Off-road vehicle hill descent control system and method

Abstract

The application provides an off-road vehicle steep slope slow descending anti-lock control system and method, the method comprising the following steps: S1, calculating the reference speed of each wheel according to the current wheel speed peak value, the time when the wheel speed peak value appears and the wheel reference acceleration, and synthesizing the reference speed of the whole vehicle through fuzzy logic to calculate the reference acceleration of the vehicle; S2, calculating the slope through the deviation between the reference acceleration of the vehicle and the acceleration sensor; S3, calculating the basic braking pressure according to the slope and adding the compensation amount of the current speed to the basic braking pressure to obtain the feedforward braking pressure; S4, calculating the single wheel slip rate integral; S5, calculating the braking pressure compensation amount of the vehicle according to the deviation between the actual vehicle speed and the steep slope slow descending target vehicle speed, and calculating the braking pressure compensation amount of the wheel based on the deviation of the single wheel slip rate to obtain the feedback braking pressure; and synthesizing the feedforward braking pressure and the feedback braking pressure to obtain the braking pressure of the single wheel to realize the feedback regulation on the basis of the feedforward control.

Description

Technical Field

[0001] This invention belongs to the field of vehicle dynamics control technology, specifically relating to a hill descent control system and method for off-road vehicles. Background Technology

[0002] Anti-lock braking system (ABS) is an almost essential technology for vehicle braking safety. Existing ABS systems on the market usually have a certain trigger speed (such as 10km / h). When the speed is below this, ABS usually will not be triggered. Moreover, existing ABS systems are usually designed for braking under driver braking or active braking (AEB) conditions.

[0003] Hill descent control (HDD) is a crucial safety technology for off-road vehicles descending steep slopes, typically found in high-end or hardcore off-road vehicles. Off-road vehicles often face muddy or potholed surfaces on steep slopes, making wheel lock-up a serious risk during braking. Once locked, the vehicle is prone to skidding, compromising safety. However, existing ABS technology is difficult to trigger at low speeds, while off-road vehicles typically descend at low speeds. This forces HDD to either operate at high speeds, directly posing a danger, or at low speeds without ABS, potentially leading to skidding during braking. Previous patents (such as CN104442763B) have mentioned both HDD and ABS, but these typically rely on information from the ABS system and lack effective methods for coordinated control of HDD and ABS. CN117141252A, by Dayun Automotive, describes determining mechanical braking availability based on ABS (or EBS) status malfunctions, but does not address slip ratio control.

[0004] Among recently disclosed technologies, only a few provide methods for the coordinated control of ABS and hill descent control. In CN118082778A, Dongfeng Motor proposed calculating a reference vehicle speed using a preset gradient (acceleration), and determining whether to engage ABS based on the deviation between wheel speed and the reference vehicle speed. If ABS is engaged, a logic jump is used to control wheel pressure. Although the patent mentions the coordinated control of hill descent control and ABS, controlling wheel pressure based on the reference vehicle speed method is a conventional method for ABS control. It still faces problems such as errors in reference speed calculation and difficulty in judging the degree of wheel lockup when wheel speed and vehicle speed are too close at low speeds, thus failing to solve the ABS control problem at low speeds. In CN119705384A, BYD Auto presented a control framework for hill descent control and ABS coordination. This framework is also based on feedback control with logic thresholds. It also provides the hill descent speed based on the slope and current speed. Different descent speeds can be set at different slopes. Setting a higher descent speed can ensure ABS triggering. However, it also faces the same low-speed control problem as CN118082778A. In addition, this patent application adjusts the vehicle speed and the degree of brake lock through feedback control, which may lead to control effect vibration due to complex environmental changes in off-road conditions, affecting vehicle safety. Summary of the Invention

[0005] The purpose of this invention is to propose a slope descent control system and method for off-road vehicles to overcome the problems of possible errors in the calculation of reference vehicle speed and inaccurate calculation of reference road surface on muddy roads that may occur in the prior art.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] The anti-lock braking system (ABS) method for off-road vehicles on steep slope descent includes the following steps:

[0008] S1. Calculate the reference speed of each wheel based on its current peak wheel speed, the time of its peak wheel speed occurrence, and the wheel's reference acceleration; synthesize the overall vehicle reference speed using fuzzy logic based on the wheel reference speeds, and calculate the vehicle's reference acceleration based on the overall vehicle reference speed; the fuzzy logic includes:

[0009] Weight 1: Increase the weight of wheels with low dynamism;

[0010] Weight 2: Increase the weight of wheels whose wheel reference acceleration is close to the whole vehicle reference acceleration;

[0011] Weight 3: Increase the weight of wheels whose reference wheel speed is close to the reference vehicle speed;

[0012] Weight 4: Increase the weight of non-drive wheels with speeds greater than the reference vehicle speed;

[0013] Weight 5: If ABS is triggered, the wheel with the higher wheel speed has a higher weight.

