current includes: First, the driving current value of the brake driving motor is monitored in real time, and then the driving current of the brake driving motor is compensated according to the difference between the monitored driving current value and the expected driving current value of the brake driving motor, so as to correct or compensate the brake clamping force.

[0057] In an embodiment, the brake gap compensation controller compensates the brake motor current according to the gap value caused by brake wear calculated according to the motor angle at the moment when the pressure is built up after each gap elimination, and then adjusts the real-time brake clamping force. In an embodiment, the method for gap compensation of the gap compensation controller includes: First, the gap compensation controller records the motor angle of the brake driving motor when the disc brake of the electromechanical brake system eliminates the brake gap each time; then, the gap value caused by brake wear is obtained according to the historically recorded motor angle for eliminating the brake gap; finally, when the gap value is greater than a preset gap threshold value, the brake gap is compensated for wear according to the gap value.

[0058] In order to facilitate understanding of the implementation of the clamping force control and estimation strategy disclosed in the embodiment, the calculation method and principle of various compensations are described below, including: 1) The core idea of slip ratio compensation is to compensate the brake motor current according to the real-time tracking of the wheel slip ratio, and then adjust the real-time brake clamping force, so as to realize accurate tracking of the expected slip ratio.

[0059] Please refer to Figure 7 , the current compensation process of the slip ratio compensation controller in an embodiment is shown in the figure. First, set the expected slip ratio value S hope and the ideal slip ratio range (the minimum slip ratio S min and the maximum slip ratio S max ). After starting braking, calculate the real-time slip ratio S b according to the real-time wheel speed and vehicle speed of the current vehicle. Take the expected slip ratio value S hope as the tracking target, and calculate the brake motor compensation current I b based on the real-time slip ratio S a of the current vehicle. When the real-time slip ratio S b first equals the expected slip ratio S hope , consider the real-time road conditions and computing load, and relax the expected slip ratio value to the ideal slip ratio range. When the real-time slip ratio exceeds the maximum slip ratio S max , set the minimum slip ratio S min as the tracking target for tracking and calculate the brake motor current that should be compensated. Similarly, when the real-time slip ratio is less than the minimum slip ratio S min , set the maximum slip ratio S max as the tracking target and calculate the corresponding compensation current based on it, and repeat this process.

[0060] In an embodiment, the calculation of the current compensation value based on the real-time slip ratio includes the following processes: ; ; (1) where m is the single-wheel model mass, r d is the wheel rolling radius, I W is the wheel rotational inertia, ω is the wheel angular velocity, u ω is the wheel hub forward speed, F xb is the ground braking force, and T b is the brake torque acting on the wheel. In this embodiment, air resistance and wheel rolling resistance are ignored for ease of calculation.

[0061] The brake torque acting on the wheel of the disc brake is: ; (2) where f is the friction coefficient between the brake caliper and the brake disc, and F nis the braking clamping force, R is the friction force acting radius. In the first embodiment, the braking clamping force is generated by the brake push rod and the brake lever actuation, and the brake push rod thrust force is easily obtained as: ; (3) wherein k is the brake lever force amplification ratio, η is the mechanical efficiency, F push is the brake push rod thrust force.

[0062] Since the push rod is arranged to deflect by a certain angle around the fixed end, and the deflection angle is θ, the screw rod thrust force is: ; (4) According to the screw rod thrust force, the driving torque required at the nut end is: ; (5) wherein T nut is the driving torque at the nut end, F gs is the screw rod thrust force, L o is the lead of the roller screw, and η s is the mechanical efficiency of the roller screw.

[0063] Since no speed reduction mechanism is installed between the output shaft of the brake motor and the nut end of the roller screw, the output torque of the brake motor can be obtained by dividing the driving torque at the nut end by the mechanical efficiency, that is: ; (6) wherein L o is the lead of the roller screw, η sp is the spline mechanical efficiency, T α is the motor output torque, and p is set as: ; The dynamic equation of the brake motor is: ; (7) ; wherein T m is the electromagnetic torque of the brake motor, K t is the electromagnetic torque coefficient of the brake motor, I q is the equivalent q-axis current of the brake motor, J m is the moment of inertia of the brake motor, B m is the damping coefficient of the brake motor, θ m is the motor rotation angle, and T f is the friction torque.

[0064] The segmented linear tire model is set as: When S b ≤ S o , ; When S b > S o , ; (8) wherein μ is a real-time adhesion coefficient, μ h is a peak adhesion coefficient, μ g is an adhesion coefficient when the wheel is locked, S o is a slip ratio corresponding to the peak adhesion coefficient, S b is a real-time slip ratio.

