Study of the Judder Characteristics of Friction Material for an Automobile Clutch and Test Verification

The friction judder characteristics during clutch engagement have a significant influence on the NVH of a driveline.In this research,the judder characteristics of automobile clutch friction materials and experimental verification are studied.First,considering the stick-slip phenomenon in the clutch engagement process,a detailed 9-degrees-of-freedom(DOF)model including the body,each cylinder of the engine,clutch and friction lining,torsional damper,transmission and other driveline parts is established,and the calculation formula of friction torque in the clutch engagement process is determined.Second,the influence of the friction gradient characteristics on the amplification or attenuation of the automobile friction judder is analyzed,and the corresponding stability analysis and the numerical simulation of different friction gradient values are carried out with MATLAB/Simulink software.Finally,judder bench test equipment and a corresponding damping test program are developed,and the relationship between the friction coefficient gradient characteristics and the system damping is analyzed.After a large number of tests,the evaluation basis of the test is determined.The research results show that the friction lining with negative gradient characteristics of the friction coefficient will have a judder signal.When the friction gradient value is less than-0.005 s/m,the judder signal of the measured clutch cannot be completely attenuated,and the judder phenomenon occurs.When the friction gradient is greater than-0.005 s/m,the judder signal can be significantly suppressed and the system connection tends to be stable.

Running‑In Behavior of Wet Multi‑plate Clutches:Introduction of a New Test Method for Investigation and Characterization

Wet multi-plate clutches are relevant components of modern drivetrain applications,not only in terms of function but also safety and comfort.Especially at the beginning of their lifetime,distinct changes of the friction behavior may occur and make the actuation of the clutch challenging.This transcript describes the typical running-in behavior of wet multi-plate clutches and gives a general definition for running-in of clutches.Moreover,a new test method to systematically investigate the running-in behavior of clutches is introduced.This test method contains a test procedure to characterize the running-in behavior on different load levels.Furthermore,a multi-stage procedure to evaluate and characterize the running-in behavior of clutches with mathematical approaches and new characteristic values is given.The quality of the test method is demonstrated on the example of three different tribological systems from dual clutch transmissions(DCT)and automatic transmissions(AT)application using paper friction linings.

A numerical flat plate friction line and its application

This paper studies the regression of a numerical two-dimensional flat plate friction line using the RANS method with the SST k - co turbulence model. Numerical simulations with different inlet turbulence kinetic energies are first conducted. Comparing with the experimental data, the finest grid and the appropriate inlet turbulence kinetic energy are selected to compute the fiat plate friction resistance at 14 Reynolds numbers. Two numerical friction lines are obtained by the least squares root fitting method and one similar to that of the ITTC-1957 line and the cubic polynomials in logarithmic scales, and the results are compared to the friction line proposals available in the open literature. Finally, the full scale viscous resistance predictions of DTMB5415, KVLCC2, SUBOFF are compared between the numerical friction line and the friction line proposals available in the open literature based on the form factor approach. It is shown that the form factor keeps relatively constant via the numerical friction line for the bare hull, but the form factor concept in extrapolating the model test results is not appropriate for appended hulls. It is suggested that for computing a form factor numerically, it is best to use a numerical friction line.