A method for analyzing and evaluating automobile brake judder

Abstract

The present invention discloses a brake jitter analysis and evaluation method, which selects a specific sample car brake disc for a brake system bench test to obtain the braking torque fluctuation value generated by the thickness difference of the brake disc; establishes a multi-body dynamics model of the sample car in the simulation software, and establishes the braking torque calculation model of the normal braking system and the braking torque calculation model containing torque fluctuation according to the braking system parameters; after calculating and updating the braking torque fluctuation coefficient, the model is simulated for brake jitter; and finally obtains the amplitude of the vibration rate frequency domain value of the circumferential tangent of the steering wheel of the sample car and the longitudinal and lateral vibration rate at the seat rail, which is used as the characteristic value basis for evaluating the anti-brake jitter performance of the automobile. The method of the present invention combines bench testing and simulation models, converts the thickness difference of the brake disc into a braking torque fluctuation that can be directly input into the multi-body dynamics model, reproduces the characteristics of the braking torque fluctuation changing with the vehicle speed in the model, improves the accuracy of the simulation, and can effectively shorten the research and development cycle.

Description

Technical Field

[0001] The invention belongs to the field of automobile chassis performance development, and in particular relates to an automobile brake jitter analysis and evaluation method. Background Art

[0002] Automobile brake judder refers to the phenomenon that the steering wheel and the body of the vehicle shake violently during the braking process when the vehicle is driving at high speed. It usually occurs during braking at medium deceleration and is a typical major brake failure. Brake judder seriously affects the comfort and driving experience of the vehicle and interferes with the vehicle's handling performance.

[0003] The mechanism of brake judder is that the braking torque generated by the automobile braking system fluctuates, causing the vibration of the brake, which is transmitted to the steering wheel and the body through the suspension system and the steering system, causing the steering wheel and the seat to vibrate, causing the driver to feel uncomfortable. The root cause is the uneven contact between the brake disc and the brake caliper when the brake is working, which is mainly determined by the thickness difference and end face runout of the brake disc. Among them, the thickness difference (Disk Thickness Variation, DTV) of the brake disc is the main factor.

[0004] At present, in the process of automobile product development, the evaluation and prediction method for brake judder phenomenon is usually a real-car brake driving evaluation, and the brake judder fault is checked by replacing the suspension-related parts. The real-car test requires a long preparation time and needs to wait for the prototype to be fully manufactured. It has the disadvantages of long implementation cycle, high cost, and inability to predict risks early. On the other hand, the troubleshooting method of using parts replacement makes the fault analysis inefficient and cannot quickly verify the chassis design parameters and key influencing factors in the evaluation of anti-brake judder performance. Summary of the invention

[0005] In view of the above situation, the present invention proposes a method for analyzing and evaluating automobile brake jitter, which solves the shortcomings of long actual vehicle testing cycle and high cost, and realizes efficient evaluation and prediction of the automobile's anti-brake jitter performance in a simulation environment.

[0006] The brief principle of the present invention is as follows: by selecting a specific sample car brake disc for a brake system bench test, the braking torque fluctuation value generated by the thickness difference of the brake disc is obtained. A multi-body dynamics model of the sample car is established in the simulation software, and the braking torque calculation model of the normal braking system and the braking torque containing torque fluctuation are respectively established according to the braking system parameters. After calculating and updating the braking torque fluctuation coefficient, the model is subjected to brake jitter simulation. Finally, the amplitude of the vibration rate frequency domain value of the sample car's steering wheel circumferential tangent and the longitudinal and lateral vibration rate at the seat rails is obtained as the characteristic value basis for evaluating the vehicle's anti-brake jitter performance. The specific technical scheme of the present invention is as follows:

[0007] Step S1, select a specific sample vehicle brake disc, the thickness difference of which is the upper limit value Dmax allowed by the design, perform a brake bench test on the brake disc, and obtain a braking torque fluctuation value Tv generated by the thickness difference of the brake disc.

