Wheel Anti-lock braking system and method applicable to hill braking

Abstract

Disclosed in the present application is a wheel anti-lock braking system applicable to hill braking. In the wheel anti-lock braking system, a wheel speed identification module is used for identifying a vehicle wheel speed signal and a wheel acceleration signal; a vehicle speed acquisition module is used for calculating a vehicle body speed signal; a driving intention identification module is used for obtaining a front and a rear axle enable flag bit; a state machine module is used for determining whether the working state of a low-speed hill anti-lock braking system is a standby state or a shutdown state, and starting a conventional anti-lock braking system when the working state of the low-speed hill anti-lock braking system is a shutdown state; the state machine module receives the front and rear axle enable flag bits, and transmits the front and rear axle enable flag bits to a control logic module when the working state of the low-speed hill anti-lock braking system is a standby state; and the control logic module is used for sending a low-speed hill anti-lock braking system control command when wheels show a tendency to lock up. The present application realizes anti-lock braking control over wheels at low speeds, especially during hill braking, which cannot be achieved by conventional wheel anti-lock braking systems.

Description

Wheel anti-lock braking system and method suitable for hill braking CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Chinese patent application No. 202410233251.8 filed on March 1, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present application relates to the field of vehicle braking technology, and in particular to a wheel anti-lock braking system and method suitable for hill braking. Background Art

[0003] In recent years, anti-lock braking systems (ABS) have gained widespread adoption and development in the automotive industry. ABS prevents wheel lock during braking by controlling the friction between the tires and the road. Early braking systems used traditional hydraulic brakes, but these systems can easily cause wheel lock during sudden braking, compromising vehicle control and stability and increasing the risk of accidents. To address this issue, automakers began exploring and developing advanced braking systems that could effectively prevent wheel lock. This led to the development of anti-lock braking systems. ABS uses sensors to monitor wheel speed. If it detects impending wheel lock, it immediately adjusts brake pressure through the hydraulic system to maintain optimal braking. However, current mainstream anti-lock braking systems have a speed threshold at which they disengage. This results in poor vehicle stability when driving at low speeds on off-road slopes and low-lying surfaces, making them prone to skidding and loss of control.

[0004] Currently, mainstream anti-lock braking systems primarily use wheel speed, vehicle speed, and wheel acceleration as control thresholds to determine the appropriate mode for the system. However, these systems are ineffective in some low-speed driving conditions. This is primarily due to their inability to accurately identify the vehicle's wheel speed, vehicle speed, and driver intent during low-speed driving, as well as the appropriate mode switching control logic for these conditions.

[0005] Current mainstream anti-lock braking systems automatically disengage below a certain speed threshold. However, for vehicles frequently used off-road, especially those requiring off-road driving on slopes, research into wheel anti-lock braking systems is insufficient. Conventional ABS won't trigger during low-speed braking on slopes, and the low adhesion coefficient of off-road surfaces can easily lead to wheel lock.

[0006] Therefore, there is an urgent need to develop an anti-lock braking system (ABS) capable of activating under low-speed off-road ramp conditions to address the shortcomings of conventional ABS systems in such braking conditions. ABS systems for hill braking estimate the vehicle's wheel speed and vehicle speed at low speeds, identify the driver's driving intent, and incorporate mode switching control logic for these conditions. This enables low-speed ABS, particularly when braking on a ramp, that conventional ABS systems cannot achieve. ABS systems for hill braking ensure vehicle stability while also ensuring braking performance. Developing an ABS system suitable for low-speed braking, particularly on off-road ramps, is a pressing issue. Summary of the Invention

[0007] The purpose of this application is to provide a wheel anti-lock braking system and method suitable for hill braking. By estimating the vehicle's wheel speed and vehicle speed during low-speed driving, identifying the driver's driving intention, and incorporating mode switching control logic for these conditions, this system achieves low-speed, especially hill braking, anti-lock control that conventional wheel anti-lock braking systems cannot achieve. This system ensures vehicle stability while also ensuring braking performance.

[0008] To achieve this purpose, the present application designs a wheel anti-lock braking system suitable for hill braking, which is characterized by comprising: a wheel speed recognition module for recognizing vehicle wheel speed signals and wheel acceleration signals under hill conditions;

[0009] The vehicle speed acquisition module is used to calculate the vehicle speed signal based on the vehicle wheel speed signal, the vehicle acceleration signal and the anti-lock braking system activation flag;

[0010] The driving intention recognition module is used to identify the driving intention based on the vehicle wheel speed signal, body speed signal, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle direction information, steep slope descent activation flag and low-speed off-road cruise activation flag, and obtain the front and rear axle enable flags;

[0011] The state machine module is used to determine whether the low-speed ramp anti-lock braking system is in standby or disabled based on the vehicle body speed, the conventional anti-lock braking system reference speed, and the preset speed threshold for entering or exiting the low-speed ramp anti-lock braking system, and to determine whether the conventional anti-lock braking system is activated based on the activation conditions of the conventional anti-lock braking system. The state machine module receives the front and rear axle enable flags and transmits the front and rear axle enable flags to the control logic module when the low-speed ramp anti-lock braking system is in standby state.

[0012] The control logic module is used to obtain the current wheel slip rate and wheel cylinder pressure signal based on the vehicle wheel speed signal, body speed signal, front and rear axle enable flag, steep slope descent function activation flag, low-speed off-road cycle function activation flag and four-wheel control mode signal, and judge whether the wheel has a locking tendency based on the current wheel slip rate, wheel cylinder pressure signal and wheel acceleration, and issue a low-speed slope anti-lock braking system control instruction when the wheel has a locking tendency.

