Three-closed-loop control method suitable for EMB

Abstract

The invention belongs to the technical field of electronic mechanical braking, and relates to a three-closed-loop control method suitable for an EMB. Comprises: determining a state machine state according to an input signal; and determining a three-closed-loop control strategy and a control target according to the state of the state machine. Through a target and feedback switching state machine, integrated control of braking, clearance keeping and resetting functions is realized, and the system is simple in structure and quick in response; a three-closed-loop control strategy is adopted, an outer ring adaptively selects control variables (clamping force, the number of sectors or the position) according to a state machine, and an inner ring guarantees execution precision and dynamic performance through a rotating speed and current closed loop; shortest stroke control can be achieved in the braking process, the braking response speed is increased, meanwhile, it is ensured that a gap is constant, and braking dragging is avoided; the resetting process is high in automation degree, the friction blocks are convenient to maintain and replace, and the maintainability of the system is improved.

Description

Technical Field

[0001] This invention belongs to the field of electromechanical braking technology and relates to a three-closed-loop control method suitable for EMB. Background Technology

[0002] The EMB (Electronic Braking System) is a new type of braking system used in commercial and passenger vehicles. Its control signals and braking actuation utilize an electrical system, replacing conventional air-pressure braking systems. The EMB caliper's caliper controller calculates and determines the motor to drive the disc brake according to a corresponding control strategy, achieving functions such as service braking, constant brake gap, and caliper reset.

[0003] EMB calipers mainly consist of a brushless DC motor, a planetary gear system, a ball screw pair, a pressure sensor, a position sensor, brake pads, a caliper body, and a housing. The clamping force is acquired via a pressure sensor; the position sensor can acquire the screw position, but its accuracy is relatively poor; the brushless motor's rotor position is acquired via three Hall effect sensors with a 120-degree phase difference.

[0004] Service Braking Function: During vehicle operation, the electronic brake pedal outputs a specific braking signal value, which is fed back to the vehicle domain controller in real time. The vehicle domain controller calculates and sends braking demand commands to the controllers at each wheel, causing the controllers to drive the motors to rotate at the corresponding speeds to generate braking clamping force, thus decelerating the vehicle. When the electronic brake pedal is released, the controller drives the motors to rotate in the opposite direction at the corresponding speed to release the brake and return to the constant braking gap position. During this process, the electronic brake pedal is dynamic, from actuation to holding and finally returning to the initial position. During this process, the chassis controller sends real-time braking demand signals to the EMB controller. The corresponding EMB follows the braking demand signal to increase force, maintain pressure (lock), and release to return to the original position. At the same time, the controller collects the speed signals output by each wheel speed sensor in real time and communicates them to the vehicle domain controller via CAN, which facilitates the vehicle domain controller to coordinate the braking clamping force output by the EMB and composite EMB of each wheel.

[0005] Brake gap constant function: During vehicle braking, when a brake release signal is received, the controller controls the motor to reverse to the position of constant gap.

[0006] Caliper assembly reset function: The controller receives the EMB caliper assembly reset command from the domain controller via the CAN bus, controlling the EMB motor to return to the initial position for easy replacement of the friction block. Therefore, a control method is urgently needed to simultaneously meet the requirements of three EMB motor actions. Summary of the Invention

[0007] This invention provides a three-closed-loop control method suitable for EMB, which simultaneously satisfies the functions of service braking, constant brake clearance, and caliper assembly reset.

[0008] The technical solution of the present invention is as follows: A three-closed-loop control method suitable for EMB, comprising: S10: Determine the state machine state based on the input signal; The state machine states include: constant gap state, gap elimination state, braking force output state, gap recovery state, motor retraction state, and initial state; S20: Determine the three-loop control strategy and control objective based on the state machine state; The control objective for the constant gap state is the number of Hall sectors, and the control strategy is: sector number-speed-current closed loop; The control objective for eliminating the gap state is the clamping force, and the control strategy is: clamping force-speed-current closed loop; The control target for the braking force output state is the clamping force, and the control strategy is: clamping force-speed-current closed loop; The control objective for restoring the gap state is the number of Hall sectors, and the control strategy is: sector number-speed-current closed loop; The control target for the motor retraction state is the position sensor voltage, and the control strategy is: position-speed-current closed loop; The control target for the initial state is the position sensor voltage, and the control strategy is a closed-loop control of position, rotation speed, and current.