[0065] The formula for obtaining the real-time slip ratio is: ; (9) The derivative of the real-time slip ratio is: ; (10) According to the piecewise linear tire model, the relationship between the ground braking force and the slip ratio is: ; (11) wherein F xb is the ground braking force, λ is a to-be-determined coefficient, a and d are adjustable constant parameters, μ sd and μ st are adjustment parameters related to the preset vehicle driving road conditions. In an embodiment, μ st = 1.3 and μ sd = 0.62.

[0066] ; wherein F z is the vertical force of the road on the tire.

[0067] Substituting formula (1), formula (6), and formula (7) into formula (10), the slip ratio controller model is: ; (12) wherein the controlled object is denoted as u = I q S By controlling the real-time slip ratio S b to approach the expected slip ratio value S hope , the minimum slip ratio S min , or the maximum slip ratio S max , the slip ratio-based compensation current I q S can be calculated according to formula (8) and formula (11).

[0068] The mathematical model of the slip ratio controller derived in this embodiment is a general relationship between the vehicle slip ratio and the braking motor current, which can be combined with different algorithms to improve the current compensation accuracy.

[0069] 2) The core idea of anti-interference compensation is to obtain the estimated value of disturbance compensation current according to the rotation angle and current information of the brake motor by the sliding mode observer, so as to effectively compensate the disturbance caused by the complex and difficult-to-model disturbance items to the system, and improve the tracking accuracy of the brake clamping force. The design mode of the sliding mode observer is as follows. The dynamic differential equation of the permanent magnet synchronous motor is: ; (13) Set J m is the moment of inertia of the brake motor, B m is the damping coefficient of the brake motor, K t is the electromagnetic torque coefficient of the brake motor, K m is the torsional stiffness of the brake motor shaft, is the rotation angle of the brake motor, is the angular velocity of the brake motor, is the angular acceleration of the brake motor, and the formula is: ; (14) Further simplify the equation, set: ; (15) Where, α, β are intermediate parameters, which have no actual physical meaning. Finally, the sliding mode observer is designed as follows: ; (16) Where, is the observed value of the angular acceleration of the brake motor, and w(t) is the complex and difficult-to-model disturbance item of the system.

[0070] ; ρ is the controller parameter, and S is the sliding surface, , is the observed value of the angular velocity of the brake motor. Set the sliding surface S as: ; (17) Then: ; (18) Another u(x)=u o sign(S) is replaced There is: ; (19) Where, sign(S) is the sign function of S. Take According to the sliding surface reaching condition There is: ; (20) Take At this time, it can meet At this time, the system gradually converges. By replacing the sign(S) function with the improved switch function sigmoid(S), the chattering phenomenon of the sign(S) function can be effectively improved.

[0071] ; wherein k1 and k2 are preset adjustment parameters.

[0072] When the sliding mode motion occurs, the system is on the sliding surface, satisfying , which plays an equivalent control role, and at this time: ; (21) wherein u eq is a switch signal of the speed error, which not only contains the current information, but also contains the high-frequency signal generated by the control. After the switching control quantity is filtered by a low-pass filter, the equivalent control quantity, i.e., the estimated current , is obtained. ; (22) wherein ω0 is a cutoff frequency, and ω0=ω m / K, ω m is the braking motor speed, and K is a preset parameter constant. In an embodiment, K is 1 or 2.

[0073] In summary, the complex disturbance term of the braking motor current is compensated. In addition, by continuously adjusting the observed value of the q-axis current , the actual braking motor speed is kept consistent with the estimated braking motor speed, and at this time, the q-axis current observed by the sliding mode observer is the estimated braking motor current disturbed by the complex and difficult-to-model disturbance term .

[0074] 3) The core purpose of gap compensation is to consider the gap value error generated by each braking wear. The gap controller will record the motor angle at the moment when the gap is eliminated each time, and calculate the gap value generated by braking wear according to the difference between the motor angle at the moment and the theoretical pressure building moment. When the gap value is less than the threshold value, no compensation is performed; when the gap value is greater than the threshold value, the corresponding compensation current is calculated, and the motor is rotated by the corresponding angle after the vehicle finishes braking and before the next braking, so as to realize compensation for the gap.