[0008] Specifically, a brake bench test is performed using a brake inertia test bench, and specific brake discs, brake calipers, wheel hubs and other brake system components of the prototype vehicle are installed on the test bench. The mass of the inertia wheel loaded on the test bench is set according to the vehicle inertia of the prototype vehicle, the spindle speed of the test bench is adjusted to make the brake disc reach the specified initial braking velocity V, and the brake line pressure of the test bench is adjusted to make the brake disc brake at a constant braking deceleration a. The initial braking velocity V and braking deceleration a selected for the test are medium-intensity braking conditions during high-speed driving where automobile brake judder often occurs. During the braking process, when the braking torque is stabilized, the difference between the peak and the trough of the braking torque is measured, which is the braking torque fluctuation value Tv generated by the limit state excitation of the brake disc thickness difference;

[0009] Step S2, establishing a multi-body dynamics model of the prototype vehicle in the simulation software, and establishing a calculation model of the braking torque Tn normally generated by the braking system on each side according to the braking system parameters.

[0010] Specifically, the multi-body dynamics model of the prototype vehicle consists of a body system, a chassis system, a steering system, a braking system, and a tire model. The prototype vehicle's parameters such as vehicle mass, moment of inertia, and center of mass coordinates are input into the body system of the model; the prototype vehicle's suspension parameters such as spring stiffness, bushing stiffness, and shock absorber damping are input into the chassis system; the steering system parameters such as steering gear ratio, steering gear torsion bar stiffness, and steering wheel moment of inertia are input into the steering system; and the brake system parameters such as brake friction coefficient u, brake disc effective radius R, and brake cylinder piston area A are input into the braking system. The braking torque Tn normally generated by the braking system is determined by these braking system parameters and the brake line pressure P required for the braking deceleration.

[0011] The calculation formula of the braking torque Tn normally generated by the braking system on each side of the sample vehicle is as follows:

[0012] Tn=2·A·P·u·R

[0013] Where Tn is the braking torque normally generated by the unilateral braking system;

[0014] A is the brake cylinder piston area;

[0015] P is the brake line pressure;

[0016] u is the brake friction coefficient;

[0017] R is the effective radius of the brake disc.

[0018] Step S3, input the braking torque fluctuation into the braking torque calculation model of the braking system of the multi-body dynamics model. Because the front wheel braking force contribution is much greater than the rear wheel when the vehicle brakes, and the unilateral braking torque fluctuation will make the left and right braking forces of the vehicle unbalanced, causing more significant braking tremor, so the braking torque Ta containing the torque fluctuation is input into the left front side braking torque calculation model of the braking system, and the braking torque calculation models of the right front side and the left and right rear sides maintain the normally generated braking torque Tn.

[0019] Furthermore, under normal circumstances, the uneven thickness of the brake disc reaches a peak at a certain point on the end surface of the brake disc. According to the working principle of the disc brake, when the brake disc rotates one circle, the uneven thickness of the brake disc will produce a brake pressure fluctuation, which will lead to a period of braking torque fluctuation. Therefore, the fluctuation period of the braking torque is corresponding to the rotation period of the brake disc. The periodic fluctuation of the braking torque is approximated as a trigonometric function. According to the relationship between the braking torque fluctuation and the same period of the brake disc rotation, it can be deduced that the braking torque Ta containing torque fluctuation is jointly determined by the normal braking torque Tn, the braking torque fluctuation coefficient k, and the rotation direction of the brake disc. The calculation formula is as follows:

[0020] Ta=Tn·(1-k·SIN(A))

[0021] Where Ta is the braking torque including torque fluctuation;

[0022] Tn is the braking torque normally generated by the braking system on that side;

[0023] k is the braking fluctuation coefficient, and its initial value is 0;

[0024] A is the change in the angle of the brake disc relative to the caliper over time.

