Vehicle wheel end torque control method, brake controller, and vehicle

Abstract

The application discloses a vehicle wheel end torque control method, comprising: acquiring a vehicle state signal; when determining that an anti-lock braking system is activated, performing coordinated control according to the direction of motor torque and the road surface state; if the motor torque is negative and a preset low adhesion drive anti-skid condition is not met, controlling the motor torque to approach zero according to a first preset slope, and simultaneously controlling hydraulic braking force to increase according to a second preset slope; if the motor torque is positive, controlling the motor torque to decrease according to a third preset slope, and simultaneously controlling the hydraulic braking force to decrease according to a fourth preset slope. The vehicle wheel end torque control method of the application can improve the braking stability of the vehicle by performing differentiated coordinated strategies according to the direction of motor torque and the road surface state when the anti-lock braking system is activated, and by respectively performing the control strategies of hydraulic compensation and hydraulic pressure reduction, so that the motor torque can smoothly exit and the hydraulic braking force can be synchronously compensated. The application also discloses a brake controller and a vehicle.

Description

Technical Field

[0001] This invention belongs to the field of automotive technology. Specifically, this invention relates to a method for controlling wheel-end torque, a brake controller, and a vehicle. Background Technology

[0002] During braking, new energy vehicles experience both hydraulic braking force and electric motor force at the wheel ends. When the anti-lock braking system is activated, current technology typically controls the motor torque to immediately reset to zero.

[0003] However, this strategy has obvious drawbacks. If there is a large negative torque at the wheel end, directly resetting to zero will cause a sudden drop in braking force. Due to the lag in hydraulic compensation, it is easy to cause the vehicle to lurch forward or disrupt stability control. If there is positive torque, directly resetting to zero will cause redundancy in hydraulic braking force and cause the wheels to lock up accidentally.

[0004] Existing technologies also cannot effectively coordinate motor torque and hydraulic braking force, making it difficult to balance the smoothness and stability of vehicle braking. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a method for controlling wheel-end torque in vehicles, with the purpose of improving vehicle braking stability.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a vehicle wheel-end torque control method, comprising:

[0007] Acquire vehicle status signals, including wheel slip ratio and motor torque;

[0008] When the anti-lock braking system is activated, coordinated control is performed based on the direction of the motor torque and the road conditions.

[0009] If the motor torque is negative and the preset low-adhesion drive anti-slip condition is not met, the motor torque is controlled to approach zero according to the first preset slope, and the hydraulic braking force is controlled to increase according to the second preset slope.

[0010] If the motor torque is positive, control the motor torque to decrease according to the third preset slope, and at the same time control the hydraulic braking force to decrease according to the fourth preset slope.

[0011] The determination that the anti-lock braking system is activated specifically includes:

[0012] Calculate the slip ratio of each wheel;

[0013] When the slip ratio of any wheel reaches or exceeds a first preset threshold, and the duration of this state exceeds a first delay threshold, the anti-lock braking system is determined to be activated, and the coordinated control mode flag is set.

[0014] The first preset threshold is 0.18~0.22, and the first delay threshold is 9~11ms.

[0015] In the step where the motor torque is negative and the preset low-adhesion drive anti-slip condition is not met, controlling the motor torque and hydraulic braking force specifically includes:

[0016] Send a torque increase request signal to the vehicle controller to cause the drive motor to perform torque reduction control according to the first preset slope until the absolute value of the motor torque is reduced to the dead zone range.

[0017] The hydraulic system controlling the anti-lock braking system builds pressure and replenishes fluid according to the second preset slope.

[0018] The target wheel cylinder pressure during the pressure building and fluid replenishment process is calculated based on the equivalent coefficients of the initial hydraulic pressure, wheel end torque, and hydraulic pressure, as well as the change in motor torque. As the absolute value of the motor torque decreases, the target wheel cylinder pressure increases synchronously and linearly.

[0019] The target cylinder pressure P during the pressure building and fluid replenishment process target The following formula is used to calculate:

[0020] P target = P base +(|T req (0)|-|T req (t)|) / k eff

[0021] Among them, P base To prevent the initial hydraulic pressure at the moment of activation of the anti-lock braking system, T req (0) T is the motor torque at the moment the anti-lock braking system is activated. req (t) represents the motor torque in the current cycle, k eff This is the equivalent coefficient for wheel end torque and hydraulic pressure.

[0022] If the motor torque is positive, the motor torque is controlled to decrease according to a third preset slope, while the hydraulic braking force is controlled to decrease according to a fourth preset slope. Specifically, this includes:

[0023] Send a torque reduction request signal to the vehicle controller to cause the drive motor to gradually reduce torque to zero according to the third preset slope;

[0024] The hydraulic system controlling the anti-lock braking system reduces the wheel cylinder pressure according to the fourth preset slope.

[0025] The absolute value of the fourth preset slope is equal to the absolute value of the third preset slope.

[0026] The preset low-adhesion driving anti-slip conditions include a first condition and a second condition.

[0027] The first condition includes: the road surface adhesion coefficient is lower than the second preset threshold, and the driver's required torque is zero;

[0028] The second condition includes: the motor torque is negative, the anti-lock braking system is activated, and the drive anti-slip control system is activated.

[0029] The road surface adhesion coefficient is estimated based on the peak slip ratio and adhesion coefficient curve during the adjustment process of the anti-lock braking system, or based on a comprehensive judgment of wheel speed acceleration and ambient temperature.

[0030] The vehicle wheel-end torque control method further includes:

[0031] If the motor torque is negative and the preset low-adhesion drive anti-slip condition is met, the drive anti-slip control strategy is executed to adjust the motor torque.

