CN-121977994-A - Accelerated aging and vapor barrier test method and system for automobile brake fluid under complex environment

CN121977994ACN 121977994 ACN121977994 ACN 121977994ACN-121977994-A

Abstract

The invention discloses a method and a system for testing accelerated aging and vapor resistance of automobile brake fluid in a complex environment, wherein the method comprises the steps of completing the preparation of the brake fluid and the recording of a basic state value thereof and calibrating a sensor required by test; the method comprises the steps of performing environment simulation and working condition circulation, rapidly ageing brake fluid to a real failure critical state, providing an equivalent sample for a vapor resistance test, simultaneously sampling after different working condition circulation, continuously running a six-stage concentration circulation on a Gao Yuanjiao straight road based on a vehicle subjected to accelerated ageing until reaching a termination condition, simultaneously collecting all sensor data, standing the vehicle after circulation is stopped, enabling heat to be conducted, air bubbles to be gathered, evaluating pedal state and braking efficiency through static pedal stepping and dynamic braking, then extracting a brake fluid sample to confirm water content and boiling point, finally recording vapor resistance triggering related data and outputting a report, and finally completing final inspection and evaluation. The real aging process of the brake fluid is accurately simulated.

Inventors

Jiang Bigang
HUANG YOUXIAN
YANG DONGYANG
HAN FEI
WANG JIGUANG
Pan Zhongpu
LI JUNSHU
HE JIANLIANG

Assignees

中汽研汽车检验中心(昆明)有限公司

Dates

Publication Date: 20260505
Application Date: 20251230

Claims (10)

