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Abstract: The four-wheel alignment parameters of a vehicle are closely related to the suspension. The vehicle suspension is crucial for the driving performance, safety, and comfort of a vehicle. DTAS 3D provides tolerance simulation analysis methods for various types of suspensions. Keywords: DTAS 3D, front and rear suspensions, tolerance simulation analysis, motion coupling, dimensional tolerance analysis, dimension chain calculation, dimensional engineering —— Diteuo (Shanghai) Technology Development Co., Ltd. I. Overview of Suspension Tolerance Analysis The suspension refers to the collective term for the connecting devices between the vehicle body (or chassis) and the wheels (or axles), and it is an important component of a vehicle. The vehicle suspension is crucial for the driving performance, safety, and comfort of a vehicle. Meanwhile, the four-wheel alignment parameters are closely related to the suspension and also play a key role in the proper operation of the vehicle. While in motion, a car encounters various types of road irregularities and bumps. The suspension system, through the coordinated action of components such as springs and shock absorbers, is able to effectively buffer and absorb these vibrations, reducing the movement and shaking of the vehicle’s body and thereby providing passengers with a smoother and more comfortable riding experience. The suspension system plays a key role in the handling stability of a vehicle. It ensures good contact between the wheels and the ground, allowing the tires to effectively transmit force and torque under various driving conditions. During turning, braking, and accelerating, the suspension system controls the vehicle’s attitude changes by distributing the wheel loads appropriately, ensuring that the car moves as intended by the driver and thereby improving driving safety and handling. The objective of the suspension tolerance simulation analysis is to determine the impact of each tolerance on the four-wheel alignment parameters. The four-wheel parameters for the front and rear wheels include wheel camber, toe, and for the front wheels, there is also the kingpin angle, among others. Official website: www.dtas-china.com. For inquiries: 18721334000. DTAS 3D offers two methods for simulating chassis suspension tolerances: one is to create a static virtual assembly of the chassis, using techniques such as multi-constraint assembly and rotational assembly, in order to combine tolerance analysis with motion analysis in the simulation process. The second method is to establish various kinematic pairs and drives. Although the modeling approaches differ slightly in these two methods, their essence and results are the same. The two 3D modeling approaches of DTAS can handle the following suspension types: MacPherson, double wishbone, three-link, four-link, five-link, H-arm, etc. The MacPherson strut front suspension is a classic type of front suspension; due to some of its drawbacks, suspensions such as the double wishbone front suspension have been developed as alternatives to it. Applying the MacPherson front suspension design to the rear suspension results in a three-link rear suspension, commonly known as the chopstick suspension; it features a simple structure and low cost. As the demands for handling performance increased, suspensions based on three-link structures evolved into four-link (trailing arm suspension), five-link, H-arm, and other types of suspensions. This paper mainly discusses the modeling methods for the double wishbone front suspension and the five-link rear suspension. As shown in the figure: II. Tolerance analysis of double-wishbone front suspension and five-link rear suspension. Modeling approach: For the double-wishbone front suspension, the following kinematic pairs are established, including 2 driving pairs – one for wheel movement and the other for steering drive. The five-link rear suspension, having 5 links, features 10 ball joints in total with the frame’s steering knuckle; shock absorbers and similar components can establish slider joints, ball joints, etc. The wheel hop drive is mounted on the steering knuckle. For the five-link rear suspension, in addition to kinematic pair modeling, the multi-constraint assembly modeling method can also be employed, as shown in the figure below. Multiple constraints are used to control the distance between the steering knuckle mounting point and the subframe mounting point, thereby ultimately controlling the final orientation of the steering knuckle. Multi-constraint assembly is applicable not only to five-link rear suspensions but also to various other types of front and rear suspensions. Multi-constraint assembly has advantages such as faster solution speed and simpler modeling compared to kinematic pair modeling. Virtual measurements: In DTAS 3D, various virtual measurements can be established, including the toe angle, camber angle, caster angle of the front wheels, as well as the difference or sum of the left and right toe angles of the front wheels. Simulation results: Motion trajectory analysis, including the analysis of the trajectories of the wheels under different conditions, such as steering angles and wheel bounce heights. Fluctuation patterns of various four-wheel parameters: contribution analysis, transfer coefficient analysis, etc.; the sensitivity and contribution of each tolerance to the four-wheel parameters, providing guidance for subsequent optimization. Simulation animations: Tolerance simulation animations for double wishbone suspensions, five-link suspensions, and other types of suspensions; Simulation animations for MacPherson suspensions, split double wishbone suspensions, three-link suspensions, and H-arm suspensions. III. Conclusions and Future Prospects: DTAS 3D meets the needs for tolerance simulation analysis of various automotive suspensions, and it offers multiple modeling methods for both static and dynamic joints, thereby supporting the analysis of a vehicle’s handling and comfort characteristics. The various components of the mechanism are flexible bushings, and how to integrate the simulation of mechanism motion, tolerances, and flexibility is a major challenge in current and future suspension tolerance analysis.