CN1329722C - Cargo vehicle ABS road identification method - Google Patents

Abstract

The invention claims to protect a road surface identification method for anti-lock braking system (ABS) of trucks, which relates to the technical field of automotive electronic control. It takes the maximum wheel speed of the vehicle wheel as the reference speed of the vehicle, and then calculates it according to the angular acceleration of the wheel. The frictional force of the ground on each wheel is used to calculate the mass of the car and the body parameters of the car under load, and thus to obtain the normal pressure of the car wheel, thereby calculating the adhesion coefficient of the ground. Then calculate the slip rate of the wheel, and then calculate the theoretical adhesion coefficient of different road surfaces under the current slip rate according to the theoretical formula, and compare the two calculated adhesion coefficients to identify the road surface condition. The method is suitable for the anti-lock braking system (ABS) of automobiles, especially for road identification of trucks under different loading conditions.

Description

A ABS road surface identification method for trucks

technical field

The invention belongs to the technical field of automobile electronic control, and in particular relates to a road surface identification method of ABS of a truck.

Background technique

The ABS automobile anti-lock braking system is an important electronic system to ensure that the wheels of the car do not lock during the braking process. Therefore, the ABS system must recognize the road conditions in real time. However, due to the limited number of sensors mounted on the car body, the only information that ABS can obtain is the speed of the wheels. Therefore, the ABS road recognition algorithm must be able to identify road information from limited information. For this reason, Chen Jun and others published "ABS Road Surface Recognition Based on Competitive Neural Network" in the Journal of Northeastern University in June 2003, Volume 24, Issue 6, using neural network technology for road surface identification technology, Journal of Agricultural Machinery, published in September 2001 "Research on ABS Fuzzy Control System Based on Automatic Road Identification" uses the method of comparing the theoretical deceleration of the wheel with the actual deceleration of the wheel to identify the road surface. Jin-Oh Hahn et al. use the method based on GPS to identify the friction coefficient between the tire and the ground (Jin-Oh Hahn , Rajesh Rajamani, and Lee Alexander. GPS-Based Real-Time Identification of Tire-Road Friction Coefficient, IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, VOL.10, NO.3). However, looking at the above methods, the method based on the neural network needs a large amount of sample data to train the network, and the method of comparing the theoretical deceleration of the wheel with the actual deceleration of the wheel needs to know the mass of the car, and the ABS system does not know that the car is loaded with any mass. Therefore, this method cannot realize the automatic identification of the road surface in the ABS of the truck, and the GPS-based method requires the car to be equipped with a global positioning system, so the cost is relatively high.

Contents of the invention

The invention relates to a new method suitable for truck ABS road surface identification with low cost, simple calculation method and no need for network training. The present invention proposes a method for ABS road identification of trucks, the purpose of which is to solve the problems existing in existing road identification methods that require a large amount of sample data for training, or that the method of comparing the theoretical deceleration of the wheel with the actual deceleration of the wheel cannot obtain the load. The disadvantages of car quality and high manufacturing cost.

The technical solution adopted to solve the above technical problems is: use the wheel speed sensor to extract the wheel speed signal during the braking process online, obtain the angular acceleration of the four wheels in the braking process of the car, and extract the maximum wheel speed as the reference speed of the car, and then According to the formula to calculate the braking torque generated by the car brakes, and then calculate the ground friction force on the four wheels respectively from the angular acceleration of the four wheels and the braking torque of the four wheel brakes, according to the ground friction force on the four wheels and The acceleration of the car body is calculated to obtain the mass of the car, and then the height of the car's center of mass and the distance between the center of mass and the distance from the front axle to the rear axle are calculated from the mass of the car. Calculate the normal pressure on the four wheels of the car, and then calculate the current adhesion coefficient from the positive pressure and the ground friction force on the wheels. Finally, the theoretical adhesion coefficient of different road surfaces under the current slip rate is calculated by the theoretical formula, and the adhesion coefficient calculated by the normal pressure and friction force is continuously calculated and compared with the theoretical adhesion coefficient of different road surfaces. If calculated by the normal pressure and friction force If the obtained adhesion coefficient is close to the adhesion coefficient under a certain road surface for two consecutive times, the current road surface condition can be identified and the wheel is judged to be on the road surface.

Description of drawings

Figure 1 Flowchart of truck ABS road identification method

Figure 2 Four-wheel vehicle system model

Detailed ways

The implementation process of the road surface identification method is described in detail in conjunction with the accompanying drawings and embodiments. Figure 1 shows the flow chart of the truck ABS road surface identification method. The steps are as follows:

1. Use the wheel speed sensor to extract the wheel speed signal online during the braking process: the linear velocity ν of the car and the angular velocity ω of the wheel to obtain the slip ratio of the four wheels in the car braking, and then calculate the wheel slip during braking according to the formula Rate: $S=\frac{v-\mathrm{r\ω}}{v}\×100\%$

where r is the rolling radius of the wheel when it is not subject to ground braking force.

