A method for controlling the segmented engagement of a parking pawl of an electromechanical brake

Abstract

The application discloses a kind of electronic mechanical brake's parking pawl subsection engagement control method, it is applied to the system including motor, transmission mechanism, brake, ratchet wheel fixed on motor shaft, pawl, electromagnet and controller.The method is first driven motor positive rotation until the clamping force of brake reaches target value, then drive electromagnet to make pawl pop out, then drive motor to preset the reverse rotation of clearance compensation target speed to reduce the clearance between pawl and ratchet wheel, while maintaining the clamping force above the safe lower limit.During reverse rotation, according to the joint criterion of current rate of change and speed resistance amount, the locking contact is judged, after judging, first limited reverse drive is maintained within the preset guide time to make the ratchet wheel slide into the tooth valley along the working surface of pawl, then gradually reduce the current to near zero according to the preset unloading trajectory.When motor angular velocity and current are lower than threshold value and continue for a preset time, it is determined that mechanical locking is completed and the motor drive is cut off.

Description

Technical Field

[0001] This invention relates to the field of automotive brake-by-wire and parking brake technology, specifically to a method for segmented engagement control of the parking pawl in an electromechanical brake. Background Technology

[0002] EMB (Electromechanical Braking System) generates braking force by using a motor-driven transmission mechanism to clamp the brake pads. To reduce power consumption and improve parking reliability during the holding phase, a parking ratchet-pawl locking mechanism is typically integrated into the EMB system. The ratchet is interference-fitted onto the motor shaft, while the pawl is driven by an electromagnet to extend and retract. During parking, the motor first establishes and reaches the target clamping force. Then, the pawl engages with the ratchet. Finally, the motor drive is turned off, and the electromagnet power supply is cut off. The pawl remains extended by a spring inside the electromagnet, and the parking force is maintained by a mechanical locking mechanism.

[0003] In existing technical solutions, the pawl engagement process is usually assisted by fixed low-speed reverse or fixed angle / fixed time retraction, and the completion of engagement is determined by signals such as time, position or motor speed stop.

[0004] However, this method presents significant engineering problems in practical EMB applications. The ratchet engagement process relies heavily on passive collisions, resulting in significant impact, noise, and severe tooth wear. Furthermore, existing solutions lack clear segmented control over critical stages such as clearance elimination, locking contact, rolling into the tooth groove, and torque unloading. Consequently, the consistency of the engagement process is poor under conditions of temperature changes, component wear, assembly tolerance fluctuations, and braking force variations. Relying solely on time, angle, or speed is insufficient to ensure that the parking torque has been fully transferred to the ratchet-pawl mechanism. If the motor is directly deactivated while under load, it may lead to the release of residual elastic energy, secondary impacts, and difficulties in subsequent unlocking. Summary of the Invention

[0005] This invention proposes a segmented engagement control method for parking pawls in electromechanical brakes, which solves the problem that the engagement process of existing parking pawls relies on passive collisions.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for segmented engagement control of a parking pawl in an electromechanical brake. The method is applied to a system including a motor, a transmission mechanism, a brake, a ratchet fixed on the motor shaft, a pawl cooperating with the ratchet, an electromagnet driving the pawl, and a controller, and includes the following steps: Step S1: Use the controller to drive the motor to rotate forward until the clamping force of the brake reaches the preset target value; Step S2: Use the controller to drive the electromagnet to make the pawl pop out towards the ratchet wheel; Step S3: Use the controller to drive the motor to rotate in the opposite direction at a preset backlash reduction target speed to reduce the gap between the pawl and the ratchet, and maintain the clamping force within a range not lower than the lower limit of the clamping force safety. During the reverse rotation of the motor, the pawl and the ratchet are locked into contact based on the combined criterion of the motor current change rate and the motor speed resistance. Step S4: After the locking contact is determined, the controller drives the motor with a reverse drive current not exceeding the preset current upper limit within the preset guidance time, so that the ratchet slides into the tooth valley along the working surface of the pawl; the actual motor current at the end of the preset guidance time is recorded as the unloading start current, and the unloading start current is gradually reduced according to the preset unloading trajectory until the absolute value of the motor current is lower than the preset current threshold. Step S5: When the absolute value of the motor angular velocity is lower than the preset speed threshold and the absolute value of the motor current is lower than the preset current threshold, and the above two conditions continue for a preset confirmation time, it is determined that the mechanical lock is completed and the drive of the motor is cut off.

