<div>Trajectory tracking control, as one of the core technologies of intelligent driving vehicles, determines the driving performance and safety of intelligent driving vehicles and has received extensive attention and research. In recent years, most of the research results of trajectory tracking control are only applicable to conventional working conditions; however, the actual operating conditions of intelligent driving vehicles are complex and variable, so the research of trajectory tracking control algorithm should be extended to the high-speed low-adhesion coefficient, large curvature, variable curvature, and other compound limit working conditions. This requires more consideration of the vehicle dynamics in the controller design. In this article, a comprehensive review of trajectory tracking control under extreme operating conditions is conducted from three levels: vehicle dynamics model, vehicle speed tracking (longitudinal motion control), and path tracking (transverse motion control), and the existing research results are analyzed and summarized to obtain the research trends and pain points and difficulties in each field. On this basis, the future outlook of trajectory tracking control is proposed, which is expected to provide some help and inspiration to the research workers in this field.</div>

To solve the shortcomings and structural defects of the tripod joint, a novel structure named ‘double roller tripod joint’ is designed in this paper with the following features: (1) gothic arc-shaped tracks, (2) outer rollers with semi-toroid outer surfaces, (3) cylindrical inner rollers and (4) spherical trunnions. Based on spatial Cartesian kinematics and vector method, a novel method for kinematic analysis of the double roller tripod joint is proposed. The proposed method is validated by bench tests. By comparing the kinematics between the double roller tripod joint and tripod joint, it can be concluded that the double roller tripod joint has prominent advantages such as 0° relative pitch angles between the rollers and tracks and better constant velocity property. In addition, compared with other tripod-type joints, the proposed double roller tripod joint also has advantages in performances, manufacturability and assembling ability.

To systematically investigate the contact constraint relationships and the influences of fit clearances on the kinematic performances of a double roller tripod joint (DRTJ), a method for the kinematic analysis of DRTJs is proposed based on the principle of conjugate surfaces. In the proposed method, the constraint relations between rollers and tracks as well as between rollers and trunnions are firstly derived based on the principle of conjugate surfaces. Then, according to the constructed constraint relationships, the kinematic analysis model of a DRTJ considering the influences of fit clearances is established. Next, the effectiveness of the proposed method is validated by measuring the relative displacements and angles between rollers and tracks via experiment. Finally, kinematic analyses are carried out and the main results show that the relative pitch angle between rollers and tracks are always kept as zeroes under any working condition by designing the shapes of rollers' outer surfaces to be semi-toroid. The fit clearances have little influence on the kinematic performances of the DRTJ, thus proper fit clearances between rollers and tracks as well as between rollers and trunnions can be designed to improve the lubricating conditions of the DRTJ.

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