A rain day vehicle braking distance estimation method based on intelligent tires

Abstract

The application discloses a rain day vehicle braking distance estimation method based on intelligent tires, which can estimate the vehicle braking distance S through the road surface water depth N, the tire inflation pressure P, the vehicle vertical load T, the tire pattern longitudinal groove width D and the tread wear E. The method considers the road surface water depth, combines the tire inflation pressure, the vehicle vertical load, the tire pattern longitudinal groove width and the tread wear, and aims at estimating the vehicle braking distance under the extreme road conditions in the rain day, so as to guarantee the safety of the driver when braking.

Description

Technical Field

[0001] This invention relates to a method for predicting vehicle braking distance in rainy weather based on smart tires. Background Technology

[0002] The accident rate is higher in rainy weather than in normal weather because the water film on the road surface greatly reduces the friction between the tires and the road surface. Especially when the vehicle is braking, drivers often cannot judge the braking distance, leading to rear-end collisions. With the development of technology, research on vehicle braking safety has emerged, but most of these studies focus on indirect methods to prevent potential dangers during braking and consider relatively limited environmental factors.

[0003] Existing patents include US17026228: a vehicle following control method based on real-time calculation of dynamic safe following distance; US17670527: an intelligent safe vehicle speed measurement method and system considering road conditions; US14978849: a method and device for braking vehicles; CN201721168007.X: a device for improving vehicle driving safety in rainy weather; CN202110040849.1: a method for testing and calculating vehicle braking distance; and CN201610637899.7: a safety braking device and method for autonomous vehicle safety braking. Most of these methods indirectly achieve safety during braking by estimating the real-time distance between the vehicle and the vehicle in front using machine vision technology, or by improving the braking device. However, they lack a direct reference target for the driver to avoid rear-end collisions during braking, and they do not consider extreme situations such as wet roads in rainy weather, thus having significant shortcomings in actual braking safety during rainy weather.

[0004] The development of smart tire technology has enabled us to obtain more and more information from tires, such as tread wear and inflation pressure. Based on this advanced concept, this invention designs a method for predicting vehicle braking distance in rainy weather using smart tires. This method directly estimates the vehicle's braking distance in rainy weather using available parameters such as road surface water depth N, tire inflation pressure P, vehicle vertical load T, tire tread groove width D, and tread wear E. Summary of the Invention

[0005] The present invention provides a method for predicting vehicle braking distance in rainy weather based on smart tires in order to solve the problems existing in the prior art.

[0006] The technical solutions adopted in this invention are as follows:

[0007] A method for predicting vehicle braking distance in rainy weather based on smart tires, including

[0008] Step 1: Use ABAQUS simulation software to build a three-dimensional model of tire-water film-road surface, select the fluid motion model, and build a fluid-structure interaction model to simulate tire hydroplaning when a vehicle is driving on the road in rainy weather.

[0009] Step 2: Based on the working principle of automotive ABS control, the slip ratio is set to 20% when the vehicle speed is >15km / h; and 100% when the vehicle speed is <15km / h, in order to simulate the braking conditions of the vehicle in rainy weather.

[0010] Step 3: For four-wheeled passenger vehicles equipped with disc brakes, derive the braking torque of the front and rear wheels of the four-wheeled passenger vehicle by simultaneously applying Newton's second law, the law of rotation, and the slip ratio formula. , The ABAQUS simulation software directly outputs the slip ratio and corresponding normal force at the contact points between the front and rear tires and the road surface. , ;

[0011] Calculate the tangential friction between the front and rear tires and the road surface. , The frictional energy between the front and rear tires and the road surface is calculated, and the frictional energy of the front and rear wheel brakes is calculated using the kinetic energy theorem. , The rate of change of friction energy between the front and rear tires and the road surface is obtained by differentiation; finally, the total braking time t and braking distance S of the four-wheeled passenger vehicle are calculated.

