A passenger car brake friction coefficient test method

Abstract

The present application relates to a kind of passenger car brake friction coefficient test method, it is characterized in that: using whole vehicle method carries out brake friction coefficient test, specific steps are as follows: confirming test condition, sliding test, front axle braking, rear axle braking and data processing, according to formula (1)~(2) calculation correction pipeline pressure and correction brake deceleration, according to formula (3) calculation friction plate braking force, according to formula (4) calculation friction plate pressure, according to formula (5) calculation disc brake friction coefficient, according to formula (6) calculation drum brake brake efficiency factor.There is beneficial effect: by establishing a set of standardized passenger car brake friction coefficient test method, mainly used to carry out the friction coefficient calculation of brake based on whole vehicle, in whole vehicle standardization research and development process, can greatly shorten test cycle, save test cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of automobile test, and particularly relates to a passenger car brake friction coefficient test method. BACKGROUND

[0002] The whole vehicle braking performance has an important effect on vehicle safety, and the passenger car brake friction coefficient has a significant influence on the whole vehicle braking performance, so the brake friction coefficient needs to be measured in vehicle development and benchmarking. The patent with the authorized announcement number CN101916304B discloses a brake friction performance virtual bench test method, which comprises the following steps: 1, determining the function relationship between the tested brake friction coefficient and temperature μ=f(T), the process is as follows: establishing a three-dimensional geometric model, establishing a three-dimensional thermal-mechanical coupling finite element model, carrying out coupling temperature field simulation analysis on the established three-dimensional thermal-mechanical coupling finite element model, and obtaining the function relationship between the tested brake friction coefficient and temperature μ=f(T); 2, using the thermal decay test method to test the friction performance of the tested brake in the virtual bench, including the steps of first thermal decay-recovery test and second thermal decay and efficiency test. The patent with the authorized announcement number CN111398162B discloses a commercial vehicle air pressure disc brake assembly friction coefficient test method, which comprises a test part and a data processing part, wherein the test part comprises the following steps: calibration of the relationship between the input air pressure P of the brake air chamber and the clamping force N of the air pressure brake caliper; determination of the brake torque T; the data processing part comprises the following steps: establishing a mathematical model of the input air pressure and the clamping force; normality test of the brake torque data; using the friction coefficient calculation method, combined with the data record in the effective braking time, to calculate the average friction coefficient in the first braking process. The above-mentioned patents are respectively for the brake friction coefficient of the bench test and the commercial vehicle test, and the brake friction coefficient of the bench test is the characteristic of the brake system alone. Since the brake is matched with the whole vehicle, the friction characteristics of the brake play an important role in the performance of the whole vehicle and the assembly, so the brake friction characteristics based on the whole vehicle need to be considered once, so as to more conveniently test the braking performance of the vehicle.

[0003] In the whole vehicle benchmarking, a large number of whole vehicle tests are often carried out based on the whole vehicle method, such as handling stability, power performance, braking performance, etc. The vehicle brake friction coefficient has an important influence on the whole vehicle braking performance, so the brake friction coefficient needs to be measured in vehicle development and benchmarking. SUMMARY

[0004] The purpose of the present application is to overcome the deficiencies of the above-mentioned technology, and provide a passenger car brake friction coefficient testing method, which uses the whole vehicle method to test the brake friction coefficient, can more accurately reflect the brake efficiency of the brake in the whole vehicle assembly; when the whole vehicle is tested, the test period is greatly reduced, and the friction coefficient and brake effect of the brake in the whole vehicle assembly are accurately measured.

[0005] To achieve the above-mentioned purpose, the following technical solution is adopted: a passenger car brake friction coefficient testing method, characterized by: using the whole vehicle method to test the brake friction coefficient, and the specific steps are as follows:

[0006] I. Confirm the test conditions

[0007] 1) Confirm the sample vehicle conditions, site conditions and environmental conditions;

[0008] II. Coasting test

[0009] The vehicle is tested at an initial speed of 80km / h, and the vehicle coasting deceleration under this condition is recorded. The test needs to be conducted in both forward and reverse directions;

[0010] III. Front axle braking

[0011] 1) Before the test, the rear axle brake pipe needs to be disconnected, so that the vehicle is braked only by the front axle brake;

