A bidirectional compensation control method for driving a motor and an EMB composite brake

Abstract

This invention relates to the field of automotive braking control technology, and more particularly to a bidirectional compensation control method for a combined drive motor and EMB braking system. The method includes: predicting braking intent and simultaneously eliminating drive motor transmission backlash and EMB mechanical backlash; comparing the response time of the drive motor and the EMB upon braking triggering, and prioritizing the output of braking torque from the motor with the shorter response time; estimating the EMB brake disc temperature online; entering a temperature cycle when the brake disc temperature reaches an upper threshold, where the drive motor switches to a power-consuming state for reverse compensation and replaces the EMB in outputting braking torque, reducing the EMB braking torque to zero to cool the brake disc; entering an energy cycle when the temperature drops to a lower threshold, where the drive motor switches back to regenerative braking state and the EMB supplements the insufficient torque; comparing the energy consumed in the temperature cycle with the energy recovered in the energy cycle, and adjusting the lower threshold accordingly. This invention suppresses brake fade while improving braking response speed and energy recovery efficiency.

Description

Technical Field

[0001] This invention relates to the field of automotive braking control technology, and in particular to a bidirectional compensation control method for combined braking of a drive motor and an EMB. Background Technology

[0002] With the development of electric vehicles and intelligent driving technologies, composite braking systems are gradually becoming standard configurations in vehicle braking systems. A composite braking system typically consists of a regenerative braking device from the drive motor and an electromechanical brake (EMB). The former converts the vehicle's kinetic energy into electrical energy, which is stored in the battery, by the drive motor operating in a generator mode, while simultaneously generating braking torque. The latter generates braking torque through friction by having the calipers clamp the brake discs via a motor. In practical applications, the two braking devices work together to meet the vehicle's total braking force requirements according to the braking commands assigned by the vehicle controller. Regarding control strategies, existing technologies typically use the regenerative braking of the drive motor as the primary braking source, prioritizing its energy recovery capabilities. The EMB supplements the remaining braking torque only when the regenerative braking force is insufficient, forming a hierarchical control architecture with regenerative braking as the primary method and friction braking as a secondary method. Building upon this, some existing technologies further consider the impact of factors such as battery state of charge, vehicle status, and motor status on braking force distribution to improve the coordination between energy recovery efficiency and braking performance.

[0003] However, existing composite braking control methods still face the following problems in practical applications. On the one hand, under long-term braking conditions, continuous friction of the EMB causes a sharp increase in brake disc temperature. The coefficient of friction decreases with increasing temperature, resulting in a decrease in braking torque, i.e., thermal fade, which threatens driving safety. Existing solutions mostly adopt a passive cooling strategy that directly reduces the EMB braking torque when the temperature exceeds a threshold. This approach fails to maintain the stability of the total braking torque while reducing the EMB thermal load. On the other hand, brake disc thermal management and drive motor energy recovery are independent of each other under the existing control architecture, lacking a collaborative optimization mechanism. This makes it difficult to simultaneously ensure braking safety and energy recovery efficiency under harsh conditions such as long downhill slopes, and the contradiction between the risk of thermal fade and the demand for energy recovery is particularly prominent.

[0004] Chinese Patent Publication No. CN121133648A discloses a regenerative braking composite control method for an electromechanical braking system, comprising: real-time acquisition of vehicle status information; calculation of total required braking force and current required deceleration based on vehicle brake pedal signals; real-time calculation of the maximum regenerative braking force currently available in the regenerative braking system based on vehicle status information; calculation of dynamic allocation coefficient based on required deceleration, vehicle speed, wheel slip ratio, and vehicle stability control signals; distribution of braking force according to a preset multi-level threshold strategy; and generation of regenerative braking target force and compensation braking force commands for each wheel end of the EMB based on the braking force distribution results. It is evident that the regenerative braking composite control method for an electromechanical braking system has the following problems: the method focuses on braking force threshold allocation based on deceleration and vehicle speed, and torque smoothness and coordination during the switching process, without addressing online estimation of EMB brake disc temperature. Under long-term braking conditions, it cannot actively protect against brake disc thermal fade, and brake disc thermal management and drive motor energy recovery are controlled independently, lacking a mechanism for synergistic optimization between the two. Summary of the Invention

[0005] To address this, the present invention provides a bidirectional compensation control method for a combined drive motor and EMB braking system, which overcomes the problems in the prior art where brake disc thermal fade leads to brake torque attenuation, and where brake disc thermal management and energy recovery are independently controlled and difficult to coordinate.

[0006] To achieve the above objectives, the present invention provides a bidirectional compensation control method for a combined braking system of a drive motor and EMB, comprising: Step S1: Obtain the vehicle's required acceleration. Based on the derivative of the required acceleration, determine whether there is a braking intention. When it is determined that there is a braking intention, instruct the drive motor to reduce the torque to zero in order to eliminate the transmission system clearance. Instruct the EMB to eliminate the mechanical clearance between the caliper and the brake disc. Step S2: When braking trigger is detected, the response time of the drive motor and the response time of the EMB are obtained, and the one with the smaller response time is selected as the preferred actuator. Step S3: Determine the current brake disc temperature of the EMB based on the online brake disc temperature estimation model; Step S4: When the current temperature of the brake disc is greater than or equal to the preset upper limit temperature threshold, a temperature cycle is entered, the EMB braking torque is reduced to zero, and the drive motor is switched from regenerative braking state to power consumption state, so that the braking torque output by the drive motor in the power consumption state increases in accordance with the amount of reduction of the EMB braking torque. Step S5: When the EMB braking torque is zero and the current temperature of the brake disc is less than or equal to the preset lower limit temperature threshold, the energy cycle is entered, the EMB braking torque is increased, and the drive motor is switched from the power consumption state to the regenerative braking state. Step S6: Obtain the electrical energy consumed by the drive motor in the power-consuming state during the temperature cycle, and obtain the electrical energy recovered by the drive motor in the regenerative braking state during the energy cycle; adjust the preset lower limit temperature threshold based on the comparison result of the consumed electrical energy and the recovered electrical energy.