[0025] Step S4, in the simulation software, an initial braking simulation is performed on the multi-body dynamics model of the prototype vehicle, and after calculating and updating the braking torque fluctuation coefficient k value, a braking judder simulation is performed.

[0026] Specifically, the simulated vehicle speed of the prototype vehicle model and the brake line pressure P of the braking system are adjusted so that the prototype vehicle model travels in a straight line at the same initial braking speed V as in step S1 and brakes at a braking deceleration a. Since the initial braking fluctuation coefficient k is 0, the braking torque Ta of the left front side is equal to the normal braking torque Tn at this time. According to the calculation formula of the braking torque fluctuation coefficient, the k value in the braking torque calculation model of the left front side is calculated and updated, and the braking simulation is performed again under the same working condition. The prototype vehicle model will experience braking tremor under the excitation of the left front side braking torque fluctuation.

[0027] The calculation formula of the braking torque fluctuation coefficient k is as follows:

[0028] k=0.5·Tv / Tn

[0029] Where k is the braking torque fluctuation coefficient;

[0030] Tv is the braking torque fluctuation value;

[0031] Tn is the braking torque normally generated by the braking system on that side;

[0032] Step S5, in the simulation software, obtain the amplitudes of the frequency domain values ​​of the steering wheel circumferential tangential vibration rate Vsw, the longitudinal vibration rate Vstx at the seat rail, and the lateral vibration rate Vsty of the prototype vehicle as the characteristic value basis for evaluating the anti-braking judder performance of the vehicle.

[0033] Specifically, the braking torque fluctuation generated by the brake is transmitted from the suspension to the steering gear, causing the steering wheel to produce circumferential tangential vibration, and at the same time, it is transmitted from the suspension to the subframe, causing longitudinal and lateral vibrations at the body seat, thereby causing discomfort to the driver's hands and body. During the occurrence of brake tremor, the vibration rate at each location changes with the time period. In order to facilitate identification and processing, the time domain value of the vibration needs to be Fourier transformed and converted into a frequency domain value. Finally, the steering wheel circumferential tangential vibration rate Vsw, the longitudinal vibration rate Vstx and the lateral vibration rate Vsty at the seat rail under the frequency domain value are obtained as the characteristic value basis for evaluating the anti-brake tremor performance of the vehicle. The smaller the amplitude of the vibration rate, the weaker the intensity of the resonance generated when the vehicle has brake tremor, and the better the driver's comfort.

[0034] Compared with the prior art, the benefits of the present invention are as follows:

[0035] 1. The present invention converts the thickness difference of the brake disc into a braking torque fluctuation that can be directly input into the automobile multi-body dynamics model by combining bench testing and simulation models, thereby solving the problem that the automobile multi-body dynamics model cannot directly handle the influence of the thickness difference of the brake disc on the braking torque and avoiding the shortcomings of using theoretical empirical value input methods;

[0036] 2. Based on the relationship that the fluctuation of the braking torque and the rotation of the brake disc are in the same period, the present invention uses trigonometric functions to associate the fluctuation of the braking torque with the rotational orientation of the brake disc, and reproduces the characteristics of the fluctuation of the braking torque with the vehicle speed in the model, which is consistent with the actual situation and improves the accuracy of the simulation;

[0037] 3. The present invention uses the amplitude of the steering wheel's circumferential tangential vibration rate, the longitudinal vibration rate at the seat rail, and the lateral vibration rate as the characteristic value basis for evaluating the automobile's anti-brake jitter performance. The analysis result corresponds to the actual driver's subjective feeling, making the brake jitter prediction more accurate, and can quickly verify the chassis design parameters through the model to achieve efficient analysis and optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention is a flow chart of a method for analyzing and evaluating automobile brake jitter.

[0039] Figure 2 Schematic diagram of the multi-body dynamics model of the sample vehicle in the embodiment of the present invention.

[0040] Figure 3 It is a schematic diagram of the braking torque fluctuation generated by the braking system of the model in the embodiment of the present invention.