[0013] Beneficial effects of this application:

[0014] The present application estimates the wheel speed and vehicle speed of the vehicle when the vehicle is traveling at low speeds, identifies the driver's driving intention, and combines this with the mode switching control logic used in these working conditions to achieve low-speed anti-lock braking control of the wheels, especially during braking on slopes, which is not achievable by conventional wheel anti-lock braking systems. Compared with conventional wheel anti-lock braking systems that will exit control at a certain higher vehicle speed, under the conditions of braking in low-speed off-road slope conditions, wheel locking is reduced, thereby suppressing the side slip of the vehicle on the slope, ensuring its directional stability, while taking into account the vehicle's braking efficiency mainly through the uncontrolled axle, thereby improving the vehicle's active safety performance during braking. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a schematic diagram of signal transmission of an anti-lock braking system for wheels applicable to hill braking according to the present application;

[0016] FIG2 is a flowchart of the driving intention recognition module of the anti-lock braking system for hill braking of the present application;

[0017] FIG3 is a schematic diagram of wheel speed calculation of the low-speed wheel speed identification module of the present application;

[0018] FIG4 is a flowchart of the state machine module in this application. DETAILED DESCRIPTION

[0019] The following is a further detailed description of this application in conjunction with the accompanying drawings and specific technical solutions:

[0020] Technical solution 1:

[0021] As shown in Figures 1 to 4, a wheel anti-lock braking system suitable for braking on a slope is characterized by comprising: a wheel speed recognition module for recognizing a vehicle wheel speed signal and a wheel acceleration signal under a slope condition;

[0022] The vehicle speed acquisition module is used to calculate the vehicle body speed signal based on the vehicle wheel speed signal, the body acceleration signal (obtained by the wheel inertial navigation system) and the anti-lock braking system activation flag;

[0023] The driving intention recognition module is used to identify driving intention based on vehicle wheel speed signals, body speed signals, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle direction information, steep slope descent activation flag and low-speed off-road cruise activation flag (below 15kph is low speed) to obtain the front and rear axle enable flags;

[0024] The state machine module is used to determine whether the low-speed ramp anti-lock braking system is in standby or off based on the vehicle body speed, the conventional anti-lock braking system reference speed, and the preset speed threshold for entering or exiting the low-speed ramp anti-lock braking system (set according to the speed range required by the low-speed ABS function). It also determines whether the conventional anti-lock braking system is activated based on the activation conditions of the conventional anti-lock braking system. If both the low-speed ramp anti-lock braking system and the conventional anti-lock braking system meet the activation conditions, the conventional anti-lock braking system is activated. The state machine module receives the front and rear axle enable flags and transmits the front and rear axle enable flags to the control logic module when the low-speed ramp anti-lock braking system is in standby state.

[0025] The control logic module is used to obtain the current wheel slip rate and wheel cylinder pressure signal based on the vehicle wheel speed signal, body speed signal, front and rear axle enable flag, steep slope descent function activation flag, low-speed off-road cycle function activation flag and four-wheel control mode signal, and judge whether the wheel has a locking trend based on the current wheel slip rate, wheel cylinder pressure signal and wheel acceleration, and issue low-speed slope anti-lock braking system control instructions (boost, decompression and pressure maintenance signals) when the wheel has a locking trend.

[0026] In the above technical solution, the road slope information is used to determine the positive and negative values ​​of the slope. The brake pedal status information is divided into the brake pedal being pressed and the brake pedal not being pressed. The vehicle driving direction information is judged by the built-in function of the intention recognition module. The input of the built-in function comes from the ECU, which is the direction signals of the four tires.

[0027] The above technical solution also includes an ABS downgrade or shutdown determination module, which controls the wheel anti-lock braking system to downgrade or shut down based on vehicle fault information. This design allows for timely adjustment of ABS output commands on low-speed ramps when certain signal faults occur, preventing unintended driving conditions caused by misjudgments and eliminating abnormal vehicle conditions due to signal anomalies.

[0028] In the above technical solution, the ABS degradation or shutdown judgment module controls the low-speed slope anti-lock braking system function to be degraded when receiving a chassis domain controller power supply overvoltage or undervoltage fault, an emergency braking function EPS failure fault, a slope signal abnormality, a vehicle acceleration signal abnormality, a steep slope descent function activation flag abnormality, and / or a low-speed off-road cruise function activation flag abnormality; for example, a slope signal failure affects the driving condition recognition and control threshold switching; a wheel speed direction failure affects the driving condition recognition and control threshold switching;

[0029] The ABS downgrade or shutdown determination module controls the low-speed hill-level anti-lock braking system function to be disabled if it detects a CAN network communication failure, abnormalities in the pulse count signal and accumulated time interval signal used to calculate wheel speed, abnormal brake pedal status, and / or abnormal master cylinder pressure signals. For example, a failure of signals related to the low-speed wheel speed recognition module is a serious fault, affecting wheel acceleration, vehicle speed, slip ratio calculation, and downstream logic threshold control. A failure of signals related to the driver intention recognition module is a serious fault, affecting the activation of the wheel anti-lock braking system function during low-speed braking on a downstream hill. A failure of actuator-related signals is a serious fault, affecting actual wheel cylinder pressure estimation and pressure tracking control. A communication failure is a serious fault. If CAN communication is blocked and causes a serious fault, external signals cannot be received.

[0030] In the aforementioned technical solution, in the low-speed hill ABS function-degraded mode, the low-speed hill ABS controller will execute a redundant control strategy in the backup core that relies on minimal sensor signals, ensuring only basic ABS functionality. In the low-speed hill ABS function-off mode, the low-speed hill ABS system is deactivated, and wheel anti-lock braking is no longer guaranteed, with only basic braking maintained. If the function is determined to be degraded, the wheels will still be prevented from locking as much as possible. If the function is determined to be off, ABS command output will be immediately stopped.