[0007] Furthermore, in step S4, when the EMB braking torque is zero and the current temperature of the brake disc is less than or equal to a preset lower temperature threshold, the temperature cycle is exited.

[0008] Furthermore, in step S5, when the current temperature of the brake disc is greater than or equal to a preset upper limit temperature threshold, the energy cycle is terminated.

[0009] Furthermore, in the energy cycle, the current temperature of the brake disc is obtained, and when the current temperature of the brake disc is greater than or equal to the preset upper limit temperature threshold, a new temperature cycle is executed.

[0010] Furthermore, in step S1, the required acceleration is determined based on the driver's braking required acceleration, the autonomous driving system's required acceleration, and the vehicle's functional required acceleration.

[0011] Furthermore, in step S2, the response time of the drive motor is the time required for the drive motor to reduce its current torque to zero and switch to the regenerative braking torque output state; the response time of the EMB is the time required for the EMB to eliminate the remaining mechanical clearance between the caliper and the brake disc.

[0012] Further, in step S2, when the drive motor is the preferred actuator, the drive motor enters a regenerative braking state to provide braking torque. After the EMB completes its own backlash elimination, it remains in a standby state until the EMB needs to provide compensation torque, or the current braking ends. When the EMB is the preferred actuator, the EMB provides initial braking torque. When the drive motor can output regenerative braking torque, the regenerative braking torque of the drive motor is increased, and the braking torque of the EMB is decreased, so that the increase in the regenerative braking torque of the drive motor corresponds to the decrease in the braking torque of the EMB.

[0013] Furthermore, in step S5, the drive motor switches from the power consumption state to the regenerative braking state, wherein the regenerative braking state is the maximum regenerative braking state.

[0014] Furthermore, in step S3, the online brake disc temperature estimation model determines the current temperature of the brake disc based on the EMB caliper clamping force, the decay relationship of the brake disc friction coefficient with temperature, the wheel angular velocity, the effective radius of the brake disc, the mass of the brake disc, the specific heat capacity of the brake disc, the heat dissipation area of ​​the brake disc, the air convection heat transfer coefficient, and the ambient temperature.

[0015] Further, in step S6, adjusting the preset lower limit temperature threshold based on the comparison result of the consumed electrical energy and the recovered electrical energy includes: When the recovered electrical energy is greater than the consumed electrical energy, the preset lower limit temperature threshold is lowered; When the recovered electrical energy is less than the consumed electrical energy and the battery state of charge is greater than or equal to a preset state of charge threshold, the preset lower limit temperature threshold is reduced. When the recovered electrical energy is less than the consumed electrical energy and the battery state of charge is less than the preset state of charge threshold, the preset lower limit temperature threshold is increased.

[0016] Compared with the prior art, the beneficial effects of the present invention are that, by combining gap elimination coordination, actuator optimization and bidirectional compensation control method based on temperature and energy balance, the present invention solves the problems of braking response delay, brake thermal fade and the disconnect between thermal management and energy recovery under a unified framework, and achieves a comprehensive improvement in braking safety, response speed and vehicle energy efficiency.

[0017] Furthermore, by monitoring the derivative of the required acceleration, the present invention simultaneously instructs the drive motor to reduce torque to eliminate transmission backlash and the EMB to eliminate caliper backlash before braking is triggered, so that the actuator is already in a ready state to respond immediately when braking is triggered, thereby shortening the braking torque build-up time and improving the braking response speed.

[0018] Furthermore, this invention compares the remaining response times of the drive motor and EMB in real time and selects the smaller one as the preferred actuator. When the torque of one changes, the other synchronously compensates in the opposite direction to keep the total braking force constant. This ensures that the braking system can always establish braking torque along the shortest path, while avoiding braking force fluctuations during actuator switching.

[0019] Furthermore, this invention establishes an online temperature estimation model for the brake disc that includes the temperature decay characteristics of the friction coefficient, tracks the thermal state of the brake disc in real time, and triggers an alternating control process consisting of temperature cycle and energy cycle accordingly. When the EMB overheats, the drive motor compensates in reverse with a power consumption state to maintain the total braking force, allowing the brake disc to obtain a cooling opportunity, thereby suppressing the risk of thermal fade and ensuring the stability of braking performance under continuous braking conditions.