[0014] S2. Calculate the slope by measuring the deviation between the vehicle's reference acceleration and the acceleration sensor.

[0015] S3. Calculate the base braking pressure based on the slope, and add the compensation amount of the current speed to the base braking pressure to obtain the feedforward braking pressure of the vehicle for steep slope descent anti-lock braking.

[0016] S4. Calculate the integral of the slip ratio of a single wheel to determine the degree of vehicle lock-up;

[0017] S5. Calculate the vehicle's braking pressure compensation based on the deviation between the actual vehicle speed and the target vehicle speed for steep slope descent, and calculate the wheel's braking pressure compensation based on the deviation of the single-wheel slip ratio to obtain the feedback braking pressure; combine the feedforward braking pressure and the feedback braking pressure to obtain the braking pressure of a single wheel, so as to realize feedback adjustment based on feedforward control.

[0018] Preferably, the step of calculating the reference speed of each wheel based on the current peak wheel speed, the time when the peak wheel speed occurs, and the wheel reference acceleration is as follows:

[0019]

[0020] in: for Time Wheel Reference speed, The values ​​are FL, FR, RL, and RR, which represent the front left, front right, rear left, and rear right wheels, respectively. For the currently recorded The wheels that appear at all times Peak wheel speed; The current moment; The wheel is calculated based on peak wheel speed. Reference acceleration; Reference acceleration The wheel obtained by filtering calculation based on acceleration:

[0021]

[0022]

[0023] in: It is the weight of the single-wheel acceleration; For the previous record The wheels that appear at all times Peak wheel speed; This is the reference acceleration for the entire vehicle.

[0024] Preferably, the update of the wheel speed peak value specifically involves determining whether the current wheel speed peak value is a true peak value when a wheel speed peak value occurs.

[0025] Based on the current peak wheel speed Calculate the pseudo-reference acceleration of a single wheel :

[0026]

[0027] If the reference acceleration is to be used Meet physical constraints If the peak wheel speed and reference acceleration are updated, then no update is performed. and These are the maximum and minimum acceleration values, respectively; the peak value of the updated wheel speed and the reference acceleration are specifically as follows:

[0028] Peak wheel speed Peak wheel speed recorded before occurrence and corresponding time The value is assigned to the peak wheel speed of the previous record. and corresponding time Utilizing the current peak wheel speed And update the current record at the current time t and corresponding time .

[0029] Preferably, the process of synthesizing the vehicle reference speed based on the reference speeds of each wheel using fuzzy logic is as follows:

[0030] Weight of each wheel The calculation is as follows:

[0031]

[0032]

[0033]

[0034]

[0035] in: A weighting factor representing the preset fuzziness or degree; The weighting factor represents the preset fuzziness and degree. Indicates wheel The degree of urgency; and These are the minimum and maximum values ​​of the abruptness of all wheels; These represent the left and right endpoints of the criterion for a small deviation in the degree of agitation, respectively. These represent the left and right endpoints of the criteria for determining small wheel abruptness, respectively; temp1, temp2, and temp3 are all intermediate values. , and These are fuzzy logic mini-operation functions, fuzzy logic AND operation functions, and fuzzy logic OR operation functions, respectively. The corresponding computational logic is as follows:

[0036]

[0037]

[0038] in: For the input variables of the fuzzy logic small operation function, These represent constants for fuzzy logic small operation functions; These represent the two input variables of the fuzzy logic and the operational function. For fuzzy logic and operation functions, constants are used. Represents two input variables of a fuzzy logic or operation function. It is a constant for fuzzy logic or operation functions;

[0039] Weight of each wheel The calculation is as follows:

[0040]

[0041] in: The wheel is calculated by filtering based on the reference acceleration. The acceleration; The left and right endpoints represent the criteria for determining small wheel acceleration;

[0042] Weight of each wheel The calculation is as follows:

[0043]

[0044]

[0045]

[0046]

[0047] in: A weighting factor representing the preset fuzziness or degree; The weighting factor represents the preset fuzziness and degree. For wheels Reference speed; The reference speed of the vehicle at the previous moment; These represent the left and right endpoints of the criterion for determining that the deviation between the reference wheel speed and the reference vehicle speed is small, respectively. and These are the minimum and maximum values ​​of the deviation between the reference wheel speed and the reference vehicle speed; These represent the left and right endpoints of the judgment condition with a small deviation range, respectively; temp4, temp5, and temp6 are all intermediate quantities;