[0007] Preferably, in step S3, the controller monitors the cumulative reverse rotation angle of the motor and limits the cumulative reverse rotation angle to a range not exceeding the maximum allowable angle; The maximum permissible angle is the smaller value between the upper limit of the geometric clearance of the mechanism and the upper limit of the clamping force constraint. The upper limit of the geometric clearance of the mechanism is determined according to the angle range between two adjacent teeth corresponding to the number of teeth of the ratchet; The upper limit of the clamping force constraint is converted to the angle on the motor shaft in the following way: divide the difference between the current clamping force and the lower limit of the clamping force by the equivalent stiffness of the clamping side to obtain the allowable back displacement of the output end of the transmission mechanism, and then convert it to the angle on the motor shaft according to the transmission ratio of the transmission mechanism. If the cumulative reverse rotation angle reaches the maximum allowable angle but the locking contact is still not determined, the controller exits the current reverse rotation process.

[0008] Preferably, the equivalent stiffness of the clamping side is obtained through offline calibration by bench testing and stored as a lookup value related to temperature, target clamping force range, and brake pad wear of the brake; or it is obtained online by the controller based on small disturbance response.

[0009] Preferably, in step S3, the condition for determining that the pawl and the ratchet have locked contact is: when the rate of change of the motor current is greater than the current rate of change threshold and the motor speed resistance is greater than the speed resistance threshold, and the above two conditions are continuously satisfied for a preset number of sampling periods. The motor current change rate is the difference between the filtered current value at the current sampling moment and the filtered current value at the beginning sampling moment of the same sliding window, divided by the time length corresponding to the sliding window; the motor speed resistance is the absolute value of the difference between the backlash elimination target speed and the filtered speed at the current sampling moment.

[0010] Preferably, in step S1, the holding current after the clamping force stabilizes is recorded, and the current change rate threshold is the product of the adaptive coefficient and the holding current plus the noise margin; the speed resistance threshold is set according to the preset ratio of the gap elimination target speed, the speed estimation noise, and the speed fluctuation range allowed by the system.

[0011] Preferably, in step S4, the controller uses a ramp trajectory or an exponential trajectory as the preset unloading trajectory during the process of gradually reducing the motor current; wherein the ramp trajectory refers to the unloading starting current linearly decreasing to below the preset current threshold within a preset unloading time, and the exponential trajectory refers to the unloading starting current decaying exponentially according to a preset time constant; the preset unloading time or the preset time constant is determined based on the vehicle noise and vibration target, the maximum allowable disturbance torque, and the time required for the pawl to slide into the tooth valley.

[0012] Preferably, when the controller gradually reduces the motor current to near zero according to the preset unloading trajectory, a limited virtual impedance correction is superimposed on the unloading trajectory, or a virtual spring damping control is used alone to replace the preset unloading trajectory; the parameters of the virtual impedance correction are determined according to the maximum allowable disturbance torque, the target speed attenuation rate, and the vehicle noise and vibration index.

[0013] Preferably, the method further includes a retry and fail-safe step: if locking contact is still not determined when the cumulative reverse rotation angle reaches the maximum allowable angle during the gap elimination stage, the controller restores the clamping force to no less than the clamping force safety lower limit, drives the motor to rotate forward by a preset tooth offset angle, drives the electromagnet to retract the pawl, and re-executes all steps S2 to S5; the tooth offset angle is determined according to the number of teeth of the ratchet; If the condition that the motor angular velocity and motor current are both below their respective thresholds is not met after the longest waiting time since the controller determines that the locking contact has occurred, the controller will re-execute step S4; if the mechanical locking confirmation condition is still not met after re-execution, the controller will restore the clamping force to no less than the clamping force safety lower limit, drive the motor to rotate forward by a preset tooth offset angle, drive the electromagnet to retract the pawl, and re-execute all steps from step S2 to step S5. If the maximum number of consecutive retries is not successful, the controller reports a locking failure fault and maintains the motor output to meet the safety lower limit of the parking clamping force.

[0014] Preferably, the controller obtains the clamping force by one of the following methods: directly measuring it through a force sensor arranged on the brake, push rod, or force transmission chain; or estimating it through motor current, motor displacement, transmission ratio of the transmission mechanism, and equivalent stiffness of the clamping side.

[0015] Preferably, the electromagnet is controlled by an H-bridge drive circuit. The H-bridge drive circuit applies a voltage in a first direction to the electromagnet coil to drive the pawl to pop out, and applies a voltage in a second direction opposite to the first direction to drive the pawl to retract. The pawl is locked in the pop-out position after popping out by a linked spring retaining structure, so that the pawl remains engaged with the ratchet after the electromagnet is de-energized.