[0075] 4) Different weight values are set for slip rate compensation, anti-interference compensation, and gap compensation to achieve optimal braking current compensation effect. Please refer to Figure 8 , which is a compensation schematic diagram of the clamping force estimation in an embodiment. The expected braking motor tracking current after compensation is: (23) where I q_hope is the desired braking motor tracking current, K p , K i , K d are the proportional, integral, and derivative coefficients, respectively, is the speed error, A, B, C, D are the compensation current weight coefficients, I q GAP is the compensation current calculated by the brake gap compensation controller, I q S is the compensation current for the slip rate, I q SMO is the compensation current for the sliding mode controller.

[0076] The clamping force control and estimation strategy disclosed in this embodiment takes the brake clamping force as a disturbance term, and estimates the brake clamping force by estimating the extended state of the disturbance term, i.e., the rate of change of the disturbance term. The designed extended state observer outputs the observation value of the brake motor angle while observing and estimating the clamping force, and judges the reliability of the clamping force estimation by comparing the observation value of the brake motor angle with the actual value, e θ is the difference between the observation value of the brake motor angle and the actual value, i.e., when e θ is within a certain threshold, it is determined that the estimated value of the brake clamping force is reliable, otherwise the clamping force estimation fails and needs to be corrected.

[0077] The clamping force estimator is designed as follows: according to formula (2), formula (3) and formula (6), we have: (24) Therefore, the torque balance equation of the motor can be written in the following form: (25) Let ξ = -F n × L o ÷ [2π × (k × η × η s × η sp × cos θ × J m )], then the dynamics equation of the motor can be expressed as: ; ; (26) where W(t) is defined as the derivative of ξ.

[0078] Then the improved extended state observer is designed as follows: ; ; ; (27) wherein, is the observation value of the angular velocity of the brake motor, λ1, λ2, λ3 are observation gains, and the observation of the clamping force within a limited time is realized by adjusting the values of λ1, λ2, and λ3.

[0079] is the difference between the observation value of the rotation angle of the brake motor and the actual rotation angle; is the extended state set by the system for tracking ξ, and the estimated clamping force is finally observed as .

[0080] In an embodiment of the present application, the calculation of the compensation current is realized by the slip rate controller, the gap compensation controller, and the sliding mode observer, which is used for the drive current control of the brake drive motor. The estimation of the brake clamping force is realized by improving the extended state observer, which is used for the clamping force control of the brake motor. Finally, the above-mentioned control contents are integrated to realize the precise control of the brake clamping force.

[0081] The clamping force control and estimation strategy disclosed in the embodiments of the present application is used to calculate the brake clamping force of the wheel brake when the vehicle brakes. The slip rate compensation controller is used to monitor the wheel slip rate of the braked wheel, and the drive current of the brake drive motor is compensated according to the monitored wheel slip rate. The sliding mode observer is used to monitor the rotation disturbance electric parameter of the brake drive motor, and the drive current of the brake drive motor is compensated according to the rotation disturbance electric parameter. The gap compensation controller is used to compensate the drive current of the brake drive motor according to the historical data of the motor rotation angle for eliminating the brake gap of the disc brake. Since the influence of the vehicle driving and braking parameters such as the slip rate, the rotation disturbance, and the brake gap on the vehicle braking process is considered in the control and estimation of the brake clamping force, the generated brake clamping force is more suitable and meets the actual needs of the vehicle condition, thereby improving the safety of the vehicle braking process.

[0082] Those skilled in the art can understand that all or part of the functions of various methods in the above embodiments can be realized by hardware or by a computer program. When all or part of the functions in the above embodiments are realized by a computer program, the program can be stored in a computer readable storage medium, which can include a read-only memory, a random access memory, a magnetic disk, an optical disk, a hard disk, and the like. The above functions are realized by executing the program by a computer. For example, the program is stored in a memory of a device, and the above functions are realized by executing the program in the memory by a processor. In addition, when all or part of the functions in the above embodiments are realized by a computer program, the program can also be stored in a storage medium such as a server, another computer, a disk, an optical disk, a flash disk, or a mobile hard disk, and is saved in a memory of a local device by downloading or copying, or the system of the local device is updated, and the above functions are realized by executing the program in the memory by a processor.

[0083] The above application of specific examples to the present application is described, which is only used to help understand the present application and does not limit the present application. For those skilled in the art, according to the idea of the present application, a number of simple deductions, deformations or substitutions can be made.