[0048] Weight of each wheel The calculation is as follows:

[0049]

[0050] in: The initial weight for each round is four. ; These represent the left and right endpoints of the condition for determining that the driving wheel speed is greater than the reference vehicle speed, respectively. For large-scale fuzzy logic operations:

[0051]

[0052] in: For the input variables of the fuzzy logic large operation function, These represent constants for the large fuzzy logic operation function;

[0053] Weight of each wheel five The calculation is as follows:

[0054]

[0055] in: and These are the maximum and minimum values ​​of the reference wheel speed; It is a preset fixed value;

[0056] If ABS is not triggered, then the wheels Total weight The weights are composed of weights one through four. :

[0057]

[0058] in: It is a preset AND operation degree factor; It is a preset or computational degree factor;

[0059] If ABS is triggered, the wheels Total weight The weights are composed of weights one through five. :

[0060]

[0061] According to the wheel Total weight and reference speed Calculate the reference speed of the whole vehicle :

[0062] .

[0063] Preferably, the calculation of the vehicle's reference acceleration based on the overall vehicle reference speed is as follows:

[0064] Using the current vehicle reference speed The vehicle reference speed at the previous moment Calculate the original acceleration at time t :

[0065]

[0066] In the formula The time interval is t; the original acceleration at time t The reference acceleration of the vehicle at time t is obtained by performing mean filtering. :

[0067]

[0068] Here, n is an index variable used to iterate through integers from 0 to N-1; N represents the number of elements to be filtered.

[0069] Preferably, the slope calculation based on the deviation between the vehicle's reference acceleration and the acceleration sensor is as follows:

[0070]

[0071] in: Slope; The measured longitudinal acceleration is from the accelerometer. It is the gravitational acceleration constant; Acceleration of the vehicle; when the slope is... When there is shaking, the slope Add filtering processing.

[0072] Preferably, the step of calculating the base braking pressure based on the slope and adding a compensation amount based on the current speed to the base braking pressure to obtain the feedforward braking pressure for the vehicle's hill descent control anti-lock braking system is as follows:

[0073] Calculate the foundation braking pressure based on the slope. :

[0074]

[0075] in: Slope; The total mass of the vehicle; It is the gravitational acceleration constant; The constant that converts braking system pressure into longitudinal braking force of the vehicle. , These represent the braking force constants of the left front, right front, left rear, and right rear wheels, respectively.

[0076] Calculate the increment of braking pressure :

[0077]

[0078] in: It is a calibrated constant. For reference speed of the whole vehicle;

[0079] Calculate feedforward braking pressure :

[0080] .

[0081] Preferably, the calculation of the integral of the slip ratio of a single wheel is as follows:

[0082] Calculate the slip ratio of a single wheel The slip ratio of a single wheel is integrated to represent the degree of wheel lockup:

[0083]

[0084]

[0085] in: For wheels Reference speed; For reference speed of the whole vehicle; The integral value of the slip ratio for a single wheel. This is the integral value of the slip ratio from the previous moment. This is the attenuation coefficient.

[0086] Preferably, the step of calculating the vehicle's braking pressure compensation based on the deviation between the actual vehicle speed and the target vehicle speed for steep slope descent, and calculating the wheel's braking pressure compensation based on the deviation of the single-wheel slip ratio, to obtain the feedback braking pressure; combining the feedforward braking pressure and the feedback braking pressure to synthesize the braking pressure of a single wheel, thereby achieving feedback adjustment based on feedforward control, as detailed below:

[0087] The braking pressure compensation is calculated based on the deviation between the actual vehicle speed and the target speed for hill descent control. :

[0088]

[0089] in: The feedback control constant is greater than zero; The target speed for slow descent on a steep slope; For reference speed of the whole vehicle;

[0090] Calculate the braking pressure compensation of the wheel based on the deviation of the single-wheel slip ratio. Among them, the braking pressure compensation of the wheels Divided into pressure adjustment of the skid wheel Braking pressure compensation for unslipped wheels ;

[0091] Pressure adjustment of the skid wheel for:

[0092]

[0093] Where: j is the sliding wheel; Let be the integral value of the slip ratio of the slipping wheel j; This is the preset pressure adjustment constant for the slipper wheel;

[0094] Braking pressure compensation for unslipped wheels for:

[0095]

[0096] Where: j' represents the wheel that has not slipped; K j' and K j , respectively, represent the braking force constants corresponding to the non-slipping wheel and the slipping wheel; m is the total number of non-slipping wheels;

[0097] The feedforward braking pressure and the feedback braking pressure are combined to form the braking pressure of a single wheel. :

[0098]

[0099] in: This is the feedforward braking pressure.