[0020] Furthermore, this invention compares the consumed and recovered electrical energy during the alternating execution of temperature and energy cycles, and adaptively adjusts the lower limit threshold of the brake disc temperature accordingly. This allows the brake disc temperature to fluctuate within a safe range while tending towards a long-term energy balance, thus taking into account both brake disc thermal protection and vehicle energy recovery efficiency. Attached Figure Description

[0021] Figure 1 This is a flowchart of the bidirectional compensation control method for the combined braking of the drive motor and EMB according to the present invention; Figure 2 This is a schematic diagram of the priority response of the drive motor in step S2 of the bidirectional compensation control method of drive motor and EMB combined braking of the present invention. Figure 3 This is a schematic diagram of the EMB priority response in step S2 of the bidirectional compensation control method for combined braking of the drive motor and EMB of the present invention. Figure 4 This is a schematic diagram of the temperature cycle and energy cycle in steps S4 to S5 of the bidirectional compensation control method of the drive motor and EMB combined braking of the present invention. In the diagram, t1 is the moment the brake pedal is depressed; t2 is the moment the drive motor generates regenerative torque; t3 is the moment the EMB gap is completely eliminated; t4 is the moment when the braking mode is fully switched to regenerative torque; τ1 is the moment the first temperature cycle begins; τ2 is the moment the first energy cycle begins; τ3 is the moment the second temperature cycle begins; and τ4 is the moment the second energy cycle begins. Detailed Implementation

[0022] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0023] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0024] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0025] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0026] Please seeFigure 1 The diagram shows a flowchart of the bidirectional compensation control method for combined braking of a drive motor and EMB according to the present invention. The present invention provides a bidirectional compensation control method for combined braking of a drive motor and EMB, comprising: Step S1: Obtain the vehicle's required acceleration. Based on the derivative of the required acceleration, determine whether there is a braking intention. When it is determined that there is a braking intention, instruct the drive motor to reduce the torque to zero in order to eliminate the transmission system clearance. Instruct the EMB to eliminate the mechanical clearance between the caliper and the brake disc. Specifically, in step S1, the required acceleration is determined based on the driver's braking required acceleration, the autonomous driving system's required acceleration, and the vehicle's functional required acceleration.

[0027] In one specific embodiment, the vehicle's required acceleration a is obtained. x,d The specific formula is as follows: a x，d =max(a x，d，d a x，d，a a x，d，o ); Based on the aforementioned acceleration of demand, a x,d Calculate its time derivative a' x，d , when a' x，d <a' x，d，thr At that time, it was determined that there was an intention to brake.

[0028] When the braking intention is determined, the drive motor is instructed to reduce the torque to zero to eliminate the transmission system backlash, and the EMB is instructed to eliminate the mechanical backlash between the caliper and the brake disc.

[0029] Where, a x，d，d The acceleration required for driver braking, measured in m / s². 2 The value is determined by the brake pedal displacement sensor signal through the pedal displacement-deceleration mapping relationship; a x，d，a Acceleration of demand for autonomous driving systems, in m / s 2 The output is provided in real time by the autonomous driving domain controller; a x，d，o Acceleration for vehicle functional requirements, in m / s² 2 The vehicle function requirements are output in real time by the vehicle function controller, and these vehicle function requirements are at least derived from the braking requirements of the adaptive cruise control function.

[0030] a' x，d The time derivative of the required acceleration is given in m / s². 3 a' x，d，thr The preset acceleration derivative threshold is in m / s². 3 The value range is -5.0 m / s 3 ~-1.5m / s3 Preferably, a' x，d，thr The value is -3.0 m / s³, which is based on the vehicle braking intention prediction test calibration and is used to balance the sensitivity of braking intention recognition and the false trigger rate.

[0031] Understandably, in the above formula, `max` is the maximum value function, which selects the largest value from the acceleration demands from three sources: driver demand, autonomous driving system demand, and vehicle function demand, as the unified vehicle demand acceleration. When the vehicle is braking, the acceleration demand is negative. The maximum value operation essentially selects the acceleration value with the smallest algebraic absolute value among the sources, i.e., the most moderate braking demand, to avoid over-braking. Based on this, the actuator optimization and torque distribution stages after braking trigger meet the actual braking torque demand. The judgment condition of the acceleration derivative is used to capture the rapid decrease process of the demand acceleration. This rapid decrease corresponds to the scenario where the driver releases the accelerator pedal or the autonomous driving system issues a command to rapidly reduce the driving torque. At this time, the acceleration derivative is negative, and the greater the rate of decrease, the larger the absolute value of the derivative. When the derivative value is lower than the preset derivative threshold, it indicates that the system has entered the braking preparation stage, thus recognizing the braking intention in advance before the brake pedal is pressed.

[0032] Understandably, during actual driving, the driver, autonomous driving system, and vehicle functions may simultaneously or sequentially generate deceleration demands of varying intensities. Unifying these diverse demands into a single demand acceleration provides a consistent input benchmark for subsequent gap elimination, actuator optimization, and torque distribution. Based on this unified demand acceleration, continuous monitoring of its time derivative allows for the detection of impending braking signs as soon as the accelerator pedal begins to release and the demand acceleration rapidly decreases, rather than waiting for the brake pedal to be actually depressed before initiating a response. Upon recognizing the braking intent, pre-preparation commands are simultaneously sent to the drive motor and EMB: the drive motor reduces torque to zero in advance, gradually eliminating mechanical backlashes such as gear tooth backlash and spline backlash in the transmission system. This allows the motor to directly enter regenerative braking mode upon receiving the formal regenerative braking command without needing to undergo the torque zeroing and gap elimination process again; the EMB pre-drives the caliper to move towards the brake disc, eliminating the gap between the friction block and the brake disc surface. This allows the EMB to immediately establish clamping force upon receiving the formal clamping command without consuming time in the gap elimination stroke. This pre-preparation mechanism pre-digests the inherent response delays of the two types of actuators before braking is triggered, ensuring that both types of actuators are in a ready state to immediately output braking torque when the formal braking command is issued, thereby shortening the braking response setup time.