[0012] Step 4: Select different road surface water depth N, tire inflation pressure P, vehicle vertical load T, tire tread groove width D, and tread wear E, and design several test schemes. Use the established fluid-structure interaction model to perform simulation, output the required normal pressure and slip ratio, calculate the vehicle braking distance, and use a BP neural network to fit the relationship between the five factors of road surface water depth, tire inflation pressure, vehicle vertical load, tire tread groove width, and tread wear and the braking distance.

[0013] Furthermore, in step two, since the vehicle braking process lasts for several seconds, the method of equivalent discretization of the braking interval is adopted to avoid errors caused by the severe tire deformation due to the braking simulation lasting for several seconds.

[0014] Furthermore, the equivalent discretization method for the braking range is as follows: the continuous process of vehicle braking speed range 120~0 km / h is equivalently discretized into 8 sub-intervals, and the speed of each sub-interval is as follows:

[0015] 120km / h-105km / h, 105km / h-90km / h, 90kn / h-75km / h, 75km / h-60km / h, 60km / h-45km / h, 45km / h-30km / h, 30km / h-15km / h, 15km / h-0km / h;

[0016] Within the speed range of 120~15km / h, the slip ratio is controlled at 20% for each speed point; within the speed range of less than 15km / h, the slip ratio is set to 100%.

[0017] The slip ratio is controlled at the velocity corresponding to the endpoint of each discrete sub-interval for simulation. After simulation by ABAQUS simulation software, the slip ratio of the front and rear tires and the corresponding normal force at the contact point between the tires and the road surface are output.

[0018] Furthermore, in step three, for four-wheeled passenger vehicles equipped with disc brakes, according to Newton's second law and the law of rotation:

[0019] ,

[0020] ,

[0021] ,

[0022] in:

[0023] , This refers to the frictional force between the front and rear wheels and the road surface.

[0024] , The moment of inertia of the front and rear wheels;

[0025] , The angular velocities of the front and rear wheels;

[0026] , The rolling radius of the front and rear wheels;

[0027] , This refers to the braking torque of the front and rear wheels;

[0028] For the overall vehicle weight;

[0029] The slip ratio formula is:

[0030] ,

[0031] By applying Newton's second law and the law of rotation simultaneously, we can obtain the braking torque of the front and rear wheels:

[0032] ,

[0033] ,

[0034] Since this is designed for four-wheeled passenger vehicles equipped with disc brakes, during vehicle braking, the hydraulic cylinder in the disc brake drives the piston caliper to press the friction pads against the brake disc. The pressure between the friction pads and the brake disc is:

[0035] ,

[0036] The friction braking force is:

[0037] ,

[0038] in:

[0039] The contact radius between the piston caliper and the brake disc;

[0040] The coefficient of friction between the friction pad and the brake disc;

[0041] Brake fluid pressure is the ratio of friction braking force to the cross-sectional area of ​​the brake wheel cylinder.

[0042] ,

[0043] ,

[0044] in:

[0045] A is the cross-sectional area of ​​the brake wheel cylinder;

[0046] , For the hydraulic pressure of the front and rear wheel cylinders;

[0047] After simulation using ABAQUS software, the normal force and slip ratio at the contact points between the front and rear tires and the road surface were obtained.

[0048] Therefore, the tangential friction force exerted by the road surface on the front and rear tires is:

[0049] ,

[0050] ,

[0051] in:

[0052] This is the coefficient of friction between the tire and the road surface;

[0053] , This refers to the normal force at the contact points between the front and rear tires and the road surface.

[0054] The frictional energies between the front and rear tires and the road surface are respectively:

[0055] ,

[0056] ,

[0057] According to the kinetic energy theorem, the frictional energy of the front and rear wheel brakes... , for:

[0058] ,

[0059] ,

[0060] Differential calculation yields the rate of change of frictional energy between the tire and the road surface. , and the rate of change of frictional energy of the front and rear brakes , :

[0061] ,

[0062] ,

[0063] ,

[0064] ,

[0065] in:

[0066] L is the total slip distance of the front and rear wheels during braking. and The slip distance at the i-th node in the contact area between the front and rear wheels and the road surface. , The slip ratio of the contact points between the front and rear wheels and the road surface; Let be the effective radius of the brake disc, and be an inherent design parameter of the brake.