[0016] The advantages of this invention include at least the following: 1. The segmented control through backlash elimination, contact recognition, flexible engagement, torque unloading, and locking confirmation makes the engagement process controllable, significantly reducing impact and noise; 2. By combining contact identification based on current change rate and speed resistance, the accuracy of identifying the locking contact moment is improved, resulting in better meshing consistency under different temperature, wear and assembly tolerance conditions; 3. By using a preset unloading trajectory, the motor-side torque is gradually reduced to near zero, achieving a smooth transfer of parking torque to the ratchet and pawl mechanism, reducing secondary impacts and unlocking difficulties caused by load-bearing enable failure. 4. Mechanical locking is confirmed by a combination of speed, current and duration criteria, and parking reliability is improved through retry and fail-safe strategies. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the motor, ratchet, and pawl in an embodiment of the present invention; Figure 2 This is a general flowchart of the parking control according to an embodiment of the present invention; Figure 3 This is a flowchart of the pawl flexible engagement control in an embodiment of the present invention; Figure 4 This is a schematic diagram of the motor current change during parking according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the clamping force change curve during the parking process according to an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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 are within the protection scope of the present invention.

[0019] like Figure 1 As shown, this embodiment of the invention provides a segmented engagement control method for a parking pawl in an electromechanical brake. This method is applied to an electromechanical brake system with a parking lock mechanism. The system includes a motor, a transmission mechanism, a brake, a ratchet fixedly mounted on the motor shaft, a pawl that engages with the ratchet, an electromagnet, an H-bridge drive circuit, and a controller. The ratchet is interference-fitted onto the motor output shaft, and the ratchet teeth are designed to rotate freely when the motor rotates in the clamping direction, while the pawl engages the ratchet to lock it in the reverse direction.

[0020] The controller connects to the motor driver, electromagnet drive circuit, current sampling module, angle and speed feedback module, and clamping force acquisition module to perform parking pressure build-up, pawl ejection, gap elimination, contact recognition, flexible engagement, mechanical locking confirmation, and fault handling control. Internally, the controller maintains a state machine that switches between control stages according to preset state transition conditions, ensuring the orderly execution of the entire parking locking process.

[0021] In this embodiment, the clamping force signal The force can be directly acquired by a force sensor mounted on the brake, push rod, or transmission chain. In the absence of a dedicated force sensor, the controller can estimate the clamping force based on motor current, motor displacement, the gear ratio of the reduction mechanism, and the equivalent stiffness of the clamping mechanism. Specifically, the controller can calculate the motor output torque to the push rod end based on the known gear ratio, and then combine this with the force-displacement characteristic curve of the clamping mechanism near the current operating point to obtain an estimated clamping force. Without a dedicated force sensor, the controller uses the estimated clamping force as the basis for control and judgment. Both methods can meet the clamping force feedback requirements of each step in this embodiment.

[0022] The pawl actuator includes an electromagnet, an H-bridge drive circuit, and a spring-holding structure linked to the pawl. The H-bridge drive circuit is connected to the electromagnet coil and is used to selectively apply a positive or reverse voltage across the coil to change the direction of the coil current and thus the direction of the electromagnet's magnetic field.

[0023] When the controller controls the H-bridge to apply a voltage in the first direction to the electromagnet coil, a current in the first direction is formed in the coil. The electromagnet generates an electromagnetic force that moves the pawl in the ejection direction, thereby pushing the pawl to eject towards the ratchet. After the pawl reaches the ejection position, it can be locked in the ejected state by its own spring structure, thus eliminating the need for the electromagnet to be continuously energized to maintain it.

[0024] When it is necessary to release the mechanical lock or disengage the pawl from the ratchet, the controller controls the H-bridge to apply a voltage in the opposite direction to the first direction to the electromagnet coil, creating a reverse current in the coil. The electromagnet then generates an electromagnetic force in the opposite direction to the ejection. This reverse electromagnetic force overcomes the spring force, as well as the frictional resistance and possible engagement resistance during the pawl's movement, thereby driving the pawl to move in the retraction direction and disengage from the engagement position.

[0025] With the aforementioned bidirectional excitation method, the electromagnet can achieve both pawl ejection and pawl retraction control. Simultaneously, the pawl is held in position by a spring after ejection, which helps reduce system holding power consumption and improves positional stability in the parking lock state.

[0026] Step S1: Parking pressure build-up and maintenance.

