Prediction of driveline vibrations caused by ageing the limited slip coupling

Abstract

The prediction of the wet-clutch service life still remains a challenge for scientists and engineers. Previous research has shown the significance of the wet-clutch friction characteristics on the driveline dynamics. To avoid driveline vibrations an increasing friction coefficient with increasing sliding speed is desirable. Consequently, prediction of the occurrence of driveline vibrations relies on a detailed knowledge of how the friction characteristics are affected by wet-clutch degradation, as well as an understanding of the driveline dynamics. Wet clutches are used in both automatic transmissions and all-wheel-drive systems in cars, where they are referred to as limited slip couplings by manufacturers. Wet clutches used in automatic transmissions are subjected to high slip levels, but for very limited time periods. In all-wheel-drive systems, where the limited slip coupling can be used to control the torque transfer to, for example, the rear wheels, the slip levels are low but continuous. Most wet-clutch research has been performed for clutches in automatic transmissions and not for clutches used in all-wheel-drive systems. Thus, a simulation model was developed to evaluate how different operating conditions of the limited slip coupling influence degradation of the friction characteristics and the tendencies towards driveline vibrations. First, the changes in the friction characteristics with the time of ageing are simulated. The friction characteristics after ageing are used as the input to a simplified driveline model, which is used to evaluate the occurrence of vibrations. It is shown how the developed simulation model can be used as an efficient tool for engineers. The developed simulation model can be used to predict how the operating conditions for the limited slip coupling influence degradation of the friction characteristics.

Mechanism analysis of vehicle start-up judder based on gradient characteristic of Stribeck effect

“…Negative damping was introduced into the powertrain system because of the negative gradient of μ − v characteristic, which made the powertrain system unstable and more prone to start-up judder. Similar conclusions about the start-up judder mechanism can be found in the works of Berglund et al, 5 Crowther et al, 6 and Shin et al 7 However, none of these references had explained the process of introduction of negative damping. In addition to the negative gradient of μ − v characteristic, there are other factors that influence the start-up judder, including external motivation, 8 installation and manufacturing error, 9 and thermal effect.…”

Effect of clutch lining frictional characteristics on take-up judder

“…Jarvis and Mills [3] presented clutch judder as a vibration, primarily induced by friction in dry clutches. However, this phenomenon is not only confined to dry clutches as shown by Berglund et al [4]. Centea et al [5][6] showed that clutch take-up judder is influenced by the gradient of coefficient of friction variation with the relative speed at the clutch lining interfaces (i.e.…”

Investigation on friction-induced judder of vehicle driveline based on a nonlinear friction model

“…It can be seen from equation ( 1) that when the relative speed v is large, g( v) approaches 0, and the influence of the stribeck effect is very small, so equation ( 4) can be approximated to equation (6). When the relative speed is close to the critical speed v s , g( v) approaches 1=e, and the stribeck effect cannot be ignored.…”

“…When the gradient of the friction coefficient with relative speed is negative, the system's comprehensive damping effect is negative, which can easily cause the system to be unstable and then cause the self-excited judder. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Based on the conclusion, many scholars have concentrated on the influencing factors of clutch friction coefficient. Li et al 23 analyzed the influence of friction materials on clutch judder through the comparative analysis of 18 kinds of frictional lining specimens.…”