[0031] In the above technical solution, under slope conditions, the wheel speed recognition module receives the wheel speed sensor pulse number signal and the wheel speed sensor pulse accumulation time interval signal sent by the ECU in each sampling period, and calculates the vehicle wheel speed signal using the following formula:

[0032]

[0033] in, For each sampling period, the wheel speed sensor pulse number signal is: is the wheel speed sensor pulse accumulation time interval signal; the wheel speed sensor gear ring number and tire circumference are inherent parameters of the wheel, and the vehicle wheel speed calculated at this time is the real vehicle wheel speed signal;

[0034] When the wheel speed recognition module fails to read the wheel speed sensor pulse count signal and / or wheel speed sensor pulse accumulation time interval signal sent by the ECU, it calculates the vehicle wheel speed using the following method:

[0035] First, the wheel speed sensor pulse accumulation time interval signal in the previous sampling period with wheel speed sensor pulse signal As a benchmark, when the cumulative time without wheel speed sensor pulse signal is less than the wheel speed sensor pulse cumulative time interval signal in the previous sampling period with wheel speed sensor pulse signal When the wheel speed maintains the vehicle wheel speed calculated in the last sampling period with wheel speed sensor pulse signal, the accumulated time when there is no wheel speed sensor pulse signal is greater than the wheel speed sensor pulse accumulated time interval signal in the last sampling period with wheel speed sensor pulse signal. When the wheel speed sensor pulse accumulation time interval signal is The preset time is accumulated based on the current sampling period, and the wheel speed sensor pulse number signal of the current sampling period maintains the wheel speed sensor pulse number signal in the previous sampling period with the wheel speed sensor pulse signal. The wheel speed is calculated using Formula 1 based on the number of input signals. This calculated wheel speed is the estimated wheel speed signal. At very low speeds, the above signal may not be received for several or even dozens of cycles. In this case, there is no true wheel speed signal, and the above method is needed to estimate the wheel speed. Even at low vehicle speeds, when there are no valid and accurate input signals, a relatively accurate wheel speed can still be obtained.

[0036] In the above technical solution, when the wheel speed of the current cycle is the real vehicle wheel speed signal, the wheel speed recognition module calculates the wheel acceleration signal using the real vehicle wheel speed signal;

[0037] When the current cycle's wheel speed is an estimated vehicle wheel speed signal, the wheel speed identification module estimates the wheel acceleration signal for the current sampling cycle using the previous true vehicle wheel speed signal and wheel acceleration signal. Specifically, when there is no true wheel speed signal and the estimated wheel speed remains the true wheel speed of the previous sampling cycle, the wheel acceleration signal is estimated by accumulating the running loop cycle (the model code's running cycle) based on the wheel speed difference signal obtained in the previous sampling cycle and the time difference corresponding to the wheel speed difference in the previous sampling cycle. The wheel acceleration signal is then filtered using a Butterworth digital filter to obtain an accurate wheel acceleration signal. The Butterworth digital filter is used to filter out abnormally large accelerations. This processing makes the wheel acceleration more suitable for the wheel acceleration requirements of the control logic module. When the true wheel speed is available, the wheel acceleration is directly calculated. When the true wheel speed is not available, appropriate processing is performed to estimate the wheel acceleration for use by subsequent modules.

[0038] The Butterworth filter filters the front wheel acceleration to , the filtered wheel acceleration is ,but:

[0039]

[0040]

[0041] Among them, x is the wheel speed before filtering, y is the wheel speed after filtering, is the order of the designed filter, B0, B1, B2, A0, A1, A2 are the empirical parameters of the filter determined by experiments, z is a formula, according to the different indexes in the upper right corner, corresponding to the current moment, the previous moment, is the sampling frequency, i.e. the frequency at which the wheel acceleration signal is sent, which is consistent with the model period and is 0.005s; is the filter cutoff frequency, Indicates that the designed filter is a low-pass filter. is the matrix form of the above empirical parameters, The name of the function representing the Butterworth filter.

[0042] In the above technical solution, the specific method for the vehicle speed acquisition module to calculate the vehicle speed signal based on the vehicle wheel speed signal, the vehicle acceleration signal and the anti-lock braking system activation flag is as follows:

[0043] When the anti-lock braking system activation flag is not, the wheel speed signal of the current cycle identified by the vehicle speed acquisition module is Kalman filtered. The wheel speed signal is the wheel speed signal of the four wheels in one cycle. Select the largest wheel speed among the four vehicle wheel speeds and the third largest wheel speed Vehicle speed as a reference Estimated basis; when the reference vehicle speed <Third largest wheel speed When the reference vehicle speed is Increase the speed by a preset gradient (e.g., 0.65g acceleration, (0.65(g)*9.8*3.6*0.005(s), i.e. +0.115kph)) to a speed greater than or equal to the third largest wheel speed; when the reference vehicle speed is Greater than the first maximum wheel speed , let the reference vehicle speed Reduce the speed at a preset gradient (e.g., -1.25g acceleration, i.e., -0.225kph) until it is less than or equal to the first maximum wheel speed. ≤Reference vehicle speed ≤The first maximum wheel speed When the reference vehicle speed remain unchanged;

[0044] When the anti-lock braking system activation flag is yes, the wheel speed signal of the current cycle identified by the vehicle speed acquisition module is Kalman filtered. The wheel speed signal includes the wheel speed signals of the four wheels. Select the largest wheel speed among the four vehicle wheel speeds Vehicle speed as a reference Estimated benchmark, when referring to vehicle speed <The first maximum wheel speed When the reference vehicle speed is Increase with a preset gradient until it is greater than the first maximum wheel speed ; When the reference vehicle speed Greater than the first maximum wheel speed When the vehicle speed is The gradient of the decrease is ,in is the longitudinal acceleration of the vehicle body, when the reference vehicle body speed = Maximum wheel speed When the reference vehicle speed The reference vehicle speed after the above adjustment remains unchanged. The above design can obtain a relatively accurate vehicle speed signal under non-ABS and ABS working conditions.

