A clamping force control and estimation strategy for an electromechanical brake system

Abstract

The application discloses a clamping force control and estimation strategy of an electromechanical brake system, which is used for calculating the brake clamping force of a wheel brake when a vehicle brakes. A slip rate compensation controller is used for monitoring the wheel slip rate of a braked wheel, and compensating the driving current of a brake driving motor according to the monitored wheel slip rate; a sliding mode observer is used for monitoring the rotating disturbance electric parameters of the brake driving motor, and compensating the driving current of the brake driving motor according to the rotating disturbance electric parameters; and a gap compensation controller is used for compensating the driving current of the brake driving motor according to the motor rotation angle historical data for eliminating the brake gap of a disc brake. Since the influence of the vehicle driving and braking parameters such as the slip rate, the rotating 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 demand of the vehicle condition, and the safety of the vehicle braking process is 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:

[0006] 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.

[0007] 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.

[0008] In an embodiment, the clamping force control and estimation strategy further comprises:

[0009] The clamping force acquisition unit further comprises a sliding mode observer; the sliding mode observer is used for monitoring a rotating disturbance electrical parameter of the brake driving motor, and compensating a driving current of the brake driving motor according to the rotating disturbance electrical parameter, so as to anti-interference compensate the brake clamping force; wherein the rotating disturbance electrical parameter comprises a dynamic change amount of a motor rotation angle and a dynamic change amount of a motor driving current.

[0010] In an embodiment, the clamping force control and estimation strategy further comprises:

[0011] 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 the 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.

[0012] In an embodiment, the clamping force control and estimation strategy further comprises:

[0013] 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 driving current values of respective compensations.

[0014] 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:

[0015] 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;

[0016] According to the historically recorded motor rotation angle of eliminating the brake gap, a gap value caused by brake wear is obtained;

[0017] When the gap value is greater than a preset gap threshold value, the brake gap is wear compensated according to the gap value.

[0018] 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:

[0019] 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.

[0020] When the electronic mechanical brake system acquires the brake signal, the driving current of the brake driving motor is compensated according to the difference between the expected slip ratio S hope and the real-time slip ratio S b .

[0021] In the process of the electronic mechanical brake system performing the same vehicle braking, 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 .

[0022] 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:

[0023] 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.

[0024] In an embodiment, the slip observer compensates the driving current of the brake driving motor according to the rotating disturbance electrical parameter, including:

[0025] The driving current value of the brake driving motor is monitored in real time;

[0026] 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.

[0027] In an embodiment, the slip observer compensates the driving current of the brake driving motor according to the rotating disturbance electrical parameter, including:

[0028] The motor angle value of the brake driving motor is monitored in real time;

[0029] 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.

[0030] According to a second aspect, an embodiment provides a computer readable storage medium, wherein a program is stored on the medium, and the program can be executed by a processor to implement the clamping force control and estimation strategy according to the first aspect.

[0031] According to a third aspect, a computer program product is provided in an embodiment, comprising computer programs and / or instructions, which, when executed by a processor, implement the clamp force control and estimation strategy as described in the first aspect.

[0032] According to the clamp force control and estimation strategy of the above-mentioned embodiments, 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 clamp force, the generated braking clamp force is more in line with and meets the actual needs of the vehicle condition, thereby improving the safety of the vehicle braking process. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 FIG. 1 is a structural block diagram of an electromechanical brake system according to an embodiment;

[0034] Figure 2 FIG. 2 is a mechanical structure section view of a mechanical execution module according to an embodiment;

[0035] Figure 3 FIG. 3 is an appearance structure view of a mechanical execution module according to an embodiment;

[0036] Figure 4 FIG. 4 is a flowchart of an electromechanical brake control strategy according to an embodiment;

[0037] Figure 5 FIG. 5 is a flowchart of a clamp force control and estimation strategy according to an embodiment;

[0038] Figure 6 FIG. 6 is a flowchart of a slip rate compensation according to an embodiment;

[0039] Figure 7 FIG. 7 is a current compensation flowchart of a slip rate compensation controller according to an embodiment;

[0040] Figure 8 FIG. 8 is a compensation diagram of clamp force estimation according to an embodiment. DETAILED DESCRIPTION

[0041] The application will be described in further detail below with reference to the drawings. Like elements in different embodiments are denoted by like reference numerals. In the following description, numerous specific details are described to provide a thorough understanding of the application. However, those of skill in the art will recognize that the application can be practiced without one or more of the specific details. In other instances, well-known structures have not been described in order to avoid obscuring the application. In the following description, all directional references, such as, for example, upper, lower, left, right, above, below, top, bottom, behind, in front of, rearward, forward, first, second, etc., are used only for the convenience of the reader's understanding of the present application and do not constitute a limitation of the present application. In addition, the term "comprising" is used throughout the specification and in claims to mean that other elements can also be included, not excluding other elements or steps.

