Injection-Molded Ball Joint Bearing for Consistent Torque
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Solution Overview
Problem
Existing ball joint assembly methods face challenges in achieving consistent operational torque and accommodating internal tolerances, particularly in high-load suspension applications where surface imperfections can lead to undesired free play or stiffness.
Innovation Solution
A ball joint design featuring a housing with a bore and a plastic bearing that includes a spherical surface engaging the ball, with a protrusion filling a groove and recess, and a sealing perimeter lip for interference fit, along with a method of injecting grease through a hole in the stud and ball, and using a cap and connector to form a monolithic plastic structure, ensuring consistent torque and sealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a pre-molded plastic bearing cup is used with snap-fit assembly, then the bearing can be easily installed, but consistent operational torque cannot be achieved and surface imperfections cause free play or stiffness
Solution Approach 1:
The bearing is injection molded directly onto the ball within the housing, merging three previously separate components (housing, ball, bearing) into a single integrated structure. This eliminates assembly steps while ensuring precise positioning and consistent torque characteristics by making the bearing position fixed relative to both the housing and ball during the molding process.
Solution Approach 2:
The bearing is pre-positioned and molded onto the ball before the final housing assembly is completed. The injection molding process performs the bearing installation action during manufacturing rather than as a separate assembly step, ensuring proper positioning before the housing is fully enclosed and sealed.
2Reliability
If the housing is cast over the resin bearing, then gaps between housing and bearing are eliminated, but the housing material is limited to low-strength zinc or aluminum die cast
Solution Approach 1:
The plastic bearing acts as an intermediary component that is molded directly onto the ball and positioned within the housing bore. This intermediary approach allows the housing to be made from high-strength steel without direct contact between the casting process and the bearing, as the bearing is already attached to the ball before housing assembly. The bearing material temperature requirements are satisfied while enabling high-strength housing materials.
Solution Approach 2:
The bearing is pre-attached to the ball through injection molding before the housing is assembled around it. This preliminary action ensures the bearing is securely positioned and eliminates gaps between the housing and bearing without requiring the housing to be cast over the bearing at high temperatures that would damage the resin material.
3Reliability
If over-crimping is used to force the bearing into engagement, then the bearing flows into gaps accommodating surface imperfections, but the assembly method is challenging and difficult to provide consistent torque
Solution Approach 1:
The bearing, ball, and housing are merged into a single integrated structure through injection molding. The bearing is molded directly onto the ball within the housing, creating a monolithic assembly that eliminates the need for separate bearing installation steps and complex crimping operations. This integration ensures consistent torque while accommodating surface imperfections through the molded bearing's ability to conform to the spherical surfaces.
Solution Approach 2:
The mechanical crimping process is replaced with an injection molding process. Instead of using mechanical force to crimp and force the bearing into engagement, the bearing is molded in place using molten plastic that flows into and accommodates surface imperfections, then solidifies to create a permanent, consistent connection without requiring complex assembly equipment or operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves consistent torque and enhanced sealing, addressing the issues of free play and stiffness, while allowing for the use of high-strength steel housings and providing improved lubrication and load characteristics.
Implementation Method 1
Plastic is injected into a space between the housing and the ball to form a bearing having a bearing surface engaging the ball
Implementation Method 2
The bearing is shrunk to form a recess in the bearing surface
Implementation Method 3
grease is provided between the first side and the ball
Data Source
AI summary
A ball joint includes a stud extending from a ball. A housing has a bore that receives the ball. The housing has an interior surface facing the ball that includes a groove. A plastic bearing is arranged between the ball and the housing. The plastic bearing has first and second sides opposite one another. The first side has a spherical surface engaging the ball. The second side has a protrusion opposite the spherical surface that is received in and fills the groove and a recess in the spherical surface opposite the protrusion.