[0012] 2) During the test, the vehicle is accelerated to more than 80km / h, and the gear position is set to "N". When the vehicle speed is coasting to 80km / h, the brake pedal is pressed, so that the vehicle quickly reaches the pre-selected deceleration steady state value, and the deceleration is stabilized. The vehicle is driven at a constant deceleration until it stops, and the pipe pressure and deceleration data during the whole process are recorded. The deceleration steady state value is gradually increased until the maximum deceleration of the vehicle is reached, and the above test is repeated. The recommended pre-selected deceleration steady state value is 1m / s 2 , 2m / s 2 , 3m / s 2 , 4m / s 2 , 5m / s 2 , 6m / s 2 , 7m / s 2 , or selected according to the actual braking capacity of the vehicle;

[0013] IV. Rear axle braking

[0014] 1) Before the test, the front axle brake pipe needs to be disconnected, so that the vehicle is braked only by the rear axle brake;

[0015] 2) Test, the vehicle to accelerate to more than 80km / h, the vehicle gear is in "N" gear, the vehicle sliding, when the vehicle speed sliding to 80km / h, step on the brake pedal, make the vehicle quickly reach the preselected deceleration steady state value, and stabilize the deceleration uniform deceleration forward, until the vehicle stops, record the pipeline pressure and deceleration data during the whole process, gradually improve the brake deceleration steady state value, until the maximum deceleration the vehicle can reach, repeat the above test; The preselected deceleration steady state value is recommended 0.5m / s 2 , 1m / s 2 , 1.5m / s 2 , 2m / s 2 , 2.5m / s 2 , 3m / s 2 , 3.5m / s 2 , or according to the actual braking capacity of the vehicle to select;

[0016] Five, data processing

[0017] The data collected by sliding test and front and rear axle braking test are analyzed and processed, and the friction coefficient of disc brake or the efficiency factor of drum brake is calculated;

[0018] Analysis of test raw data

[0019] 1) Calculate the average pipeline pressure P m and the average deceleration of the vehicle a m when the vehicle speed is reduced from 60km / h to 30km / h, respectively;

[0020] 2) According to the sliding test in both directions, calculate the average sliding deceleration a0 when the vehicle speed is reduced from 60km / h to 30km / h, and the pipeline pressure zero drift value P0 of the vehicle, respectively;

[0021] 3) Calculate the corrected pipeline pressure and corrected brake deceleration

[0022] P = P m -P0

[0023] a = a m -a0

[0024] In the formula: P--corrected pipeline pressure; P m- --average pipeline pressure; P0--pipeline pressure zero drift value;

[0025] a--corrected brake deceleration; a m --average deceleration of the vehicle; a 0-- average sliding deceleration;

[0026] 4) Calculate the brake force of the friction plate:

[0027]

[0028] wherein:

[0029] F f Brake force of friction plate, N;

[0030] m - Test mass of vehicle, kg;

[0031] a - Corrected brake deceleration, m / s 2 ;

[0032] R t - Rolling radius of tire, mm;

[0033] R b - Acting radius of brake, mm.

[0034] 5) Calculate friction plate pressure

[0035]

[0036] wherein:

[0037] F p - Cylinder thrust, N;

[0038] P - Corrected line pressure, MPa;

[0039] D c - Cylinder diameter of brake, mm.

[0040] 6) Calculate friction coefficient of brake

[0041] Friction coefficient of disc brake is:

[0042] Brake efficiency factor of drum brake is:

[0043] Further, the confirmation test conditions include test sample vehicle conditions, site conditions and environmental conditions, wherein the test sample vehicle conditions should meet the factory specified technical conditions, the vehicle is in good condition, the tire pressure is adjusted to the design pressure value, the error is not more than ±10 kPa; the tread pattern height is not less than 90% of the new pattern; the test site adhesion coefficient is 0.8 or more, and the site is dry, flat, clean, and the wind speed is not more than 3 m / s; the environmental conditions: atmospheric temperature is in the range of 0℃ to 40℃.