Claims

1. A clamping force control and estimation strategy for an electromechanical braking system, characterized in that, include: The electromechanical braking system includes a clamping force acquisition unit, used to calculate the braking clamping force of the wheels when the vehicle is braking; The clamping force acquisition unit includes a slip ratio compensation controller; the slip ratio compensation controller is used to monitor the wheel slip ratio of the braked wheel, and compensate the drive current of the brake drive motor according to the monitored wheel slip ratio, so as to compensate the brake clamping force for slip ratio.

2. The clamping force control and estimation strategy as described in claim 1, characterized in that, Also includes: The clamping force acquisition unit also includes a sliding mode observer; The sliding mode observer is used to monitor the rotational interference electrical parameters of the brake drive motor and to compensate the drive current of the brake drive motor based on the rotational interference electrical parameters in order to compensate for the interference of the braking clamping force; wherein, the rotational interference electrical parameters include the dynamic change of the motor rotation angle and the dynamic change of the motor drive current.

3. The clamping force control and estimation strategy as described in claim 2, characterized in that, Also includes: The clamping force acquisition unit further includes a gap compensation controller; the gap compensation controller is used to compensate the drive current of the brake drive motor based on historical data of the motor rotation angle of the brake drive motor when the disc brake in the electromechanical braking system eliminates the braking distance, so as to compensate the gap of the brake clamping force and thereby eliminate the change in the braking distance caused by the wear of the braking action; the braking distance is used to indicate the contact distance between the brake caliper and the brake disc of the brake.

4. The clamping force control and estimation strategy as described in claim 3, characterized in that, Also includes: When performing slip ratio compensation, anti-interference compensation, and clearance compensation on the braking clamping force, different weight values ​​are set for the respective compensated drive current values.

5. The clamping force control and estimation strategy as described in claim 3, characterized in that, The gap compensation controller compensates the drive current of the brake drive motor based on historical data of the motor rotation angle of the brake drive motor when the disc brake in the electromechanical braking system eliminates the braking gap, including: The gap compensation controller records the motor rotation angle of the brake drive motor each time the disc brake in the electromechanical braking system eliminates the braking gap; The gap value caused by brake wear is obtained based on the motor rotation angle at which the braking distance is eliminated according to historical records. When the gap value is greater than a preset gap threshold, wear compensation is performed on the braking distance based on the gap value.

6. The clamping force control and estimation strategy as described in claim 2, characterized in that, The slip ratio compensation controller compensates the drive current of the brake drive motor based on the monitored wheel slip ratio, including: Obtain a preset desired slip ratio S hope And monitor the real-time slip rate S of the wheels. b ; When the electromechanical braking system acquires a braking signal, it determines the desired slip ratio S. hope and real-time slip ratio S b The difference is used to compensate for the drive current of the brake drive motor; During the same vehicle braking process performed by the electromechanical braking system, when the real-time slip ratio S b First and expected slip ratio S hope After they are equal, based on the real-time slip ratio S b The dynamic range of change is used to compensate for the drive current of the brake drive motor. The basis is the real-time slip ratio S b The dynamic variation range compensates for the drive current of the brake drive motor, including: When the real-time slip ratio S b The minimum slip ratio S is less than a preset value. min Or greater than a preset maximum slip ratio S max When the conditions are met, the drive current of the brake drive motor is compensated in the positive direction and supplemented in the negative direction, respectively; otherwise, the drive current of the brake drive motor is not compensated.

7. The clamping force control and estimation strategy as described in claim 2, characterized in that, The sliding mode observer compensates for the drive current of the brake drive motor based on the rotational disturbance electrical parameters, including: Real-time monitoring of the drive current value of the brake drive motor; The driving current of the brake drive motor is compensated based on the difference between the monitored driving current value and the expected driving current value of the brake drive motor, so as to correct or compensate for the braking clamping force.

8. The clamping force control and estimation strategy as described in claim 2, characterized in that, The sliding mode observer compensates for the drive current of the brake drive motor based on the rotational disturbance electrical parameters, including: Real-time monitoring of the motor rotation angle value of the brake drive motor; The driving current of the brake drive motor is compensated based on the difference between the motor rotation angle value obtained from monitoring and the expected motor rotation angle value, so as to correct or compensate for the brake clamping force.

9. A computer-readable storage medium, characterized in that, The medium stores a program that can be executed by a processor to implement the clamping force control and estimation strategy as described in any one of claims 1 to 8.

10. A computer program product comprising a computer program and / or instructions, characterized in that, When the computer program and / or instructions are executed by the processor, they implement the clamping force control and estimation strategy as described in any one of claims 1 to 8.

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