[0009] Furthermore, the input signal includes: Clamping force setpoint, clamping force feedback, enable motor reset, position feedback, position setpoint, number of Hall sector sectors.

[0010] Furthermore, the judgment condition for the constant gap state is: after the system is powered on, the number of Hall sectors = the first threshold of the number of sectors or in the state of restoring the gap, the absolute value of the number of sectors < the second threshold of the number of sectors; The condition for determining the state of eliminating gap is: under the state of constant gap, the clamping force given is greater than or equal to the clamping force given threshold. The condition for determining the braking force output state is: under the state of eliminating gaps, |clamping force given - clamping force feedback| < difference threshold; The condition for determining the recovery gap state is: under the braking force output state, the clamping force given = the clamping force given threshold; The condition for determining the motor retraction state is: under constant gap conditions, the motor reset enable = motor reset enable threshold. The initial state is determined when the position feedback reaches the initial value in the motor retraction state.

[0011] Furthermore, the first threshold for the number of sectors is 0, and the second threshold for the number of sectors is 3.

[0012] Furthermore, the difference threshold is 1~2kN.

[0013] Furthermore, the clamping force is given a threshold value of 2~4kN.

[0014] Furthermore, the clamping force is given a threshold value of 0.

[0015] Furthermore, the motor reset enable threshold is 1.

[0016] Furthermore, the clamping force-speed-current closed loop consists of: an outer loop for clamping force, which calculates the speed command based on the deviation between the clamping force given and the feedback; a middle loop for speed, which calculates the current command based on the deviation between the speed command and the estimated speed; and an inner loop for current, which generates a PWM signal to drive the motor based on the deviation between the current command and the actual current. The sector number-speed-current closed loop consists of: an outer loop (sector number loop) that calculates speed commands with Hall sector number = 0 as the control target; a middle loop (speed loop) that calculates current commands based on the deviation between the speed commands and the estimated speed; and an inner loop (current loop) that generates PWM signals to drive the motor based on the deviation between the current commands and the actual current. The position-speed-current closed loop consists of: an outer loop (position loop) that calculates the speed command based on the position sensor voltage reaching a preset initial value as the control target; a middle loop (speed loop) that calculates the current command based on the deviation between the speed command and the estimated speed; and an inner loop (current loop) that generates a PWM signal to drive the motor based on the deviation between the current command and the actual current.

[0017] The beneficial effects of this invention are: By switching between target and feedback state machines, integrated control of braking, gap maintenance, and reset functions is achieved, resulting in a simple system structure and fast response. A three-loop control strategy is adopted, with the outer loop adaptively selecting control variables (clamping force, sector number, or position) based on the state machine, and the inner loop ensuring execution accuracy and dynamic performance through speed and current closed loops. It can achieve shortest stroke control during braking, improving braking response speed while ensuring constant gap and avoiding braking drag. The reset process is highly automated, facilitating maintenance and replacement of friction blocks and improving system maintainability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the circuit structure of the present invention.

[0019] Figure 2 This is a schematic diagram of the state machine state transition of the present invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. The described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] In the technical solution of the present invention, Figure 1 This is a structural schematic diagram of the three-closed-loop control method applicable to EMB according to the present invention, as shown below. Figure 1 As shown, the present invention includes: S10: Determine the state machine state based on the input signal; The state machine states include: constant gap state, gap elimination state, braking force output state, gap recovery state, motor retraction state, and initial state; S20: Determine the three-loop control strategy and control objective based on the state machine state; The control objective for the constant gap state is the number of Hall sectors, and the control strategy is: sector number-speed-current closed loop; The control objective for eliminating the gap state is the clamping force, and the control strategy is: clamping force-speed-current closed loop; The control target for the braking force output state is the clamping force, and the control strategy is: clamping force-speed-current closed loop; The control objective for restoring the gap state is the number of Hall sectors, and the control strategy is: sector number-speed-current closed loop; The control target for the motor retraction state is the position sensor voltage, and the control strategy is: position-speed-current closed loop; The control target for the initial state is the position sensor voltage, and the control strategy is a closed-loop control of position, rotation speed, and current.

[0022] The input signal includes: Clamping force setpoint, clamping force feedback, enable motor reset, position feedback, position setpoint, number of Hall sector sectors.