[0100] The off-road vehicle hill descent control system includes a processor, a memory, and a computer program stored in the memory. When the processor executes the computer program, it specifically performs any of the steps in the above-mentioned off-road vehicle hill descent control method.

[0101] Compared with the prior art, the present invention has the following beneficial effects:

[0102] This invention effectively improves estimation accuracy through fuzzy logic, while avoiding the problem of complex logic in traditional reference speed calculation methods. Addressing the issue of difficulty in judging and controlling wheel lock-up and inconsistent vehicle control performance at low speeds due to wheel speeds being too close to vehicle speed, this invention proposes a lock-up criterion based on the slip ratio integral, which can effectively identify small slips. Furthermore, it employs a combination of feedforward and feedback methods to improve the algorithm's accuracy and anti-interference capabilities. Attached Figure Description

[0103] Figure 1 This is a flowchart of the method of the present invention;

[0104] Figure 2 A diagram showing the wheel speeds when the vehicle's ABS engages.

[0105] Figure 3 This is a speed diagram for a steep descent; the target speed is 16 km / h, which remains relatively stable at 6 seconds.

[0106] Figure 4 To and Figure 3 The corresponding braking pressure diagram. Detailed Implementation

[0107] The following is in conjunction with the appendix Figure 1-4 The technical solution of the present invention will be described in detail below.

[0108] This invention proposes a method for anti-lock braking control of steep slope descent in off-road vehicles, as detailed below:

[0109] S1. Calculate the reference speed of each wheel based on the current peak wheel speed, the time when the peak wheel speed occurs, and the wheel reference acceleration; synthesize the whole vehicle reference speed based on the reference speed of each wheel using fuzzy logic, and calculate the reference acceleration of the vehicle based on the whole vehicle reference speed.

[0110] S1.1: Calculate the reference speed for each wheel, as follows:

[0111]

[0112] in: for Time Wheel Reference speed, The values ​​are FL, FR, RL, and RR, which represent the front left, front right, rear left, and rear right wheels, respectively. For the currently recorded The wheels that appear at all times Peak wheel speed; The current moment; The wheel is calculated based on peak wheel speed. Reference acceleration; Reference acceleration The wheel obtained by filtering calculation based on acceleration:

[0113]

[0114]

[0115] in: This is the weight of the single-wheel acceleration, for example, it can be set to 0.7; For the previous record The wheels that appear at all times Peak wheel speed; This is the reference acceleration for the entire vehicle.

[0116] Specifically, the wheel speed peak update involves determining the current wheel speed peak value when a peak value is reached. Is this a true peak value?

[0117] This logic is primarily based on the premise that, in calculating the reference vehicle speed, the peak wheel speed should be close to the vehicle speed, and the acceleration calculated from the peak speed should meet certain physical constraints. In the formula This is the maximum acceleration, limited by the steep slope descent software, for example, 2 m / s². 2 , This is the minimum acceleration, which corresponds to the maximum braking intensity and is related to the braking system; for example, it is -7 m / s². 2 ;

[0118] If based on the current wheel speed peak Calculated pseudo-reference acceleration If this physical constraint is met, then update the peak wheel speed. Peak wheel speed recorded before occurrence and corresponding time The value is assigned to the peak wheel speed of the previous record. and corresponding time Utilizing the current peak wheel speed And update the current record at the current time t and corresponding time Otherwise, no refresh will be performed; reference acceleration will be used. The calculation is as follows:

[0119] .

[0120] S1.2: Calculate the reference speed of the entire vehicle:

[0121] After obtaining the reference speeds of each wheel, the wheel speeds are combined into the overall vehicle reference speed. The idea is to synthesize the overall vehicle reference speed using fuzzy logic, and increase the weight when the following logic is met: 1) the wheel jerk is small; 2) the wheel reference acceleration is close to the overall vehicle reference acceleration; 3) the wheel speed is close to the reference vehicle speed; 4) the speed of non-drive wheels is greater than the reference vehicle speed; 5) if ABS is triggered, the wheel with the higher wheel speed has a higher weight.

[0122] One implementation method is as follows:

[0123] Weight of each wheel The calculation is as follows:

[0124]

[0125]

[0126]

[0127]

[0128] in: A weighting factor representing the preset fuzziness or degree; The weighting factor represents the preset fuzziness and degree. Indicates wheel The degree of urgency; and These are the minimum and maximum values ​​of the abruptness of all wheels; These represent the left and right endpoints of the criterion for a small deviation in the degree of agitation, respectively. These represent the left and right endpoints of the criteria for determining a small wheel abruptness, respectively; temp1, temp2, and temp3 are all intermediate values, where temp2 indicates that the abruptness deviation should not be too large, and temp3 indicates that the abruptness deviation should not be too large.