[0042] In addition, the features, operations, or steps described in the specification can be combined in any suitable manner without departing from the scope of the present application. In addition, the steps in the method description can be performed in any suitable order without departing from the scope of the present application. Therefore, the various sequences in the specification and the drawings are merely for the purpose of clarity and description, and do not mean that the sequence is mandatory unless otherwise specified.

[0043] In this document, the terms "first", "second", etc. are used only to distinguish one object from another, and do not necessarily have any technical meaning. In this document, the terms "connected" and "coupled" are used only to mean that one object is directly or indirectly connected or coupled to another object, unless otherwise specified.

[0044] Example 1:

[0045] When a vehicle is running in an automatic driving or intelligent assisted driving mode, if driving intervention is needed, only driving direction intervention control and vehicle braking intervention control can be used. One way of vehicle braking 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 for vehicle braking to the brake disc, and the brake clamping force is positively correlated with 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 for vehicle braking to be realized. Another way of vehicle braking intervention control is to set through function software (for example, when the vehicle speed control is performed according to a preset driving mode, the vehicle needs to be accelerated or 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.

[0046] In an embodiment of the present application, the working state of the electronic mechanical brake system includes three working stages, namely, a building stage, a following stage and an eliminating stage. In the building stage, the brake caliper is attached to the brake disc in advance (without applying a brake force to the brake disc), so that the brake clearance of the disc brake can be eliminated in advance, and the timeliness and reliability of vehicle braking intervention control can be improved. Especially when the vehicle is driven in a defensive manner (after stepping on the brake pedal), it can be subjectively informed to the driver whether the current stepping force and / or depth has eliminated the brake clearance (i.e., whether the current electronic mechanical brake system is working in the building stage).

[0047] Please refer to Figure 1Fig. 1 is a structural block diagram of an electromechanical brake system in an embodiment, the electromechanical brake system comprising an electronic control module 100 and a mechanical execution module 200. The electronic control module 100 comprises 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 comprises a brake driver 201, a brake actuator 202 and a disc brake 203.

[0048] Please refer to Figure 2 and Figure 3 , respectively, are a mechanical structure section view and an appearance structure view of the mechanical execution module in an embodiment. The brake driver 201 comprises a brake driving motor 1, a motor output shaft 2 and a motor controller assembly 3. The brake actuator 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 driving 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 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 driving 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 rail restricts the lead screw 6 to only axial movement. The lead screw 6 guide rail 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, which 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, which is used to store energy when the brake caliper 16 and the brake disc 17 are in contact, and release energy when the electromechanical brake system works in the elimination stage, so as to quickly separate and reset the brake caliper 16 and the brake disc 17.

[0049] The electromechanical brake system disclosed in an embodiment of the present application adopts a computer to control brake control motor and brake actuator to implement braking of disc or drum brake. Compared with traditional brake device, the electronic control module replaces part of mechanical and hydraulic elements with electronic elements and compact mechanical device, and is an electromechanical integrated system. When performing vehicle braking, each controller calculates the required brake clamping force of brake disc according to vehicle state and external environment information collected by wheel speed sensor, brake pedal position sensor and other sensors, and controls brake control motor to output corresponding torque to control brake push rod to realize braking according to the calculated expected brake clamping force. Compared with 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 other systems, greatly improving the reliability and stability of the vehicle.

[0050] In Figure 2 In the mechanical actuator module shown, the motor output shaft 2 connected with the brake drive motor 1 is internally 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 to make the nut 4 rotate with the motor output shaft 2. The axial position of the nut 4 is fixed by the bearing, which restricts the nut 4 from axial displacement 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 to make the lead screw 6 move axially. One end of the lead screw 6 is received in the motor output shaft 2, and the other end is processed into a hex-shaped boss. On the one hand, the boss can constrain the rotation freedom of the lead screw 6 while allowing the lead screw 6 to move axially in the internally processed hex-shaped channel of the housing 8, so that the lead screw 6 does not rotate around the axis; on the other hand, the boss increases the contact area between 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 between the guide 7 and the brake push rod 10 allows the guide 7 to rotate at a small angle around their connection 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 return spring 9 is arranged on the front end cover 11 (the housing in the brake push rod arrangement area), which can store energy during braking and release energy during release, and is used for rapid return after braking.