[0023] The condition for determining the constant gap state is: after the system is powered on, the number of Hall sectors = the first threshold of the number of sectors or in the state of restoring the gap, the absolute value of the number of sectors < the second threshold of the number of sectors; The condition for determining the state of eliminating gap is: under the state of constant gap, the clamping force given is greater than or equal to the clamping force given threshold. The condition for determining the braking force output state is: under the state of eliminating gaps, |clamping force given - clamping force feedback| < difference threshold; The condition for determining the recovery gap state is: under the braking force output state, the clamping force given = the clamping force given threshold; The condition for determining the motor retraction state is: under constant gap conditions, the motor reset enable = motor reset enable threshold. The initial state is determined when the position feedback reaches the initial value in the motor retraction state.

[0024] The first threshold for the number of sectors is 0, and the second threshold for the number of sectors is 3.

[0025] The difference threshold is 1~2kN.

[0026] The clamping force is given a threshold value of 2~4kN.

[0027] The clamping force is given a threshold value of 0.

[0028] The motor reset enable threshold is 1.

[0029] The following is a specific example: The condition for determining the constant gap state is: either the absolute value of the number of sectors is <3 when the gap is restored; The condition for determining the state of eliminating gap is: under the state of constant gap, the clamping force is ≥3kN; The condition for determining the braking force output state is: under the state of eliminating gaps, |clamping force given - clamping force feedback| < 1kN; The condition for determining the recovery gap state is: under the braking force output state, the clamping force given = 0; The condition for determining the motor retraction state is: under constant gap conditions, the motor reset enable = 1; The initial state is determined when the position feedback reaches the initial value in the motor retraction state.

[0030] The input signals include: clamping force given FN_REF, clamping force feedback FN_FBD, enable motor reset Enmotor_RST, position feedback VPOS_FBD, position given VPOS_REF, and Hall sector count VPOS_REF. The state machine states include: 000: constant gap state (non-braking); 001: gap elimination state (during braking, motor feed); 010: braking force output state (stalled rotor); 011: gap recovery state (during brake release, motor retraction); 100: motor retraction state (returning to EMB caliper factory settings); 101: initial state (returning to EMB caliper factory settings, replacing friction blocks).

[0031] The input sources for both setpoint and feedback are selected based on the EMB state machine. In the "Eliminate Backlash and Stall Output" state, clamping force is the control objective, and the control strategy is a three-loop control strategy of "clamping force-speed-current". In the "Restore Backlash and Constant Backlash" state, the control objective is to set the number of Hall sensor sectors for motor rotation to 0, and the control strategy is a three-loop control strategy of "sector number-speed-current". In the "Motor Reverse and Motor Initialization" state, the voltage value of the motor's position sensor is the control objective, and the control strategy is a three-loop control strategy of "position-speed-current".

[0032] The working principle of this invention is: The EMB state machine transition strategy is based on the instructions of the chassis domain controller, such as... Figure 2 As shown, the state machine is determined and selected, and the input sources for the given and feedback in the three-loop strategy are switched according to the different state machines.

[0033] (1) When performing the service braking function: judge the clamping force command issued by CAN. If the clamping force is greater than 3kN, then enter the gap elimination stage. At this time, the EMB controller uses the clamping force as the control target to perform "clamping force-speed-current" control. When the absolute value deviation of the clamping force is less than 1 kN, the state machine enters the stall output state. When the absolute value deviation of the clamping force is greater than 3kN, the state machine exits the stall state and enters the force closed-loop regulation state.

[0034] (2) When performing the gap recovery function: In the stall output state, the system judges the clamping force command issued by CAN. When the command is 0, the system enters the gap recovery state. At this time, the EMB controller performs "sector number-speed-current" control with the sector number equal to 0 as the control target. When the deviation between the given sector number and the feedback sector number is less than 3, the system enters the gap constant state.

[0035] (3) When performing the motor reset function: In the constant gap state, determine whether the CAN bus sends a generator reset enable signal. When the enable signal is Enmotor_RST, the EMB motor returns to the initial position. At this time, "position-speed-current" control is performed with the position signal equal to 0 as the control target, and the initial position signal is used as the control target. After reaching the position, it enters the initial state. When the enable signal is Enmotor_RST of 0, the EMB controller performs "sector number-speed-current" control with the sector number equal to 0 as the control target, and returns to the constant gap state.