[0027] like Figure 2 As shown, during the parking process, after completing the pre-safety check, the controller first executes step S1. The controller drives the motor to rotate forward, which pushes the brake to clamp the brake pads through the transmission mechanism, causing the clamping force to gradually increase until the target parking clamping force is reached. Alternatively, the clamping force may reach a target motor angle or displacement corresponding to the target clamping force. After the clamping force reaches the target value and remains stable, the controller records the motor current at this time as the holding current. This holding current will serve as a reference value for subsequent flexible engagement and unloading control, reflecting the level of motor output torque required to maintain the target clamping force under the current operating conditions.

[0028] Step S2: The pawl pops out.

[0029] like Figure 3 As shown, after step S1 is completed, the controller enters the pawl flexible engagement process, first executing step S2. The controller drives the electromagnet to eject the pawl towards the ratchet, while the motor maintains its current position or keeps the current constant during this process to ensure that the clamping force does not change.

[0030] At this point, there is usually an actual clearance between the pawl and the ratchet, which is referred to as the motor shaft and can be expressed as the initial clearance angle. The initial clearance angle is the objective angular clearance between the pawl and the ratchet after the pawl is ejected. Its value can vary with assembly tolerances, wear conditions, temperature, and the relative tooth positions of the pawl and the ratchet. After the electromagnet ejects the pawl, it may not necessarily land directly at the lowest point of the ratchet tooth valley. It often stops at a position near the tooth tip or tooth slope. At this time, although the pawl may have slight physical contact with the ratchet tooth surface, the ratchet tooth surface has not yet formed an effective blockage for the pawl in the locking direction. Therefore, it is necessary to drive the motor to rotate in the opposite direction through subsequent steps to establish an effective engagement between the ratchet tooth surface and the pawl in the locking direction.

[0031] In embodiments equipped with a pawl position switch or pawl position sensor, the system can determine whether the pawl has extended to its designated position. In embodiments without dedicated position detection, the system directly proceeds to the subsequent gap elimination stage after the pawl extends, and determines whether the pawl and ratchet are in contact using subsequent locking contact identification criteria.

[0032] Step S3: Gap elimination and locking contact identification.

[0033] To gradually bring the ratchet teeth towards the pawl engagement position in the locking direction, the controller drives the motor at a relatively small reverse speed. Alternatively, it can rotate in the opposite direction according to a preset small reverse displacement trajectory to gradually reduce the angular distance between the ratchet teeth and the pawl in the locking direction. Since the ratchet is fixed on the motor shaft, the ratchet rotates along with the motor when it reverses, causing the ratchet teeth to gradually approach the ejected pawl. The controller does not need to accurately obtain the initial clearance angle beforehand. The specific values ​​only need to be determined by implementing restricted retraction control under the conditions of satisfying the clamping force safety constraint and the reverse retraction angle constraint. (Target speed for backlash elimination) A speed range of -150rpm to -50rpm can be selected based on the motor speed rating to ensure rapid change in reverse current to prevent timeout, while also avoiding excessive speed that could cause shock and instability. To prevent excessive drop in clamping force during retraction, the controller sets limits on motor current or motor torque to ensure that the clamping force never falls below the safety lower limit. During the gap elimination process, the controller accumulates the reverse rotation angle of the motor. Monitor the angle and ensure it does not exceed the maximum permissible angle. The maximum permissible angle is determined by two constraints: the upper limit of the mechanism's geometric clearance and the upper limit of the clamping force constraint, and the smaller of the two values ​​is taken.

[0034] The upper limit of the geometric clearance of the mechanism is determined by the number of ratchet teeth, which defines the corresponding angular range between two adjacent teeth. For example, a ratchet has... Z When there is one tooth, the angle between two adjacent teeth is 360 degrees divided by 1 / 360. ZThis is the upper limit of the geometric clearance of the mechanism. The upper limit of the clamping force constraint is based on the current clamping force and the safety lower limit. and the equivalent stiffness of the clamping side The calculation yields the following result. Specifically, the maximum allowable reverse rotation angle corresponding to the upper limit of the clamping force constraint is equal to the difference between the current clamping force and the lower safety limit divided by the equivalent stiffness, and then converted to the angle on the motor shaft.

[0035] Clamping side equivalent stiffness This is used to characterize the force and displacement characteristics of the clamping mechanism near the current working point after parking pressure build-up. Under small disturbance conditions, the change in clamping force and the change in displacement approximately satisfy a linear relationship, therefore, it can be used... Lower limit of clamping force This is correspondingly converted to the maximum allowable displacement or angle of the motor shaft retraction. The equivalent stiffness can be obtained through offline calibration via bench testing and stored as a lookup value related to temperature, target clamping force range, and brake pad wear. In other embodiments, it can also be obtained online by the controller based on the response to small disturbances. During online identification, the controller can apply a small displacement disturbance after parking pressure build-up is completed, and calculate the equivalent stiffness at the current operating point based on the ratio of the change in clamping force to the change in displacement.