[0045] The above vehicle wheel speed signal is filtered using the Kalman filter algorithm:

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054] in, is the posterior estimate of the wheel speed state variable; is the prior estimate of the state variable; is the state variable posterior error covariance matrix; is the state variable prior error covariance matrix; is the Kalman gain; It is the wheel speed signal; is the wheel speed signal after filtering by the Kalman algorithm, is the error covariance of wheel speed and wheel acceleration, A is the state variable matrix, is the transposed matrix of the state variables, is the process noise covariance matrix, is the observation matrix, is the transposed matrix of the observation matrix, is the measurement noise covariance matrix;

[0055] In the above technical solution, the driving intention recognition module is used to identify the driving intention based on the vehicle wheel speed signal, body speed signal, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle direction information, steep slope descent activation flag and low-speed off-road cruise activation flag. The specific method for obtaining the front and rear axle enable flags is as follows:

[0056] The system uses road slope information to determine whether the absolute value of the road slope is greater than the slope threshold. If it is less than or equal to the slope threshold, the current road surface is determined to be flat or has a very small slope. At this time, the rear axle is activated to prevent rear axle locking and maintain vehicle driving stability.

[0057] When the vehicle body speed is greater than a threshold value (such as 1km / h) for consecutive preset cycles (such as 20 cycles, 5 milliseconds per cycle) and the wheel speeds of all four wheels are 0, the front and rear axles are deactivated and it is considered that the vehicle is rolling down the slope. When the vehicle body speed is less than the set threshold value (such as 1km / h) for consecutive preset cycles (such as 20 cycles, 5 milliseconds per cycle) and the wheel speeds of all four wheels are 0, the front and rear axles are deactivated and it is considered that the vehicle is stopped. This stop may not mean that the vehicle is really completely stopped, but when this condition is met, the low-speed ABS will not work.

[0058] This design prevents parking and rolling down a slope, which deactivates low-speed ABS. (Rolling down a slope occurs when both wheel speeds are zero but the vehicle speed is greater than zero.) While rolling down a slope should theoretically be impossible, if it does occur, control should be discontinued. Ensure that ABS is not engaged when the vehicle is parked or rolling down a slope. When these conditions are detected, the front and rear axle enable flags are deactivated.

[0059] If the brake pedal is depressed and the master cylinder pressure is greater than 0, or the hill descent control system is activated and the master cylinder pressure is greater than 0, or the low-speed off-road cycle is activated and the master cylinder pressure is greater than 0 during the current cycle, it is judged as a braking condition. Otherwise, it is judged as a non-braking condition, in which case both the front and rear axles are inactive.

[0060] When the absolute value of the road gradient is greater than the gradient threshold, the vehicle speed is greater than a set threshold (e.g., 1 km / h), and all four wheel speeds are not zero, and the brake pedal is depressed and the master cylinder pressure is greater than zero, or the hill descent control system is activated and the master cylinder pressure is greater than zero, or the low-speed off-road cycle is activated and the master cylinder pressure is greater than zero, the vehicle's driving condition is determined by the vehicle's forward direction and the positive or negative value of the gradient. For example, if the vehicle is traveling forward and the gradient is less than zero, it is determined to be traveling downhill, and vehicle dynamics indicate that the rear axle is activated. If the vehicle is traveling forward and the gradient is greater than zero, it is determined to be traveling uphill, and vehicle dynamics indicate that the front axle is activated. If the vehicle is traveling in reverse and the gradient is greater than zero, it is determined to be traveling in reverse downhill, and vehicle dynamics indicate that the front axle is activated. If the vehicle is traveling in reverse and the gradient is less than zero, it is determined to be traveling in reverse uphill, and vehicle dynamics indicate that the front axle is activated. This design identifies the vehicle's driving condition and determines the enable flags for the front and rear axles.

[0061] In the above technical solution, the state machine module determines the operating state of the low-speed hill ABS system in the following manner: when the vehicle body speed LSA_VehSpd is greater than the low-speed hill ABS system's minimum exit speed (SpeedlowOFF) and the conventional ABS system reference speed v_Veh_x provided by the ECU is less than or equal to the low-speed hill ABS system's maximum entry speed (SpeedhighON), the low-speed hill ABS system's operating state switches from OFF to STANDBY. When the vehicle body speed LSA_VehSpd is less than the low-speed hill ABS system's minimum exit speed (SpeedlowOFF) or the conventional ABS system reference speed v_Veh_x provided by the ECU is greater than the low-speed hill ABS system's maximum entry speed (SpeedhighON), the low-speed hill ABS system's operating state switches from STANDBY to OFF. This design accurately controls the entry and exit speeds of the low-speed hill ABS.

[0062] In the above technical solution, the specific method for the control logic module to obtain the current slip rate of each wheel is:

[0063] (2)

[0064] in, is the wheel slip rate; is the wheel speed signal after Kalman algorithm filtering; is the vehicle body speed, and r is the wheel radius.

[0065] To avoid division by zero and zero vehicle speed, logic is added to the model to output the calculated slip ratio when the vehicle speed is greater than a certain value. If the vehicle speed is less than this value, the division is skipped and the output slip ratio is a constant. The maximum wheel cylinder pressures on the front and rear axles are recorded, as well as the maximum wheel pulse intervals on the front and rear axles. Because low-select control logic is used (for two wheels on the same axle, control intervenes as soon as one shows signs of locking, even if the other wheel has not yet shown signs of locking), the front and rear wheels are not controlled independently. Therefore, the wheel cylinder pressures and pulse intervals for the front and rear wheels must be determined. While the wheel cylinder pressures for both wheels (front or rear) are typically the same, they may differ. When these differ, the larger of the two wheel cylinder pressures is used for calculation to avoid a lower wheel cylinder pressure. The interval between the last pulse signal is important to prevent wheel locking. Therefore, the larger time interval between the front and rear wheels is used, and control is performed based on the wheel with the larger time interval and the wheel most likely to lock. The front and rear axle control logic is divided into two types: when the low-speed hill ABS system is not activated and when it is activated. Both front and rear axle control logic is identical.