[0067] Assuming all of the vehicle's kinetic energy is converted into frictional energy between the tires and the braking system, according to the work-energy theorem:

[0068] ,

[0069] Discretizing it yields:

[0070] ,

[0071] Therefore, the vehicle is Time spent within the interval for:

[0072] ,

[0073] This yields the vehicle's total braking time t and total braking distance S:

[0074] ,

[0075] ,

[0076] in: For a vehicle in a discrete sub-interval The increase in time spent internally.

[0077] Furthermore, in step four, "arranging and designing several experimental schemes" means: using a uniform design experiment to obtain a total of 70 sets of experimental sample data.

[0078] The present invention has the following beneficial effects:

[0079] This invention takes into account the depth of water accumulation on the road surface, combined with tire inflation pressure, vehicle vertical load, tire tread groove width, and tire wear. Its purpose is to predict the vehicle braking distance under extreme road conditions in rainy weather, ensuring the safety of drivers during braking. Attached Figure Description

[0080] Figure 1 The fluid-structure interaction model established for this invention.

[0081] Figure 2 This is a graph showing the relationship between slip ratio and wheel braking adhesion coefficient.

[0082] Figure 3 This is a flowchart for "equivalent discretization of braking interval".

[0083] Figure 4 This is a schematic diagram of the forces acting on the wheel during braking.

[0084] Figure 5 The BP neural network model established for this invention.

[0085] Figure 6 This is an error diagram showing the difference between the simulation results and the predicted results. Detailed Implementation

[0086] The invention will now be further described with reference to the accompanying drawings.

[0087] When driving in the rain, the presence of a film of water between the tires and the road surface significantly increases the braking distance. Compared to sunny weather, it is more difficult for drivers to judge the braking distance, making rear-end collisions and other traffic accidents more likely. Current safety measures for driving in the rain mostly involve improving braking systems, adding auxiliary tools, and maintaining a safe following distance. However, these measures do not directly reduce the danger of braking in the rain for the driver.

[0088] This invention abandons the traditional concept and uses a method to predict the vehicle braking distance S by considering the road surface water depth N, tire inflation pressure P, vehicle vertical load T, tire tread groove width D, and tire wear E.

[0089] Combination Figures 1 to 6 The present invention provides the following technical solution: taking into account the depth of water accumulation on the road surface, combined with tire inflation pressure, vehicle vertical load, tire tread groove width and tread wear, the purpose is to estimate the vehicle braking distance under extreme road conditions in rainy weather, so as to ensure the safety of the driver when braking.

[0090] To achieve the above objectives, the present invention provides a method for predicting vehicle braking distance in rainy weather based on smart tires, comprising the following steps:

[0091] Step 1: Use ABAQUS simulation software to build a three-dimensional model of tire-water film-road surface, select the fluid motion model, and build a fluid-structure interaction model to simulate tire hydroplaning when a vehicle is driving on the road in rainy weather.

[0092] Among them: the tire-water film-road surface fluid-structure interaction model established in step one is as follows: Figure 1 As shown, the tire model is 205 / 55 R 15, with three longitudinal grooves on the tread. Compared to four-groove tires, three-groove tires have a larger contact area with the road surface and reduce the probability of foreign objects getting stuck in the grooves, so they are now widely used. The tire surface pattern is a uniform pitch tread pattern. Fluid-structure interaction is implemented using a fluid motion model, applying an initial velocity of water to impact the tire to simulate vehicle movement. In this fluid motion model, the tire is fixed, so there is no need to lay a long water film, greatly reducing the computer simulation time.

[0093] Step Two: Considering the working principle of automotive ABS control, a slip ratio of 20% is set when the vehicle speed is >15km / h; and a slip ratio of 100%, i.e., complete lock-up, is set when the vehicle speed is <15km / h. This simulates the braking conditions of the vehicle in rainy weather. Considering that the braking process lasts for several seconds, the error of explicit transient simulation would be too large. Therefore, the "braking range equivalent discretization" method is adopted to avoid errors caused by the severe tire deformation due to the several seconds of braking simulation.