[0032] The execution of the drive anti-slip control strategy to adjust the motor torque specifically includes:

[0033] Hydraulic compensation pressure build-up is not performed;

[0034] In response to the torque increase request from the drive anti-slip control system, the drive motor is controlled to transition from the current negative torque state to the positive torque state until the slip ratio of the drive wheel returns to the preset safe range.

[0035] The preset safety range is defined as the drive wheel slip rate being continuously lower than a preset slip threshold.

[0036] The vehicle wheel-end torque control method further includes:

[0037] When the motor torque returns to zero and hydraulic compensation or pressure reduction is completed, or when the anti-lock braking system disengages during the coordination process, the torque coordination control is terminated.

[0038] If the vehicle controller does not respond or the drive motor feedback is abnormal within several consecutive control cycles, it will exit the coordination mode.

[0039] The first preset slope ranges from 1000 N•m / s to 5000 N•m / s.

[0040] The value range of the third preset slope is -10000 N•m / s to ~500 N•m / s.

[0041] The present invention also provides a brake controller, comprising:

[0042] Memory, used to store computer programs;

[0043] A processor is used to implement the vehicle wheel-end torque control method when executing the computer program.

[0044] The present invention also provides a vehicle including the aforementioned brake controller.

[0045] The vehicle wheel-end torque control method of this invention implements differentiated coordination strategies based on the direction of motor torque and road conditions when the anti-lock braking system is activated. This involves executing hydraulic compensation and hydraulic decompression control strategies respectively, achieving smooth motor torque withdrawal and synchronous compensation of hydraulic braking force, thereby improving vehicle braking stability. Under negative torque conditions, the synchronous coordination of motor torque withdrawal and hydraulic pressure build-up avoids vehicle lurching caused by momentary loss of braking force. Under positive torque conditions, the synchronous coordination of motor torque reduction and hydraulic decompression avoids wheel-end lock-up caused by redundant hydraulic braking force. Ultimately, this improves vehicle stability on complex road surfaces. Attached Figure Description

[0046] Figure 1 This is a diagram illustrating the interaction of wheel-end torque coordination control signals under ABS activation conditions, provided in an embodiment of the present invention.

[0047] Figure 2 This is a flowchart of wheel-end torque control under ABS activation conditions provided in an embodiment of the present invention;

[0048] The diagram is labeled as follows: 100, brake controller; 200, vehicle controller; 300, left front wheel speed signal; 400, right front wheel speed signal; 500, left rear wheel speed signal; 600, right rear wheel speed signal. Detailed Implementation

[0049] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the present invention. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. Rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0050] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," and similar expressions used in this document are for illustrative purposes only.

[0051] It should be noted that in the following embodiments, the terms "first," "second," and "third" do not represent an absolute distinction in structure and / or function, nor do they represent the order of execution; they are merely for the convenience of description.

[0052] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly associated with those skilled in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0053] The technical concept of this invention includes: With the rapid development of new energy vehicle technology, the structure of vehicle braking systems is becoming increasingly complex. During braking, the vehicle is usually simultaneously affected by hydraulic braking force and motor force. The motor force mainly includes two types: regenerative torque and driving torque. Specifically, regenerative torque is mainly generated during the coasting energy recovery phase after the driver releases the accelerator pedal, or during the braking energy recovery phase when the Cooperative Regenerative Brake System (CRBS) is working; while driving torque mainly occurs under low-speed conditions. When neither the CRBS nor the coasting energy recovery function is activated, if the driver releases the accelerator pedal and quickly depresses the brake pedal, due to the lag in the withdrawal of driving torque, residual driving torque often remains at the wheel ends. During vehicle operation, if emergency braking occurs and the Anti-lock Braking System (ABS) is triggered, the presence of the aforementioned regenerative torque or driving torque at the wheel ends will severely interfere with the normal adjustment logic of the ABS, affecting braking safety. In existing technologies, the conventional approach is that after the anti-lock braking system (ABS) is activated, the vehicle control unit (VCU) identifies the ABS status and immediately executes a motor torque zeroing strategy to eliminate interference from motor torque on ABS regulation. Furthermore, existing technologies have also proposed torque regulation methods under ABS activation, such as gradually reducing torque or controlling the magnitude and speed of electric braking force output. However, the inventors have found that the existing strategies of directly zeroing or gradually reducing motor torque after ABS activation have significant drawbacks and shortcomings in practical applications, mainly in the following aspects:

[0054] Firstly, the instantaneous zeroing of negative torque can easily trigger longitudinal impacts on the vehicle. When the anti-lock braking system (ABS) activates and there is a large negative torque (i.e., regenerative torque) at the wheel end, if the vehicle controller directly zeroes the motor torque, the total braking force at the wheel end will drop sharply and instantaneously. Theoretically, the ABS should simultaneously perform hydraulic compensation to make up for the lack of braking force. However, for the widely used One-box hydraulic braking system, due to hardware architecture limitations, it cannot achieve real-time coordinated fluid replenishment with the vehicle controller, resulting in a lag in hydraulic buildup. This can easily cause the vehicle to exhibit a noticeable "lurching" phenomenon, severely affecting braking comfort and stability.

[0055] Secondly, low-friction road conditions can easily disrupt the vehicle's stability control logic. On roads with low coefficient of friction, if the vehicle is under light braking and the regenerative braking system and coasting feedback are still active, the negative feedback torque may cause the drive wheel slip ratio to increase rapidly, triggering the anti-lock braking system. Simply resetting the motor's negative torque to zero in this situation would disrupt the stability control logic of the drive traction control (DTC) system. A proper control logic should prioritize the intervention of the drive traction control system, monitoring the slip ratio and implementing torque increase control to restore wheel speed, thereby maintaining vehicle stability. The current direct zero-torque strategy clearly cannot meet this requirement.