[0033] Step S2: When braking trigger is detected, the response time of the drive motor and the response time of the EMB are obtained, and the one with the smaller response time is selected as the preferred actuator. Please continue reading. Figure 2 and Figure 3 As shown, these are schematic diagrams of the priority response of the drive motor in step S2 of the bidirectional compensation control method of the drive motor and EMB combined braking of the present invention, and schematic diagrams of the priority response of EMB in step S2 of the bidirectional compensation control method of the drive motor and EMB combined braking of the present invention, respectively. Specifically, in step S2, the response time of the drive motor is the time required for the drive motor to reduce its current torque to zero and switch to the regenerative braking torque output state; the response time of the EMB is the time required for the EMB to eliminate the remaining mechanical clearance between the caliper and the brake disc.

[0034] Specifically, in step S2, when the drive motor is the preferred actuator, the drive motor enters a regenerative braking state to provide braking torque. After the EMB completes its own backlash elimination, it remains in a standby state until the EMB needs to provide compensation torque, or the current braking ends. When the EMB is the preferred actuator, the EMB provides initial braking torque. When the drive motor can output regenerative braking torque, the regenerative braking torque of the drive motor is increased, and the braking torque of the EMB is decreased, so that the increase in the regenerative braking torque of the drive motor corresponds to the decrease in the braking torque of the EMB.

[0035] In one specific embodiment, when the brake pedal is detected to be depressed and braking is triggered, the response time t of the drive motor is acquired in real time. M and EMB response time t C Comparing t M With t C The smaller one is selected as the preferred actuator.

[0036] like Figure 2 As shown, when the drive motor is the preferred actuator, i.e., t M <t C At the moment the brake pedal is depressed (t1), the drive motor immediately enters the regenerative braking state, generating a regenerative braking torque M at time t2. m During the period from t1 to t3, the EMB performs a gap elimination action. After the EMB completes its own gap elimination at time t3, it remains in a standby state until the EMB needs to provide compensation torque or the braking ends.

[0037] like Figure 3 As shown, when EMB is the preferred actuator, i.e., t C <t MAt time t1 when the brake pedal is depressed, the EMB first outputs braking torque; by time t3, the EMB has eliminated its own backlash; at time t2, the drive motor is ready to output regenerative braking torque, and enters the torque switching process, controlling the drive motor to output regenerative braking torque M. m Gradually increase, while controlling the EMB braking torque M e Gradually decrease, while satisfying the following constraints: M' t =M' m +M' e ; During the torque switching process from t2 to t4, the drive motor provides feedback braking torque M. m Gradually increase, EMB braking torque M e The braking torque M of the EMB gradually decreases until time t4. e Once reduced to zero, the torque switching is complete.

[0038] Among them, t M The response time of the drive motor, measured in milliseconds (ms), represents the time required for the drive motor to reduce its current torque to zero and switch to regenerative braking torque output. It is calculated and provided in real-time by the drive motor controller based on the current motor torque and speed. C The response time of the EMB, measured in milliseconds (ms), represents the time required for the EMB to eliminate the remaining mechanical clearance between the caliper and the brake disc. It is calculated and provided in real-time by the EMB controller based on the current amount of remaining clearance and the caliper drive motor speed. M t The target braking torque is expressed in Nm (m). m The regenerative braking torque of the drive motor, measured in Nm. e This refers to the EMB braking torque, expressed in Nm.

[0039] M' t M' represents the rate of change of the target braking torque, in Nm / s. m The feedback braking torque change rate of the drive motor is expressed in Nm / s and is taken as a positive value during the torque switching process. M' e M' represents the rate of change of EMB braking torque, in Nm / s, and is negative during the torque switching process. e The absolute value is calibrated based on the subjective evaluation of braking smoothness, and preferably, its absolute value is 1000 Nm / s.

[0040] It is understandable that the above constraint relationship indicates that the rate of change of the target braking torque over time is equal to the sum of the rate of change of the regenerative braking torque of the drive motor and the rate of change of the EMB braking torque. Therefore, when the EMB torque increases at a rate M' e Or the rate of decrease in feedback torque M' m When any one is determined, since M't Since one is known, the other is also determined. When the EMB torque drops to zero, the switch to pure regenerative braking is completed. When the EMB braking torque decreases to zero, the total braking torque is entirely borne by the regenerative braking torque of the drive motor, completing the transition from friction braking to pure regenerative braking.

[0041] Understandably, at the moment of brake triggering, the drive motor and EMB are in different preparation states: the drive motor may have already reduced its torque to zero and eliminated transmission backlash due to the pre-charge operation in step S1, or it may still have residual torque or backlash because the pre-charge has not yet been completed; the EMB may have eliminated all or most of the mechanical backlash, or it may still have residual backlash because the caliper movement has not yet reached its position during the pre-charge stage. By acquiring and comparing their respective remaining preparation times in real time, the one that is more fully prepared and can establish braking torque earlier is selected to respond first, so that the driver can feel the immediate establishment of braking torque after the braking command is issued, rather than waiting for a delay. Figure 2 As shown, when the drive motor responds first, its regenerative braking torque immediately provides basic braking force. During this period, the EMB completes the elimination of remaining backlash and is ready to go at any time. Once the motor's regenerative braking torque reaches its upper limit and the total demand has not yet been met, the EMB seamlessly intervenes to compensate from the standby state to the clamping state. Figure 3 As shown, when the EMB responds first, it immediately establishes clamping force to provide braking torque by utilizing the eliminated gap, making up for the time window when the drive motor still needs time to complete the torque to zero and the gap elimination. After the drive motor is ready, the drive motor's feedback braking torque increases synchronously at an equal rate, based on the rate of decrease of the EMB's braking torque. The process of the two torques increasing and decreasing in opposite directions is strictly corresponded by the constraint relationship, so that the total braking torque felt by the driver remains constant from beginning to end. The change in the source of braking torque is transparent to the driver and will not produce discomfort such as sudden changes in pedal force or fluctuations in vehicle deceleration.