[0094] Wherein: the slip ratio setting in step two is taken from... Figure 2 The curve showing the relationship between slip ratio and tire braking adhesion coefficient shows that when the slip ratio is controlled at 20%, the tire can obtain the maximum road adhesion.

[0095] The flowchart for the "equivalent discretization of the braking interval" described in step two is as follows: Figure 3 As shown, this refers to the equivalent discretization of the continuous braking speed range of 120~0 km / h into 8 sub-intervals.

[0096] The speeds for each sub-section are as follows: 120km / h-105km / h, 105km / h-90km / h, 90km / h-75km / h, 75km / h-60km / h, 60km / h-45km / h, 45km / h-30km / h, 30km / h-15km / h, and 15km / h-0km / h.

[0097] Within the speed range of 120~15km / h, the slip ratio is controlled at 20% for each speed point, and set to 100% for speeds less than 15km / h. The slip ratio is controlled at the speed points corresponding to the endpoints of each discrete sub-interval for simulation, and the normal pressure and slip ratio at the grounding node are output using post-processing.

[0098] Step 3: For four-wheeled passenger vehicles equipped with disc brakes, derive the braking torque of the front and rear wheels by simultaneously applying Newton's second law, the law of rotation, and the slip ratio formula. , Because simulation technology is used (i.e., ABAQUS simulation software), the normal force at the contact point between the front and rear tires and the road surface is... , The corresponding slip ratio can be directly output, and the tangential friction force between the front and rear tires and the road surface can be calculated. , The frictional energy of the front and rear wheel brakes can be calculated using the kinetic energy theorem. , The rate of change of frictional energy is obtained by differentiation. Since all the vehicle's kinetic energy is converted into frictional energy between the tires, the road surface, and the braking system, an equation can be established based on the kinetic energy theorem and the law of conservation of energy. After discretizing this equation, the time increment spent by the vehicle within an equivalent discrete sub-interval can be obtained. Thus, the total braking time t and braking distance S can be calculated.

[0099] In step three, the total braking time for a four-wheeled passenger vehicle equipped with disc brakes is as follows:

[0100] ,

[0101] in: For a vehicle in a discrete sub-interval The increase in time spent internally;

[0102] The total braking distance is:

[0103] ,

[0104] A diagram illustrating the forces acting on the tires during braking is shown below. Figure 4 As shown, the derivation of the formulas involved in step three is given below.

[0105] The following section explains the calculation derivation of the total braking time t and braking distance S mentioned in step three.

[0106] For four-wheeled passenger vehicles, according to Newton's second law and the law of rotation:

[0107] ,

[0108] ,

[0109] ,

[0110] in:

[0111] , This refers to the frictional force between the front and rear wheels and the road surface.

[0112] , The moment of inertia of the front and rear wheels;

[0113] , The angular velocities of the front and rear wheels;

[0114] , The rolling radius of the front and rear wheels;

[0115] , This refers to the braking torque of the front and rear wheels;

[0116] For the overall vehicle weight.

[0117] The slip ratio formula is:

[0118] ,

[0119] By applying Newton's second law and the law of rotation simultaneously, we can obtain the braking torque of the front and rear wheels:

[0120] ,

[0121] ,

[0122] Since this is designed for four-wheeled passenger vehicles equipped with disc brakes, during vehicle braking, the hydraulic cylinder drives the piston caliper to press the friction pads against the brake disc. The pressure between the friction pads and the brake disc is:

[0123] ,

[0124] The friction braking force is:

[0125] ,

[0126] in:

[0127] The contact radius between the piston caliper and the brake disc;

[0128] The friction coefficient is the coefficient of friction between the friction pad and the brake disc.

[0129] Brake fluid pressure is the ratio of friction braking force to the cross-sectional area of ​​the brake wheel cylinder.

[0130] ,

[0131] ,

[0132] in:

[0133] A is the cross-sectional area of ​​the brake wheel cylinder;

[0134] , This refers to the hydraulic pressure of the front and rear wheel cylinders.