[0056] Third, directly resetting the positive torque to zero may cause wheel lock-up. When the anti-lock braking system is activated, there is a large positive torque (i.e., residual drive torque) at the wheel end. If the vehicle controller directly resets the motor torque to zero, the hydraulic braking pressure originally used to overcome the driving force will instantly become redundant braking force, resulting in a sudden increase in wheel braking force. This can easily cause wheel lock-up, deviating from the driver's braking intention.

[0057] Furthermore, while the aforementioned existing technologies involve torque regulation under anti-lock braking system (ABS) operating conditions, they mostly focus on reducing the impact of torque changes on the system through methods such as gradual slow retraction. They do not address the coordination and compensation problem between the hydraulic braking system and the motor torque withdrawal, nor do they disclose the processing logic under positive torque conditions. Therefore, they cannot simultaneously achieve the dual control objectives of smooth motor torque withdrawal and stable hydraulic regulation of the ABS system. The technical solution of this invention is as follows:

[0058] Firstly, embodiments of the present invention provide a method for controlling wheel-end torque in vehicles. This method is mainly applied to electric vehicles or hybrid vehicles. During vehicle operation, especially on low-friction surfaces or under emergency braking conditions, the method provided by the present invention can effectively coordinate the driving motor's power and hydraulic braking force. This solves the problem of excessive fluctuations in total wheel-end braking force caused by sudden changes in motor braking torque when the anti-lock braking system is activated, which can lead to vehicle vibration, increased braking distance, or instability. Furthermore, for special conditions involving drive slippage on low-friction surfaces, a priority arbitration mechanism for the drive anti-slip control strategy is introduced to further improve vehicle stability during start-up or acceleration on icy or slippery surfaces.

[0059] Specifically, the control logic of the vehicle wheel-end torque coordination control method provided in this embodiment of the invention is mainly executed by the brake controller, and the vehicle wheel-end torque control method includes the following steps:

[0060] S100: Acquire vehicle status signals, including wheel slip ratio and motor torque;

[0061] S200: When the anti-lock braking system is detected to be activated, coordinated control is performed according to the direction of the motor torque and the road conditions.

[0062] If the motor torque is negative and the preset low-adhesion drive anti-slip condition is not met, the motor torque is controlled to approach zero according to the first preset slope, and the hydraulic braking force is controlled to increase according to the second preset slope.

[0063] If the motor torque is positive, control the motor torque to decrease according to the third preset slope, and at the same time control the hydraulic braking force to decrease according to the fourth preset slope.

[0064] In step S100 above, the brake controller continuously receives vehicle status signals via the bus during vehicle power-on operation. These vehicle status signals include, but are not limited to, wheel speed sensor signals, motor torque signals requested by the vehicle controller, driver-demanded torque signals, regenerative braking status signals, motor drag torque activation signals, brake pedal opening signals, and accelerator pedal opening signals.

[0065] Specifically, the wheel speed sensor signals directly reflect the rotational speed of each wheel of the vehicle. The brake controller reads the pulse signals of each wheel in real time through wheel speed sensors configured for each wheel, and converts them into the corresponding wheel speed value.

[0066] The motor torque signal requested by the vehicle controller is the desired motor output torque calculated by the vehicle controller based on the driver's intentions and battery status. This torque value can be positive or negative; a positive value represents driving torque, and a negative value represents braking torque, i.e., regenerative braking torque. In vehicles with regenerative braking coordination control, this motor torque signal is a key input for the brake controller to perform coordinated control, directly reflecting the magnitude of the braking or driving force currently applied to the wheels by the drive motor.

[0067] The driver's torque demand signal is typically calculated by the vehicle controller based on the displacement of the accelerator and brake pedals, reflecting the driver's expectation of acceleration or deceleration. The regenerative braking status signal indicates whether the vehicle is currently in regenerative braking mode and the level of regenerative braking intensity. The motor drag torque activation signal identifies whether the motor is applying reverse drag torque without the pedal being depressed. The brake pedal opening signal is directly acquired by the brake pedal sensor, reflecting the intensity of the driver's braking operation. The accelerator pedal opening signal is acquired by the accelerator pedal sensor, reflecting the intensity of the driver's acceleration operation.

[0068] After acquiring the aforementioned vehicle status signals, the brake controller calculates the wheel speeds based on the wheel speed sensor signals. Simultaneously, the brake controller combines this with the estimated vehicle reference speed to calculate the wheel slip ratio.

[0069] In step S100 above, when it is determined that the anti-lock braking system is activated, the specific steps include:

[0070] Calculate the slip ratio of each wheel;

[0071] When the slip ratio of any wheel reaches or exceeds a first preset threshold, and the duration of this state exceeds a first delay threshold, the anti-lock braking system is determined to be activated, and the coordinated control mode flag is set.

[0072] Specifically, the formula for calculating the wheel slip ratio s is:

[0073] s = (V ref – V wheel )\ V ref

[0074] Among them, V ref V serves as the vehicle's reference speed. wheel This refers to the wheel speed.

[0075] In this embodiment of the invention, the first preset threshold is 0.18~0.22, and the first delay threshold is 9~11ms. For example, the first delay threshold can be set to 10ms. When the wheel slip ratio reaches the first preset threshold, and this state lasts for more than 10ms, the anti-lock braking system is determined to be activated, and the system enters the wheel-end torque coordination control mode. Setting the first delay threshold prevents the anti-lock braking system from being falsely triggered. Only when the wheel slip ratio exceeds the threshold for a certain period of time is the actual locking trend confirmed, thereby improving the robustness of the system.