[0044] Further, the test sample vehicle conditions: before the test, the vehicle brake system is run-in:

[0045] Under the full load state of the vehicle, the initial speed is 80% of the highest vehicle speed ≤120 km / h, and the vehicle speed is increased to 3 m / s 2The deceleration of the selected deceleration is started to brake, when the speed is reduced to 50% of the initial speed, the pedal is released, the vehicle speed is accelerated to the initial speed, and the test is repeated; the total number of running-in is 200 times.

[0046] Further, the selected deceleration steady-state value of the front and rear axles should at least include 6 groups.

[0047] Beneficial effects: by establishing a set of standardized passenger car brake friction coefficient test method, mainly used for developing brake friction coefficient calculation based on the whole vehicle, in the whole vehicle development process, can greatly shorten the test cycle, save the test cost. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is the flowchart of the present application. DETAILED DESCRIPTION

[0049] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the present application is described in detail below in combination with the drawings and specific embodiments. It should be noted that the embodiments and features in the embodiments can be combined with each other without conflict. In the following description, a large number of specific details are described in order to facilitate a full understanding of the present application, and the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as understood by those skilled in the art in the technical field of the present application. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments and are not intended to limit the present application.

[0050] In the embodiments of the present application, in order to facilitate the description without limiting the present application, the term "connection" used in the patent application specification and claims of the present application is not limited to physical or mechanical connection, but can include electrical connection, whether direct or indirect. "Up", "down", "below", "left", "right" and the like are only used to indicate relative positional relationship, when the absolute position of the described object changes, the relative positional relationship also changes accordingly.

[0051] As shown in the drawings, the present embodiment provides a passenger car brake friction coefficient test method, which is implemented as follows:

[0052] (I) Test condition confirmation:

[0053] ① Vehicle condition:

[0054] The test vehicle is in good condition, and the test can only be carried out after it is determined that the test vehicle has met the technical conditions specified by the manufacturer.

[0055] The tire pressure is adjusted to the design pressure value, with an error of not more than ±10 kPa; the tread pattern height is not less than 90% of the new pattern.

[0056] Before the test, the vehicle braking system needs to be run-in:

[0057] a) The vehicle is fully loaded, and the initial speed is 80% of the maximum vehicle speed (less than or equal to 120 km / h), and the deceleration is 3 m / s2, and when the speed decreases to 50% of the initial speed, the pedal is released, and the speed is accelerated to the initial speed, and the test is repeated.

[0058] b) The total number of run-ins is 200 times. If it cannot be completed continuously due to conditions, the number of tests can be adjusted according to the specific situation.

[0059] ② Site conditions:

[0060] The test site should have an adhesion coefficient of 0.8 or more, and the site should be dry, flat and clean. The wind speed should be no more than 3 m / s.

[0061] ③ Environmental conditions:

[0062] The atmospheric temperature should be within the range of 0℃ to 40℃.

[0063] (II) Coasting test:

[0064] The vehicle is tested at an initial speed of 80 km / h, and the vehicle's coasting deceleration is recorded under this condition. Both forward and reverse directions need to be tested. The forward and reverse directions of the test road described in this example refer to, for example, driving from south to north and from north to south. The selected vehicle model was tested, and the test results are shown in Table 1.

[0065] Table 1 Coasting deceleration results

[0066] Direction Forward Reverse Average Coasting deceleration (m / s 2 )]]> 0.85 0.81 0.83

[0067] (III) Front axle braking:

[0068] Before the test, disconnect the rear axle brake pipe, so that the vehicle is only braked by the front axle brake.

[0069] During the test, the vehicle is accelerated to more than 80 km / h, and the vehicle gear is in "N" gear. The vehicle is coasting, and when the vehicle speed is coasting to 80 km / h, the brake pedal is pressed to make the vehicle quickly reach the pre-selected deceleration steady-state value, and the deceleration is stabilized. The vehicle is uniformly decelerated forward until the vehicle stops, and the pipe pressure and deceleration data during the entire process are recorded.

[0070] Gradually increase the steady-state value of braking deceleration until the maximum deceleration that the vehicle can reach, repeat the above test. The selected deceleration steady-state value should contain at least 6 groups. The recommended pre-selected deceleration steady-state value is 1 m / s 2 , 2 m / s 2 , 3 m / s 2 , 4 m / s 2 , 5 m / s 2 , 6 m / s 2 , 7 m / s 2 , or can be selected according to the actual braking capacity of the vehicle.