[0135] After post-processing the simulation using ABAQUS software, the normal force and slip ratio at the contact points between the front and rear tires and the road surface can be obtained. Therefore, the tangential frictional force exerted by the road surface on the front and rear tires is:

[0136] ,

[0137] ,

[0138] in:

[0139] This is the coefficient of friction between the tire and the road surface;

[0140] , This refers to the normal force at the contact points between the front and rear tires and the road surface.

[0141] The frictional energy between the front and rear tires and the road surface is:

[0142] ,

[0143] ,

[0144] According to the kinetic energy theorem, the frictional energy of the front and rear wheel brakes... , for:

[0145]

[0146]

[0147] Differential calculation yields the rate of change of frictional energy between the tire and the road surface. , and the rate of change of frictional energy of the front and rear brakes , :

[0148] ,

[0149] ,

[0150] ,

[0151] ,

[0152] in:

[0153] L is the total slip distance of the front and rear wheels during braking. and The slip distance at the i-th node in the contact area between the front and rear wheels and the road surface. , The slip ratio of the front and rear wheels at the contact points with the road surface (which can be obtained directly through simulation post-processing); Let be the effective radius of the brake disc, and be the inherent design parameter of the brake.

[0154] Assuming all of the vehicle's kinetic energy is converted into frictional energy between the tires and the braking system, according to the work-energy theorem:

[0155] ,

[0156] Discretizing it yields:

[0157] ,

[0158] Therefore, the vehicle is Time spent within the interval for:

[0159] ,

[0160] This yields the total braking time t and braking distance S:

[0161] ,

[0162] .

[0163] Step 4: Select different road surface water depth N, tire inflation pressure P, vehicle vertical load T, tire tread groove width D, and tread wear E, and arrange them appropriately to design a uniform design test to obtain a total of 70 sets of test sample data.

[0164] The established fluid-structure interaction model is used for simulation to output the required data such as the nodal normal pressure and nodal slip ratio between the tire and the road surface, and the vehicle braking distance is calculated.

[0165] This invention considers the complex mechanical relationship between the tire, water layer, and road surface, and uses a BP neural network to fit the relationship between various influencing factors (road surface water depth, tire inflation pressure, vehicle vertical load, tire tread groove width, and tread wear combined) and braking distance. The BP neural network model is as follows: Figure 5 As shown. Preliminary fitting results are as follows. Figure 6 As shown, the predicted curve and the actual simulation curve have a high degree of overlap.

[0166] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for predicting vehicle braking distance in rainy weather based on smart tires, characterized in that: include: Step 1: Use ABAQUS simulation software to build a three-dimensional model of tire-water film-road surface, select the fluid motion model, and build a fluid-structure interaction model to simulate tire hydroplaning when a vehicle is driving on the road in rainy weather. Step 2: Based on the working principle of automotive ABS control, the slip ratio is set to 20% when the vehicle speed is >15km / h; and 100% when the vehicle speed is <15km / h, in order to simulate the braking conditions of the vehicle in rainy weather. Step 3: For four-wheeled passenger vehicles equipped with disc brakes, derive the braking torque of the front and rear wheels of the four-wheeled passenger vehicle by simultaneously applying Newton's second law, the law of rotation, and the slip ratio formula. , The ABAQUS simulation software directly outputs the slip ratio and corresponding normal force at the contact points between the front and rear tires and the road surface. , ; Calculate the tangential friction between the front and rear tires and the road surface. , The frictional energy between the front and rear tires and the road surface is calculated, and the frictional energy of the front and rear wheel brakes is calculated using the kinetic energy theorem. , The rate of change of friction energy between the front and rear tires and the road surface and the rate of change of friction energy between the front and rear wheel brakes are obtained by differentiation; finally, the total braking time t and braking distance S of the four-wheeled passenger vehicle are calculated. Step 4: Select different road surface water depth N, tire inflation pressure P, vehicle vertical load T, tire tread groove width D, and tread wear E, and design several test schemes. Use the established fluid-structure interaction model to perform simulation, output the required normal pressure and slip ratio, calculate the vehicle braking distance, and use a BP neural network to fit the relationship between the five factors of road surface water depth, tire inflation pressure, vehicle vertical load, tire tread groove width, and tread wear and the braking distance.