[0076] The accuracy of the vehicle reference speed directly affects the accuracy of the slip ratio calculation. In this embodiment of the invention, the maximum wheel speed method combined with the vehicle's longitudinal acceleration integral method is used to estimate the vehicle reference speed V. ref For each wheel, calculate its slip ratio. When the slip ratio s of any wheel... i If the first preset threshold is reached or exceeded, and the duration of this state exceeds the first delay threshold, the brake controller determines that the anti-lock braking system is activated and immediately sets the "wheel-end torque coordination control mode" flag. Once the coordination control mode flag is set, the brake controller enters the coordination control logic and executes the corresponding coordination control strategy according to the direction of the motor torque and the road surface conditions at this time.

[0077] In step S200 above, after the brake controller determines that the anti-lock braking system is activated, it first reads the motor torque signal currently requested by the vehicle controller, and the motor torque is recorded as T. req After the anti-lock braking system is activated, the brake controller needs to read the motor torque currently requested by the vehicle controller, denoted as T. req The brake controller will control the motor torque T. req With dead zone T dead Comparison. Dead zone T dead Defined as the torque zero drift value, dead zone T dead Set to ±5 N•m.

[0078] If T req <-T dead The brake controller determines that the vehicle is in a negative torque condition. This condition indicates that the vehicle is in CRBS energy recovery mode or coasting feedback mode, and the system then enters the negative torque coordinated control process.

[0079] If T req >+T dead The brake controller determines that the vehicle is in a positive torque condition. This condition indicates that there is residual drive torque at the wheel ends, and the system then enters the positive torque coordinated control process.

[0080] If |T req |≤T deadThe brake controller determines that torque coordination is not required at this time, and the system directly executes the hydraulic adjustment of the conventional anti-lock braking system.

[0081] When the brake controller determines that the anti-lock braking system is activated, if the motor torque is negative, it indicates that the vehicle is undergoing regenerative braking. At this time, the brake controller further determines whether the preset low-adhesion drive anti-slip condition is met. If the condition is not met, the negative torque conventional coordinated control strategy is executed. The logic of the negative torque conventional coordinated control strategy is as follows: when the anti-lock braking system needs to intervene to reduce pressure and prevent wheel lock-up, due to the presence of negative motor torque, simply reducing the hydraulic braking force may not be sufficient to eliminate slippage, or it may cause a sudden decrease in the total braking force at the wheel end, causing vehicle impact. Therefore, in this embodiment of the invention, a strategy of dynamic compensation through hydraulic braking force and motor power is adopted to ensure a smooth transition of the total braking force at the wheel end, avoiding longitudinal impact and forward lurching of the vehicle.

[0082] Furthermore, in the step where the motor torque is negative and the preset low-adhesion drive anti-slip condition is not met, controlling the motor torque and hydraulic braking force specifically includes:

[0083] Send a torque increase request signal to the vehicle controller to cause the drive motor to perform torque reduction control according to the first preset slope until the absolute value of the motor torque is reduced to the dead zone range.

[0084] The hydraulic system controlling the anti-lock braking system builds pressure and replenishes fluid according to the second preset slope.

[0085] The torque increase request signal does not request the drive motor to generate positive driving force, but rather requests the drive motor to reduce the absolute value of its negative torque, i.e., to reduce torque. The brake controller takes over the motor torque T requested by the vehicle controller. req The takeover described here refers to the brake controller operating at the actual motor torque T. req Starting from a certain value, a torque increase signal, TorqueIncreaseReq, is sent to quickly zero the torque at the wheel end. For example, it requests the drive motor to increase the negative torque of -500 N•m to 0 N•m at a certain slope, effectively reducing the motor's power output. This operation assists the anti-lock braking system in restoring stable wheel rotation by eliminating the motor braking component that causes wheel lock-up.

[0086] While performing the above operations, the brake controller compensates for lost torque through the hydraulic system to avoid deceleration loss. To ensure the stability of the control system, the brake controller requires timing control. Specifically, when the vehicle controller receives the wheel-end torque coordination control flag, the vehicle controller needs to maintain the motor torque T... req The value no longer changes, and it responds to the torque increase request sent by the brake controller.

[0087] The brake controller is based on the current negative torque T req The slope calibration parameters are determined based on the numerical values ​​and the vehicle's ride comfort requirements, thereby determining the first preset slope k. neg The first preset slope k neg If positive, the total unwinding time = |T req | / |k neg |, that is, the motor torque T req The absolute value divided by the first preset slope k neg The absolute value determines it.

[0088] The brake controller sends a progressively increasing target value for the motor torque to the vehicle controller every 10ms. This means the absolute value of the motor's negative torque decreases linearly. Upon receiving the target value, the vehicle controller triggers the corresponding action from the drive motor controller. Simultaneously, the brake controller monitors the actual torque feedback of the drive motor in real time. If the brake controller detects that the actual torque reduction rate deviates from the requested value by more than the allowable deviation, it triggers a closed-loop correction mechanism. The allowable deviation is set at ±10%. After triggering the closed-loop correction, the brake controller adjusts the target value for the next cycle to correct the deviation.

[0089] Meanwhile, to maintain a constant total braking force at the wheel ends and ensure that the driver's perceived deceleration does not change abruptly, the brake controller must control the hydraulic system to increase the hydraulic braking force. The brake controller controls the hydraulic system to inject brake fluid into the brakes, causing the wheel cylinder pressure to start from the initial hydraulic pressure at the moment the anti-lock braking system is activated, and increase according to the second preset slope k. comp It rises until the target wheel cylinder pressure is reached.