[0036] The present invention provides a three-closed-loop control method for EMB, the core of which is to combine a state machine judgment strategy with a three-closed-loop control circuit to achieve adaptive control under various braking conditions.

[0037] I. State Machine Judgment Strategy The state machine determines and switches states based on the following input signals: Clamping force given (from CAN command) Clamping force feedback (from pressure sensor) Enable motor reset (from CAN command) Location feedback (from location sensor) Position given (reset target position) Hall sector count (from Hall sensor) The system has six states, each represented by a three-bit binary code: Constant gap state (code 000): The default state after system power-on. In this state, a constant gap is maintained between the brake pads and the brake disc, and the Hall sector count is 0. In this state, if there is no braking command and no reset command, the system maintains the current state.

[0038] Clearance state (code 001): When a braking command with a clamping force of ≥3kN is received, the system enters the clearance elimination state from the clearance constant state. The motor rotates forward, pushing the brake pads toward the brake disc until they make contact.

[0039] Braking force output state (code 010): When the clamping force feedback is close to the given value, that is, when |clamping force given - clamping force feedback| < 1kN, the system enters the braking force output state (stalled state), and the motor maintains the current position and outputs a constant clamping force.

[0040] Restore gap state (code 011): When the braking command is released, that is, when the clamping force is given = 0, the system enters the gap restoration state from the braking force output state, the motor reverses, and the brake pads return to the constant gap position.

[0041] Motor retraction state (code 100): When the gap is constant, if a motor reset enable signal is received (enable motor reset = 1), the system enters the motor retraction state, and the motor continues to reverse to the mechanical initial position.

[0042] Initial state (code 101): When the position feedback voltage reaches the initial value (usually 1V), the system enters the initial state, at which time maintenance operations such as friction block replacement can be performed.

[0043] Two- or three-loop closed-loop control circuits Based on the current state output by the state machine, the system automatically selects the appropriate three-loop control strategy: Clamping force-speed-current closed loop: suitable for eliminating gap conditions and braking force output conditions. The outer loop is the clamping force loop, which calculates the speed command based on the deviation between the clamping force given and the feedback; the middle loop is the speed loop, which calculates the current command based on the deviation between the speed command and the estimated speed; the inner loop is the current loop, which generates a PWM signal to drive the motor based on the deviation between the current command and the actual current.

[0044] Sector Count-Speed-Current Closed-Loop: Applicable to both constant and recoverable gap states. The outer loop is the sector count loop, which calculates the speed command with Hall sector count = 0 as the control target; the middle loop is the speed loop, which calculates the current command based on the deviation between the speed command and the estimated speed; the inner loop is the current loop, which generates a PWM signal to drive the motor based on the deviation between the current command and the actual current.

[0045] Position-Speed-Current Closed Loop: Applicable to motor retraction and initial states. The outer loop is the position loop, which calculates the speed command based on the position sensor voltage reaching a preset initial value as the control target; the middle loop is the speed loop, which calculates the current command based on the deviation between the speed command and the estimated speed; the inner loop is the current loop, which generates a PWM signal to drive the motor based on the deviation between the current command and the actual current.

[0046] III. System Workflow Combination Figure 1 and Figure 2 The specific workflow of the control method described in this invention is as follows: System power-on initialization: After the controller is powered on, it checks whether the Hall sector count is 0. If so, it enters the constant gap state; otherwise, it controls the motor to rotate until the sector count returns to zero before entering this state.

[0047] Execute service braking function: If a clamping force of ≥3kN is received, the system enters the gap elimination state and adopts clamping force-speed-current closed-loop control. When the clamping force deviation is less than 1kN, it enters the braking force output state, continues to maintain the clamping force closed loop, and the motor enters the stalled pressure holding mode. If the clamping force becomes 0, it enters the recovery gap state, switches to sector number-speed-current closed loop, and controls the motor to reverse until the sector number returns to zero. When the sector number deviation is less than 3, it is determined that the system has returned to the constant gap position, and the system returns to the constant gap state.