[0036] If the cumulative back angle Reaching the maximum permissible angle If the pawl and ratchet are still not detected to be in contact, the controller will exit the current reverse rotation process and enter a retry or fail-safe procedure.

[0037] The locking contact referred to in this embodiment refers to the state in which the ratchet teeth effectively mechanically block the pawl in the locking direction during the reverse rotation of the motor. Its characteristic is a sudden change in the motor load that can be detected by current and speed signals. After the pawl is ejected, there may be slight physical contact with the ratchet teeth, but this slight contact does not produce a detectable load change and is not considered locking contact as described in this embodiment.

[0038] During the rollback process, the controller operates at a sampling period. For motor current and motor angular velocity Real-time sampling is performed, and the sampled signal is low-pass filtered to obtain the filtered current. and filtering speed A low-pass filter is used to suppress the interference of motor driver switching ripple and sensor measurement noise on subsequent criteria. Its cutoff frequency should be higher than the characteristic frequency of current and speed changes caused by pawl contact, and lower than the motor PWM switching frequency.

[0039] The controller uses a sliding window differential calculation to determine the rate of change of current, and the calculation formula is as follows.

[0040] ; in, This represents the number of sampling points corresponding to the sliding window length. Sliding window differencing offers better noise immunity compared to adjacent sampling point differencing. The window length... The larger the value, the better the smoothing effect, but the slower the response speed. In actual calibration, a balance needs to be struck between recognition sensitivity and anti-interference capability.

[0041] At the same time, the controller calculates the speed resistance based on the gap elimination target speed and filtering speed set in step S3, and the calculation formula is as follows.

[0042] .

[0043] When the pawl contacts the ratchet, the motor load suddenly increases, manifested as a sharp rise in the rate of change of current and a deviation of the actual speed from the target speed, resulting in speed resistance. Based on the above physical phenomena, the controller uses a combined criterion of the rate of change of current and the amount of speed resistance to identify locking contact. The specific judgment condition is: rate of change of current... Greater than the current change rate threshold And the speed is hindered by Greater than the speed resistance threshold And the above two conditions are satisfied consecutively. N During each sampling cycle, the controller determines that the pawl and ratchet have locked into contact. This condition is met continuously. N The requirement of this step serves to eliminate jitter and can effectively avoid misjudgments caused by occasional current spikes or speed fluctuations.

[0044] like Figure 4 As shown, the current change curve clearly reflects the abrupt change in current at the moment of locking contact. During the gap elimination phase, the current fluctuates slightly around the holding current, while a significant jump occurs at the moment the pawl contacts the ratchet, followed by a gradual decrease during the unloading phase.

[0045] During the execution of step S3, if the locking contact criterion has not yet been met, and the motor has accumulated a reverse rotation angle... Maximum permissible angle not reached If the controller continues to perform gap elimination control, and if the locking contact is not detected when the cumulative retraction angle reaches the maximum allowable angle, the controller exits the current reverse rotation process and enters the retry or fault-safe procedure.

[0046] Step S4: Flexible engagement and smooth torque transfer.

[0047] like Figure 3As shown, after determining in step S3 that the pawl and ratchet have locked contact, the controller enters the flexible engagement and torque smooth transfer stage. This embodiment uses a segmented unloading trajectory as the main control scheme, which guides the ratchet to roll smoothly along the working surface of the pawl and tend towards the tooth valley after the pawl and ratchet contact each other. At the same time, the output torque of the motor side gradually decreases in a controlled manner, thereby realizing the smooth transfer of parking torque from the motor side to the ratchet and pawl mechanical locking mechanism.

[0048] Step S4 is executed in two stages. The first stage is the engagement guidance stage, in which the controller performs the engagement for a preset short duration. The internally controlled reverse drive causes the ratchet to roll along the pawl's working surface and slide into the tooth groove. Because the ratchet teeth are designed to lock when the motor reverses, once the pawl falls into the tooth groove, the ratchet's reverse rotation is blocked by the pawl and cannot continue. Therefore, there is no issue of the pawl being pushed past the tooth groove. Even if the pawl happens to fall near the tooth groove when it pops out, because the engagement guide segment is very short, the current increases after the motor's reverse rotation is blocked, but the ratchet stops rotating, which will not adversely affect subsequent operations.