[0090] The hydraulic system of the anti-lock braking system actively builds pressure on the wheels that slip, |k comp |=|k neg Specifically, the equivalent coefficient K is set. eff This is the coefficient relating wheel-end torque and hydraulic pressure, reflecting the efficiency of the hydraulic system in converting brake fluid pressure into wheel-end braking force. Equivalent coefficient K eff The unit is N•m / bar, and this coefficient can be obtained through calculation.

[0091] The target wheel cylinder pressure during the pressure building and fluid replenishment process is calculated based on the equivalent coefficients of the initial hydraulic pressure, wheel end torque, and hydraulic pressure, as well as the change in motor torque. As the absolute value of the motor torque decreases, the target wheel cylinder pressure increases synchronously and linearly.

[0092] Target cylinder pressure P during pressure building and fluid replenishment process target The following formula is used to calculate:

[0093] P target = P base +(|Treq (0)|-|T req (t)|) / k eff

[0094] Among them, P target T represents the target cylinder pressure to be achieved in the current cycle. req (0) T is the motor torque at the moment the anti-lock braking system is activated. req (t) represents the motor torque in the current cycle, k eff P is the equivalent coefficient for wheel end torque and hydraulic pressure. base To determine the initial hydraulic pressure at the moment the anti-lock braking system is activated, this value can be directly measured using a pressure sensor located in the master cylinder. This formula ensures that as the absolute value of the motor's negative torque decreases, the pressure in the target wheel cylinder increases synchronously and linearly. This control method guarantees a smooth transition of the total braking force at the wheel ends.

[0095] Using the above formula, the brake controller can accurately calculate the hydraulic pressure value that needs to be compensated. In the above formula, |T req (0)|-|T req (t) represents the change in the absolute value of the motor's negative torque from the moment the anti-lock braking system is activated to the current moment. Since the motor's negative torque is decreasing (approaching zero), this difference is positive, representing the reduction in braking force at the motor end.

[0096] In this embodiment of the invention, the brake controller employs a feedforward plus proportional-integral closed-loop control strategy. Based on real-time feedback from the wheel cylinder pressure sensor, the brake controller adjusts the pulse width modulation duty cycle of the hydraulic system's inlet valve and booster valve to ensure that the actual pressure accurately tracks the target wheel cylinder pressure P. target The control objective of this process is to keep the total braking force at the wheel ends constant. The formula for calculating the total braking force at the wheel ends is F. total = P hyd ×K eff + |T motor (t) |, where P hyd T represents the actual wheel cylinder hydraulic pressure. motor (t) represents the motor torque at the current moment. The brake controller uses closed-loop control to keep the fluctuation of the total braking force at the wheel ends within ±3%.

[0097] When the absolute value of the motor torque drops below the dead zone and this state lasts for more than the stabilization delay (e.g., 20 milliseconds), and the hydraulic pressure reaches the target wheel cylinder pressure, the brake controller clears the coordination mode flag and exits torque coordination. Subsequently, the anti-lock braking system enters the normal pure hydraulic adjustment phase, which involves cyclical control of pressure increase, pressure holding, or pressure release based on the slip ratio target.

[0098] In this embodiment of the invention, based on the current negative torque Treq The value and the ride comfort of the vehicle determine the torque reduction slope calibration parameters. The range of the first preset slope (motor torque reduction slope) is 1000N•m / s to 5000N•m / s. For example, the first preset slope is set to 3000N•m / s.

[0099] In step S200 above, when the brake controller determines that the anti-lock braking system is activated, if the motor torque is positive, it indicates that the vehicle is in driving condition and the driving force causes wheel slippage. At this time, a positive torque coordination control strategy is executed, controlling the motor torque to decrease according to the third preset slope, and simultaneously controlling the hydraulic braking force to decrease according to the fourth preset slope, specifically including:

[0100] Send a torque reduction request signal to the vehicle controller to cause the drive motor to gradually reduce torque to zero according to the third preset slope;

[0101] The hydraulic system controlling the anti-lock braking system reduces the wheel cylinder pressure according to the fourth preset slope.

[0102] Under drive slip conditions, the driving force generated by the drive motor is the root cause of excessive wheel acceleration and increased slip ratio. Therefore, the primary task is to quickly remove the driving force generated by the drive motor. The brake controller requests the vehicle controller via the bus to reduce the torque of the drive motor to zero. Meanwhile, the handling logic of the hydraulic braking force differs from that of a conventional anti-lock braking system (ABS). In a conventional ABS, pressure is usually reduced upon detecting slip. However, under the positive torque condition in this embodiment, if the driver simultaneously depresses the brake pedal, there may be some pressure in the wheel cylinders. To coordinate with the removal of the motor torque, prevent wheel lock-up due to the loss of driving force without reduction in braking force, or maintain smooth vehicle deceleration, it is necessary to synchronously control the hydraulic system to reduce the wheel cylinder pressure.

[0103] Specifically, the detailed process of implementing the positive torque coordinated control strategy is as follows:

[0104] The brake controller is based on the current positive torque value T req The slope calibration parameters are determined based on the vehicle's ride comfort requirements, thereby determining the third preset slope kpos, which is a negative value.

[0105] Then, the brake controller sends a gradually decreasing target torque value to the vehicle controller, causing the torque of the drive motor to drop linearly to zero.

[0106] Then, the hydraulic system of the anti-lock braking system synchronously reduces the pressure in the target wheel cylinder. The absolute value of the fourth preset slope is equal to the absolute value of the third preset slope, |k_pos|.