[0041] Figure 4 It is a schematic diagram of converting the time domain value of the vibration rate into the frequency domain value in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to more clearly illustrate the purpose, technical route and advantages of the present invention, specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0043] The present invention provides an automobile brake jitter analysis and evaluation method, which is applied to the development of automobile chassis performance. The background of this embodiment is to evaluate and predict the anti-brake jitter performance of a prototype car under development to verify the rationality of the chassis design.

[0044] Example: See Figure 1-Figure 4 .

[0045] like Figure 1 The flowchart of the method of the present invention is shown. The method of analyzing and evaluating automobile brake jitter of the present invention comprises the following steps:

[0046] Step S1. Select a specific sample vehicle brake disc, the thickness difference of which is the upper limit value Dmax allowed by the design, perform a brake bench test on the brake disc, and obtain a braking torque fluctuation value Tv generated by the thickness difference of the brake disc;

[0047] Step S2. Establish a multi-body dynamics model of the prototype vehicle in the simulation software, and establish a calculation model of the braking torque Tn normally generated by the braking system on each side according to the braking system parameters;

[0048] Step S3. Input the braking torque fluctuation into the braking torque calculation model of the braking system of the multi-body dynamics model: input the braking torque Ta containing the torque fluctuation into the left front braking torque calculation model, and the braking torque calculation models of the right front side and the left rear side and the right rear side maintain the normally generated braking torque Tn;

[0049] Step S4. Performing an initial braking simulation on the multi-body dynamics model of the sample vehicle with the braking torque input in step S3, calculating and updating the braking torque fluctuation coefficient k value, and then performing a braking tremor simulation;

[0050] Step S5. Obtain the amplitudes of the frequency domain values ​​of the circumferential tangential vibration rate Vsw of the steering wheel of the prototype vehicle, the longitudinal vibration rate Vstx at the seat rail, and the lateral vibration rate Vsty from the brake jitter simulation results of the prototype vehicle in step S4 as characteristic values ​​for evaluating the anti-brake jitter performance of the vehicle.

[0051] See also Figure 1-Figure 4 The method of the present invention is further described below through a specific automobile brake jitter analysis and evaluation process.

[0052] Step S1. The allowable thickness difference requirement for the front wheel brake disc of the prototype vehicle is DTV≤20um. A specific brake disc with a thickness difference of Dmax=20um is selected, and a brake bench test is performed using a brake inertia test bench. Install specific brake discs, brake calipers, wheel hubs and other brake system components of the prototype vehicle on the test bench, and set the inertia wheel mass loaded on the test bench according to the vehicle inertia of the prototype vehicle. The test conditions are an initial braking speed of 120km / h and a braking deceleration of 0.25g, where the braking judder phenomenon of this vehicle type often occurs. Adjust the spindle speed of the test bench so that the initial braking speed V=120km / h, and adjust the brake line pressure of the test bench so that the braking deceleration is a=0.25g. During the braking process, when the braking torque is stably established, the difference between the peak and the trough of the braking torque is measured, that is, the braking torque fluctuation value Tv=104N·m;

[0053] Step S2. Establish a multi-body dynamics model of the prototype vehicle in the simulation software Adams, such as Figure 2 As shown. In the body system of the model, input the whole vehicle parameters such as the whole vehicle mass, moment of inertia, and center of mass coordinates of the prototype vehicle; in the chassis system, input the suspension parameters such as the spring stiffness, bushing stiffness, and shock absorber damping of the prototype vehicle; in the steering system, input the steering system parameters such as the steering gear ratio, steering gear torsion bar stiffness, and steering wheel moment of inertia. In order to solve the braking torque Tn normally generated on each side of the braking system during simulation, the brake friction coefficient u, the brake disc effective radius R, and the brake cylinder piston area A are input into the expression of the braking torque calculation model on each side according to the formula Tn=2·A·P·u·R.