[0066] In the above technical solution, the specific method for the control logic module to determine the wheel locking tendency and issue the corresponding low-speed slope anti-lock braking system control command is as follows:

[0067] When the working state of the low-speed ramp anti-lock braking system is OFF, the output left front wheel control command LSA_command_L1 and the right front wheel control command LSA_command_R1 are both 0, indicating that the low-speed ramp anti-lock braking system is OFF. At this time, the conventional anti-lock braking system is operating;

[0068] When the working state of the low-speed slope anti-lock braking system is Standby and the front axle enable flag is 1, the low-speed slope anti-lock braking system will be triggered after the following conditions are met, and the maximum wheel cylinder pressure value P when the low-speed slope anti-lock braking system starts to decompress will be recorded. max :

[0069]

[0070] is the left front wheel deceleration, a1 is the upper threshold of the wheel deceleration threshold, is the deceleration of the right front wheel; is the slip rate of the left front wheel, s1 is the upper threshold of the slip rate, s2 is the lower threshold of the slip rate, is the right front wheel slip rate, is the vehicle speed, It is the front axle enable flag. The minimum exit speed of the anti-lock braking system on a low-speed slope; Indicates that, Indicates or.

[0071] When the following conditions are met, the decompression is completed and the lowest wheel cylinder pressure P at this time is recorded. min :

[0072]

[0073] Wherein, a2 is the lower threshold of the wheel deceleration threshold, and slip is the slip rate.

[0074] When the working state of the low-speed slope anti-lock braking system changes from the inactive state to the active state (after the low-speed slope ABS issues the decompression command for the first time, it is considered that it has changed from the inactive state to the active state), the wheel cylinder will first enter the steady-state pressure maintenance state. After a certain period of time, it will be determined whether the wheel is in the locked state. If so, it will enter the non-steady-state control of the wheel. If not, the minimum wheel cylinder pressure P at this time will be recorded. min , and enter the steady-state control of the wheels:

[0075] Exit from the active state: When the current axis enable flag LSA_Enable_FA changes to 0, it will return to the inactive state, and the control command output of each wheel will be 0 (no control);

[0076] When the wheel is in non-steady-state control and the wheel cylinder performs the first decompression, the decompression times counting signal is 0 and the target wheel cylinder pressure is P min , in order to avoid the pressure reduction being less than P min When the difference between the estimated wheel cylinder pressure and the target pressure is less than a certain pressure, the wheel cylinder pressure enters the pressure holding stage in the pressure reduction phase. The counting signal is incremented by one. After a certain period of pressure holding, the pressure is reduced again. This time, the pressure reduction value is set to another fixed value. The control is exited and the pressure holding stage in the steady state is entered when the following conditions are met:

[0077]

[0078] When the wheel is in steady-state control and the wheel cylinder is pressurized for the first time, the counting signal is 0 and the pressure gradient of the first pressurization is (P max -P min) / 2, the gradient of subsequent boost is (P max -P min ) / 4. To avoid the situation where the boost value may be too small, the minimum value of the boost gradient is set to a certain pressure value. When the difference between the target pressure and the estimated wheel cylinder pressure is less than the set pressure value, or the time interval between the last pulse of the front wheel is greater than a certain time, the wheel cylinder will enter the pressure holding stage of the boost. After a certain pressure holding time and when the time interval between the last pulse is less than a certain value, the wheel cylinder will enter the pressure boost stage. The count number is increased by one. When the following conditions are met, the steady state is exited and the unsteady state control is entered. The highest pressure P at this time is recorded. max :

[0079]

[0080] in, Indicates the maximum value of the pulse time interval between the two wheels of the front axle.

[0081] Technical Solution 2

[0082] A wheel anti-lock braking method suitable for braking on a slope comprises the following steps:

[0083] Step 1: Identify the vehicle wheel speed signal and wheel acceleration signal under the slope condition;

[0084] Step 2: Calculate the vehicle body speed signal based on the vehicle wheel speed signal, the vehicle body acceleration signal, and the anti-lock braking system activation flag;

[0085] Step 3: Identify the driving intention based on the vehicle wheel speed signal, body speed signal, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle direction information, steep slope descent activation flag, and low-speed off-road cruise activation flag, and obtain the front and rear axle enable flags;

[0086] Step 4: Determine whether the low-speed hill ABS system is in standby mode or disabled based on the vehicle body speed, the conventional ABS reference speed, and the preset speed threshold for entering or exiting the low-speed hill ABS system. If the low-speed hill ABS system is disabled, activate the conventional ABS system. The state machine module receives the front and rear axle enable flags and transmits them to the control logic module when the low-speed hill ABS system is in standby mode.

[0087] Step 5: Obtain the current wheel slip rate and wheel cylinder pressure signal based on the vehicle wheel speed signal, body speed signal, front and rear axle enable flags, steep slope descent function activation flag, low-speed off-road cycle function activation flag and four-wheel control mode signal, and determine whether the wheel has a locking tendency based on the current wheel slip rate, wheel cylinder pressure signal and wheel acceleration, and issue a low-speed slope anti-lock braking system control command when the wheel has a locking tendency.

[0088] In step 1, the ECU identifies the wheel speed value based on the number of pulses generated by the wheel speed sensor in each cycle and the cumulative interval time between the pulse signals generated by the wheel speed sensor in each cycle. Through estimation and filtering, it effectively identifies the wheel speed under low-speed (below 15kph) off-road conditions and calculates the wheel acceleration, providing wheel speed and wheel acceleration signals to subsequent modules.

[0089] In step 2, the vehicle body speed signal is estimated using the wheel speed signal, longitudinal acceleration signal, and anti-lock braking system activation flag signal. Under slope braking conditions, the vehicle body speed signal can be effectively estimated when the wheel speed is separated from the vehicle speed, providing the vehicle body speed signal for the control logic and state machine parts.

[0090] In step 3, the driving intention is identified based on the vehicle wheel speed signal, body speed signal, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle driving direction information, steep slope descent activation flag and low-speed off-road cruise activation flag, and the front and rear axle enable flags are obtained. At the same time, the driving condition information is obtained. The driving condition information includes reverse downhill, forward downhill, non-slope driving, forward uphill, reverse uphill and non-braking conditions, which provide a reference for the control logic. According to the different identified conditions, the corresponding control threshold values ​​will be calibrated or compensated respectively.