[0051] The brake lever rotates around the hinge 13 after receiving the action of the brake push rod 10, transmits power to the push disc 15, so that the push disc 15 pushes the brake calipers 16 on both sides of the brake disc to displace, and then clamps the brake disc 17 to realize braking.

[0052] Please refer toFigure 4 For a flowchart of an electronic mechanical brake control strategy in an embodiment, an electronic mechanical brake control strategy is also disclosed in an embodiment of the present application, applied to the electronic mechanical brake system as described above, specifically comprising:

[0053] The working states of the electronic mechanical brake system include a building phase, a following phase and an eliminating phase. In the building phase, the brake caliper is attached to the brake disc to eliminate the brake gap of the disc brake of the electronic mechanical brake system. The disc brake includes the brake caliper and the brake disc. In the following phase, the brake clamping force for vehicle braking is applied to the brake disc by the brake caliper. In the eliminating phase, the brake caliper is separated from the brake disc. When the electronic mechanical brake system does not obtain a brake signal, the electronic mechanical brake system works in the eliminating phase or normal driving. When the electronic mechanical brake system obtains a first brake signal, the electronic mechanical brake system works in the building phase. When the electronic mechanical brake system obtains a second brake signal, the electronic mechanical brake system works in the following phase. The first brake signal and the second brake signal correspond to different stroke depth ranges of the brake pedal respectively.

[0054] In an embodiment, the electronic mechanical brake control strategy further comprises:

[0055] First, the motor angle of the brake gap after each execution of the eliminating phase is recorded, then the gap value generated by brake wear is obtained according to the historically recorded motor angle of the brake gap, and finally when the gap value is greater than a preset gap threshold, the brake gap is compensated for wear according to the gap value.

[0056] In an embodiment, the size value 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 the brake driving motor.

[0057] In an embodiment, the driving current of the brake driving motor is positively related to the size value of the brake clamping force, and the electronic mechanical brake control strategy further comprises:

[0058] 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 for 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 for the brake clamping force.

[0059] 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 to the original position, thereby reducing the negative effects such as energy loss and mechanism wear caused by incomplete 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 to the original position. 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 to completely separate the brake caliper from the brake disc and return the brake mechanism to the original 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 to the original position during the elimination stage.

[0060] 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 the 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.

[0061] 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.

[0062] 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 from the speed control target to the position control target is performed, so that each mechanism is quickly returned and the brake is completely separated.

[0063] 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.

[0064] 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.

[0065] Embodiment two

[0066] 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.

[0067] 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 application, the clamping force control and estimation strategy comprises:

[0068] Step 101, slip rate compensation.

[0069] The clamping force acquisition unit comprises a slip rate compensation controller, 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, so as to compensate the brake clamping force.

[0070] Step 102, anti-interference compensation.

[0071] The clamping force acquisition unit further comprises a sliding mode observer, which is configured to monitor a rotating disturbance electric parameter of the brake driving motor and compensate 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.

[0072] In step 103, gap compensation is performed.

[0073] The clamping force acquisition unit further comprises a gap compensation controller, which is configured to compensate 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 to identify the fitting distance of the brake caliper and the brake disc.

[0074] In step 104, a weight value is set.

[0075] 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.

[0076] Please refer to Figure 6 Fig. 1 is a flowchart 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.

[0077] In step 201, a real-time slip rate is acquired.

[0078] 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.

[0079] In step 202, compensation is performed according to the difference.

[0080] 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 .

[0081] In step 203, dynamic compensation is performed.

[0082] 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 Sb The dynamic variation range of the slip rate S b The dynamic variation range of the slip rate S

[0083] When the real-time slip rate S b is less than a preset minimum slip rate S min or greater than a preset maximum slip rate 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.

[0084] 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 terms to the system, so as to improve the tracking accuracy of the brake clamping force.

[0085] In an embodiment, the method for anti-interference compensation of the sliding mode observer for the dynamic variation of the motor angle includes:

[0086] 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.

[0087] In an embodiment, the method for anti-interference compensation of the sliding mode observer for the dynamic variation of the motor driving current includes:

[0088] 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.

[0089] 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:

[0090] 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, the brake gap is compensated for wear according to the gap value.

[0091] To facilitate understanding of the implementation of the clamping force control and estimation strategy disclosed in the embodiment, the calculation methods and principles of various compensations are described below, specifically including:

[0092] 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 braking clamping force, so as to finally realize accurate tracking of the expected slip ratio.