1. The method for testing the accelerated aging and the vapor resistance of the automobile brake fluid in the complex environment is characterized by comprising the following steps of: S1, firstly replacing brand new brake fluid, and checking the state of a brake system, then measuring the initial water content and boiling point of the new brake fluid, recording a reference value, and then installing and calibrating a sensor and a data acquisition system required by a steam resistance test; s2, aging the brake fluid to a real failure critical state rapidly through environmental simulation and working condition circulation, providing an equivalent sample for a vapor resistance test, and sampling after different working condition circulation; S3, continuously running a six-stage concentration cycle on a Gao Yuanjiao straight road based on the vehicle subjected to accelerated aging until a termination condition is reached, and simultaneously collecting all sensor data; S4, after circulation is stopped, standing the vehicle to enable heat conduction and air bubble aggregation, then evaluating pedal state and braking efficiency through static pedal stepping and dynamic braking, then extracting a brake fluid sample to confirm water content and boiling point, finally recording air resistance triggering related data and outputting a report, and finally completing final inspection and evaluation.
2. The method for testing the accelerated aging and the vapor barrier of the automobile brake fluid under the complex environment according to claim 1, wherein the environmental simulation and the working condition circulation in the S2 comprise three stages, namely: The first stage is to absorb moisture at high temperature and high humidity, and in the environmental bin with set temperature and humidity, the vehicle is first operated in specific working condition, and then flameout and standing are carried out to accelerate the moisture absorption of brake fluid, the second stage is to carry out salt spray corrosion pretreatment, spray salt solution to the vehicle brake caliper in normal temperature environment to simulate corrosion scene to catalyze the aging of brake fluid, and the third stage is to carry out high heat load oxidation, and in the environmental bin with set temperature and altitude, the vehicle is repeatedly subjected to sliding, braking and accelerating circulation to excite the thermal oxidation deterioration of brake fluid.
3. The method for testing the accelerated aging and the vapor barrier of the automobile brake fluid under the complex environment according to claim 1, wherein the specific operation of sampling after different working condition cycles in the step S2 is as follows: after each 24-hour aging cycle, 5-10ml of brake fluid sample is extracted from the brake master cylinder liquid storage tank by using a sterile syringe, and then detection is immediately carried out, namely, on the one hand, the water content of the sample is measured, and on the other hand, the equilibrium reflux boiling point of the sample is measured by using a boiling point tester.
4. The method for testing the accelerated aging and the vapor resistance of the automobile brake fluid under the complex environment according to claim 1 is characterized in that the termination conditions of the environmental simulation and the working condition circulation in the S2 are that when the water content of the brake fluid measured by sampling reaches 3.0+/-0.2%, the equivalent target aging period is considered to be successful, and meanwhile, the boiling point is correspondingly reduced to be below the minimum value of DOT4 standard.
5. The method for testing accelerated aging and vapor barrier of automobile brake fluid under a complex environment according to claim 1, wherein the six-stage concentration cycle in S3 is specifically: The first stage, the vehicle accelerates from the current speed to the target speed; a second stage of applying a brake to maintain a set average deceleration for a certain time; The third stage, the vehicle normally runs and the vehicle speed is reduced to the appointed speed; fourth stage, accelerating to target speed again; A fifth stage of applying the brake to maintain another set average deceleration until the vehicle speed drops to zero; And a sixth stage, completely releasing the brake and the accelerator pedal, and allowing the vehicle to freely slide to a specified speed or for a specified time.
6. The method for testing the accelerated aging and the vapor barrier of the automobile brake fluid under the complex environment according to claim 1, wherein the termination condition in the step S3 is specifically as follows: the cycle termination condition can be met by firstly completing preset cycle times, secondly triggering air resistance early warning by multi-parameter fusion criteria, and thirdly confirming that the brake pedal is obviously soft or long in stroke through subjective evaluation.
7. The method for testing the accelerated aging and the vapor barrier of the automobile brake fluid under the complex environment according to claim 6, wherein the specific judgment method for triggering the vapor barrier early warning by the multi-parameter fusion criterion is as follows: The method comprises the steps of identifying steam resistance and distinguishing heat deterioration through a temperature-hydraulic-pedal three-dimensional criterion to ensure objective and reliable judging results, calculating corrected wet boiling points corresponding to altitudes, verifying whether the temperature of wheel cylinder brake fluid continuously exceeds the value, verifying the pressure fluctuation amplitude and curve form of a hydraulic system or the stroke increment and stroke-force curve slope change of a pedal, judging the steam resistance when the temperature criterion is met and simultaneously meeting the hydraulic criterion or pedal criterion, and judging the steam resistance or other faults when only meeting a single criterion.
8. The method for testing the accelerated aging and the vapor barrier of the automobile brake fluid under the complex environment according to claim 7, wherein the judging method of the pressure fluctuation amplitude and the curve form of the hydraulic system is as follows: monitoring the pressure curve form through a main cylinder and a partial pressure sensor, and extracting three key characteristics: The pressure fluctuation amplitude is judged, the pressure sequence in the sliding window is set as P i , i is E [1, 2. ], n ], and the standard deviation is calculated For the average value of the pressure in the window, a fluctuation coefficient is defined When F is greater than F 0 , determining that the fluctuation amplitude exceeds the standard, wherein F 0 is the maximum fluctuation coefficient of the same window in the heat fading state, and calibrating by the heat fading characteristic data; Setting the pedal displacement starting time as t d , defining the pressure rising starting time as t p ,t p as the time when the pressure exceeds the static pressure by 2% for the first time, determining that the hysteresis is prolonged when tau > tau 0 , determining that tau 0 is the maximum hysteresis time of the same working condition in a normal state according to the reference test data, wherein the hysteresis time tau=t p -t d ; Verifying the shape association of pressure curve, calculating the second derivative sequence of pressure curve If there are not less than 5 sampling points in succession E is the upper limit of the absolute value of the second derivative of the heat decay linear attenuation section, and is judged to be a flat top section, if the second derivative exists alternately And Is determined to be "saw tooth like fluctuation"; the hydraulic criterion is met when F > F 0 and τ > τ 0 , and a "plateau" or "saw tooth wave" is detected at the same time.
9. The method for testing the accelerated aging and the vapor barrier of the automobile brake fluid under the complex environment according to claim 7, wherein the judgment method for the stroke increment of the pedal and the gradient change of the stroke-force curve is as follows: Let the actual travel be S m , the baseline travel be S b , define the travel increment S b is a stroke reference value under the same pedal force when the brake fluid is not aged; Synchronously setting the maximum stroke increment in the heat fading state as delta S h , and meeting a stroke increment core criterion when delta S > delta S h ; Let the current pedal force variation be Δf c and the corresponding stroke variation be Δs c , define the current force-stroke slope Calculating a baseline state slope Delta F b is the same-amplitude pedal force variation in the baseline state, delta S c b is the stroke variation corresponding to delta F b in the baseline state, and the slope of the heat fading state is calculated Δf h is the same-amplitude pedal force variation in the heat-fade state, and Δs c h is the stroke variation corresponding to Δf h in the heat-fade state; By establishing a correlation with the difference between the baseline slope and the heat decay slope, when K c <K b -2×(K b -K h ) a slope drop criterion is met, forming a "soft pedal" feature, this decision logic distinguishes between "soft pedal" and "hard stroke increase" of heat decay by correlation of the heat decay slope K h with the baseline slope K b .
10. An accelerated aging and vapor barrier test system for automobile brake fluid in a complex environment, comprising: The brake fluid preparation and sensing calibration unit is used for replacing brand new brake fluid and checking the state of a brake system, measuring the initial water content and boiling point of the new brake fluid, recording a reference value, and then installing and calibrating a sensor and a data acquisition system required by a vapor resistance test; The brake fluid accelerated aging unit is used for rapidly aging the brake fluid to a real failure critical state through environmental simulation and working condition circulation, providing an equivalent sample for a vapor resistance test, and simultaneously sampling after different working condition circulation; the plateau circulation test unit is used for continuously running a six-stage concentration cycle on a Gao Yuanjiao straight road based on the vehicle subjected to accelerated aging until a termination condition is reached, and collecting all sensor data; And the final checking and evaluating unit is used for standing the vehicle to enable heat to be conducted and air bubbles to be gathered after circulation is stopped, evaluating the pedal state and the braking efficiency through static pedal stepping and dynamic braking, then extracting a brake fluid sample to confirm the water content and the boiling point, finally recording air resistance triggering related data and outputting a report, and finishing final checking and evaluating.