[0129] In this embodiment and All values ​​are taken as 0.85; Take respectively and ; Take respectively and The above All these values ​​can be changed; different effects can be achieved by giving different parameters.

[0130] , and These are fuzzy logic mini-operation functions, fuzzy logic AND operation functions, and fuzzy logic OR operation functions, respectively. The corresponding computational logic is as follows:

[0131]

[0132]

[0133]

[0134] in: For the input variables of the fuzzy logic small operation function, These represent constants for fuzzy logic small operation functions; These represent the two input variables of the fuzzy logic and the operational function. For fuzzy logic and operation functions, constants are used. Represents two input variables of a fuzzy logic or operation function. It is a constant for fuzzy logic or operation functions;

[0135] Weight of each wheel The calculation is as follows:

[0136]

[0137] in: The wheel is calculated by filtering based on the reference acceleration. The acceleration; The left and right endpoints represent the criteria for determining small wheel acceleration; in this embodiment... Take respectively and ;

[0138] Weight of each wheel The calculation is as follows:

[0139]

[0140]

[0141]

[0142]

[0143] in: A weighting factor representing the preset fuzziness or degree; The weighting factor represents the preset fuzziness and degree. For wheels Reference speed; The reference speed of the vehicle at the previous moment; These represent the left and right endpoints of the criterion for determining that the deviation between the reference wheel speed and the reference vehicle speed is small, respectively. and These are the minimum and maximum values ​​of the deviation between the reference wheel speed and the reference vehicle speed; These represent the left and right endpoints of the judgment condition for a small deviation range, respectively; temp4, temp5, and temp6 are all intermediate values, with temp4 indicating that the reference wheel speed is close to the reference vehicle speed;

[0144] In this embodiment and All values ​​are taken as 0.85; Take respectively and ; Take respectively and ;

[0145] Weight of each wheel The calculation is as follows:

[0146]

[0147] in: The initial weight for each round is four. ; These represent the left and right endpoints of the condition for determining that the driving wheel speed is greater than the reference vehicle speed; in this embodiment... Take respectively and ;

[0148] For large-scale fuzzy logic operations:

[0149]

[0150] in: For the input variables of the fuzzy logic large operation function, These represent constants for the large fuzzy logic operation function;

[0151] Weight of each wheel five The calculation is as follows:

[0152]

[0153] in: and These are the maximum and minimum values ​​of the reference wheel speed; It is a preset fixed value; in this embodiment Pick ;

[0154] If ABS is not triggered, then the wheels Total weight The weights are composed of weights one through four. :

[0155]

[0156] in: It is a preset AND operation degree factor; It is a preset or operation degree factor; in this embodiment and All values ​​are taken as 0.85;

[0157] If ABS is triggered, the wheels Total weight The weights are composed of weights one through five. :

[0158]

[0159] According to the wheel Total weight and reference speed Calculate the reference speed of the whole vehicle :

[0160] .

[0161] S1.3: Calculate the reference acceleration of the vehicle based on the overall vehicle reference speed;

[0162] Using the current vehicle reference speed The vehicle reference speed at the previous moment Calculate the original acceleration at time t :

[0163]

[0164] In the formula For time intervals;

[0165] When the calculated raw vehicle acceleration exhibits significant fluctuations, it needs to be filtered. One feasible method is mean filtering, which involves applying mean filtering to the raw acceleration at time t. The reference acceleration of the vehicle at time t is obtained by performing mean filtering. :

[0166]

[0167] Here, n is an index variable used to iterate through integers from 0 to N-1; N represents the number of elements to be filtered. If jitter is significant, a larger N, such as 10, can be selected.

[0168] S2, Slope determination.

[0169] The data measured by the vehicle's longitudinal acceleration sensor is the superposition of the vehicle's actual acceleration and the longitudinal component of gravity. After obtaining the vehicle's reference acceleration, the slope can be calculated by the deviation between the vehicle's reference acceleration and the acceleration sensor reading. The calculation method is as follows:

[0170]

[0171] In the formula: Slope; For the measured longitudinal acceleration of the accelerometer, It is the gravitational acceleration constant; For vehicle acceleration; if the above calculations If there is significant jitter, filtering can be added to it.

[0172] S3. Pressure feedforward control based on slope estimation.

