Aircraft Hybrid Bearing Preload for Thermal Clearance Stability
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Solution Overview
Problem
Aircraft transmissions using hybrid rolling bearings face issues due to differing coefficients of thermal expansion between ceramic rolling elements and alloy steel rings, leading to clearance changes and stability problems under varying temperatures and lubrication conditions.
Innovation Solution
The use of preloaded elastic members and specific bearing configurations, such as back-to-back or face-to-face mounting, with axial preload systems that include disk springs or helical springs, to maintain stable axial clearances and prevent overloading, while allowing for thermal expansion adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If hybrid rolling bearings with ceramic rolling elements and alloy steel rings are used, then weight is reduced and dynamic behavior is improved, but assembly clearances increase significantly when operating temperature rises due to different coefficients of thermal expansion
Solution Approach 1:
The patent introduces adjustable clearance parameters through the elastic member preloading system. The elastic member (disk spring or helical spring) allows dynamic adjustment of the clearance between rolling elements and rings, compensating for thermal expansion differences. This maintains optimal clearance values across varying temperatures while preserving the weight and dynamic benefits of hybrid ceramic-steel bearings.
Solution Approach 2:
The patent transforms the static bearing clearance into a dynamic parameter that can be adjusted in real-time. The elastic member acts as a compliant element that automatically adapts the clearance to temperature conditions, making the bearing system self-regulating. This dynamic adjustment prevents clearance-related instability while maintaining the inherent advantages of hybrid bearing materials.
2Temperature
If the operating temperature rises, then the rings expand more than the rolling elements causing increased assembly clearances, but the increased clearances result in deterioration of bearing performance and stability
Solution Approach 1:
The patent applies preliminary preloading force through elastic members before thermal expansion occurs. This preloading creates an initial compressive state that counteracts the tendency for clearance increase during heating. The elastic member is pre-compressed to generate a force that maintains contact between rolling elements and rings even when thermal expansion creates gaps, thereby preserving bearing stability across the operating temperature range.
Solution Approach 2:
The patent explicitly accounts for differential thermal expansion between alloy steel rings and ceramic rolling elements. By incorporating elastic members with appropriate stiffness and preloading, the design compensates for the expansion mismatch. The elastic element absorbs the dimensional changes caused by thermal expansion while maintaining the functional relationship between bearing components, preventing performance deterioration.
3Temperature
If the operating temperature lowers significantly, then the rings contract more than the rolling elements causing reduced assembly clearances, but the reduced clearances result in overloading of the rings and rolling elements
Solution Approach 1:
The elastic member is preloaded to create an initial state that prevents excessive clearance reduction during cooling. The preloading force is calibrated to become less dominant as temperature decreases, allowing the bearing to accommodate contraction without creating excessive contact stresses. This preliminary setup ensures that the bearing transitions smoothly through temperature cycles without overloading.
Solution Approach 2:
The elastic member provides dynamic compliance that adapts to temperature-induced dimensional changes. During cooling, the elastic element's compliance allows for controlled clearance reduction without transmitting excessive loads to the rolling elements and rings. The system dynamically balances the contraction forces, preventing overloading while maintaining operational integrity across the full temperature range.
4Stability of the object's composition
If preloaded elastic members are used to maintain stable axial clearances, then bearing stability is improved, but device complexity increases
Solution Approach 1:
The patent combines the elastic member preload function with the existing bearing support structure. Rather than adding a completely separate adjustment mechanism, the elastic elements (disk springs or helical springs) are integrated into the bearing assembly, merging the clearance control function with the structural support function. This reduces the overall complexity increase while achieving stable axial clearances.
Solution Approach 2:
The elastic preloaded members create a self-regulating system that automatically maintains optimal clearance without external control or adjustment mechanisms. The elastic elements self-adjust based on temperature and load conditions, eliminating the need for complex external control systems, actuators, or adjustment procedures. This self-service approach minimizes the added complexity while achieving the stability objective.
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
This configuration ensures stable transmission performance across a broad temperature range, maintains robust axial preload, and reduces the risk of overloading and fatigue, ensuring efficient operation from -50°C to over 200°C with critical lubrication conditions.
Implementation Method 1
The use of preloaded elastic members and specific bearing configurations, such as back-to-back or face-to-face mounting, with axial preload systems that include disk springs or helical springs
Implementation Method 2
the different coefficient of thermal expansion between the material of the rolling bodies and that of the rings. In fact, the assembly clearances between the rings and the rolling elements increase significantly when the operating temperature rises
Data Source
Figure 1
Figure 2~7
Figure 3~4
AI summary
An aircraft (1) is described comprising: a support element (16; 16'); a shaft (12; 12') rotating about an axis (E, E'); a pair of oblique roller bearings(17; 17') mounted so as to couple the shaft (12; 12') to the support element (16; 16') rotatingly about the axis (E, E'); the roller bearings (17; 17') comprising: respective first races (18, 19; 18', 19') cooperating radially in contact with a first component (16, 12; 16', 12') defined by one from the support element (16; 16') and the shaft (12; 12'); respective second races (19, 18; 19', 18') cooperating radially in contact with a second component (12, 16; 12', 16') defined by the other from the support element (16; 16') and the shaft (12; 12'); and respective pluralities of rolling elements (20; 20') adapted to roll on the first and second races (18, 19; 18' 19'; 19, 18; 19', 18'); the aircraft (1) further comprises a pair of preloaded elastic members (21; 21'), which couple the first races 18, 19; 18', 19') to the first component (16, 12; 16', 12') respectively, axially and in an elastically yielding manner.