[0107] In this process, the formula for calculating the target wheel cylinder pressure is:

[0108] P target (t) = P base +(|T req (0)|-|T req (t)|) / k eff

[0109] Among them, P target (t) represents the target wheel cylinder pressure at the current moment. req (0) T is the motor torque at the moment the anti-lock braking system is activated. req (t) represents the motor torque at the current moment, k eff P is the equivalent coefficient for wheel end torque and hydraulic pressure. base The initial hydraulic pressure before the anti-lock braking system is activated can be directly measured by a pressure sensor installed in the master cylinder. This formula ensures consistent wheel-end torque, facilitating subsequent hydraulic control of the anti-lock braking system.

[0110] Next, closed-loop pressure control is implemented. The brake controller ensures the accuracy of the decompression process through closed-loop regulation. The brake controller adjusts the pulse width modulation duty cycle of the hydraulic system's relief valve to ensure that the pressure sensor feedback value tracks the target slope. This step ensures that the decompression rate is synchronized with the motor's torque reduction rate.

[0111] Finally, once the motor torque reaches zero and the hydraulic pressure drops to the target wheel cylinder pressure value, the brake controller clears the coordination flag. Subsequently, the anti-lock braking system switches to normal adjustment mode.

[0112] In this embodiment of the invention, the absolute value of the fourth preset slope is equal to the absolute value of the third preset slope. That is, the rate of pressure reduction in the hydraulic system is synchronized with the rate of torque reduction in the drive motor. This synchronous control ensures that the change in the total braking force at the wheel end caused by the reduction in motor driving force and hydraulic pressure is controllable, ensuring a smooth change in the total braking force at the wheel end and avoiding situations such as vehicle shaking caused by asynchrony between sudden reduction in driving force and sudden reduction in hydraulic pressure.

[0113] In this embodiment of the invention, the value range of the third preset slope is -500 N•m / s to -10000 N•m / s, and can be specifically calibrated according to the ride comfort of the vehicle. For example, the third preset slope is set to -3000 N•m / s, which allows for rapid cutoff of driving force to suppress wheel slippage as quickly as possible.

[0114] In this embodiment of the invention, the value range of the fourth preset slope is 500 N•m / s to 10000 N•m / s. For example, the fourth preset slope is set to 3000 N•m / s. By coordinating the hydraulic pressure and the drive torque synchronously, vehicle impact and sudden changes in vehicle body posture during ABS adjustment can be avoided.

[0115] In this embodiment of the invention, a special working condition processing logic is specifically provided, namely, priority control for low-friction road surface driving anti-skid. The preset low-friction driving anti-skid conditions include a first condition and a second condition;

[0116] The first condition includes: the road surface adhesion coefficient is lower than the second preset threshold, and the driver's required torque is zero. The driver's required torque is the third preset threshold, that is, the driver has not pressed the accelerator pedal.

[0117] The second condition includes: the motor torque is negative, the anti-lock braking system is activated, and the drive anti-slip control system is activated.

[0118] Specifically, the road surface adhesion coefficient reflects the frictional characteristics of the current road surface, and the second preset threshold is set to 0.3 or 0.4. When the road surface adhesion coefficient is lower than the second preset threshold, it can be identified as a low-adhesion road surface, such as an icy or waterlogged road surface. A zero torque demand from the driver indicates that the driver currently has no intention to accelerate, and the vehicle should be in a coasting or braking state.

[0119] In the second condition, a negative motor torque indicates that the vehicle is performing energy recovery. Activation of the anti-lock braking system (ABS) indicates that the wheels are showing a tendency to lock up. Activation of the traction control system (TCS / DTC) indicates that the system has detected excessive slippage of the drive wheels. During the process of recovering negative torque while coasting, due to the low-friction road surface, the negative torque from the motor may cause the drive wheels to lock up momentarily and slide in the opposite direction, or the vehicle's longitudinal dynamics may cause the traction control system to detect a risk of instability. At this time, both the ABS and traction control systems are activated simultaneously, and the drive motor is in a negative torque state.

[0120] In this embodiment of the invention, the road surface adhesion coefficient is estimated based on the peak slip ratio and adhesion coefficient curve during the anti-lock braking system (ABS) adjustment process, or based on a comprehensive judgment of wheel speed acceleration and ambient temperature. Specifically, there are two main methods for obtaining the road surface adhesion coefficient. The first method is estimation based on the peak slip ratio and adhesion coefficient curve during the ABS adjustment process. In the initial stage of ABS adjustment, wheel speed decreases, slip ratio increases, and road braking force increases accordingly until the peak adhesion point is reached. By analyzing the slip ratio change rate and vehicle deceleration during this process, the current adhesion coefficient is obtained by looking up a table or calculation. The second method is based on a comprehensive judgment of wheel speed acceleration and ambient temperature. If the ambient temperature is extremely low and wheel speed acceleration fluctuates drastically, it can be inferred that the road surface is in an icy state, and the adhesion coefficient is extremely low.

[0121] The vehicle wheel-end torque control method of this invention further includes:

[0122] If the motor torque is negative and the preset low-adhesion drive anti-slip condition is met, the drive anti-slip control strategy is executed to adjust the motor torque.

[0123] Furthermore, implementing the drive anti-slip control strategy to adjust the motor torque specifically includes:

[0124] Hydraulic compensation pressure build-up is not performed;

[0125] In response to the torque increase request from the drive anti-slip control system, the drive motor is controlled to transition from the current negative torque state to the positive torque state until the slip ratio of the drive wheel returns to the preset safe range.