[0093] Please refer to Figure 7 , the current compensation flowchart of the slip ratio compensation controller in an embodiment, first, set the expected slip ratio value S hope and the ideal slip ratio range (slip ratio minimum value S min and slip ratio maximum value S max ). After starting braking, calculate the current 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 a based on the real-time slip ratio S b of the current vehicle. When the real-time slip ratio S b is equal to the expected slip ratio S hope for the first time, consider the real-time road conditions and algorithm load, and relax the expected slip ratio value to the ideal slip ratio range. When the real-time slip ratio exceeds the slip ratio maximum value S max , set the slip ratio minimum value 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 slip ratio minimum value S min , set the slip ratio maximum value S max as the tracking target, and calculate the corresponding compensation current based on it, and repeat this process.

[0094] In an embodiment, the calculation of the current compensation value from the real-time slip ratio includes the following processes:

[0095] ; ; (1)

[0096] 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 order to facilitate calculation, the effects of air resistance and wheel rolling resistance are ignored in this embodiment.

[0097] The braking torque of the disc brake acting on the wheel is:

[0098] (1)

[0099] wherein f is the friction coefficient between the brake caliper and the brake disc, F n is the brake clamping force, and R is the radius of the friction force. In the first embodiment, the brake clamping force is generated by the brake push rod and the brake lever, and the pushing force of the brake push rod is easily obtained as:

[0100] (2)

[0101] wherein k is the brake lever force amplification ratio, η is the mechanical efficiency, and F push is the pushing force of the brake push rod.

[0102] Since the push rod is arranged to be deflected by a certain angle around the fixed end, and the deflection angle is denoted as θ, the pushing force of the screw rod is:

[0103] (3)

[0104] According to the pushing force of the screw rod, the driving torque required at the nut end is:

[0105] (4)

[0106] wherein T nut is the driving torque at the nut end, F gs is the pushing force of the screw rod, L o is the lead of the roller screw, and η s is the mechanical efficiency of the roller screw.

[0107] 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, i.e.:

[0108] (5)

[0109] wherein L o is the lead of the roller screw, η sp is the mechanical efficiency of the spline, and T α is the output torque of the motor. In order to simplify the equation, p is set as:

[0110] (6)

[0111] The dynamic equation of the brake motor is:

[0112] (7)

[0113] ;

[0114] wherein, T m is the electromagnetic torque of the braking motor, K t is the electromagnetic torque coefficient of the braking motor, I q is the equivalent q-axis current of the braking motor, J m is the moment of inertia of the braking motor, B m is the damping coefficient of the braking motor, θ m is the motor rotation angle, T f is the friction torque.

[0115] The piecewise linear tire model is set as:

[0116] When S b ≤ S o , ;

[0117] When S b > S o , ; (8)

[0118] wherein, μ is the real-time adhesion coefficient, μ h is the peak adhesion coefficient, μ g is the adhesion coefficient when the wheel is locked, S o is the slip ratio corresponding to the peak adhesion coefficient, S b is the real-time slip ratio.

[0119] The formula for obtaining the real-time slip ratio is:

[0120] ; (9)

[0121] The derivative of the real-time slip ratio is:

[0122] ; (10)

[0123] According to the piecewise linear tire model, the relationship between the ground braking force and the slip ratio is:

[0124] ; (11)

[0125] 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 road conditions of the vehicle. In an embodiment, μ st = 1.3 and μ sd = 0.62.

[0126] ;

[0127] where F z is the vertical force of the road surface on the tire.

[0128] Substituting formula (1), formula (6), and formula (7) into formula (10), the slip rate controller model is:

[0129] ; (12)

[0130] where, the controlled object u = I q S , by controlling the real-time slip rate S b tends to the expected slip rate value S hope , the minimum slip rate S min or the maximum slip rate S max , combined with formula (8) and formula (11), the slip rate-based compensation current I q S .

[0131] The slip rate controller mathematical model derived in this embodiment is a general relationship between vehicle slip rate and brake motor current, which can be combined with different algorithms to improve current compensation accuracy.

[0132] 2) The core idea of anti-interference compensation is to obtain the estimated value of disturbance compensation current from the slip mode observer according to the rotation angle and current information of the brake motor, which can directly and effectively compensate 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. The design mode of the slip mode observer is as follows, and the dynamic differential equation of the permanent magnet synchronous motor is:

[0133] ; (13)

[0134] Let J m be the moment of inertia of the brake motor, B m be the damping coefficient of the brake motor, K t be the electromagnetic torque coefficient of the brake motor, K m be the torsional stiffness of the brake motor shaft, be the rotation angle of the brake motor, be the angular velocity of the brake motor, be the angular acceleration of the brake motor, then the formula is:

[0135] ; (14)

[0136] Further simplify the equation, set:

[0137] ; (15)

[0138] Where, a, β are intermediate parameters, no actual physical meaning. Finally, the sliding mode observer is designed as follows:

[0139] (16)

[0140] Where, is the observed value of the angular acceleration of the braking motor, w(t) is the disturbance term which is complex and not suitable for modeling.