[0173] S3.1: Calculate the basic braking pressure;

[0174] At a given gradient, when a vehicle maintains a constant speed downhill, all the resistance forces acting on the vehicle are the same as the component of gravity acting on the longitudinal slope, that is: In the formula The total mass of the vehicle. For braking system pressure, The constant that converts braking system pressure into longitudinal braking force of the vehicle. Let the total resistance of the vehicle be denoted as . Considering that the resistance of off-road vehicles is usually small when going downhill (wind resistance, driving resistance, etc.), it can be ignored, thus yielding the basic braking pressure. It should be:

[0175]

[0176] Because each wheel provides braking force during braking, It can also be expressed as In the formula These represent the braking force constants of the left front, right front, left rear, and right rear wheels, respectively.

[0177] S3.2: Calculate the increment of braking pressure ;

[0178] When a vehicle is traveling too fast, it is necessary to appropriately increase the braking pressure to prevent dangerous situations caused by speeding. Specifically, this can be done by... Add a compensation amount based on the current speed, that is:

[0179]

[0180] In the formula It is a calibrable constant;

[0181] Based on this, the total braking pressure can be calculated as follows: .

[0182] S4. Slip ratio integral calculation method based on reference vehicle speed.

[0183] To prevent wheel lock-up during hill descent control, braking pressure needs to be controlled based on the degree of wheel lock-up. However, since the braking intensity may be very small during hill descent, the degree of vehicle lock-up (slip ratio) may be very small. Traditional ABS control algorithms that directly determine the degree of lock-up based on slip ratio and then control wheel pressure are difficult to identify such small slip. Therefore, a lock-up determination method based on slip ratio integral is proposed.

[0184] Calculate the slip ratio of a single wheel Integrate the slip ratio of a single wheel:

[0185]

[0186]

[0187] In the formula The integral value of the slip ratio for a single wheel. This is the integral value of the slip ratio from the previous moment. This is the decay coefficient, which can be a number between 0 and 1. The smaller the number, the faster the decay needs to be. This decay rate prevents it from increasing over time. Continue to increase, this will prevent It is mainly affected by time rather than slip ratio. After the attenuation coefficient, a large slip ratio in a short period of time or a small slip ratio in a long period of time will lead to... The pressure increases, and this is the operating condition that requires ABS control intervention for steep slope descent.

[0188] S5, Feedback pressure regulation.

[0189] The pressure feedforward control described above can keep the vehicle at a constant speed under ideal conditions. However, it cannot precisely control the specific speed value, and under disturbances (such as slope estimation error, ABS triggering, braking force constant error, etc.), it will inevitably be impossible to keep the vehicle at a constant speed. Therefore, feedback adjustment needs to be added on the basis of feedforward control.

[0190] S5.1: Calculate the feedback adjustment amount based on the speed deviation;

[0191] The control pressure is adjusted based on the deviation between the actual vehicle speed and the target speed for hill descent control. The logic is that if the actual speed is too high, the braking pressure should be increased to slow the vehicle down, and vice versa. One feasible approach is to compensate the braking pressure proportionally. , calculated as

[0192]

[0193] In the formula The feedback control constant is greater than zero and can be calibrated. The target speed for slow descent on a steep slope;

[0194] S5.2: Calculate the deviation feedback based on the single wheel slip ratio;

[0195] When a single wheel experiences a large slip ratio, the braking pressure on that wheel should be reduced, while other wheels should supplement the braking force to maintain the overall braking force unchanged.

[0196] Calculate the braking pressure compensation of the wheel based on the deviation of the single-wheel slip ratio. Among them, the braking pressure compensation of the wheels Divided into pressure adjustment of the skid wheel Braking pressure compensation for unslipped wheels ;

[0197] Pressure adjustment of the skid wheel for:

[0198]

[0199] Where: j is the sliding wheel; Let be the integral value of the slip ratio of the slipping wheel j; This is the preset pressure adjustment constant for the slipper wheel;

[0200] Braking pressure compensation for unslipped wheels for:

[0201]

[0202] Where: j' represents the wheel that has not slipped; K j' and K j , respectively, represent the braking force constants corresponding to the non-slipping wheel and the slipping wheel; m is the total number of non-slipping wheels;

[0203] S5.3: Combine the feedforward braking pressure and the feedback braking pressure into the braking pressure of a single wheel:

[0204] .

[0205] The present invention also proposes an anti-lock braking system for hill descent control of off-road vehicles, including a processor, a memory, and a computer program stored in the memory. When the processor executes the computer program, it specifically performs any of the steps in the above-mentioned anti-lock braking control method for hill descent control of off-road vehicles.

