Study On The Principle And Test Method Of The Scaling Test Of The Friction Material And Its Equipment

1.ForewordThe friction and wear tests for friction material of automobile could be separated into small sample test and dynamometer test. The dynamometer test has a fine simulation and its test data are highly acceptable, except for its complicated test process, long test period, high equipment investment and high test cost. The small sample test is fast and simple, its equipment investment and test cost are lower, but its test results cannot be used to characterize the friction material from all sides and to evaluate it correctly. The comparability problem between small sample test and dynamometer test-- large test data difference--has existed for a long time. Recently, a tendency of uniting the two test methods is emerging out and the dynamometer test takes more and more important position gradually. As the development of the uniting trend of the test criterion going forward, improving the comparability between the small sample test and dynamometer test has become an important research task in the friction material industry of automobile through ameliorating the test methods and the test equipments.The paper is convinced, through analyses, that the essential reason of bad comparability between the small sample test and dynamometer test is that the two tests don't have the test similarity; therefore, a research precept is provided of applying scaling test based on similarity principle to the friction and wear tests for friction material of automobile to study the comparability of the two tests.2.Scaling test principle of friction materialThe principle and application of the scaling test are introduced; the gist and significance applying the scaling test to the friction and wear tests for friction material of automobile are described; the theoretic elements of the scaling test is studied, such as the content of similarity principle and three theorems of similarity; according to the similarity principle, the simulating rule, the types of simulating parameter and the similarity constant of the scaling test are confirmed; the study scheme and trial principle of the scaling test applying the single surface friction of sample to imitate the double surfaces friction of 1:1 dynamometer test are provided and the relationship between the parameters of the two tests is confirmed.3.Study on the method of scaling testAccording to the simulating rule and the similarity constant of relative imitating parameters, the scaling sample of friction material and the scaling brake plate are designed; the theoretic elements adopting SAEJ2681 as the criterion of scaling test is described and the trial items, content, test process and its evaluating index of the criterion are introduced; the condition parameters of the scaling test are confirmed and its data processing method are studied.4.Development of 1:5 scaling tester for friction materialAccording to the requirement of the scaling test, the basic conception of 1:5 scaling dynamometer is put forward; referring to the technical parameters of 1:1 dynamometer nowadays and the similarity constant of scaling parameters, the main technical parameters of scaling tester are confirmed; on the side of configuration and function, the main shaft system, the sliding table system, the loading system, the cooling and dust absorbing system and the computer controlling system are mainly introduced; the test program is figured out with JFL language and its program controlling interface is introduced; the controlling and measuring of the rotation of main shaft, the friction temperature, the brake force and torque are analyzed; at last, the working process of scaling dynamometer is introduced.5.Comparison of 1:5 scaling tester and 1:1 testerTo examine the reliability, the measuring precision, the test-retest reliability of test data of the 1:5 scaling tester newly designed, the verifying trial is performed. Its results show that the controlling precision of the test parameters of scaling dynamometer, such as rotation and brake force etc., satisfies the requirement of the test method and criterion of dynamometer; the variation trend of friction coefficient of friction material samples of the two testers is same; the friction coefficient and evaluating index of the same sampling point are very close; the test-retest reliability of test data is fine; all those explain that the scaling dynamometer newly designed can be used as the tester of scaling test for friction material.To examine the comparability of the 1:5 scaling test and 1:1 test, the comparative trials are separately performed on the 1:5 scaling dynamometer tester and 1:1 dynamometer tester according to one same standard test method SAEJ2681, the small sample of scaling and the actual brake pad of 1:1 dynamometer are taken from same batch and the material quality of their brake plates are same. The test data shows: the test parameters of the scaling dynamometer and the 1:1 dynamometer satisfy the similarity relation confirmed by trial imitation rules; the variation trend of their friction coefficient is same; their evaluating index, such as friction coefficient taken from same sampling point, are very close. All those express that the test data of scaling dynamometer