Wheel anti-lock braking system and method suitable for hill braking

Abstract

The present invention discloses a wheel anti-lock braking system suitable for hill braking. Its wheel speed recognition module is used to identify vehicle wheel speed signals and wheel acceleration signals; the vehicle speed acquisition module is used to calculate the vehicle body speed signal; the driving intention recognition module is used to obtain front and rear axle enable flags; a state machine module is used to determine whether the low-speed hill anti-lock braking system is in standby or off mode, and when the low-speed hill anti-lock braking system is off mode, activates the conventional anti-lock braking system; the state machine module receives the front and rear axle enable flags and transmits them to a control logic module when the low-speed hill anti-lock braking system is in standby mode; and the control logic module is used to issue a low-speed hill anti-lock braking system control command when a wheel shows a tendency to lock. The present invention achieves low-speed, particularly hill anti-lock braking, anti-lock control of wheels that cannot be achieved by conventional wheel anti-lock braking systems.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle braking, and in particular to a wheel anti-lock braking system and method suitable for braking on a slope. Background Art

[0002] 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. Consequently, vehicles traveling at low speeds on off-road slopes and low-lying surfaces suffer from poor stability, making them prone to skidding and loss of control.

[0003] 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.

[0004] 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.

[0005] Therefore, there is an urgent need to develop an anti-lock braking system (ABS) that can be activated under low-speed off-road slope conditions to compensate for the shortcomings of conventional ABS systems in such braking conditions. ABS systems for hill braking achieve low-speed, especially hill braking, anti-lock control, which is unattainable with conventional ABS systems, by estimating the vehicle's wheel speed and vehicle speed at low speeds, identifying the driver's driving intent, and incorporating mode switching control logic for these conditions. ABS systems for hill braking ensure vehicle stability while also balancing braking performance. Developing an ABS system suitable for low-speed braking, particularly for off-road slopes, has become a pressing issue. Summary of the Invention

[0006] The purpose of this invention 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 intent, 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.

[0007] To achieve this purpose, the present invention is designed to provide 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;

[0008] 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;

[0009] 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;

[0010] 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.

[0011] 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.

[0012] Beneficial effects of the present invention:

[0013] The present invention 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 mode switching control logic for 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 anti-lock braking systems. Compared with conventional anti-lock braking systems that exit control at a certain higher vehicle speed, the present invention reduces wheel locking under braking conditions in low-speed off-road slope conditions, 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

[0014] Figure 1 A schematic diagram of signal transmission of an anti-lock braking system for wheels applicable to hill braking according to the present invention;

[0015] Figure 2 This is a working flow diagram of a driving intention recognition module of an anti-lock braking system for hill braking according to the present invention;

[0016] Figure 3 This is a schematic diagram of wheel speed calculation of the low-speed wheel speed recognition module of the present invention;

[0017] Figure 4 This is a working diagram of the state machine module in the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0019] Example 1:

[0020] like Figures 1 to 4 A wheel anti-lock braking system suitable for braking on a slope is shown, characterized in that it includes: a wheel speed recognition module for recognizing a vehicle wheel speed signal and a wheel acceleration signal under a slope condition;

[0021] The vehicle speed acquisition module is used to calculate the vehicle body speed signal based on the vehicle wheel speed signal, the vehicle body acceleration signal (obtained by the wheel inertial navigation system) and the anti-lock braking system activation flag;

[0022] The driving intention recognition module is used to identify the driving intention based on the vehicle's 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 (below 15kph is considered low speed) to obtain the front and rear axle enable flags;

[0023] The state machine module is used to determine whether the working state of the low-speed ramp anti-lock braking system is standby or the function is turned off based on the vehicle body speed, the reference speed of the conventional anti-lock braking system, 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), and to determine whether the conventional anti-lock braking system is activated based on the activation conditions of the conventional anti-lock braking system. If the low-speed ramp anti-lock braking system and the conventional anti-lock braking system meet the activation conditions at the same time, 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 working state of the low-speed ramp anti-lock braking system is standby;

[0024] 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 command (boost, decompression and pressure maintenance signals) when the wheel has a locking tendency.

[0025] 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.

[0026] 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.

[0027] 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;

[0028] 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.

[0029] 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.