[0042] Step S3: Determine the current brake disc temperature of the EMB based on the online brake disc temperature estimation model; Specifically, in step S3, the online brake disc temperature estimation model determines the current temperature of the brake disc based on the EMB caliper clamping force, the decay relationship of the brake disc friction coefficient with temperature, the wheel angular velocity, the effective radius of the brake disc, the mass of the brake disc, the specific heat capacity of the brake disc, the heat dissipation area of ​​the brake disc, the air convection heat transfer coefficient, and the ambient temperature.

[0043] In one specific embodiment, the online brake disc temperature estimation model determines the current temperature of the brake disc in the following manner.

[0044] First, calculate the braking torque generated by the EMB on the brake disc: M e =2×μ(Td )×F n ×R e ; Here, coefficient 2 indicates that the calipers are clamped on both sides.

[0045] Within a single time step Δt, the work done by the braking torque, i.e. the heat energy Q generated, is... gen for: Q gen =M e ×∣ω×Δt∣; Where ω×Δt is the angle through which the brake disc rotates within the time step Δt.

[0046] During the time step, the brake disc dissipates heat energy Q through convection. diss for: Q diss =h×A×(T d -T a )×Δt; The net energy change ΔE of the brake disc during the time step is: ΔE=Q gen- Q diss ; The temperature change ΔT of the brake disc during the time step is: ΔT=ΔE / (m×C p ); Based on the temperature T at the previous moment k Get the current temperature T k+1 for: T k+1 =T k +ΔT; Among them, M e F is the braking torque generated by the EMB on the brake disc, expressed in Nm. n The clamping force of the EMB caliper, measured in N, is estimated in real time by the EMB controller based on the clamping force sensor or motor current; μ(T) d () represents the coefficient of friction of the brake disc, which is dimensionless and varies with temperature T. d The variation is determined by the friction coefficient-temperature decay characteristic curve, which is pre-calibrated through hot friction tests on the brake disc material; R eω is the effective radius of the brake disc, in meters, defined as the radial distance from the center of the friction block to the center of rotation of the brake disc, determined by the brake's geometric design parameters; ω is the wheel angular velocity, in rad / s, obtained by real-time measurement and conversion by the wheel speed sensor; Δt is the computation time step of the online brake disc temperature estimation model, in seconds, ranging from 0.01s to 0.10s, preferably 0.05s, determined based on the controller's calculation cycle and the real-time requirements of temperature estimation; h is the air convection heat transfer coefficient, in W / (m³). 2 The value of ℃ is related to vehicle speed and is obtained in real time by looking up a pre-calibrated vehicle speed-convective heat transfer coefficient mapping table; A is the heat dissipation area of ​​the exposed surface of the brake disc, in m². 2 The dimensions are determined by the geometry of the brake disc; T d The current temperature of the brake disc is expressed in °C; the initial value is taken as the ambient temperature. (T) a The ambient temperature, in °C, is obtained in real time by an external temperature sensor on the vehicle; m is the mass of the brake disc, in kg, determined by the density and geometric volume of the brake disc material; C p Q represents the specific heat capacity of the brake disc, expressed in J / (kg·℃), determined by the brake disc material. gen Q represents the heat energy generated by the EMB friction on the brake disc within a single time step, measured in J. diss ΔE represents the heat energy lost by the brake disc to the surrounding air through convection within a single time step, measured in J. ΔE represents the net energy change of the brake disc within a single time step, measured in J; ΔT represents the temperature change of the brake disc within a single time step, measured in °C. k The brake disc temperature at the previous moment is expressed in °C. The ambient temperature T is used for the initial calculation. a As the initial value; T k+1 The current brake disc temperature is expressed in °C, which is the updated brake disc temperature obtained after the time step Δt.

[0047] It is understandable that in the above formula, the braking torque M e The coefficient of friction is obtained by multiplying the caliper clamping force, the coefficient of friction, and the effective radius by a factor of 2. The factor of 2 is used because EMB brake discs typically employ a dual-sided clamping structure, with each caliper generating a set of frictional forces that work together on the brake disc. The coefficient of friction μ(T) d The value is not a fixed value, but a function that varies with temperature. This attenuation relationship is the key difference between this model and general thermodynamic models. As the brake disc temperature increases, the friction coefficient decreases, and the braking torque generated under the same clamping force decreases accordingly. The heat generation is the product of the braking torque and the angle through which the brake disc rotates, indicating that all frictional work is converted into heat energy. The heat dissipation adopts Newton's cooling formula, that is, the convective heat transfer is proportional to the product of the heat transfer coefficient, the heat dissipation area, and the temperature difference between the brake disc and the environment.