[0091] In step 4, the state machine module determines the operating state of the low-speed hill-drift anti-lock braking system (SAS), including standby and off, based on the conventional ABS reference speed signal and the speed signal obtained by the low-speed vehicle estimation module. SAS switches with the conventional wheel ABS system based on the reference speed (in most cases, only one is active. However, to prevent frequent switching, a short range near the speed threshold allows both to be activated, but the conventional ABS control command takes precedence). ABS control activation is determined based on the wheel state (activation occurs when the ABS system issues its first pressure reduction command. If either the wheel slip rate or wheel acceleration exceeds the threshold, either a pressure reduction command or a pressure maintenance command is executed). The conventional ABS's decision is primary, and only one of the two can be active at a time.

[0092] This technical solution uses the control logic module in step five to determine the wheel's motion state based on real-time information such as wheel speed, wheel acceleration, processed pulse time interval signals, reference vehicle speed, and slip ratio. When a wheel shows a clear tendency to lock (when the current wheel deceleration exceeds a threshold), the brake pressure is promptly adjusted (first implementing a pressure hold command, and then, if the slip ratio continues to increase, implementing a pressure reduction command or a pressure hold command during pressure reduction). This prevents prolonged wheel locking and ultimately improves the vehicle's braking safety and lateral stability. This reduces wheel locking when braking on a slope while traveling at low speed, ensuring directional stability while also improving braking efficiency and active safety during braking.

[0093] Technical Solution 3

[0094] A computer-readable storage medium stores a computer program, which implements the steps of the above method when executed by a processor.

[0095] Technical Solution 4

[0096] A computer program product comprises a computer program, wherein the computer program implements the steps of the above method when executed by a processor.

[0097] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

Claims

1. A wheel anti-lock braking system suitable for braking on a slope, comprising: The wheel speed recognition module is used to identify the vehicle wheel speed signal and wheel acceleration signal under slope conditions; The vehicle speed acquisition module is used to calculate the vehicle speed signal based on the vehicle wheel speed signal, the vehicle acceleration signal and the anti-lock braking system activation flag; The driving intention recognition module is used to identify the driving intention based on the vehicle wheel speed signal, body speed signal, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle direction information, steep slope descent activation flag and low-speed off-road cruise activation flag, and obtain the front and rear axle enable flags; The state machine module is used to determine whether the low-speed ramp anti-lock braking system is in standby or disabled based on the vehicle body speed, the conventional anti-lock braking system reference speed, and the preset speed threshold for entering or exiting the low-speed ramp anti-lock braking system, and to determine whether the conventional anti-lock braking system is activated based on the activation conditions of the conventional anti-lock braking system. The state machine module receives the front and rear axle enable flags and transmits the front and rear axle enable flags to the control logic module when the low-speed ramp anti-lock braking system is in standby state. The control logic module is used to obtain the current wheel slip rate and wheel cylinder pressure signal based on the vehicle wheel speed signal, body speed signal, front and rear axle enable flag, steep slope descent function activation flag, low-speed off-road cycle function activation flag and four-wheel control mode signal, and judge whether the wheel has a locking tendency based on the current wheel slip rate, wheel cylinder pressure signal and wheel acceleration, and issue a low-speed slope anti-lock braking system control instruction when the wheel has a locking tendency.

2. The wheel anti-lock braking system suitable for hill braking according to claim 1, further comprising an ABS degradation or shutdown judgment module, the ABS degradation or shutdown judgment module being used to control the wheel anti-lock braking system to perform functional degradation or functional shutdown according to vehicle fault information.

3. The wheel anti-lock braking system suitable for hill braking according to claim 2, wherein: The ABS degradation or shutdown judgment module controls the low-speed slope anti-lock braking system function degradation when receiving the chassis domain controller power overvoltage or undervoltage fault, emergency braking function EPS failure fault, slope signal abnormality, vehicle acceleration signal abnormality, steep hill descent function activation flag abnormality and / or low-speed off-road cruise function activation flag abnormality; The ABS degradation or shutdown judgment module controls the low-speed slope anti-lock braking system function to be shut down when receiving CAN network communication failure, abnormal pulse count signal and cumulative time interval signal for calculating wheel speed, abnormal brake pedal status and / or abnormal master cylinder pressure signal.

4. The wheel anti-lock braking system suitable for hill braking according to claim 3, wherein: In the low-speed hill ABS function degradation mode, the low-speed hill ABS controller will run a redundant control strategy that relies on minimal sensor signals in the backup core; in the low-speed hill ABS function shutdown mode, the low-speed hill ABS will exit the active state.

5. The wheel anti-lock braking system suitable for hill braking according to claim 1, wherein: Under slope conditions, the wheel speed recognition module receives the wheel speed sensor pulse number signal and wheel speed sensor pulse accumulation time interval signal sent by the ECU in each sampling period, and calculates the vehicle wheel speed signal using the following formula: （1） in, For each sampling period, the wheel speed sensor pulse number signal is: is the wheel speed sensor pulse accumulation time interval signal; the wheel speed sensor gear ring number and tire circumference are inherent parameters of the wheel, and the vehicle wheel speed calculated at this time is the real vehicle wheel speed signal; When the wheel speed recognition module fails to read the wheel speed sensor pulse count signal and / or wheel speed sensor pulse accumulation time interval signal sent by the ECU, it calculates the vehicle wheel speed using the following method: First, the wheel speed sensor pulse accumulation time interval signal in the previous sampling period with wheel speed sensor pulse signal As a benchmark, when the cumulative time without wheel speed sensor pulse signal is less than the wheel speed sensor pulse cumulative time interval signal in the previous sampling period with wheel speed sensor pulse signal When the wheel speed maintains the vehicle wheel speed calculated in the last sampling period with wheel speed sensor pulse signal, the accumulated time when there is no wheel speed sensor pulse signal is greater than the wheel speed sensor pulse accumulated time interval signal in the last sampling period with wheel speed sensor pulse signal. When the wheel speed sensor pulse accumulation time interval signal is The preset time is accumulated based on the current sampling period, and the wheel speed sensor pulse number signal of the current sampling period maintains the wheel speed sensor pulse number signal in the previous sampling period with a wheel speed sensor pulse signal. , and use formula 1 to calculate the vehicle wheel speed. The calculated vehicle wheel speed at this time is the estimated vehicle wheel speed signal.