[0030] 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:

[0031]

[0032] Where Wss_edges is the number of wheel speed sensor pulses per sampling period, delta_time is the accumulated time interval of wheel speed sensor pulses; the number of wheel speed sensor gear rings and the tire circumference are inherent parameters of the wheel, and the calculated vehicle wheel speed at this time is the actual vehicle wheel speed signal;

[0033] 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:

[0034] First, the wheel speed sensor pulse accumulation time interval signal delta_time in the previous sampling period with a wheel speed sensor pulse signal is used as a reference. When the accumulation time without a wheel speed sensor pulse signal is less than the wheel speed sensor pulse accumulation time interval signal delta_time in the previous sampling period with a wheel speed sensor pulse signal, the wheel speed maintains the vehicle wheel speed calculated in the previous sampling period with a wheel speed sensor pulse signal. When the accumulation time without a wheel speed sensor pulse signal is greater than the wheel speed sensor pulse accumulation time interval signal delta_time in the previous sampling period with a wheel speed sensor pulse signal, a preset time is accumulated based on the wheel speed sensor pulse accumulation time interval signal delta_time in the previous sampling period with a wheel speed sensor pulse signal, and the wheel speed sensor pulse number signal in the current sampling period maintains the wheel speed sensor pulse number signal Wss_edges in the previous sampling period with a wheel speed sensor pulse signal. The vehicle wheel speed is calculated using Formula 1. The vehicle wheel speed calculated at this time is the estimated vehicle wheel speed signal. When the vehicle is traveling at very low speeds, the aforementioned signals may not be received for several or even dozens of cycles. Consequently, there is no true wheel speed signal, and the aforementioned method is required to estimate the wheel speed. Even at low speeds, when there are no valid and accurate input signals, a relatively accurate wheel speed can still be obtained.

[0035] 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;

[0036] When the wheel speed of the current cycle is an 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 (the running cycle of the model code) 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. 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 certain cases of abnormally large acceleration. This processing of the wheel acceleration makes it more suitable for the wheel acceleration requirements in the control logic module. When the real wheel speed is available, the wheel acceleration is directly calculated. When the real wheel speed is not available, the wheel acceleration is estimated accordingly for use by subsequent modules.

[0037] The Butterworth filter filters the front wheel acceleration to x[N] and the rear wheel acceleration to y[N], then:

[0038]

[0039] [B,A]=butter(order,fc / (fs / 2),'low')

[0040] Among them, x is the wheel speed before filtering, y is the wheel speed after filtering, order is the order of the designed filter, B0, B1, B2, A0, A1, A2 are the empirical parameters of the filter determined by experiments, and z is a formula. According to the different indices in the upper right corner, they correspond to the current moment, the previous moment, and f c is the sampling frequency, i.e. the frequency of the wheel acceleration signal, which is consistent with the model period and is 0.005s; f s is the filter cutoff frequency, low indicates that the designed filter is a low-pass filter, [B, A] is the matrix form of the above empirical parameters, butter indicates the function name of the Butterworth filter,

[0041] 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:

[0042] 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 in one cycle. 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 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 V ref Greater than the first maximum wheel speed ω max1 When the reference vehicle speed V ref The speed is reduced by a preset gradient (e.g., by an acceleration of -1.25g, i.e., a gradient of -0.225kph) 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 max1When the reference vehicle speed V ref remain unchanged;

[0043] 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 <The first maximum wheel speedω max1 When 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 When the reference vehicle speed V ref The reference vehicle speed V after the above adjustment remains unchanged. ref The above design can obtain a relatively accurate vehicle speed signal under non-ABS and ABS working conditions.

[0044] The above vehicle wheel speed signal is filtered using the Kalman filter algorithm:

[0045] Xk = [0; 0]

[0046] Pk=[1e6,0;0,1e6]

[0047] Xk_1=A×Xk

[0048] Pk_1=A×Pk×A T +Q

[0049] Kk=(Pk_1×H T )÷(H×Pk_1×H T +R)

[0050] Xk=(Xk_1+K k ×(Z K -H×Xk_1))

[0051] LSA_vkalman=[1,0]×Xk

[0052] Pk=(I-Kk×H)×Pk_1

[0053] Among them, Xk is the posterior estimate of the wheel speed state variable; Xk_1 is the prior estimate of the state variable; Pk is the posterior error covariance matrix of the state variable; PK_1 is the prior error covariance matrix of the state variable; K K is the Kalman gain; Z K is the wheel speed signal; LSA_vkalman is the wheel speed signal after Kalman algorithm filtering, 1e6 is the error covariance of wheel speed and wheel acceleration, A is the state variable matrix, A T is the transposed matrix of the state variable, Q is the process noise covariance matrix, H is the observation matrix, and H T is the transposed matrix of the observation matrix, R is the measurement noise covariance matrix;

[0054] 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:

[0055] 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.