2. Obtain the braking torque generated by the automobile brake according to the gas pressure of the brake chamber

The empirical values obtained through experiments are stored in the database, and the braking factor k _p of the brake, the pressure P of the brake air chamber, and the pressure P _m required to overcome the spring force in the brake cylinder are obtained. The braking torque of the wheel is provided by the pressure generated by the gas in the brake chamber of the brake, and the relationship between the gas pressure in the brake chamber and the braking torque M _b satisfies the following formula: $m_b=\left\{\begin{array}{cc}0& p-p_m<0\\ k_p(p-p_m)& p-p_m>0\end{array}\right.$

The gas pressure of the brake chamber is related to the inflation time of the brake chamber and the end value of inflation. Its "pressure-time" dynamic characteristic curve is an asymptotic curve, similar to an S-shaped curve, and an exponential S-shaped curve is adopted. equation: $p\left(t\right)=\frac{a}{1+b\&CenterDot;e^{m\&CenterDot;t}}$ Among them, a is the end value of air chamber inflation, b and m are two gains, which have no specific physical meaning and can be determined through experiments.

3. Calculate the ground friction force on the four wheels

During the braking process of the car, the wheels are affected by the braking torque generated by the brakes and the friction torque of the ground. The braking torque generated by the brakes will decelerate the wheels, while the friction torque of the ground will accelerate the wheels. The angular acceleration of the wheel can be obtained from the rotational speed of the wheel. When the moment of inertia of the wheel is known, the friction force F _si on the wheel can be calculated by the following formula

Among them, M _bi is the braking torque of the i-th wheel, J _i is the moment of inertia of the i-th wheel and other parameters are extracted and stored in the database through measurement, is the angular acceleration of the i-th wheel, which is calculated by the difference method from the wheel speeds measured twice before and after.

4. By taking the maximum value of the two measured wheel speeds as the speed of the car body, and then calculate the acceleration of the car body by the differential method, calculate the mass of the car according to the ground friction force on the four wheels and the acceleration of the car body, and then The height of the center of mass of the car and the distance of the center of mass from the front axle and the rear axle are calculated from the mass of the car. Calculate the mass of the car based on the ground friction force on the 4 wheels

是车辆横摆的角速度，v_y是车辆横向运动速度。Where ∑F _si is the sum of the friction forces on the wheels,  _x is the linear acceleration of the car in the longitudinal direction,

is the angular velocity of the vehicle yaw, v _y is the lateral velocity of the vehicle.

Taking the maximum wheel speed as the reference speed of the car, establish a four-wheeled vehicle system model as shown in Figure 2, (where v _x is the vehicle longitudinal velocity, v _y is the vehicle lateral velocity, v is the vehicle speed, F _xi is the longitudinal Friction force, F _yi is the lateral friction force on the wheel,  is the yaw angle of the vehicle, β is the angle between the vehicle body and the longitudinal direction), it can be seen from Figure 2 that v _y =v sinβ, since β is very small, so sinβ is approximately 0, that is to say v _y can be approximately 0, and the speed of the car body can be approximated by the reference speed. The methods for calculating the reference speed roughly include the maximum wheel speed method, the slope method, the X-II method and the recursive method. The reference speed calculated by this method is very close to the vehicle body speed measured by the speed sensor. Considering the simplicity of the maximum wheel speed method, the maximum wheel speed method can be used as the calculation method of the vehicle body acceleration, so the above formula can be simplified as $m=\frac{\mathrm{\&Sigma;}{f}_{\mathrm{the\; si}}}{{\stackrel{.}{v}}_x}.$ If the mass of the truck is M ₁ when the truck is unloaded, the distance from the front axle to the center of mass is a ₁ , the distance from the rear axle to the center of mass is b ₁ , the height of the center of mass is h ₁ , the mass of the truck is M ₂ when the truck is fully loaded, the front axle The distance to the center of mass is a ₂ , the distance from the rear axle to the center of mass is b ₂ , and the height of the center of mass is h ₂ , it can be approximated that with the increase of the load, the change of the height h of the center of mass of the car and the distance a between the center of mass of the car and the front axle The change of satisfies a linear relationship, that is,

$\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

5. According to the mass of the car, the acceleration of the body and the parameters of the body, calculate the normal pressure on the wheel and the ground friction on the wheel to calculate the adhesion coefficient

The positive pressure on the wheels of the car during braking is not only a function of the mass of the car, but also a function of the linear acceleration of the car and the parameters of the body. The relationship is as follows:

$\left\{\begin{array}{c}{N}_1=m((b\&CenterDot;g-{\stackrel{.}{v}}_{x}h)/2L+{\stackrel{.}{v}}_{\mathrm{the\; y}}h/2C)\\ N_2=m((b\&CenterDot;g-{\stackrel{.}{v}}_{x}h)/2L-{\stackrel{.}{v}}_{\mathrm{the\; y}}h/2C)\\ N_3=m((a\&CenterDot;g+{\stackrel{.}{v}}_{x}h)/2L+{\stackrel{.}{v}}_{\mathrm{the\; y}}h/2C)\\ N_4=m((a\&CenterDot;g+{\stackrel{.}{v}}_{x}h)/2L-{\stackrel{.}{v}}_{\mathrm{the\; y}}h/2C)\end{array}\right.$ Where N _i is the positive pressure on the i-th wheel, M is the mass of the vehicle, v _x is the longitudinal velocity of the vehicle, v _y is the lateral velocity of the vehicle, C is the wheelbase of the vehicle, a and b are the front and rear axles to the center of mass of the vehicle The distance, L is the vehicle wheelbase.

Since v _y is very small, the above formula can be simplified as $\left\{\begin{array}{c}{N}_1=m(b\&Center\; Dot;g-{\stackrel{.}{v}}_{x}h)/2L\\ N_2=m(b\&Center\; Dot;g-{\stackrel{.}{v}}_{x}h)/2L\\ N_3=m(a\&CenterDot;g+{\stackrel{.}{v}}_{x}h)/2L\\ N_4=m(a\&CenterDot;g+{\stackrel{.}{v}}_{x}h)/2L\end{array}\right.$

Then the adhesion coefficient between any wheel and the ground can be obtained by the following formula: ${\mathrm{\&mu;}}_i=\frac{N_i}{f_{\mathrm{the\; si}}}$

6. According to the current road surface slip rate collected by the sensor, the theoretical adhesion coefficient of different road surfaces under the current slip rate is calculated by the theoretical formula, and stored in the memory. When the car is running on different road surfaces, the friction force on the wheels is related to the slip rate. Under the same slip rate s, the adhesion coefficient μ produced by different road surfaces is different, and the relationship is as follows:

The current adhesion coefficient calculated from the positive pressure and friction force is continuously calculated and compared with the theoretical adhesion coefficient of the corresponding road surface. If the current adhesion coefficient is close to the theoretical adhesion coefficient under a certain road surface for two consecutive times, it can be judged that the wheel is on the road. On the road, and the state of the road the car is currently driving on.

The method of the invention is simple and the calculation is rapid. It only needs to calculate the ground friction force and the mass of the car according to the angular acceleration of the four wheels, and then calculate the normal pressure on the wheels and obtain the current adhesion coefficient, and then according to the slippage of the wheels Calculate the theoretical adhesion coefficient of the wheel on different road surfaces, and finally compare the current adhesion coefficient with the theoretical adhesion coefficient to judge the state of the road on which the car is driving. This method overcomes the shortcomings of the neural network-based road surface recognition method that requires a large amount of sample data to train the network and has high costs.

Claims (5)

1. A truck ABS road identification method, characterized in that, comprising the steps: (1) The wheel speed sensor extracts the vehicle wheel speed signal during the braking process online, and calculates the slip rate of the wheel during vehicle braking according to the wheel speed signal; (2) Calculate the braking torque produced by the automobile brake according to the gas pressure in the brake chamber; (3) The ground friction force received by the wheel is determined by the braking torque generated by the brake on the wheel and the angular acceleration of the wheel; (4) Calculate the quality of the car according to the ground friction force and the acceleration of the vehicle body, then determine the height of the center of mass and the distance between the center of mass and the front axle and the rear axle of the car according to the quality, and determine the normal pressure on the wheels according to the mass, vehicle body acceleration and vehicle body parameters; (5) Determine the current adhesion coefficient according to the ground friction force and normal pressure received by the wheel; (6) Extract the theoretical adhesion coefficients of different road surfaces under the current slip rate; (7) Compare the current adhesion coefficient with the theoretical adhesion coefficient. If the result of two consecutive comparisons is close to the theoretical adhesion coefficient under a certain road surface, it is judged that the wheel is on the road surface. 2. The method according to claim 1, wherein the wheel speed signal includes the vehicle's linear velocity and wheel angular velocity. 3. The method according to claim 1, characterized in that: the angular acceleration of the wheel is determined according to the wheel speed measured by the wheel speed sensor, and the acceleration of the vehicle body is calculated using the maximum wheel speed method. 4. The method according to any one of claims 1 to 3, characterized in that: the braking torque Mb and the gas pressure P of the braking chamber satisfy the following relationship: $m_b=\left\{\begin{array}{cc}0& P-P_m<0\\ k_p(P-P_m)& P-P_m>0\end{array}\right.$ , where P _m is the pressure required to overcome the spring force in the brake cylinder, and k _p is the braking factor of the brake. 5. The method according to any one of claims 1 to 3, characterized in that: by the formula ${\mathrm{\&mu;}}_i=\frac{N_i}{f_{\mathrm{the\; si}}}$ Determine the current adhesion coefficient μ _i , where N _i and F _si represent the normal pressure and ground friction of the i-th wheel, respectively.

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