Planet Wheel Shaft Geometry for Oil Film Support Under Ovalization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The ovalization of planet wheels due to radial loading in slide-bearing supported planetary gears reduces the load carrying capacity by dividing the hydrodynamic oil pressure area into weaker and stronger regions, and narrows the wedge-shaped gap between sliding surfaces, leading to inadequate oil supply and compromised load carrying capacity.
Innovation Solution
A planet wheel shaft with a bearing portion that deviates from a circular shape in axial regions, widening the gap between the bearing portion and the planet wheel, and optimizing sliding surfaces for both tangential and radial loads, allowing for improved oil supply and load distribution, thereby reducing the negative effects of ovalization and allowing for a smaller material thickness and larger diameter of the slide-bearing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the material thickness of the planet wheel is minimized to allow larger slide-bearing diameter, then the load carrying capacity of the slide-bearing is improved, but the planet wheel ovalization under radial loading increases which divides the hydrodynamic oil pressure area and reduces lubrication effectiveness
Solution Approach 1:
The patent applies asymmetry by making the bearing portion cross-section non-circular (oval-shaped) with different thicknesses in tangential and radial directions. The greater thickness in the tangential direction compensates for planet wheel ovalization under radial loading, maintaining a more uniform gap for hydrodynamic oil pressure formation while allowing larger bearing diameter for improved load carrying capacity.
Solution Approach 2:
The patent changes the geometric parameters of the bearing portion by deviating from a circular cross-section to an oval cross-section with specific thickness ratios. This parameter change allows the bearing to accommodate planet wheel ovalization while maintaining adequate oil film formation, resolving the contradiction between bearing size and wheel stability.
2Reliability
If the planet wheel material thickness is reduced to increase slide-bearing diameter, then the load carrying capacity is improved, but the wedge-shaped gap between sliding surfaces is narrowed which decreases oil supply to hydrodynamic pressure areas
Solution Approach 1:
The asymmetric oval cross-section of the bearing portion creates a more favorable gap distribution for oil supply. The greater tangential thickness maintains adequate wedge-shaped gap dimensions for proper oil flow and hydrodynamic pressure formation, even when the overall bearing diameter is enlarged and planet wheel thickness is reduced.
3Ease of manufacture
If conventional circular cross-section bearing portions are used, then the structure is simple and manufacturing is easy, but the bearing cannot compensate for planet wheel ovalization which reduces hydrodynamic oil pressure formation
Solution Approach 1:
The patent transitions from a simple circular cross-section to an asymmetric oval cross-section. While this increases manufacturing complexity slightly, it provides the functional benefit of compensating for planet wheel ovalization and maintaining proper hydrodynamic oil pressure formation, which is critical for bearing reliability under load.
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 enhances the load carrying capacity of the slide-bearing by ensuring consistent oil supply to areas of hydrodynamic pressure, allowing for greater ovalization of planet wheels while maintaining sufficient load carrying capacity, and reducing the need for material thickness, thus increasing the diameter of the slide-bearing.
Implementation Method 1
areas where hydrodynamic oil pressure is formed for carrying load in the first direction
Implementation Method 2
the wedge-shaped gap which is between the sliding surfaces of the slide-bearing and which is wedge-shaped because of the tangential load
Data Source
Figure 1a
Figure 1b~1c
Figure 2a~2c
AI summary
A planet wheel shaft (101) comprises a bearing portion for acting as a slide-bearing in cooperation with a planet wheel (115a) of a planetary gear. On at least one axial region of the bearing portion, a cross-sectional shape deviates from a circular shape so that the bearing portion is thicker in a first direction (x) than in a second direction (y) perpendicular to the first direction. The deviation from the circular shape widens a wedge-shaped gap (107) that is between the bearing portion and the planet wheel when there is load in the first direction. This facilitates oil supply to an area where hydrodynamic oil pressure is formed for carrying load in the first direction because the widening the wedge-shaped gap compensates for narrowing the gap due to ovalization of the planet wheel caused by load in the second direction.