and 1:1 dynamometer have fine consistency and comparability; the imitation of scaling trial is close to 1:1 dynamometer test, so the scaling test can substitute, at some extent, the 1:1 dynamometer test to study the friction and wear quality for friction material of automobile.Through further analyzing the test data, a concept of similarity matrix is provided which can be used to estimate the result of the 1:1 dynamometer trial.6.Conclusion(1).The simulating rule of scaling test of friction material and the types of simulating parameter that will play a mainly action in test are confirmed. The similarity constant of the parameters relative to the scaling test, such as friction area, friction radius, trial inertial, rotation and brake force, are chosen and calculated. The test principle of 1:1 dynamometer is studied, so the study scheme and trial principle of the scaling test applying the single surface friction of sample to imitate the double surfaces friction of 1:1 dynamometer test are provided and the relationship between the parameters of the two tests is confirmed.(2).Taking the disc brake of the JETTA car as the imitation prototype, the scaling sample and scaling brake plate are designed; the position of the center point of stress on the scaling sample and the position of the scaling sample relative to the scaling brake are determined; the controlling scheme that using the braking force to imitate the pressure in the braking tube of 1:1 trial is suggested on the presupposition of the same working pressure, and the relationship between the braking force of the scaling test and the pressure in the braking tube of 1:1 trial is opened out.(3).The scaling dynamometer tester is developed that adopts the small sample, could attach inertia load, possesses the trial functions of 1:1 dynamometer and can apply the trial method and criterion of 1:1 dynamometer. Based on the technical parameters of 1:1 dynamometer and according to the similarity principle, the main technical parameters of scaling dynamometer are determined. About the structure of the scaling tester, the double shafts DC timing motor is adopted to simplify its configuration; the method of the geometric progression growth is used to configure the inertial of the flywheels; the braking force is used to imitate the pressure in the braking tube of 1:1 trial and the technology of the hydro-air pressure-added proportional control technique is adopted; using the stress sensor to make up of the closed loop feedback control system to realize the accurate control for the braking force and braking torque; the traditional installation method of the thermocouple is improved that raises the measuring precision of temperature; the device of repairing surface is designed to raise the surface precision of the brake plate; the test program is figured out with JFL language; the scaling dynamometer tester applied the national invent patent and the practical new-type patent.(4).The relative verifying trial is performed. The test data of test-retest reliability of the scaling dynamometer shows that the controlling precision of the test parameters of scaling dynamometer, such as rotation and brake force etc., satisfies the requirement of the test method and criterion of dynamometer; the test-retest reliability of test data is fine; all those explain that the scaling dynamometer newly designed can be used as the tester of scaling test for friction material. Through comparing the scaling test data with the 1:1 dynamometer data, it is could be found that the test parameters of the scaling dynamometer and the 1:1 dynamometer satisfy the similarity relation confirmed by trial imitation rules; the variation trend of their friction coefficient is same; their evaluating index, such as friction coefficient taken from same sampling point, are very close. All those express that the test data of scaling dynamometer and 1:1 dynamometer have fine consistency and comparability; the imitation of scaling trial is close to 1:1 dynamometer test, so the scaling test can substitute, at some extent, 1:1 dynamometer test to study the friction and wear quality for friction material of automobile.(5).The concept of similarity matrix is provided which, together with the test data of the scaling dynamometer, can be used to estimate the result of the 1:1 dynamometer trial under the same experiment condition.The paper shows that the test data of the scaling dynamometer tester based on the similarity principle and adopting small sample has a fine consistency and comparability with that of 1:1 dynamometer; using scaling test can raise the imitation grade of the small sample test and the reliability, so the scaling test can substitute, at some extent, the 1:1 dynamometer test to study the formulae or the friction and wear quality for friction material of automobile, as well as in the quality control system. The successfully development of the 1:5 scaling dynamometer tester provides a new way or tool to study the performance of the friction material using small sample. Using scaling test to study the friction and wear performance for friction material is helpful for improving the small sample test, enlarging its application range, greatly reducing the equipment invest and test cost at same time and raising the test efficiency.