[0054] Step S3. In the multi-body dynamics model, input the braking torque fluctuation into the braking torque calculation model of the prototype vehicle. Use the formula Ta=Tn·(1-k·SIN(A)) to modify the expression of the braking torque Tn normally generated on the left front side into the expression of the braking torque Ta containing the torque fluctuation, where the initial value of the braking torque fluctuation coefficient k is 0, and specify the expression of A in the model as the angle of rotation of the brake disc relative to the caliper. The braking torque calculation models of the right front side and the left and right rear sides maintain the expression of the braking torque Tn normally generated.

[0055] Step S4. Perform an initial braking simulation on the multi-body dynamics model of the prototype vehicle. Set the simulated vehicle speed so that the prototype vehicle model travels in a straight line at an initial velocity V = 120 km / h. Adjust the value of the brake line pressure P in the model so that the prototype vehicle model brakes at a braking deceleration of a = 0.25g. It is found that the braking torque Tn = 896 N·m normally generated on the left front side at this time, and then the braking fluctuation coefficient k = 0.058 is calculated according to the formula k = 0.5·Tv / Tn. Update the k value in the expression of the adjustment model Ta, and perform brake jitter simulation under the same working conditions. The prototype vehicle model will Figure 3 Brake judder occurs under the stimulation of the braking torque fluctuation shown.

[0056] Step S5. After the simulation is completed, the time domain values ​​of the circumferential tangential vibration rate Vsw of the steering wheel of the prototype vehicle, the longitudinal vibration rate Vstx at the seat rail, and the lateral vibration rate Vsty are obtained, and the time domain values ​​are Fourier transformed using software to convert them into frequency domain values, such as Figure 4 The amplitude of the vibration rate frequency domain values ​​at the steering wheel and seat rails are recorded, as shown in Table 1. These values ​​reflect the strength of the resonance generated during the brake judder phenomenon and the driver's comfort. The analysis results can be compared with other similar models as a basis for evaluating the characteristic value of the sample vehicle's anti-brake judder performance.

[0057] Table 1 Amplitude table of vibration velocity frequency domain values ​​at the steering wheel and seat rail

[0058]

[0059] The above embodiment is only a preferred example of the present invention, and its purpose is to further explain the technical ideas in detail, rather than to limit the method of the present invention in any form. Non-substantial modifications and equivalent substitutions made by technicians in this field to the specific technical solutions without departing from the method concept and claims of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for analyzing and evaluating automobile brake jitter, characterized in that: The steps include: Step S1. Select a specific sample vehicle brake disc, the thickness difference of which is the upper limit value Dmax allowed by the design, perform a brake bench test on the brake disc, and obtain a braking torque fluctuation value Tv generated by the thickness difference of the brake disc; Use the brake inertia test bench to carry out the brake bench test, install the brake system components of the prototype vehicle on the test bench, set the inertia wheel mass loaded on the test bench according to the vehicle inertia of the prototype vehicle, adjust the spindle speed of the test bench so that the brake disc reaches the specified initial braking speed V, adjust the brake line pressure of the test bench so that the brake disc brakes at a constant braking deceleration a, and the initial braking speed V and braking deceleration a selected for the test are medium-intensity braking conditions during high-speed driving where the automobile brake judder phenomenon often occurs. During the braking process, when the braking torque is stably established, measure the difference between the peak and the trough of the braking torque, which is the braking torque fluctuation value Tv generated by the limit state excitation of the thickness difference of the brake disc; Step S2. Establish a multi-body dynamics model of the prototype vehicle in the simulation software, and establish a calculation model of the braking torque Tn normally generated by the braking system on each side according to the braking system parameters; Step S3. Input the braking torque fluctuation into the braking torque calculation model of the braking system of the multi-body dynamics model: input the braking torque Ta containing the torque fluctuation into the left front braking torque calculation model, and the braking torque calculation models of the right front side and the left rear side and the right rear side maintain the normally generated braking torque Tn; Step S4. Performing an initial braking simulation on the multi-body dynamics model of the sample vehicle with the braking torque input in step S3, calculating and updating the braking torque fluctuation coefficient k value, and then performing a braking tremor simulation; Step S5. Obtain the amplitudes of the frequency domain values ​​of the circumferential tangential vibration rate Vsw of the steering wheel of the prototype vehicle, the longitudinal vibration rate Vstx at the seat rail, and the lateral vibration rate Vsty from the brake jitter simulation results of the prototype vehicle in step S4 as characteristic values ​​for evaluating the anti-brake jitter performance of the vehicle.