[0048] Perform motor reset function: Under constant gap conditions, if a CAN command enabling motor reset = 1 is received, the motor will enter the retraction state and adopt position-speed-current closed-loop control. When the position feedback voltage reaches the initial value (e.g., 1V), it enters the initial state; If the enable motor reset signal is cleared, the system controls the motor to rotate, bringing the sector number back to zero and returning to a constant gap state.

[0049] This invention combines state machines with three-loop control to achieve intelligent, efficient, and stable control of the EMB system under multiple operating conditions. This method is not only applicable to commercial and passenger vehicles but can also be extended to rail transit, industrial braking, and other fields, demonstrating high practical value and promising prospects for wider application.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features, and such modifications or substitutions do not cause the corresponding technical solutions to depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A three-closed-loop control method suitable for EMB, characterized in that, include: S10: Determine the state machine state based on the input signal; The state machine states include: constant gap state, gap elimination state, braking force output state, gap recovery state, motor retraction state, and initial state; S20: Determine the three-loop control strategy and control objective based on the state machine state; The control objective for the constant gap state is the number of Hall sectors, and the control strategy is: sector number-speed-current closed loop; The control objective for eliminating the gap state is the clamping force, and the control strategy is: clamping force-speed-current closed loop; The control target for the braking force output state is the clamping force, and the control strategy is: clamping force-speed-current closed loop; The control objective for restoring the gap state is the number of Hall sectors, and the control strategy is: sector number-speed-current closed loop; The control target for the motor retraction state is the position sensor voltage, and the control strategy is: position-speed-current closed loop; The control target for the initial state is the position sensor voltage, and the control strategy is a closed-loop control of position, rotation speed, and current.

2. The three-closed-loop control method for EMB as described in claim 1, characterized in that, The clamping force-speed-current closed loop consists of: an outer loop (clamping force loop) that calculates the speed command based on the deviation between the clamping force given and the feedback; a middle loop (speed loop) that calculates the current command based on the deviation between the speed command and the estimated speed; and an inner loop (current loop) that generates a PWM signal to drive the motor based on the deviation between the current command and the actual current. The sector number-speed-current closed loop consists of: an outer loop (sector number loop) that calculates speed commands with Hall sector number = 0 as the control target; a middle loop (speed loop) that calculates current commands based on the deviation between the speed commands and the estimated speed; and an inner loop (current loop) that generates PWM signals to drive the motor based on the deviation between the current commands and the actual current. The position-speed-current closed loop consists of: an outer loop (position loop) that calculates the speed command based on the position sensor voltage reaching a preset initial value as the control target; a middle loop (speed loop) that calculates the current command based on the deviation between the speed command and the estimated speed; and an inner loop (current loop) that generates a PWM signal to drive the motor based on the deviation between the current command and the actual current.

3. The three-closed-loop control method for EMB as described in claim 1, characterized in that, The input signal includes: Clamping force setpoint, clamping force feedback, enable motor reset, position feedback, position setpoint, number of Hall sector sectors.

4. The three-closed-loop control method for EMB as described in claim 3, characterized in that, The condition for determining the constant gap state is: after the system is powered on, the number of Hall sectors = the first threshold of the number of sectors or in the state of restoring the gap, the absolute value of the number of sectors < the second threshold of the number of sectors; The condition for determining the state of eliminating gap is: under the state of constant gap, the clamping force given is greater than or equal to the clamping force given threshold. The condition for determining the braking force output state is: under the state of eliminating gaps, |clamping force given - clamping force feedback| < difference threshold; The condition for determining the recovery gap state is: under the braking force output state, the clamping force given = the clamping force given threshold; The condition for determining the motor retraction state is: under constant gap conditions, the motor reset enable = motor reset enable threshold. The initial state is determined when the position feedback reaches the initial value in the motor retraction state.

5. The three-closed-loop control method for EMB as described in claim 4, characterized in that, The first threshold for the number of sectors is 0, and the second threshold for the number of sectors is 3.

6. The three-closed-loop control method for EMB as described in claim 4, characterized in that, The difference threshold is 1~2kN.

7. The three-closed-loop control method for EMB as described in claim 4, characterized in that, The clamping force is given a threshold value of 2~4kN.

8. The three-closed-loop control method for EMB as described in claim 4, characterized in that, The clamping force is given a threshold value of 0.

9. The three-closed-loop control method for EMB as described in claim 4, characterized in that, The motor reset enable threshold is 1.

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