[0056] When the vehicle body speed is greater than a threshold value (such as 1 km / 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 1 km / 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.

[0057] This design prevents parking and rolling down a slope, which deactivates low-speed ABS. (Rolling down a slope: wheel speeds are both 0, but vehicle speed is greater than 0.) While rolling down a slope shouldn't theoretically occur, if it does, the system should not engage the ABS. 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.

[0058] 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.

[0059] When the absolute value of the road slope is greater than the slope 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 forward direction and the positive and negative values ​​of the slope are used to determine the vehicle's driving condition. For example, if the vehicle is traveling forward and the slope 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 slope 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 slope 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 slope 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 can identify the vehicle's driving condition and determine the enable flags for the front and rear axles.

[0060] 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.

[0061] In the above technical solution, the specific method for the control logic module to obtain the current slip rate of each wheel is:

[0062]

[0063] Where s is the wheel slip rate; ω is the wheel speed signal after Kalman filtering; LSA_VehSpd is the vehicle body speed, and r is the wheel radius.

[0064] 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 slip ratio output is a constant. The maximum wheel cylinder pressures on the front and rear axles are recorded, as well as the maximum pulse intervals between the left and right wheels. Because low-select control logic is used (for two wheels on the same axle, control is initiated 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 wheel with the longer interval, front or rear, is used for control, based on the wheel with the longer 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 share the same logic.

[0065] 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:

[0066] 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;

[0067] 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 :

[0068] ((a_FL<-a1&&a_FR<-a1&&slip_FL>s1&&slip_FR>s1)||slip_FL>s2

[0069] ||slip_FR>s2)&&LSA_VehSpd>SpeedlowOFF&&LSA_Enable_FA

[0070] a_FL is the left front wheel deceleration, a1 is the upper deceleration threshold, a_FR is the right front wheel deceleration; slip_FL is the left front wheel slip rate, s1 is the upper slip rate threshold, s2 is the lower slip rate threshold, slip_FR is the right front wheel slip rate, LSA_VehSpd is the vehicle body speed, LSA_Enable_FA is the front axle enable flag, LSA_Enable_FA is equal to 1, SpeedlowOFF is the minimum exit speed of the low-speed ramp anti-lock braking system; && represents and, || represents 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] (a_FL>a2||(slip<s1&&a_FL>-a1))&&(a_FR>a2

[0073] ||(slip_FR<s1&&a_FR>-a1))

[0074] Wherein, a2 is the lower threshold of the wheel deceleration threshold, and slip is the slip rate.

[0075] When the working state of the low-speed slope anti-lock braking system changes from inactive to active state (after the low-speed slope ABS issues a decompression command for the first time, it is considered that it has changed from inactive to active), the wheel cylinder will first enter a steady-state pressure maintenance state. After a certain period of time, it will be determined whether the wheel is in a 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:

[0076] Exit from the active state: When the current axis enable flag LSA_Enable_FA becomes 0, it will return to the inactive state, and the control command output of each wheel will be 0 (no control);

[0077] 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:

[0078] (a_FL>a2||(slip_FL<s1&&a_FL>-a1))

[0079] &&(a_FR>a2||(slip_FR<s1&&a_FR>-a1))

[0080] 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 possibility of a single boost value being 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 :

[0081] a_FL<-a1||a_FR<-a1||slip_FL>s2

[0082] ||slip_FR>s2||LSA_dert_FA>=0.3

[0083] Among them, LSA_dert_FA represents the maximum value of the time interval between the two wheel pulses on the front axle.

[0084] Example 2:

[0085] A wheel anti-lock braking method suitable for braking on a slope comprises the following steps:

[0086] Step 1: Identify the vehicle wheel speed signal and wheel acceleration signal under the slope condition;

[0087] 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;

[0088] 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;

[0089] 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.

[0090] 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.

[0091] 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, the wheel speed is effectively identified under low-speed (below 15kph) off-road conditions, and the wheel acceleration is calculated to provide wheel speed and wheel acceleration signals to the subsequent modules.

[0092] 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.

[0093] 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.

[0094] In step 4, the state machine module determines the operating state of the low-speed hill-drift anti-lock braking system (STAB) based on the conventional ABS reference speed signal and the speed signal obtained by the low-speed vehicle estimation module. The system switches between the conventional and wheel anti-lock braking systems 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 activation is determined based on the wheel state (activation occurs when the wheel anti-lock braking 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.

[0095] In this embodiment, the control logic module in step five determines the wheel's motion state based on real-time information such as wheel speed, wheel acceleration, processed pulse interval signal, reference vehicle speed, and slip ratio. When a wheel shows a clear tendency to lock (when the front 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 a pressure reduction period). 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 the vehicle is traveling at low speed, ensuring directional stability while also improving braking efficiency and active safety during braking.