[0071] (Four) rear axle braking:

[0072] Before the test, disconnect the front axle brake pipe, so that the vehicle is only under the action of the rear axle brake.

[0073] During the test, accelerate the vehicle to more than 80 km / h, the vehicle gear is in "N" gear, the vehicle is sliding, when the vehicle speed is sliding to 80 km / h, step on the brake pedal, make the vehicle quickly reach the pre-selected steady-state value of deceleration, and stabilize the deceleration uniform deceleration forward, until the vehicle stops, record the pipe pressure and deceleration data during the whole process.

[0074] Gradually increase the steady-state value of braking deceleration until the maximum deceleration that the vehicle can reach, repeat the above test. The selected deceleration steady-state value should contain at least 6 groups. The recommended pre-selected deceleration steady-state value is 0.5 m / s 2 , 1 m / s 2 , 1.5 m / s 2 , 2 m / s 2 , 2.5 m / s 2 , 3 m / s 2 , 3.5 m / s 2 , or can be selected according to the actual braking capacity of the vehicle.

[0075] (Five) data processing:

[0076] Analyze the original test data, respectively calculate the average pipe pressure P m and the average deceleration of the vehicle a m when the vehicle speed is reduced from 60 km / h to 30 km / h.

[0077] According to the forward and reverse sliding tests, respectively calculate the average cruising deceleration a0 when the vehicle speed is reduced from 60 km / h to 30 km / h, and the pipe pressure zero drift value P0 of the vehicle.

[0078] According to formulas (1)-(2), calculate the corrected pipe pressure and the corrected braking deceleration:

[0079] P = P m - P0 (1)

[0080] a = a m - a0 (2)

[0081] The friction plate braking force is calculated according to formula (3) :

[0082]

[0083] In the formula:

[0084] F f - friction plate braking force, N;

[0085] m - vehicle test mass, kg;

[0086] a - corrected braking deceleration, m / s 2 ;

[0087] R t - tire rolling radius, mm;

[0088] R b - brake acting radius, mm.

[0089] The friction plate pressure is calculated according to formula (4) :

[0090]

[0091] In the formula:

[0092] F p - cylinder thrust, N;

[0093] P - corrected line pressure, MPa;

[0094] D c - brake cylinder diameter, mm.

[0095] The brake friction coefficient is calculated

[0096] The disc brake friction coefficient is:

[0097] The drum brake braking efficiency factor is:

[0098] The corrected line pressure and the corrected braking deceleration are calculated according to formulas (1) and (2), the friction plate braking force is calculated according to formula (3), the friction plate pressure is calculated according to formula (4), if the vehicle is a disc brake, the brake friction coefficient is calculated according to formula (5); if the vehicle is a drum brake, the brake braking efficiency factor is calculated according to formula (6).

[0099] The selected vehicle model is tested, and the required parameters and test results are shown in Table 2.

[0100] Table 2 Test parameters and test results

[0101]

[0102] The above detailed description of the reference example of the test method for the friction coefficient of the brake of a passenger vehicle is illustrative rather than restrictive, and several examples can be listed within the defined range, and thus variations and modifications without departing from the overall concept of the present application shall be within the scope of protection of the present application.