[0049] The second segment is the unloading segment. The controller records the actual motor current value at the end of the engagement initiation segment. This serves as the initial unloading current. The controller adjusts the motor current according to the preset unloading trajectory, changing it from the initial unloading current. Gradually decrease until approaching zero. The expression for the slope trajectory is: ; The expression for the exponential trajectory is as follows: ; in, The unloading time for the ramp trajectory. The time constant of the exponential trajectory can be taken as the unloading time. 0.2 to 0.3 times, the exponential trajectory after 3 Up to 5 The current then decays to near zero.

[0050] The increased motor load during contact and engagement may cause the actual current to exceed the holding current. Using the actual current as the unloading starting point can avoid a step jump in the current command and ensure a smooth decrease in torque.

[0051] The above parameters are calibrated and determined based on the vehicle noise and vibration targets, the maximum allowable disturbance torque, and the time required for the pawl to slide into the tooth valley. This ensures that the motor-side torque decreases gradually in a controlled manner rather than abruptly, thereby avoiding shocks, secondary tooth climbing, or unlocking difficulties caused by sudden unloading. The advantage of the ramp trajectory is its simplicity and constant unloading rate, while the advantage of the exponential trajectory is its faster initial unloading and gentler decay at the end, which can better suppress disturbances at the end of the torque transfer.

[0052] like Figure 5 As shown, the clamping force variation curve indicates that the clamping force remains at a stable level after pressure build-up. The fluctuation of the clamping force during gap elimination and engagement is always within a safe range, verifying the effectiveness of the above-mentioned segmented control strategy in constraining the lower limit of clamping force safety.

[0053] In some optional implementations, step S4 may also introduce virtual impedance-assisted control, i.e., superimposing a limited impedance correction amount on the segmented unloading trajectory, or using virtual spring damping control alone to further suppress the impact at the moment of contact and improve the smoothness of the meshing process. The principle of virtual impedance control is to establish a virtual spring damping model in the controller, and calculate the corrected torque command in real time based on the motor angle deviation and angular velocity, so that the motor exhibits controlled smoothness characteristics at the moment of contact. Virtual impedance parameters and It can be calibrated based on the maximum allowable disturbance torque, the target speed attenuation rate, and the vehicle noise and vibration index.

[0054] Step S5: Mechanical locking confirmation and deactivation.

[0055] like Figure 3 As shown, after the unloading phase is completed, the controller proceeds to step S5 for mechanical lock confirmation. The controller continuously monitors the motor angular velocity and motor current. When the absolute value of the motor angular velocity is less than the speed threshold... The absolute value of the motor current is less than the current threshold. And the above two conditions are maintained continuously for a period of time. At this point, the controller determines that the motor has been unloaded to near-zero torque and that the ratchet and pawl mechanism has reliably assumed constraint, thus completing the mechanical locking. The fact that both speed and current are close to zero indicates that the motor is neither driven to rotate by external torque nor outputting torque to maintain clamping force, signifying that the parking holding force is entirely provided by the mechanical locking of the ratchet and pawl.

[0056] In embodiments equipped with a pawl position switch or a pawl position sensor, the pawl position signal can also be incorporated into the locking confirmation condition as a redundant criterion to further improve the reliability of the locking state judgment.

[0057] like Figure 2 As shown, after confirming the mechanical locking is completed in step S5, the controller cuts off the motor drive and simultaneously releases the electromagnet drive. Because the pawl has a spring-loaded retaining structure linked to it, the spring force continues to lock the pawl in the pop-out position after the electromagnet is de-energized, keeping the pawl engaged with the ratchet. At this time, the parking holding force is entirely borne by the mechanical locking mechanism, and both the motor and electromagnet are in a zero-power state, achieving zero power consumption during parking.

[0058] Retry and fail-safe.

[0059] Retry and failsafe include two triggering scenarios.

[0060] The first scenario: If the locking contact is not determined when the cumulative reverse rotation angle reaches the maximum allowable angle during the gap elimination stage, the motor will first work with the drive electromagnet to retract, the controller will restore the clamping force to no less than the lower limit of the clamping force safety, the drive motor will rotate forward by a preset tooth offset angle to change the relative tooth position of the ratchet and the pawl, the drive electromagnet will then pop out again, and all steps from pawl popping out to cutting off the motor drive will be repeated; the tooth offset angle is not less than 1 / 4 and not greater than 1 / 2 of the angle between two adjacent teeth of the ratchet.