[0206] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for anti-lock braking control of steep slope descent in off-road vehicles, characterized in that, Specifically, the following steps are included: S1. Calculate the reference speed of each wheel based on the current peak wheel speed, the time when the peak wheel speed occurs, and the wheel reference acceleration. The reference speed of the whole vehicle is synthesized by fuzzy logic based on the reference speed of each wheel, and the reference acceleration of the vehicle is calculated based on the reference speed of the whole vehicle. The fuzzy logic includes: Weight 1: Increase the weight of wheels with low dynamism; Weight 2: Increase the weight of wheels whose wheel reference acceleration is close to the whole vehicle reference acceleration; Weight 3: Increase the weight of wheels whose reference wheel speed is close to the reference vehicle speed; Weight 4: Increase the weight of non-drive wheels with speeds greater than the reference vehicle speed; Weight 5: If ABS is triggered, the wheel with the higher wheel speed has a higher weight. S2. Calculate the slope by measuring the deviation between the vehicle's reference acceleration and the acceleration sensor. S3. Calculate the base braking pressure based on the slope, and add the compensation amount of the current speed to the base braking pressure to obtain the feedforward braking pressure of the vehicle for steep slope descent anti-lock braking. S4. Calculate the integral of the slip ratio of a single wheel to determine the degree of vehicle lockup; details are as follows: Calculate the slip ratio of a single wheel Integrate the slip ratio of a single wheel: in: For wheels Reference speed; For reference speed of the whole vehicle; The integral value of the slip ratio for a single wheel. This is the integral value of the slip ratio from the previous moment. The attenuation coefficient; S5. Calculate the vehicle's braking pressure compensation based on the deviation between the actual vehicle speed and the target vehicle speed for steep slope descent, and calculate the wheel's braking pressure compensation based on the deviation of the single-wheel slip ratio to obtain the feedback braking pressure; combine the feedforward braking pressure and the feedback braking pressure to obtain the braking pressure of a single wheel, so as to realize feedback adjustment based on feedforward control.

2. The anti-lock braking control method for steep slope descent of off-road vehicles according to claim 1, characterized in that, The reference speed of each wheel is calculated based on its current peak wheel speed, the time when the peak wheel speed occurs, and the wheel reference acceleration, as follows: in: for Time Wheel Reference speed, The values ​​are FL, FR, RL, and RR, which represent the front left, front right, rear left, and rear right wheels, respectively. For the currently recorded The wheels that appear at all times Peak wheel speed; The current moment; The wheel is calculated based on peak wheel speed. Reference acceleration; Reference acceleration The wheel obtained by filtering calculation based on acceleration: in: It is the weight of the single-wheel acceleration; For the previous record The wheels that appear at all times Peak wheel speed; This is the reference acceleration for the entire vehicle.

3. The anti-lock braking control method for steep slope descent of off-road vehicles according to claim 2, characterized in that, The update of the wheel speed peak value specifically involves determining whether the current wheel speed peak value is a true peak value when a wheel speed peak value occurs. Based on the current peak wheel speed Calculate the pseudo-reference acceleration of a single wheel : If the reference acceleration is to be used Meet physical constraints If the peak wheel speed and reference acceleration are updated, then no update is performed. and These are the maximum and minimum acceleration values, respectively; the peak value of the updated wheel speed and the reference acceleration are specifically as follows: Peak wheel speed Peak wheel speed recorded before occurrence and corresponding time The value is assigned to the peak wheel speed of the previous record. and corresponding time Utilizing the current peak wheel speed And update the current record at the current time t and corresponding time .