Description

Accelerated aging and vapor barrier test method and system for automobile brake fluid under complex environment Technical Field The invention belongs to the technical field of performance test of an automobile brake system, and particularly relates to a method and a system for testing accelerated aging and vapor resistance of automobile brake fluid in a complex environment. Background The brake fluid air resistance is a serious fault of a vehicle hydraulic brake system, when the working temperature of the system exceeds the boiling point of brake fluid, compressible steam bubbles can be generated in the fluid to cause the brake pedal to be soft, the stroke to be increased or even completely fail, and the explosion risk is extremely high under severe working conditions such as high temperature, high load, low air pressure (high altitude), long downhill and the like, so that the driving safety is directly endangered. Therefore, in the vehicle research and development and quality verification stage, fully checking the air resistance performance of the braking system becomes a key link for ensuring the reliability of products in a main engine factory, but how to efficiently, accurately and safely reproduce the air resistance phenomenon and complete test and evaluation becomes an industry problem. In a long downhill road section, continuous braking of a vehicle is easy to cause heat fading of a brake disc, the friction coefficient of the vehicle is reduced along with temperature rise, when the temperature of the brake disc exceeds 650 ℃ and the temperature of a friction plate exceeds 450 ℃, braking torque is linearly attenuated, but the performance can be recovered by 90% after cooling, and the air resistance of brake fluid can cause hydraulic rigidity loss due to bubble compression, which is manifested as fluctuation of braking pressure exceeding +/-15% and sudden increase of pedal stroke, and the brake fluid can be recovered only by replacement. The two failure modes are difficult to distinguish by a driver under long downhill working conditions, but the former still maintains a certain braking force, and the latter directly causes braking failure. The existing detection means have obvious defects, the pressure decay detection cannot distinguish the two, the single temperature sensor has hysteresis, the high altitude boiling point correction is not considered only through pedal travel increment judgment, and the heat decay is easily misjudged as air resistance. Three core defects exist in the current brake fluid vapor resistance test field. The method has the advantages that firstly, the aging process and the steam resistance test are required to be operated separately, the real link of aging-use-steam resistance cannot be simulated, the aging parameters are dependent on off-line detection and are difficult to match with the test requirements in real time, secondly, the plateau scene test is uncontrollable, the real vehicle test is poor in safety and high in cost and is also influenced by factors such as weather and traffic, the result is difficult to reproduce, thirdly, the steam resistance criterion is lack of quantification, the subjective feeling such as pedal softness is seriously relied, the test result is lack of scientificity and convincing, and the research and development process is slow. The industry is in urgent need of a comprehensive test method capable of safely, rapidly and accurately simulating the real aging process of brake fluid in a laboratory and on the whole vehicle level and objectively and quantitatively judging the air resistance phenomenon. Disclosure of Invention The invention aims to provide a set of aging-test integrated automobile brake fluid accelerated aging and vapor resistance test method under a complex environment, which solves the problems that aging and test are disjointed, plateau scene test is uncontrollable and vapor resistance criteria lack quantized pain points in the prior art, and realizes safe, reproducible and accurate vapor resistance test at the whole automobile level through environmental simulation, working condition circulation and multi-parameter monitoring, thereby providing scientific support for research and development verification of a brake system. In view of the above-mentioned drawbacks or improvements of the prior art, as a first aspect of the present invention, the present invention provides a method for testing accelerated aging and vapor lock of an automotive brake fluid in a complex environment, comprising: S1, firstly replacing brand new brake fluid, and checking the state of a brake system, then measuring the initial water content and boiling point of the new brake fluid, recording a reference value, and then installing and calibrating a sensor and a data acquisition system required by a steam resistance test; s2, aging the brake fluid to a real failure critical state rapidly through environmental simulation and working condition circulation,