[0061] The second scenario: If the motor angular velocity and motor current are both below their respective thresholds after the longest waiting time since the controller determined that the locking contact has been established, the controller determines that the mechanical locking has not been stably established. The controller first re-executes the flexible engagement and torque unloading steps. If the mechanical locking confirmation conditions are still not met after re-execution, the motor and electromagnet retract first, the controller restores the clamping force to no less than the lower limit of the clamping force safety, drives the motor to rotate forward by the preset tooth position offset angle, and then causes the pawl to pop out again. The controller then re-executes all steps from pawl popping out to cutting off the motor drive.

[0062] The controller maintains a first retry counter and a second retry counter. The first retry counter corresponds to the number of retries when locking contact is not determined during the gap elimination phase, and the second retry counter corresponds to the number of retries when locking contact is achieved but the locking confirmation condition is not met. When either counter reaches its maximum count, the controller reports a locking failure fault. The maximum count for the first retry counter can be 2 to 4, and the maximum count for the second retry counter can be 1 to 3. Each time the next phase is successfully entered, the corresponding counter is reset to zero.

[0063] When the number of retries in the first scenario or the number of retries in the second scenario reaches their respective maximum number of retries. When this occurs, the controller drives the electromagnet to retract the pawl, reports a locking failure fault, and maintains the motor output to meet the safe lower limit of the parking clamping force.

[0064] Longest waiting time The value range is 500ms to 1000ms, and its value should be greater than the engagement guidance time. Uninstallation time Duration of Lockout Confirmation The maximum value of the sum of the three is used to ensure that the normal execution process is not interrupted by the timeout mechanism.

[0065] In one exemplary implementation, the sampling period Take 50 microseconds, sliding window length mThree to ten sampling points can be taken, and the number of consecutive determinations can be determined. N It can be performed 2 to 8 times. Engagement guidance time. Unloading time can range from 10 milliseconds to 80 milliseconds. The lockout confirmation duration can be set from 20 milliseconds to 200 milliseconds. The time interval can range from 30 milliseconds to 200 milliseconds. The above parameters can be calibrated and adjusted according to motor inertia, ratchet tooth profile, vehicle noise and vibration requirements, and braking system stiffness.

[0066] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; only preferred embodiments of the present invention are illustrated. The descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. As long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification.

[0067] It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept, and these all fall within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the appended claims.

Claims

1. A method for segmented engagement control of a parking pawl in an electromechanical brake, characterized in that, The method is applied to a system including a motor, a transmission mechanism, a brake, a ratchet fixed on the motor shaft, a pawl cooperating with the ratchet, an electromagnet driving the pawl, and a controller, and includes the following steps: Step S1: Use the controller to drive the motor to rotate forward until the clamping force of the brake reaches the preset target value; Step S2: Use the controller to drive the electromagnet to make the pawl pop out towards the ratchet wheel; Step S3: Use the controller to drive the motor to rotate in the opposite direction at a preset backlash reduction target speed to reduce the gap between the pawl and the ratchet, and maintain the clamping force within a range not lower than the lower limit of the clamping force safety. During the reverse rotation of the motor, the pawl and the ratchet are locked into contact based on the combined criterion of the motor current change rate and the motor speed resistance. Step S4: After the locking contact is determined, the controller drives the motor with a reverse drive current not exceeding the preset current upper limit within the preset guidance time, so that the ratchet slides into the tooth valley along the working surface of the pawl; the actual motor current at the end of the preset guidance time is recorded as the unloading start current, and the unloading start current is gradually reduced according to the preset unloading trajectory until the absolute value of the motor current is lower than the preset current threshold. Step S5: When the absolute value of the motor angular velocity is lower than the preset speed threshold and the absolute value of the motor current is lower than the preset current threshold, and the above two conditions continue for a preset confirmation time, it is determined that the mechanical lock is completed and the drive of the motor is cut off.

2. The parking pawl segmental engagement control method for an electromechanical brake according to claim 1, characterized in that: In step S3, the controller monitors the cumulative reverse rotation angle of the motor and limits the cumulative reverse rotation angle to a range not exceeding the maximum allowable angle; The maximum permissible angle is the smaller value between the upper limit of the geometric clearance of the mechanism and the upper limit of the clamping force constraint. The upper limit of the geometric clearance of the mechanism is determined according to the angle range between two adjacent teeth corresponding to the number of teeth of the ratchet; The upper limit of the clamping force constraint is converted to the angle on the motor shaft in the following way: divide the difference between the current clamping force and the lower limit of the clamping force by the equivalent stiffness of the clamping side to obtain the allowable back displacement of the output end of the transmission mechanism, and then convert it to the angle on the motor shaft according to the transmission ratio of the transmission mechanism. If the cumulative reverse rotation angle reaches the maximum allowable angle but the locking contact is still not determined, the controller exits the current reverse rotation process.

