Speed Reducer Grease Segmentation for Steering Reliability
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Solution Overview
Problem
Conventional electric power steering systems face issues with grease shortage in speed reducers due to low fluidity, leading to increased steering torque and rattling noise, requiring excessive grease that can leak and increase costs, and complex structures to recirculate grease.
Innovation Solution
A speed reducer design where grease is supplied to the outer peripheral space between the worm wheel and housing, preventing extrusion and ensuring a consistent lubrication supply to the meshing section, reducing the overall grease amount and avoiding structural complications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large amount of grease is supplied to fill the entire housing space, then the meshing section is sufficiently lubricated, but the grease may enter rolling bearings affecting performance, leak through housing gaps, increase costs, and complicate the structure
Solution Approach 1:
The housing space is segmented into a grease supply section and a non-supply section. The grease supply section includes the meshing section and an outer peripheral space, while the non-supply section excludes the rolling bearing section. This segmentation allows grease to be concentrated where it is needed for lubrication while preventing it from entering the rolling bearings, thus resolving the contradiction between sufficient lubrication and preventing grease intrusion into bearings.
Solution Approach 2:
Different regions of the housing are assigned different grease supply characteristics. The meshing section and outer peripheral space are designated as grease supply regions to ensure adequate lubrication, while the rolling bearing region is excluded from grease supply. This local differentiation optimizes lubrication effectiveness in critical areas while avoiding the harmful effects of grease in non-lubrication areas, thereby resolving the contradiction between lubrication sufficiency and preventing grease leakage.
2Reliability
If conventional low fluidity grease is used, then the grease is easily extruded from the meshing section due to sliding motion, but it does not automatically return to the meshing section, causing grease shortage
Solution Approach 1:
The grease supply mechanism utilizes the rotational motion of the worm and worm wheel to automatically circulate grease from the outer peripheral space back to the meshing section. The rotating components act as self-powered grease pumps, eliminating the need for external grease circulation systems. This self-service mechanism ensures continuous grease supply to the meshing section without requiring complex additional structures, resolving the contradiction between grease retention and grease quantity.
3Reliability
If the outer peripheral space width is increased, then more grease can be stored to prevent extrusion, but the grease may move onto the side faces of the worm wheel and increase the amount of grease required
Solution Approach 1:
The width of the outer peripheral space is optimized to a specific parameter range (0.5mm to 2.0mm) to achieve the desired balance. This parameter optimization ensures that the space is sufficient to store enough grease to prevent extrusion during operation, while being narrow enough to prevent grease from moving onto the side faces of the worm wheel. By precisely controlling this dimensional parameter, the contradiction between grease supply stability and grease consumption is resolved.
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 design maintains effective lubrication, reduces rattling noise, and minimizes grease leakage, providing improved steering feel and cost efficiency by using a minimal amount of grease, ensuring the meshing section remains lubricated and preventing grease from entering rolling bearings.
Implementation Method 1
The grease supplied into the speed reducer lies between tooth surfaces of the worm and tooth surfaces of the worm wheel, and forms oil films. The oil films formed by the grease functions to assist sliding between the tooth surfaces caused by the rotation of the worm due to the rotation of the rotary shaft of the electric motor and the rotation of the worm wheel due to the rotation of the worm, and functions to buffer impacts that occur between the tooth surfaces due to the rotations
Implementation Method 2
Commonly-used grease has a low fluidity, and therefore is easily extruded from a meshing section at which the worm and the worm wheel mesh with each other, due to a sliding motion of the worm itself caused by the rotations of the worm and the worm wheel
Data Source
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AI summary
A speed reducer (18) for an electric power steering system includes a worm (19), a worm wheel (20), and a housing (21). Only a meshing section (B) where the worm (19) and the worm wheel (20) mesh with each other and a space (A) between the worm wheel (20) and the housing (21) are filled with grease. The grease in the space (A) is in contact with both tooth surfaces (20h) of the worm wheel (20) and an inner peripheral face (21c) of the housing (21), the inner peripheral face (21c) facing the worm wheel (20).