[0126] In step S200 above, when the drive anti-slip control strategy is executed to adjust the motor torque, the function of the cooperative regenerative braking system is immediately turned off, and hydraulic compensation pressure build-up is not performed. Under low-friction drive anti-slip conditions, if the hydraulic pressure continues to increase when the wheels are unstable, it will exacerbate wheel lock-up or instability. Then, in response to the torque increase request of the drive anti-slip control system, the drive motor is controlled to transition from the current negative torque state to a positive torque state until the drive wheel slip ratio recovers to the preset safe range. On extremely low-friction surfaces, the vehicle controller chooses to respond to the torque increase request of the drive anti-slip control system, that is, to allow the drive motor to output positive torque. The positive torque output by the drive motor can quickly change the rotation state of the drive wheels from the edge of lock-up or severe slippage to normal rotation, using driving force to re-establish the wheel speed of the drive wheels, improve the lateral stability of the vehicle, reduce the drive wheel slip ratio, prevent drive wheel lock-up and vehicle instability, and improve driving safety. In this mode, the control priority of the drive anti-slip control system is higher than the hydraulic compensation control of the anti-lock braking system.

[0127] In this embodiment of the invention, the preset safety range is defined as the drive wheel slip ratio continuously being lower than a preset slip threshold. This preset slip threshold can be a fixed, small value. Only when the drive wheel slip ratio remains within this safety range for a certain period of time is the vehicle considered to have regained stability, the drive anti-slip control adjustment ends, and the system can exit this control mode.

[0128] In this embodiment of the invention, on low-friction surfaces (such as ice, snow, or slippery surfaces), if the vehicle's drive wheels trigger the anti-lock braking system due to negative feedback torque, and simultaneously activate the traction control system, the wheel ends have little or no hydraulic pressure. Traditional hydraulic compensation can interfere with the traction control system's active torque recovery strategy. Therefore, this embodiment of the invention includes an arbitration mechanism. Specifically, the brake controller will not activate the "wheel-end torque coordination control flag," only activating the traction control function, and will not perform wheel-end fluid replenishment. Simultaneously, the vehicle controller's internal response prioritizes the "traction control activation flag" over the "wheel-end torque coordination control flag," completely transferring motor torque control to the traction control system. The traction control system then takes over the vehicle controller's request for motor torque T. reqStarting from this value, a torque-increasing signal TorqueIncreaseReq is sent to quickly reset the torque at the wheel end to zero.

[0129] The drive anti-slip control system actively requests the motor to quickly transition from the current negative torque to positive torque (torque boost) based on the deviation between the drive wheel slip ratio and the target slip ratio, so as to actively increase the drive wheel speed and reduce the slip ratio. The target slip ratio is set to 0.05 to 0.10.

[0130] The drive motor increases torque as requested by the traction control system until the drive wheel slip ratio returns to a safe range. When the traction control system determines that the slip ratio has returned to normal, for example, if it remains below 0.10 for 200 milliseconds, the traction control system disengages and requests the motor torque to return to zero. If the anti-lock braking system (ABS) is still active at this point, it switches to conventional ABS hydraulic adjustment; if the ABS has disengaged, it returns to normal braking mode. This strategy ensures stability on low-friction surfaces and prevents vehicle yaw instability caused by drive wheel lock-up.

[0131] The vehicle wheel-end torque control method of this invention further includes the following steps:

[0132] S300: When the motor torque returns to zero and hydraulic compensation or pressure reduction is completed, or when the anti-lock braking system disengages during the coordination process, the torque coordination control is terminated.

[0133] If the vehicle controller does not respond or the drive motor feedback is abnormal within several consecutive control cycles, it will exit the coordination mode.

[0134] The vehicle wheel-end torque control method of this invention includes a robust exit mechanism to ensure that the system can safely relinquish control under various circumstances. The exit conditions mainly include the following two categories:

[0135] The first category is the exit condition for normal completion of adjustment. Torque coordination control terminates when the motor torque returns to zero and hydraulic compensation or decompression is completed, or when the anti-lock braking system (ABS) disengages during the coordination process. Zero motor torque means that the motor's power or driving force has been completely eliminated and no longer affects wheel-end power. Completed hydraulic compensation or decompression means that the hydraulic pressure provided by the hydraulic system has reached the target pressure value. ABS disengagement means that the wheel slip ratio has returned to normal, and anti-lock intervention is no longer needed. At this point, the coordination control mode flag is cleared, the brake controller stops sending special torque increase or decrease requests to the vehicle controller, and the system returns to the normal braking or drive control mode.

[0136] The second category is fault handling exit conditions. If the vehicle controller does not respond for several consecutive control cycles (e.g., 5 cycles) or the drive motor feedback is abnormal, it exits the coordination mode. A lack of response from the vehicle controller may indicate a bus communication failure. Abnormal drive motor feedback means that although a request was sent, the actual motor torque failed to follow the change. In this situation, continuing to rely on electro-hydraulic coordinated control may lead to loss of control. Therefore, a safe exit is necessary. After exiting, the brake controller can switch to a pure hydraulic anti-lock braking system control mode, no longer relying on the drive motor's cooperation. Although this sacrifices some comfort or energy efficiency, it ensures basic braking safety.

[0137] Secondly, embodiments of the present invention also provide a brake controller, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. The memory stores the computer program. The processor executes the computer program to implement the steps of the vehicle wheel-end torque control method of the above embodiments.

[0138] Thirdly, embodiments of the present invention also provide a vehicle including the brake controller described in the above embodiments. The vehicle is a pure electric vehicle or a hybrid electric vehicle. By equipping it with this brake controller, the vehicle can achieve precise control of wheel-end torque under various complex road surfaces and operating conditions, thereby improving active safety and driving experience.