[0048] Understandably, during continuous braking by the EMB (Electronic Brake Brake), the brake disc temperature is a dynamically changing thermodynamic quantity. Its rise stems from the continuous input of heat energy converted from frictional work, while its decrease depends on convective heat dissipation from the brake disc surface to the air. The online brake disc temperature estimation model updates the brake disc temperature periodically with a time step by simultaneously calculating the heat generation and dissipation processes. On the heat generation side, the model acquires the caliper clamping force, wheel angular velocity, and effective brake disc radius in real time, and determines the heat energy generated by friction within the current time step by combining the decay relationship of the friction coefficient with temperature. The introduction of the friction coefficient-temperature decay relationship allows the model to realistically reflect the physical reality of the decrease in friction coefficient and the slowdown in heat generation rate under the same clamping force after the brake disc enters the high-temperature range. On the heat dissipation side, the model determines the corresponding convective heat transfer coefficient based on the current vehicle speed, and calculates the heat dissipated to the surrounding air by convection within the current time step by combining the heat dissipation area of ​​the brake disc and the temperature difference between the brake disc and the environment. The difference between heat generation and heat dissipation constitutes the net energy increment of the brake disc. This net increment, divided by the product of the brake disc's mass and specific heat capacity, is converted into the temperature increment within that time step. Adding this to the temperature of the previous time step yields the current temperature. Through iterative calculations across time steps, the model can track real-time changes in brake disc temperature online without the need for a direct installation of a brake disc temperature sensor. This provides a continuous, sensor-free temperature data basis for triggering subsequent temperature and energy cycles.

[0049] Please continue reading. Figure 4 As shown, it is a schematic diagram of temperature cycle and energy cycle in steps S4 to S5 of the bidirectional compensation control method of drive motor and EMB combined braking of the present invention. Step S4: When the current temperature of the brake disc is greater than or equal to a preset upper limit temperature threshold, a temperature cycle is initiated, and the EMB braking torque is reduced to zero. The drive motor is switched from regenerative braking state to power-consuming state so that the braking torque output by the drive motor in the power-consuming state increases in accordance with the decrease in EMB braking torque. Specifically, in step S4, when the EMB braking torque is zero and the current temperature of the brake disc is less than or equal to a preset lower temperature threshold, the temperature cycle is exited.

[0050] Step S5: When the EMB braking torque is zero and the current temperature of the brake disc is less than or equal to the preset lower limit temperature threshold, the energy cycle is entered, the EMB braking torque is increased, and the drive motor is switched from the power consumption state to the regenerative braking state. Specifically, in step S5, when the current temperature of the brake disc is greater than or equal to a preset upper limit temperature threshold, the energy cycle is exited.

[0051] Specifically, in step S5, the drive motor switches from the power consumption state to the regenerative braking state, wherein the regenerative braking state is the maximum regenerative braking state.

[0052] Specifically, in the energy cycle, the current temperature of the brake disc is obtained, and when the current temperature of the brake disc is greater than or equal to the preset upper limit temperature threshold, a new temperature cycle is executed.

[0053] In one specific embodiment, a preset upper temperature threshold Tupper and a preset lower temperature threshold Tlower are defined, with Tupper > Tlower.

[0054] like Figure 4 As shown, at time τ1, the current temperature T of the brake disc is... k+1 Satisfy T k+1 ≥Tupper, enter the first temperature cycle. During the temperature cycles from τ1 to τ2, control the EMB braking torque M. e Gradually reduce to zero, while simultaneously switching the drive motor from regenerative braking state to power-consuming state. The braking torque output by the drive motor in the power-consuming state corresponds to M. e The braking force increases as the amount decreases, and the total braking torque remains constant during torque switching.

[0055] During the temperature cycle execution, the current temperature T of the brake disc is continuously acquired. k+1 At time τ2, M is simultaneously satisfied. e =0 and T k+1 ≤Tlower, exit the temperature cycle and enter the first energy cycle. During the energy cycles from τ2 to τ3, control the EMB braking torque M. e The torque gradually increases from zero, while simultaneously switching the drive motor from the power-consuming state to the regenerative braking state. The regenerative braking state is the maximum regenerative braking state, where the drive motor outputs the current maximum regenerative braking torque M. m,max During the process of increasing EMB braking torque and decreasing drive motor braking torque, the total braking torque remains constant. After the switch is completed, the total braking torque is jointly borne by the drive motor regenerative braking torque and the EMB braking torque, with the drive motor providing the current maximum regenerative braking torque M. m,max The remaining required torque is provided by EMB.

[0056] During the energy cycle, the current temperature T of the brake disc is continuously acquired. k+1 At time τ3, T k+1 ≥Tupper, exit the energy cycle, and execute the second temperature cycle. In the second temperature cycle from τ3 to τ4, control the EMB braking torque M in the same manner as in the first temperature cycle.e Gradually reduce to zero and switch the drive motor to the aforementioned power-consuming state. At time τ4, M is satisfied again simultaneously. e =0 and T k+1 ≤Tlower, exit the second temperature cycle and enter the second energy cycle, and so on alternately.

[0057] Tupper is a preset upper temperature threshold, measured in °C, ranging from 350°C to 450°C. Preferably, Tupper is 400°C. It is calibrated based on the thermal fade initiation temperature of the brake disc material, which is determined by hot friction tests on the brake disc friction material. Tlower is a preset lower temperature threshold, measured in °C, ranging from 150°C to 250°C. Preferably, Tlower is 200°C, and Tlower < Tupper. It is calibrated based on the thermal recovery characteristics of the brake disc, ensuring that the coefficient of friction of the brake disc recovers to a safe operating range during the cooling process from Tupper to Tlower.