4. The anti-lock braking control method for steep slope descent of off-road vehicles according to claim 1, characterized in that, The process of synthesizing the vehicle reference speed based on the reference speeds of each wheel using fuzzy logic is as follows: Weight of each wheel The calculation is as follows: in: A weighting factor representing the preset fuzziness or degree; The weighting factor represents the preset fuzziness and degree. Indicates wheel The degree of urgency; and These are the minimum and maximum values ​​of the abruptness of all wheels; These represent the left and right endpoints of the criterion for a small deviation in the degree of agitation, respectively. These represent the left and right endpoints of the criteria for determining small wheel abruptness, respectively; temp1, temp2, and temp3 are all intermediate values. , and These are fuzzy logic mini-operation functions, fuzzy logic AND operation functions, and fuzzy logic OR operation functions, respectively. The corresponding computational logic is as follows: in: For the input variables of the fuzzy logic small operation function, These represent constants for fuzzy logic small operation functions; These represent the two input variables of the fuzzy logic and the operational function. For fuzzy logic and operation functions, constants are used. Represents two input variables of a fuzzy logic or operation function. It is a constant for fuzzy logic or operation functions; Weight of each wheel The calculation is as follows: in: The wheel is calculated by filtering based on the reference acceleration. The acceleration; The left and right endpoints represent the criteria for determining small wheel acceleration; Weight of each wheel The calculation is as follows: in: A weighting factor representing the preset fuzziness or degree; The weighting factor represents the preset fuzziness and degree. For wheels Reference speed; The reference speed of the vehicle at the previous moment; These represent the left and right endpoints of the criterion for determining a small deviation between the reference wheel speed and the reference vehicle speed, respectively. and These are the minimum and maximum values ​​of the deviation between the reference wheel speed and the reference vehicle speed; These represent the left and right endpoints of the judgment condition with a small deviation range, respectively; temp4, temp5, and temp6 are all intermediate quantities; Weight of each wheel The calculation is as follows: in: The initial weight for each round is four. ; These represent the left and right endpoints of the condition for determining that the driving wheel speed is greater than the reference vehicle speed, respectively. For large-scale fuzzy logic operations: in: For the input variables of the fuzzy logic large operation function, These represent constants for the large fuzzy logic operation function; Weight of each wheel five The calculation is as follows: in: and These are the maximum and minimum values ​​of the reference wheel speed; It is a preset fixed value; If ABS is not triggered, then the wheels Total weight The weights are composed of weights one through four. : in: It is a preset AND operation degree factor; It is a preset or computational degree factor; If ABS is triggered, the wheels Total weight The weights are composed of weights one through five. : According to the wheel Total weight and reference speed Calculate the reference speed of the whole vehicle : 。 5. The method for anti-lock braking control of steep slope descent for off-road vehicles according to claim 1, characterized in that, The calculation of the vehicle's reference acceleration based on the overall vehicle reference speed is as follows: Using the current vehicle reference speed The vehicle reference speed at the previous moment Calculate the original acceleration at time t : In the formula The time interval is t; the original acceleration at time t The reference acceleration of the vehicle at time t is obtained by performing mean filtering. : Here, n is an index variable used to iterate through integers from 0 to N-1; N represents the number of elements to be filtered.

6. The method for anti-lock braking control of off-road vehicles on steep slope descent according to claim 1, characterized in that, The slope calculation is performed by comparing the vehicle's reference acceleration with that of the acceleration sensor, as detailed below: in: Slope; The measured longitudinal acceleration is from the accelerometer. It is the gravitational acceleration constant; Acceleration of the vehicle; when the slope is... When there is shaking, the slope Add filtering processing.

7. The method for anti-lock braking control of off-road vehicles on steep slope descent according to claim 1, characterized in that, The method involves calculating the base braking pressure based on the slope and adding a compensation amount based on the current speed to the base braking pressure to obtain the feedforward braking pressure for the vehicle's hill descent control anti-lock braking system, as detailed below: Calculate the foundation braking pressure based on the slope. : in: Slope; The total mass of the vehicle; It is the gravitational acceleration constant; The constant that converts braking system pressure into longitudinal braking force of the vehicle. , These represent the braking force constants of the left front, right front, left rear, and right rear wheels, respectively. Calculate the increment of braking pressure : in: It is a calibrated constant. For reference speed of the whole vehicle; Calculate feedforward braking pressure : 。 8. The method for anti-lock braking control of steep slope descent for off-road vehicles according to claim 1, characterized in that, The method involves calculating the vehicle's braking pressure compensation based on the deviation between the actual vehicle speed and the target vehicle speed for steep slope descent, and calculating the wheel's braking pressure compensation based on the deviation of the single-wheel slip ratio to obtain the feedback braking pressure. The feedforward braking pressure and the feedback braking pressure are then combined to form the braking pressure of a single wheel, thereby achieving feedback adjustment based on feedforward control, as detailed below: The braking pressure compensation is calculated based on the deviation between the actual vehicle speed and the target speed for hill descent control. : in: The feedback control constant is greater than zero; The target speed for slow descent on a steep slope; For reference speed of the whole vehicle; Calculate the braking pressure compensation of the wheel based on the deviation of the single-wheel slip ratio. Among them, the braking pressure compensation of the wheels Divided into pressure adjustment of the skid wheel Braking pressure compensation for unslipped wheels ; Pressure adjustment of the skid wheel for: Where: j is the sliding wheel; Let be the integral value of the slip ratio of the slipping wheel j; This is the preset pressure adjustment constant for the slipper wheel; Braking pressure compensation for unslipped wheels for: Where: j' represents the wheel that has not slipped; K j' and K j , respectively, represent the braking force constants corresponding to the non-slipping wheel and the slipping wheel; m is the total number of non-slipping wheels; The feedforward braking pressure and the feedback braking pressure are combined to form the braking pressure of a single wheel. : in: This is the feedforward braking pressure.

9. A hill descent control system for off-road vehicles, characterized in that, It includes a processor, a memory, and a computer program stored in the memory. When the processor executes the computer program, it specifically performs the steps in the anti-lock braking control method for hill descent control of off-road vehicles as described in any one of claims 1-8.

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