2. The method for predicting vehicle braking distance in rainy weather based on smart tires as described in claim 1, characterized in that: In step two, since the vehicle braking process lasts for several seconds, the method of equivalent discretization of the braking range is adopted to avoid errors caused by the severe tire deformation due to the braking simulation lasting for several seconds.

3. The method for predicting vehicle braking distance in rainy weather based on smart tires as described in claim 2, characterized in that: The equivalent discretization method for the braking range is as follows: the continuous process of vehicle braking speed range from 120 to 0 km / h is equivalently discretized into 8 sub-ranges, and the speed of each sub-range is as follows: 120km / h-105km / h, 105km / h-90km / h, 90kn / h-75km / h, 75km / h-60km / h, 60km / h-45km / h, 45km / h-30km / h, 30km / h-15km / h, 15km / h-0km / h; Within the speed range of 120~15km / h, the slip ratio is controlled at 20% for each speed point; within the speed range of less than 15km / h, the slip ratio is set to 100%. The slip ratio is controlled at the velocity corresponding to the endpoint of each discrete sub-interval for simulation. After simulation by ABAQUS simulation software, the slip ratio of the front and rear tires and the corresponding normal force at the contact point between the tires and the road surface are output.

4. The method for predicting vehicle braking distance in rainy weather based on smart tires as described in claim 3, characterized in that: In step three, for four-wheeled passenger vehicles equipped with disc brakes, according to Newton's second law and the law of rotation, we obtain: ， ， ， in: , This refers to the frictional force between the front and rear wheels and the road surface. , The moment of inertia of the front and rear wheels; , The angular velocities of the front and rear wheels; , The rolling radius of the front and rear wheels; , This refers to the braking torque of the front and rear wheels; For the overall vehicle weight; The slip ratio formula is: ， By applying Newton's second law and the law of rotation simultaneously, we can obtain the braking torque of the front and rear wheels: ， ， Since this is designed for four-wheeled passenger vehicles equipped with disc brakes, during vehicle braking, the hydraulic cylinder in the disc brake drives the piston caliper to press the friction pads against the brake disc. The pressure between the friction pads and the brake disc is: ， The friction braking force is: ， in: The contact radius between the piston caliper and the brake disc; The coefficient of friction between the friction pad and the brake disc; Brake fluid pressure is the ratio of friction braking force to the cross-sectional area of ​​the brake wheel cylinder. ， ， in: A is the cross-sectional area of ​​the brake wheel cylinder; , For the hydraulic pressure of the front and rear wheel cylinders; After simulation using ABAQUS software, the normal force and slip ratio at the contact points between the front and rear tires and the road surface were obtained. Therefore, the tangential friction force exerted by the road surface on the front and rear tires is: ， ， in: This is the coefficient of friction between the tire and the road surface; , This refers to the normal force at the contact points between the front and rear tires and the road surface. The frictional energies between the front and rear tires and the road surface are respectively: ， ， According to the work-energy theorem, the frictional energy of the front and rear wheel brakes... , for: ， ， Differential calculation yields the rate of change of frictional energy between the tire and the road surface. , and the rate of change of frictional energy of the front and rear wheel brakes , : ， ， ， ， in: L is the total slip distance of the front and rear wheels during braking. and The slip distance at the i-th node in the contact area between the front and rear wheels and the road surface. , Let S be the slip ratio of the front and rear wheels at the contact points with the road surface; assuming that all the vehicle's kinetic energy is converted into frictional energy between the tires and the braking system, we can obtain the following from the kinetic energy theorem: ， Discretizing it yields: ， Therefore, the vehicle is Time spent within the interval for: ， This yields the vehicle's total braking time t and total braking distance S: ， ， in: For a vehicle in a discrete sub-interval The increase in time spent internally.

5. The method for predicting vehicle braking distance in rainy weather based on smart tires as described in claim 1, characterized in that: In step four, designing several experimental schemes means that a total of 70 sets of experimental sample data were obtained by using a uniform design experiment.

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