[0058] It is understandable that, such as Figure 4 As shown, during the temperature cycle from τ1 to τ2, the EMB braking torque gradually decreases from time τ1 to zero at time τ2. During this period, the EMB does not generate frictional heat on the brake disc, and the brake disc cools down gradually from near the Tupper through convection. During the energy cycle from τ2 to τ3, the EMB braking torque gradually increases from zero, and the drive motor synchronously switches back to the maximum regenerative braking state. The EMB re-engages in friction, causing the brake disc temperature to gradually rise from near the Tlower. When the temperature rises back to the Tupper at time τ3, the second temperature cycle is triggered. The torque change from τ3 to τ4 is consistent with that from τ1 to τ2, forming a recurring alternating structure.

[0059] Understandably, the temperature cycle and energy cycle constitute a complete closed loop for brake disc thermal management. When the brake disc temperature rises to the preset upper temperature threshold due to continuous friction from the EMB, the temperature cycle is triggered: the EMB's braking torque gradually withdraws, and the drive motor transforms from an energy recoverer to an energy consumer, actively outputting braking torque at the expense of battery power, completely replacing the EMB in the braking task; after the EMB withdraws, no new frictional heat is generated, and the brake disc dissipates heat to the surrounding air only through convection, causing the temperature to gradually decrease. When the brake disc temperature drops to the preset lower temperature threshold, it indicates that the brake disc has been sufficiently cooled, and the coefficient of friction has returned to normal levels. At this point, the energy cycle is triggered: the EMB's braking torque gradually recovers, and the drive motor synchronously switches back to the maximum regenerative braking state to recover kinetic energy, with the EMB only supplementing the insufficient regenerative braking torque of the motor. If, during the energy cycle, the brake disc heats up again to the preset upper temperature threshold due to the EMB re-engaging in friction, the energy cycle exits and a new temperature cycle begins, alternating in this manner. The lower limit of the temperature between the two cycles is dynamically corrected by the subsequent step S6 based on the energy balance comparison results, so that the electrical energy consumed by the temperature cycle and the electrical energy recovered by the energy cycle tend to be balanced during long-term operation. The brake disc temperature is stabilized between the preset upper limit temperature threshold and the preset lower limit temperature threshold, which avoids thermal decay and takes into account the energy recovery efficiency.

[0060] Step S6: Obtain the electrical energy consumed by the drive motor in the power-consuming state during the temperature cycle, and obtain the electrical energy recovered by the drive motor in the regenerative braking state during the energy cycle; adjust the preset lower limit temperature threshold based on the comparison result of the consumed electrical energy and the recovered electrical energy.

[0061] Specifically, in step S6, adjusting the preset lower limit temperature threshold based on the comparison result of the consumed electrical energy and the recovered electrical energy includes: When the recovered electrical energy is greater than the consumed electrical energy, the preset lower limit temperature threshold is lowered; When the recovered electrical energy is less than the consumed electrical energy and the battery state of charge is greater than or equal to a preset state of charge threshold, the preset lower limit temperature threshold is reduced. When the recovered electrical energy is less than the consumed electrical energy and the battery state of charge is less than the preset state of charge threshold, the preset lower limit temperature threshold is increased.

[0062] In one specific embodiment, during the execution of the temperature cycle, the electrical power of the drive motor in the power-consuming state is recorded step by step over time, and the consumed electrical energy Econ is calculated after the temperature cycle ends. During the execution of the energy cycle, the electrical power of the drive motor in the regenerative braking state is recorded step by step over time. After the energy cycle ends, the recovered electrical energy Ere is calculated. Obtain the vehicle's battery state of charge (SOC), and based on the comparison between Ere and Econ, adjust the preset lower temperature threshold Tlower according to the following rules: When Ere > Econ, Tlower decreases ΔTadj; When Ere < Econ and SOC ≥ SOCthr, Tlower decreases ΔTadj; When Ere < Econ and SOC < SOCthr, Tlower increases ΔTadj.

[0063] The adjusted Tlower is used for comparison and judgment with the current temperature of the brake disc in the subsequent energy cycle.

[0064] Wherein, Econ is the electrical energy consumed by the drive motor in the power-consuming state during the temperature cycle, in J. Ere is the electrical energy recovered by the drive motor in the regenerative braking state during the energy cycle, in J. SOC is the battery state of charge, dimensionless, expressed as a percentage, provided in real time by the battery management system. SOCthr is the preset state of charge threshold, dimensionless, expressed as a percentage, ranging from 80% to 95%, preferably 90%, calibrated based on the battery charging safety boundary and battery management strategy. ΔTadj is the single adjustment step size of the preset lower limit temperature threshold, in °C, ranging from 10 °C to 50 °C, preferably 20 °C, calibrated based on the response speed and stability of the brake disc temperature control. Too large a step size can easily lead to aggravated temperature fluctuations, while too small a step size will result in slow energy balance convergence.