2. The automobile brake tremor analysis and evaluation method according to claim 1, characterized in that: In step S2, a calculation model of the braking torque Tn normally generated by the braking system on each side is established according to the braking system parameters. The calculation formula of the braking torque Tn normally generated by the braking system on each side of the sample vehicle is as follows: Tn = 2·A·P·u·R Where Tn is the braking torque normally generated by the unilateral braking system; A is the brake cylinder piston area; P is the brake line pressure; u is the brake friction coefficient; R is the effective radius of the brake disc.

3. The automobile brake vibration analysis and evaluation method according to claim 1, characterized in that: The multi-body dynamics model of the prototype vehicle in step S2 is composed of a body system, a chassis system, a steering system, a braking system, and a tire model; the multi-body dynamics model parameters of the prototype vehicle include: Body system parameters: vehicle mass, moment of inertia and center of mass coordinates of the prototype vehicle; Chassis system parameters: spring stiffness, bushing stiffness and shock absorber damping of the prototype vehicle; Steering system parameters: steering gear ratio, steering gear torsion bar stiffness and steering wheel moment of inertia of the prototype vehicle; Braking system parameters: brake friction coefficient u of the sample vehicle, brake disc effective radius R, and brake cylinder piston area A.

4. The automobile brake tremor analysis and evaluation method according to claim 1, characterized in that: The braking torque Ta containing torque fluctuation in step S3 is calculated as follows: Ta = Tn·(1-k·SIN(A)) Where Ta is the braking torque including torque fluctuation; Tn is the braking torque normally generated by the braking system on that side; k is the braking torque fluctuation coefficient, and its initial value is 0; A is the change in the angle of the brake disc relative to the caliper over time.

5. The automobile brake tremor analysis and evaluation method according to claim 1, characterized in that: The braking tremor simulation process in step S4 is as follows: Adjust the simulated vehicle speed of the prototype vehicle model and the brake line pressure P of the braking system, so that the prototype vehicle model travels in a straight line at the same initial braking speed V as in step S1 and brakes at a braking deceleration a. Since the initial braking fluctuation coefficient k is 0, the braking torque Ta on the left front side is equal to the normal braking torque Tn at this time. According to the calculation formula of the braking torque fluctuation coefficient, calculate and update the k value in the braking torque calculation model on the left front side, and perform braking simulation again under the same working condition. The prototype vehicle model will exhibit braking tremor under the excitation of the braking torque fluctuation on the left front side.

6. The automobile brake tremor analysis and evaluation method according to claim 1, characterized in that: The calculation formula of the braking torque fluctuation coefficient k in step S4 is as follows: k = 0.5·Tv / Tn Where k is the braking torque fluctuation coefficient; Tv is the braking torque fluctuation value; Tn is the braking torque normally generated by the braking system on that side.

7. The automobile brake tremor analysis and evaluation method according to claim 1, characterized in that: The amplitudes of the frequency domain values ​​of the circumferential tangential vibration rate Vsw of the steering wheel of the sample vehicle, the longitudinal vibration rate Vstx at the seat rail, and the lateral vibration rate Vsty in step S5 are used as the characteristic value basis for evaluating the anti-braking jitter performance of the vehicle. The smaller the amplitude of the vibration rate, the weaker the intensity of the resonance generated when the vehicle brakes and jitters, and the better the driver comfort.

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