3. The parking pawl segmental engagement control method for an electromechanical brake according to claim 2, characterized in that: The equivalent stiffness of the clamping side is obtained through offline calibration by bench testing and stored as a lookup value related to temperature, target clamping force range and brake pad wear of the brake; or it is obtained online by the controller based on the small disturbance response.

4. The parking pawl segmental engagement control method for an electromechanical brake according to claim 1, characterized in that: In step S3, the condition for determining that the pawl and the ratchet have locked contact is: when the rate of change of the motor current is greater than the current rate of change threshold and the motor speed resistance is greater than the speed resistance threshold, and the above two conditions are continuously satisfied for a preset number of sampling periods. The motor current change rate is the difference between the filtered current value at the current sampling moment and the filtered current value at the beginning sampling moment of the same sliding window, divided by the time length corresponding to the sliding window; the motor speed resistance is the absolute value of the difference between the backlash elimination target speed and the filtered speed at the current sampling moment.

5. The parking pawl segmental engagement control method for an electromechanical brake according to claim 4, characterized in that: In step S1, the holding current after the clamping force stabilizes is recorded. The current change rate threshold is the product of the adaptive coefficient and the holding current plus the noise margin. The speed resistance threshold is set according to the preset ratio of the gap elimination target speed, the speed estimation noise, and the speed fluctuation range allowed by the system.

6. The parking pawl segmental engagement control method for an electromechanical brake according to claim 1, characterized in that: In step S4, the controller uses a ramp trajectory or an exponential trajectory as the preset unloading trajectory during the process of gradually reducing the motor current; wherein the ramp trajectory refers to the unloading starting current linearly decreasing to below the preset current threshold within a preset unloading time, and the exponential trajectory refers to the unloading starting current decaying exponentially according to a preset time constant; the preset unloading time or the preset time constant is determined based on the vehicle noise and vibration target, the maximum allowable disturbance torque, and the time required for the pawl to slide into the tooth valley.

7. The parking pawl segmental engagement control method for an electromechanical brake according to claim 6, characterized in that: When the controller gradually reduces the motor current to near zero according to the preset unloading trajectory, a limited virtual impedance correction amount is superimposed on the unloading trajectory, or a virtual spring damping control is used alone to replace the preset unloading trajectory; the parameters of the virtual impedance correction amount are determined according to the maximum allowable disturbance torque, the target speed attenuation rate, and the vehicle noise and vibration index.

8. The parking pawl segmental engagement control method for an electromechanical brake according to claim 2, characterized in that: The method further includes retry and fail-safe steps: if the locking contact is still not determined when the cumulative reverse rotation angle reaches the maximum allowable angle during the gap elimination stage, the controller restores the clamping force to no less than the clamping force safety lower limit, drives the motor to rotate forward by a preset tooth offset angle, drives the electromagnet to retract the pawl, and re-executes all steps S2 to S5; the tooth offset angle is determined according to the number of teeth of the ratchet; If the condition that the motor angular velocity and motor current are both below their respective thresholds is not met after the longest waiting time since the controller determines that the locking contact has occurred, the controller will re-execute step S4; if the mechanical locking confirmation condition is still not met after re-execution, the controller will restore the clamping force to no less than the clamping force safety lower limit, drive the motor to rotate forward by a preset tooth offset angle, drive the electromagnet to retract the pawl, and re-execute all steps from step S2 to step S5. If the maximum number of consecutive retries is not successful, the controller reports a locking failure fault and maintains the motor output to meet the safety lower limit of the parking clamping force.

9. The parking pawl segmental engagement control method for an electromechanical brake according to claim 1, characterized in that: The controller acquires the clamping force by one of the following methods: directly measuring it using a force sensor arranged on the brake, push rod, or force transmission chain; or estimating it using motor current, motor displacement, the transmission ratio of the transmission mechanism, and the equivalent stiffness of the clamping side.

10. The parking pawl segmental engagement control method for an electromechanical brake according to claim 1, characterized in that: The electromagnet is controlled by an H-bridge drive circuit. The H-bridge drive circuit applies a voltage in a first direction to the electromagnet coil to drive the pawl to pop out, and applies a voltage in a second direction opposite to the first direction to drive the pawl to retract. The pawl is locked in the pop-out position after popping out by a linked spring retaining structure, so that the pawl remains engaged with the ratchet after the electromagnet is de-energized.

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