[0065] It is understandable that during the alternating execution of the temperature cycle and the energy cycle, each temperature cycle consumes battery power to cool the EMB brake disc, and each energy cycle recovers energy by moderately heating the EMB and regenerative braking of the drive motor. The energy expenditure between the two cycles is not necessarily equal. If the recovered energy consistently exceeds the consumed energy during long-term operation, the system is in a net energy recovery state. Although the energy efficiency is good, the brake disc temperature may gradually accumulate and rise between cycles due to insufficient cooling time in the temperature cycle, eventually exceeding the safety limit. If the consumed energy consistently exceeds the recovered energy, the system maintains the brake disc in the low-temperature range at the expense of energy economy, resulting in a decrease in overall energy efficiency. Therefore, after each temperature cycle and energy cycle is completed, the consumed energy and recovered energy of that cycle are obtained and compared. The comparison result is used as the basis for adjusting the preset lower temperature threshold. The difference between consumed and recovered energy is fed back to the next cycle by adjusting the preset lower temperature threshold: lowering the threshold prolongs the cooling time and power consumption time of the temperature cycle, increasing energy consumption in the next cycle; raising the threshold shortens the cooling time and power consumption time of the temperature cycle, reducing energy consumption in the next cycle. The battery state of charge is introduced as a constraint in the adjustment logic. When the battery is close to full charge, the marginal benefit of continuing to recover more energy is extremely low. At this point, even if the consumed energy exceeds the recovered energy, the threshold is still lowered to prioritize ensuring sufficient cooling of the brake disc. Through this closed-loop adaptive adjustment, a dynamic balance between consumed and recovered energy is achieved during long-term operation, ensuring that the brake disc temperature always fluctuates between the preset upper and lower temperature thresholds, fundamentally avoiding thermal fade while simultaneously considering braking safety and overall vehicle energy economy.

[0066] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A bidirectional compensation control method for combined braking of a drive motor and EMB, characterized in that, include: Step S1: Obtain the vehicle's required acceleration. Based on the derivative of the required acceleration, determine whether there is a braking intention. When it is determined that there is a braking intention, instruct the drive motor to reduce the torque to zero in order to eliminate the transmission system clearance. Instruct the EMB to eliminate the mechanical clearance between the caliper and the brake disc. Step S2: When braking trigger is detected, the response time of the drive motor and the response time of the EMB are obtained, and the one with the smaller response time is selected as the preferred actuator. Step S3: Determine the current brake disc temperature of the EMB based on the online brake disc temperature estimation model; Step S4: When the current temperature of the brake disc is greater than or equal to the preset upper limit temperature threshold, a temperature cycle is entered, the EMB braking torque is reduced to zero, and the drive motor is switched from regenerative braking state to power consumption state, so that the braking torque output by the drive motor in the power consumption state increases in accordance with the amount of reduction of the EMB braking torque. Step S5: When the EMB braking torque is zero and the current temperature of the brake disc is less than or equal to the preset lower limit temperature threshold, the energy cycle is entered, the EMB braking torque is increased, and the drive motor is switched from the power consumption state to the regenerative braking state. Step S6: Obtain the electrical energy consumed by the drive motor in the power consumption state during the temperature cycle, and obtain the recovered electrical energy of the drive motor in the regenerative braking state during the energy cycle. Based on the comparison between the consumed electrical energy and the recovered electrical energy, the preset lower limit temperature threshold is adjusted.

2. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 1, characterized in that, In step S4, when the EMB braking torque is zero and the current temperature of the brake disc is less than or equal to a preset lower temperature threshold, the temperature cycle is exited.

3. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 2, characterized in that, In step S5, when the current temperature of the brake disc is greater than or equal to the preset upper limit temperature threshold, the energy cycle is exited.

4. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 3, characterized in that, In the energy cycle, the current temperature of the brake disc is obtained. When the current temperature of the brake disc is greater than or equal to the preset upper limit temperature threshold, a new temperature cycle is executed.

5. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 4, characterized in that, In step S1, the required acceleration is determined based on the driver's braking required acceleration, the autonomous driving system's required acceleration, and the vehicle's functional required acceleration.

6. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 5, characterized in that, In step S2, the response time of the drive motor is the time required for the drive motor to reduce its current torque to zero and switch to the regenerative braking torque output state; the response time of the EMB is the time required for the EMB to eliminate the remaining mechanical clearance between the caliper and the brake disc.

7. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 6, characterized in that, In step S2, when the drive motor is the preferred actuator, the drive motor enters a regenerative braking state to provide braking torque. After the EMB completes its own backlash elimination, it remains in a standby state until the EMB needs to provide compensation torque, or the current braking ends. When the EMB is the preferred actuator, the EMB provides initial braking torque. When the drive motor can output regenerative braking torque, the regenerative braking torque of the drive motor is increased, and the braking torque of the EMB is decreased, so that the increase in the regenerative braking torque of the drive motor corresponds to the decrease in the braking torque of the EMB.

8. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 1, characterized in that, In step S5, the drive motor switches from the power consumption state to the regenerative braking state, wherein the regenerative braking state is the maximum regenerative braking state.

9. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 1, characterized in that, In step S3, the online brake disc temperature estimation model determines the current temperature of the brake disc based on the EMB caliper clamping force, the decay relationship of the brake disc friction coefficient with temperature, the wheel angular velocity, the effective radius of the brake disc, the mass of the brake disc, the specific heat capacity of the brake disc, the heat dissipation area of ​​the brake disc, the air convection heat transfer coefficient, and the ambient temperature.

10. The bidirectional compensation control method for combined braking of drive motor and EMB according to claim 7, characterized in that, In step S6, based on the comparison result of the consumed electrical energy and the recovered electrical energy, the preset lower limit temperature threshold is adjusted, including: When the recovered electrical energy is greater than the consumed electrical energy, the preset lower limit temperature threshold is lowered; When the recovered electrical energy is less than the consumed electrical energy and the battery state of charge is greater than or equal to a preset state of charge threshold, the preset lower limit temperature threshold is reduced. When the recovered electrical energy is less than the consumed electrical energy and the battery state of charge is less than the preset state of charge threshold, the preset lower limit temperature threshold is increased.

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