Suspension ball hinge optimization design_Hinge knowledge_Tallsen

Suspension ball hinge is the core product of the ZF Chassis Technology Components Division, and its structural design is the core technology of the department. As the automobile industry continues to develop, the requirements for ball hinge products are also increasing. The current market demands more stringent simulation environments, complex working loads, and compliance with new regulatory requirements such as pedestrian protection and post-collision failure. To meet these demands, technical optimization of the ball joint is crucial.

The ball joint is primarily used in the front suspension, serving as the connection between the rod and the steering knuckle. This connection provides the second wheel degree of freedom, allowing for steering. In order to meet higher customer requirements, the sealing performance and fatigue wear performance of the ball joint need to be enhanced.

This article focuses on the optimization of the suspension ball hinge structure for the domestic OEM project (Dongfeng Liuzhou B20 project) of ZF's mass production. Initially, the plan was to continue using the current mass-produced parts. However, after the first round of DV tests, it was discovered that there were risks involved, including water leakage and early wear. Further analysis revealed the need to improve the design to meet the current test requirements.

Suspension ball hinge optimization design_Hinge knowledge_Tallsen

Through the analysis of other domestic OEM projects, it was found that many OEMs have formulated specific specifications for ball hinges, significantly raising the design requirements. Global OEMs are also continuously updating their specifications for ball hinges. This means that ZF products need to withstand harsher environmental conditions, more complex working conditions, and more detailed collision protection requirements. Therefore, it is necessary to research and analyze the new specifications to develop a reasonable optimization plan that can meet performance requirements at a lower cost.

to Ball Hinge:

Ball hinges maintain continuous contact and relative movement between mechanism chains. The joints where these movements occur are called ball hinges. There are two types of ball hinges: radially loaded hinges (guided ball hinges) and axially loaded hinges (loaded ball joints). The main connecting elements of the ball joint are the ball stud and the ball socket. The working performance of the ball joint, as well as other characteristics such as material, size, surface quality, load carrying capacity, and lubrication, are all important considerations.

Function and Technical Requirements of the Ball Hinge:

The function of the ball hinge is to connect the rod with the steering knuckle, providing three degrees of freedom for force and motion transmission. Two degrees of freedom are used for wheel beating and steering, while the third degree of freedom allows for elastokinematic variation for the wheel. The ball joint should have minimal elastic displacement under normal operating conditions to avoid discomfort and affect driver evaluation. Additionally, the working torque of the ball hinge should not be lower than the allowable value to prevent early wear and noise.

Suspension ball hinge optimization design_Hinge knowledge_Tallsen

Original Design Failure Mode Analysis:

During the initial stage of the B20 project, the sealing performance test revealed failure modes such as water leakage and rust. Further analysis showed that the ball hinge and steering knuckle did not fit properly, resulting in a 2.5mm gap, which posed a risk of water leakage and sealing system failure. Disassembly of the ball hinge revealed severe corrosion on the mating surface with the steering knuckle. It was concluded that the current dust-proof system did not meet the design requirements and needed improvement.

Optimal Design Scheme for Ball Hinge:

Two main factors were identified as potential contributors to the sealing test failure: assembly quality and size selection of the collar, and design failure of the dust cover. To address the assembly issue, the installation size of the collar was defined in the IPS (internal process specification). This specification provides guidelines for collar assembly, ensuring that it meets design requirements. Additionally, the dust cover and ball pin design were optimized to improve the sealing performance. The dust cover design was modified to match the expected cone angle, and the ball pin step was redesigned to increase the contact area with the dust cover.

Optimal Design Test Verification:

Samples were produced based on the optimized design scheme, and the sealing performance test was conducted. The results showed a significant improvement, with water content at the ball pin and ball shell ends ranging from only 0.1% to 0.2%. The test was successful, and the corrosion situation of the optimized design was considerably better compared to the original design.

The optimized design scheme for the ball hinge in the B20 project demonstrated improved sealing performance. While there is potential for even better performance, the current solution proved to be effective within the project's time constraints. This project highlighted the importance of thoroughly analyzing customer requirements and developing a comprehensive layout before starting production. By implementing the optimized design, ZF was able to meet the demands of the OEM project and enhance the sealing performance of the ball hinge.

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