6. The wheel anti-lock braking system suitable for hill braking according to claim 5, wherein: When the wheel speed of the current cycle is the real vehicle wheel speed signal, the wheel speed recognition module calculates the wheel acceleration signal using the real vehicle wheel speed signal; When the wheel speed of the current cycle is the estimated vehicle wheel speed signal, the wheel speed identification module uses the last real vehicle wheel speed signal and wheel acceleration signal to estimate the wheel acceleration signal of the current sampling cycle. Specifically, when there is no real wheel speed signal and the estimated wheel speed maintains the real wheel speed of the previous sampling cycle, the wheel acceleration signal is estimated by accumulating the running loop cycle based on the wheel speed difference signal obtained in the previous sampling cycle and the time difference corresponding to the wheel speed difference of the previous sampling cycle. Then, the wheel acceleration signal is filtered using a Butterworth digital filter to obtain an accurate wheel acceleration signal.

7. [Corrected 12.10.2024 according to Article 91] The anti-lock braking system for hill braking according to claim 1, wherein: The specific method for the vehicle speed acquisition module to calculate the vehicle speed signal based on the vehicle wheel speed signal, the vehicle acceleration signal and the anti-lock braking system activation flag is as follows: When the anti-lock braking system activation flag is false, the wheel speed signal of the current cycle identified by the vehicle speed acquisition module is subjected to Kalman filtering. The wheel speed signal includes the wheel speed signals of the four wheels, and the largest wheel speed ω of the four vehicle wheel speeds is selected from the wheel speed signal LSA_vkalman after Kalman filtering. max1 and the third largest wheel speed ω max3 As a reference vehicle body speed V ref Estimation basis; when the reference vehicle speed V ref <The third largest wheel speedω max3 When the reference vehicle speed V ref Increase with a preset gradient to a speed greater than or equal to the third largest wheel speed; when the reference vehicle speed V ref Greater than the first maximum wheel speed ω max1 When the reference vehicle speed V ref Reduce the wheel speed with a preset gradient until it is less than or equal to the first maximum wheel speed; when the third maximum wheel speed ω max3 ≤Reference vehicle speed V ref ≤The first maximum wheel speedω max1 When the reference vehicle speed V ref remain unchanged; When the anti-lock braking system activation flag is yes, the wheel speed signal of the current cycle identified by the vehicle speed acquisition module is subjected to Kalman filtering. The wheel speed signal includes the wheel speed signals of the four wheels, and the largest wheel speed ω of the four vehicle wheel speeds is selected from the wheel speed signal LSA_vkalman after Kalman filtering. max1 As a reference vehicle body speed V ref The estimated basis, when the reference vehicle speed V ref <When the first maximum wheel speed is ω max1 , let the reference vehicle speed V ref Increase with a preset gradient until it is greater than the first maximum wheel speed ω max1 ; When the reference vehicle speed V ref Greater than the first maximum wheel speed ω max1 When the reference vehicle speed V ref The gradient of the decrease is a x , where a x is the longitudinal acceleration of the vehicle body, when the reference vehicle body speed V ref = Maximum wheel speed ω max1 , reference body V ref The speed remains unchanged, and the reference vehicle speed V after the adjustment is ref It is the vehicle speed signal.

8. The wheel anti-lock braking system suitable for hill braking according to claim 1, wherein: The driving intention recognition module is used to identify the driving intention based on the vehicle wheel speed signal, body speed signal, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle direction information, steep slope descent activation flag and low-speed off-road cruise activation flag. The specific method for obtaining the front and rear axle enable flags is as follows: The system uses road slope information to determine whether the absolute value of the road slope is greater than the slope threshold. If it is less than or equal to the slope threshold, the current road surface is determined to be flat or has a very small slope. At this time, the rear axle is activated to prevent the rear axle from locking. When the vehicle body speed is greater than the threshold value for consecutive preset periods and the four wheel speeds are all 0, the front and rear axles are deactivated and it is considered to be rolling down the slope. When the vehicle body speed is less than the set threshold value for consecutive preset periods and the four wheel speeds are all 0, the front and rear axles are deactivated. If the brake pedal is depressed and the master cylinder pressure is greater than 0, or the hill descent control system is activated and the master cylinder pressure is greater than 0, or the low-speed off-road cycle is activated and the master cylinder pressure is greater than 0 during the current cycle, it is judged as a braking condition. Otherwise, it is judged as a non-braking condition, in which case both the front and rear axles are inactive. When the absolute value of the road slope is greater than the slope threshold, and the vehicle speed is greater than the set threshold and the wheel speeds of the four wheels are not all 0, and at the same time, the brake pedal state in the current cycle is depressed and the master cylinder pressure is greater than 0, or the steep slope descent system is activated and the master cylinder pressure is greater than 0, or the low-speed off-road cycle is activated and the master cylinder pressure is greater than 0, then the vehicle's forward direction and the positive and negative values ​​of the slope are provided to judge the vehicle's driving condition.