Claims

1. A method for testing the coefficient of friction of a passenger vehicle brake, characterized in that: The specific steps for testing the brake friction coefficient using the whole vehicle method are as follows: I. Confirming the test conditions 1) Confirm the prototype vehicle conditions, site conditions, and environmental conditions; II. Gliding Test The vehicle is subjected to a coasting test with an initial speed of 80 km / h. The vehicle's coasting deceleration under this condition is recorded. The test must be conducted in both the forward and reverse directions. III. Front Axle Braking 1) Before the test, the rear axle brake line must be disconnected so that the vehicle is braked only by the front axle brake. 2) During the test, accelerate the vehicle to a speed greater than 80 km / h, then shift the vehicle to neutral (N) and allow it to coast. When the vehicle reaches 80 km / h, apply the brake pedal to quickly bring the vehicle to the pre-selected steady-state deceleration value. Maintain this deceleration at a stable, uniform rate until the vehicle stops. Record the pipeline pressure and deceleration data throughout the process. Gradually increase the steady-state deceleration value until the vehicle reaches its maximum achievable deceleration. Repeat the above test. The recommended pre-selected steady-state deceleration value is 1 m / s². 2 2m / s 2 3m / s 2 4m / s 2 5m / s 2 6m / s 2 7m / s 2 Or select according to the actual braking capacity of the vehicle; IV. Rear Axle Braking 1) Before the test, the front axle brake line must be disconnected so that the vehicle is braked only by the rear axle brake. 2) During the test, accelerate the vehicle to a speed greater than 80 km / h, then shift the vehicle to neutral (N) and allow it to coast. When the vehicle reaches 80 km / h, apply the brake pedal to quickly bring the vehicle to the pre-selected steady-state deceleration value. Maintain this deceleration at a stable, uniform rate until the vehicle comes to a stop. Record the pipeline pressure and deceleration data throughout the process. Gradually increase the steady-state deceleration value until the vehicle reaches its maximum achievable deceleration. Repeat the above test. The recommended pre-selected steady-state deceleration value is 0.5 m / s². 2 1m / s 2 1.5m / s 2 2m / s 2 2.5m / s 2 3m / s 2 3.5m / s 2 Or select according to the actual braking capacity of the vehicle; V. Data Processing Data collected from coasting tests and front and rear axle braking tests are analyzed and processed to calculate the friction coefficient of disc brakes or the efficiency factor of drum brakes. Analyze the raw experimental data 1) Calculate the average pipeline pressure P when the vehicle speed decreases from 60km / h to 30km / h. m and average vehicle deceleration a m ; 2) Based on the coasting tests in both directions, calculate the average coasting deceleration a0 when the vehicle speed decreases from 60km / h to 30km / h, and the zero drift value of the vehicle pipeline pressure. P 0 ; 3) Calculate the corrected pipeline pressure and corrected braking deceleration. P = P m - P 0 a = a m - a 0 In the formula: P -- Correct pipeline pressure; P m- -- Average pipeline pressure; P0 -- pipeline pressure zero drift value; a--Corrected braking deceleration; a m --Average vehicle deceleration; a 0-- Average gliding deceleration; 4) Calculate the braking force of the friction plates: In the formula: F f —Friction braking force, N; m—Vehicle test mass, kg; a — Corrected braking deceleration, m / s 2 ; R t — Tire rolling radius, mm; R b —Brake operating radius, mm; 5) Calculate the friction plate pressure In the formula: F p — Cylinder thrust, N; P —Corrected pipeline pressure, MPa; D c —Brake cylinder diameter, mm; 6) Calculate the friction coefficient of the brake. The coefficient of friction for disc brakes is: The braking efficiency factor of a drum brake is: .

2. The method for testing the friction coefficient of a passenger vehicle brake according to claim 1, characterized in that: The confirmation test conditions include test vehicle conditions, site conditions, and environmental conditions. Among them, the test vehicle conditions are: the test vehicle meets the manufacturer's technical requirements and is in good condition; the tire pressure is adjusted to the design pressure value with an error of no more than ±10 kPa; the tread height is not less than 90% of the new tread height; the test site has an adhesion coefficient of 0.8 or higher, and the site is dry, flat, clean, and the wind speed is not greater than 3 m / s; the environmental conditions are: the atmospheric temperature is within the range of 0℃ to 40℃.

3. The method for testing the friction coefficient of passenger vehicle brakes according to claim 1, characterized in that: The test vehicle conditions were as follows: The vehicle's braking system underwent a break-in period before the test. With the vehicle fully loaded, the initial speed is 80% of the maximum speed ≤120km / h, and the speed is 3m / s. 2 The vehicle begins to decelerate and brake. When the speed drops to 50% of the initial speed, the pedal is released, and the speed is accelerated back to the initial speed. The test is repeated. The total number of break-in cycles is 200.

4. The method for testing the friction coefficient of a passenger vehicle brake according to claim 1, characterized in that: The selected deceleration steady-state values ​​for the front and rear axle braking should include at least 6 sets.

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