[0139] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other occasions without modification, are all within the protection scope of the present invention.

Claims

1. A method for controlling wheel-end torque of a vehicle, characterized in that, include: Acquire vehicle status signals, including wheel slip ratio and motor torque; When the anti-lock braking system is activated, coordinated control is performed based on the direction of the motor torque and the road conditions. If the motor torque is negative and the preset low-adhesion drive anti-slip condition is not met, the motor torque is controlled to approach zero according to the first preset slope, and the hydraulic braking force is controlled to increase according to the second preset slope. If the motor torque is positive, control the motor torque to decrease according to the third preset slope, and at the same time control the hydraulic braking force to decrease according to the fourth preset slope.

2. The vehicle wheel-end torque control method according to claim 1, characterized in that, The determination that the anti-lock braking system is activated specifically includes: Calculate the slip ratio of each wheel; When the slip ratio of any wheel reaches or exceeds a first preset threshold, and the duration of this state exceeds a first delay threshold, the anti-lock braking system is determined to be activated, and the coordinated control mode flag is set.

3. The vehicle wheel-end torque control method according to claim 2, characterized in that, The first preset threshold is 0.18~0.22, and the first delay threshold is 9~11ms.

4. The vehicle wheel-end torque control method according to claim 1, characterized in that, In the step where the motor torque is negative and the preset low-adhesion drive anti-slip condition is not met, controlling the motor torque and hydraulic braking force specifically includes: Send a torque increase request signal to the vehicle controller to cause the drive motor to perform torque reduction control according to the first preset slope until the absolute value of the motor torque is reduced to the dead zone range. The hydraulic system controlling the anti-lock braking system builds pressure and replenishes fluid according to the second preset slope.

5. The vehicle wheel-end torque control method according to claim 4, characterized in that, The target wheel cylinder pressure during the pressure building and fluid replenishment process is calculated based on the equivalent coefficients of the initial hydraulic pressure, wheel end torque, and hydraulic pressure, as well as the change in motor torque. As the absolute value of the motor torque decreases, the target wheel cylinder pressure increases synchronously and linearly.

6. The vehicle wheel-end torque control method according to claim 5, characterized in that, The target cylinder pressure P during the pressure building and fluid replenishment process target The following formula is used to calculate: P target = P base +(|T req (0)|-|T req (t)|) / k eff Among them, P base To prevent the initial hydraulic pressure at the moment of activation of the anti-lock braking system, T req (0) T is the motor torque at the moment the anti-lock braking system is activated. req (t) represents the motor torque in the current cycle, k eff This is the equivalent coefficient for wheel end torque and hydraulic pressure.

7. The vehicle wheel-end torque control method according to claim 1, characterized in that, If the motor torque is positive, the motor torque is controlled to decrease according to a third preset slope, while the hydraulic braking force is controlled to decrease according to a fourth preset slope. Specifically, this includes: Send a torque reduction request signal to the vehicle controller to cause the drive motor to gradually reduce torque to zero according to the third preset slope; The hydraulic system controlling the anti-lock braking system reduces the wheel cylinder pressure according to the fourth preset slope.

8. The vehicle wheel-end torque control method according to claim 7, characterized in that, The absolute value of the fourth preset slope is equal to the absolute value of the third preset slope.

9. The vehicle wheel-end torque control method according to claim 1, characterized in that, The preset low-adhesion driving anti-slip conditions include a first condition and a second condition. The first condition includes: the road surface adhesion coefficient is lower than the second preset threshold, and the driver's required torque is zero; The second condition includes: the motor torque is negative, the anti-lock braking system is activated, and the drive anti-slip control system is activated.

10. The vehicle wheel-end torque control method according to claim 9, characterized in that, The road surface adhesion coefficient is estimated based on the peak slip ratio and adhesion coefficient curve during the adjustment process of the anti-lock braking system, or based on a comprehensive judgment of wheel speed acceleration and ambient temperature.

11. The vehicle wheel-end torque control method according to claim 1, characterized in that, Also includes: If the motor torque is negative and the preset low-adhesion drive anti-slip condition is met, the drive anti-slip control strategy is executed to adjust the motor torque.

12. The vehicle wheel-end torque control method according to claim 11, characterized in that, The execution of the drive anti-slip control strategy to adjust the motor torque specifically includes: Hydraulic compensation pressure build-up is not performed; In response to the torque increase request from the drive anti-slip control system, the drive motor is controlled to transition from the current negative torque state to the positive torque state until the slip ratio of the drive wheel returns to the preset safe range.

13. The vehicle wheel-end torque control method according to claim 12, characterized in that, The preset safety range is defined as the drive wheel slip rate being continuously lower than a preset slip threshold.

14. The vehicle wheel-end torque control method according to claim 1, characterized in that, Also includes: When the motor torque returns to zero and hydraulic compensation or pressure reduction is completed, or when the anti-lock braking system disengages during the coordination process, the torque coordination control is terminated. If the vehicle controller does not respond or the drive motor feedback is abnormal within several consecutive control cycles, it will exit the coordination mode.

15. The vehicle wheel-end torque control method according to claim 1, characterized in that, The first preset slope ranges from 1000 N•m / s to 5000 N•m / s.

16. The vehicle wheel-end torque control method according to claim 1, characterized in that, The value range of the third preset slope is -10000 N•m / s to ~500 N•m / s.

17. A brake controller, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the vehicle wheel-end torque control method as described in any one of claims 1 to 16.

18. A vehicle, characterized in that, Includes the brake controller as described in claim 17.

Images