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

This paper presents a profound mechanism investigation for vehicle start-up judder phenomenon using a combination of experiment and simulation. First, from the experimental analysis, the characteristic frequency of start-up judder is mainly concentrated at about 9 Hz. A 13-degree-of-freedom powertrain branched model is established to numerically reproduce experimental phenomenon. The validity and accuracy of simulation model in reflecting the characteristics of start-up judder are verified by the experimental results in time–frequency domain. Second, through analyzing clutch friction torque, it can be concluded that the closed-loop positive feedback mechanism caused by the negative gradient characteristic of Stribeck effect is the determining factor for the start-up judder. It promotes aggravated fluctuation in rotational speed of clutch driven plate. The introduction process of negative damping that makes powertrain system divergent is explained in detail. Finally, two theoretical measures are proposed to suppress the vehicle start-up judder. One of the measures is to diminish the absolute value of the negative gradient. It weakens the aggravation effect of the closed-loop positive feedback and hence attenuates the start-up judder. Another measure is to change to positive gradient. It forms a closed-loop negative feedback process that causes the almost disappearance of start-up judder. The effectiveness of the two suppression measures verifies the correctness of the start-up judder mechanism proposed in this paper.