[0141] ;

[0142] ρ is the controller parameter, S is the sliding surface, , is the observed value of the angular velocity of the braking motor. Set the sliding surface S as:

[0143] (17)

[0144] Then:

[0145] (18)

[0146] Another u(x)=u o sign(S) is replaced There is:

[0147] (19)

[0148] Where, sign(S) is the sign function of S. Take According to the sliding surface reaching condition There is:

[0149] (20)

[0150] Take , it can satisfy At this time, the system gradually converges. Take the improved switch function sigmoid(S) instead of sign(S), which can effectively improve the chattering phenomenon of sign(S) function.

[0151] ;

[0152] Where, k1 and k2 are preset adjustment parameters.

[0153] When sliding mode motion occurs, the system is on the sliding surface, which satisfies , which plays an equivalent control role, at this time:

[0154] (21)

[0155] Where, eqis the switching signal of the speed error, which not only contains the current information, but also contains the high-frequency signal generated by the control, and the equivalent control quantity is obtained after the switching control quantity is filtered by the low-pass filter, that is, the estimated current :

[0156] ; (22)

[0157] wherein ω0 is the cut-off frequency, ω0=ω m / K, ω m is the speed of the braking motor, and K is a pre-set parameter constant. In an embodiment, K is 1 or 2.

[0158] In summary, the complex disturbance term of the braking motor current compensation is realized. In addition, by continuously adjusting the observed value of the q-axis current , the actual braking motor speed is consistent with the estimated braking motor speed, and 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 .

[0159] 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 of this time 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 this time to the next braking, so as to realize the compensation of the gap.

[0160] 4) Different weight values are set for slip rate compensation, anti-interference compensation and gap compensation to achieve the 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:

[0161] ; (23)

[0162] wherein I q_hope is the expected braking motor tracking current, K p , K i , K d are the proportional, integral and differential coefficients, is the speed error, , A, B, C, D are the weight coefficients of each compensation current, I q GAP is the compensation current calculated by the braking gap compensation controller, I q SI is the compensation current for the slip rate q SMO I is the compensation current for the sliding mode controller.

[0163] The clamping force control and estimation strategy disclosed in the embodiment takes the brake clamping force as a disturbance term, and realizes the estimation of the brake clamping force by estimating the extended state of the disturbance term, i.e. the change rate of the disturbance term. The designed extended state observer outputs the observation value of the brake motor rotation angle while observing and estimating the clamping force, and judges the reliability degree of the clamping force estimation by comparing the observation value of the brake motor rotation angle with the actual value, e θ I is the compensation current for the sliding mode controller. θ When e 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.

[0164] The clamping force estimator design process is as follows: according to formula (2), formula (3) and formula (6), we have:

[0165] ; (24)

[0166] Therefore, the torque balance equation of the motor can be written as follows:

[0167] ; (25)

[0168] 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:

[0169] ; ; ; (26)

[0170] Wherein, W(t) is defined as the derivative of ξ.

[0171] Then the improved extended state observer is designed as follows:

[0172] ;

[0173] ;

[0174] ; (27)

[0175] Wherein, 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.

[0176] is the difference between the observation value of the rotation angle of the brake motor and the actual rotation angle; is the expansion state set by the system for tracking ξ, and the estimated clamping force is finally observed as .

[0177] 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 expansion 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.

[0178] 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 parameters of the brake drive motor, and the drive current of the brake drive motor is compensated according to the rotation disturbance electric parameters. 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 slip rate, the rotation disturbance, and the brake gap and other vehicle driving and braking parameters 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.

[0179] 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.

[0180] 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. 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, so as to provide anti-interference compensation for 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; 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 brake wear; the braking distance is used to indicate the contact distance between the brake caliper and the brake disc of the brake. 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.

2. The clamping force control and estimation strategy as described in claim 1, 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.

3. The clamping force control and estimation strategy as described in claim 1, 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.

4. The clamping force control and estimation strategy as described in claim 1, 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.

5. The clamping force control and estimation strategy as described in claim 1, 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.

6. 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 5.

7. 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 5.

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