[0096] Example 3:

[0097] A computer-readable storage medium stores a computer program, which implements the steps of the above method when executed by a processor.

[0098] Example 4:

[0099] A computer program product comprises a computer program, wherein when the computer program is executed by a processor, the steps of the above method are implemented.

[0100] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A wheel anti-lock braking system suitable for braking on a slope, characterized in that: include: 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, characterized in that: It also includes an ABS degradation or shutdown judgment module, which is used to control the wheel anti-lock braking system to perform function degradation or function shutdown according to vehicle fault information.

3. The wheel anti-lock braking system suitable for hill braking according to claim 2, characterized in that: 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, characterized in that: 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, characterized in that: 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: Where Wss_edges is the number of wheel speed sensor pulses per sampling period, delta_time is the accumulated time interval of wheel speed sensor pulses; the number of wheel speed sensor gear rings and the tire circumference are inherent parameters of the wheel, and the calculated vehicle wheel speed at this time is the actual 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 delta_time in the previous sampling period with a wheel speed sensor pulse signal is used as a reference. When the accumulation time without a wheel speed sensor pulse signal is less than the wheel speed sensor pulse accumulation time interval signal delta_time in the previous sampling period with a wheel speed sensor pulse signal, the wheel speed maintains the vehicle wheel speed calculated in the previous sampling period with a wheel speed sensor pulse signal. When the accumulation time without a wheel speed sensor pulse signal is greater than the wheel speed sensor pulse accumulation time interval signal delta_time in the previous sampling period with a wheel speed sensor pulse signal, a preset time is accumulated based on the wheel speed sensor pulse accumulation time interval signal delta_time in the previous sampling period with a wheel speed sensor pulse signal, and the wheel speed sensor pulse number signal in the current sampling period maintains the wheel speed sensor pulse number signal Wss_edges in the previous sampling period with a wheel speed sensor pulse signal. The vehicle wheel speed is calculated using Formula 1. The vehicle wheel speed calculated 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, characterized in that: 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. The wheel anti-lock braking system suitable for hill braking according to claim 1, characterized in that: 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 <The first maximum wheel speedω max1 When 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 When the reference vehicle speed V ref The reference vehicle speed V after the above adjustment remains unchanged. ref It is the vehicle speed signal.

8. The wheel anti-lock braking system suitable for hill braking according to claim 1, characterized in that: 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, characterized in that: 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, characterized in that: The specific method for the control logic module to obtain the current slip rate of each wheel is: Where s is the wheel slip rate; ω is the wheel speed signal after Kalman filtering; LSA_VehSpd is the vehicle body speed; and r is the wheel radius.

11. The wheel anti-lock braking system suitable for hill braking according to claim 1, characterized in that: 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 : ((a_FL<-a1&&a_FR<-a1&&slip_FL>s1&&slip_FR>s1)||slip_FL>s2 ||slip_FR>s2)&&LSA_VehSpd>SpeedlowOFF&&LSA_Enable_FA a_FL is the deceleration of the left front wheel, a1 is the upper deceleration threshold, a_FR is the deceleration of the right front wheel; slip_FL is the slip rate of the left front wheel, s1 is the upper slip rate threshold, s2 is the lower slip rate threshold, slip_FR is the slip rate of the right front wheel, LSA_VehSpd is the vehicle body speed, LSA_Enable_FA is the front axle enable flag, LSA_Enable_FA is 1, SpeedlowOFF is the minimum exit speed of the low-speed ramp anti-lock braking system; && represents and, || represents or; When the following conditions are met, the decompression is completed and the lowest wheel cylinder pressure P at this time is recorded. min : (a_FL>a2||(slip<s1&&a_FL>-a1))&&(a_FR>a2 ||(slip_FR<s1&&a_FR>-a1)) 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: (a_FL>a2||(slip_FL<s1&&a_FL>-a1)) &&(a_FR>a2||(slip_FR<s1&&a_FR>-a1)) 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 possibility of a single boost value being 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 : a_FL<-a1||a_FR<-a1||slip_FL>s2 ||slip_FR>s2||LSA_dert_FA>=0.3 Among them, LSA_dert_FA represents the maximum value of the time interval between the two wheel pulses on the front axle.

12. A wheel anti-lock braking method suitable for braking on a slope, characterized in that: 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, characterized in that When the computer program is executed by a processor, the steps of the method according to claim 12 are implemented.

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