9. The wheel anti-lock braking system suitable for hill braking according to claim 1, wherein: The specific method for the state machine module to determine the working state of the low-speed ramp anti-lock braking system is as follows: when the vehicle body speed LSA_VehSpd is greater than the minimum exit speed SpeedlowOFF of the low-speed ramp anti-lock braking system, and the conventional anti-lock braking system reference speed v_Veh_x provided by the ECU is less than or equal to the maximum entry speed SpeedhighON of the low-speed ramp anti-lock braking system, the working state of the low-speed ramp anti-lock braking system is switched from OFF to Standby; when the vehicle body speed LSA_VehSpd is less than the minimum exit speed SpeedlowOFF of the low-speed ramp anti-lock braking system or the conventional anti-lock braking system reference speed v_Veh_x provided by the ECU is greater than the maximum entry speed SpeedhighON of the low-speed ramp anti-lock braking system, the working state of the low-speed ramp anti-lock braking system is switched from Standby to OFF.

10. The wheel anti-lock braking system suitable for hill braking according to claim 1, wherein: The specific method for the control logic module to obtain the current slip rate of each wheel is: （2） in, is the wheel slip rate; is the wheel speed signal after Kalman algorithm filtering; is the vehicle body speed; r is the wheel radius.

11. The wheel anti-lock braking system suitable for hill braking according to claim 1, wherein: The specific method by which the control logic module determines the wheel locking tendency and issues the corresponding low-speed ramp anti-lock braking system control command is as follows: When the working state of the low-speed ramp anti-lock braking system is OFF, the output left front wheel control command LSA_command_L1 and the right front wheel control command LSA_command_R1 are both 0, indicating that the low-speed ramp anti-lock braking system is OFF. At this time, the conventional anti-lock braking system is operating; When the working state of the low-speed slope anti-lock braking system is Standby and the front axle enable flag is 1, the low-speed slope anti-lock braking system will be triggered after the following conditions are met, and the maximum wheel cylinder pressure value P when the low-speed slope anti-lock braking system starts to decompress will be recorded. max : ； is the left front wheel deceleration, a1 is the upper threshold of the wheel deceleration threshold, is the deceleration of the right front wheel; is the slip rate of the left front wheel, s1 is the upper slip rate threshold, s2 is the lower slip rate threshold, is the right front wheel slip rate, is the vehicle speed, It is the front axle enable flag. The minimum exit speed of the anti-lock braking system on a low-speed slope; Indicates that, means or; When the following conditions are met, the decompression is completed and the lowest wheel cylinder pressure P at this time is recorded. min : ； Wherein, a2 is the lower threshold of wheel deceleration threshold value, and slip is the slip rate; When the low-speed slope anti-lock braking system changes from the inactive state to the active state, the wheel cylinder will first enter the steady-state pressure maintenance state. After a certain period of time, it is determined whether the wheel is in the locked state. If so, it enters the non-steady-state control of the wheel. If not, the minimum wheel cylinder pressure P at this time is recorded. min , and enter the steady-state control of the wheels: Exit from the active state: When the current axis enable flag LSA_Enable_FA changes to 0, it will return to the inactive state, and the control command output of each wheel will be 0; When the wheel is in non-steady-state control and the wheel cylinder performs the first decompression, the decompression times counting signal is 0 and the target wheel cylinder pressure is P min When the difference between the estimated wheel cylinder pressure and the target pressure is less than a certain pressure, the wheel cylinder pressure enters the pressure holding stage in the pressure reduction phase. The counting signal is incremented by one. After a certain period of pressure holding, the pressure is reduced again. This time, the pressure reduction value is set to another fixed value. The control is exited and the pressure holding stage in the steady state is entered when the following conditions are met: ； When the wheel is in steady-state control and the wheel cylinder is pressurized for the first time, the counting signal is 0 and the pressure gradient of the first pressurization is (P max -P min ) / 2, the gradient of subsequent boost is (P max -P min ) / 4. To avoid the situation where the boost value may be too small, the minimum value of the boost gradient is set to a certain pressure value. When the difference between the target pressure and the estimated wheel cylinder pressure is less than the set pressure value, or the time interval between the last pulse of the front wheel is greater than a certain time, the wheel cylinder will enter the pressure holding stage of the boost. After a certain pressure holding time and when the time interval between the last pulse is less than a certain value, the wheel cylinder will enter the pressure boost stage. The count number is increased by one. When the following conditions are met, the steady state is exited and the unsteady state control is entered. The highest pressure P at this time is recorded. max : ； in, Indicates the maximum value of the pulse time interval between the two wheels of the front axle.

12. A wheel anti-lock braking method suitable for braking on a slope, wherein: The steps include: Step 1: Identify the vehicle wheel speed signal and wheel acceleration signal under the slope condition; Step 2: Calculate the vehicle body speed signal based on the vehicle wheel speed signal, the vehicle body acceleration signal, and the anti-lock braking system activation flag; Step 3: Identify the driving intention based on the vehicle wheel speed signal, body speed signal, road slope information, brake master cylinder pressure information, brake pedal status information, vehicle direction information, steep slope descent activation flag, and low-speed off-road cruise activation flag, and obtain the front and rear axle enable flags; Step 4: Determine whether the low-speed hill ABS system is in standby mode or disabled based on the vehicle body speed, the conventional ABS reference speed, and the preset speed threshold for entering or exiting the low-speed hill ABS system. If the low-speed hill ABS system is disabled, activate the conventional ABS system. The state machine module receives the front and rear axle enable flags and transmits them to the control logic module when the low-speed hill ABS system is in standby mode. Step 5: Obtain the current wheel slip rate and wheel cylinder pressure signal based on the vehicle wheel speed signal, body speed signal, front and rear axle enable flags, steep slope descent function activation flag, low-speed off-road cycle function activation flag and four-wheel control mode signal, and determine whether the wheel has a locking tendency based on the current wheel slip rate, wheel cylinder pressure signal and wheel acceleration, and issue a low-speed slope anti-lock braking system control command when the wheel has a locking tendency.

13. A computer-readable storage medium storing a computer program, wherein: When the computer program is executed by a processor, the steps of the method according to claim 12 are implemented.

14. A computer program product comprising a computer program, wherein When the computer program is executed by a processor, the steps of the method according to claim 12 are implemented.

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