Stepped Pinion Transaxle for Compact Planetary Gear Reducer Design
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Solution Overview
Problem
Existing transaxles face limitations in downsizing due to the need to accommodate pinion shafts and bearings within small diameter pinions, leading to constraints in reducing the size of the planetary gear reducer while maintaining the reduction ratio.
Innovation Solution
The transaxle integrates a stepped pinion with a pinion shaft supported by needle bearings at both ends, utilizing bearing boss portions as stoppers to restrict axial movement, allowing for a reduced radial size and maintaining the reduction ratio, and employs an efficient oil supply system to ensure lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the diameter of the small diameter pinion is reduced to downsize the planetary gear reducer, then the reduction ratio is maintained, but the pinion shaft and needle bearings cannot be accommodated inside the small diameter pinion
Solution Approach 1:
The patent divides the pinion support structure into separate functional elements: the small diameter pinion gear, the pinion shaft, and needle bearings are separated into distinct components rather than being integrated within the pinion body. This segmentation allows each component to be optimized independently for its specific function.
Solution Approach 2:
The patent extracts the pinion shaft and needle bearings from the interior of the small diameter pinion and positions them externally. The pinion shaft extends through the small diameter pinion, and the needle bearings are positioned in bearing boss portions of the carrier rather than being housed within the pinion itself. This extraction resolves the spatial conflict between maintaining a small pinion diameter and accommodating the necessary support structures.
2Length of moving object
If the small diameter pinion is made smaller to reduce the planetary gear reducer size, then compactness is improved, but the needle bearings and pinion shaft cannot be positioned to properly support the pinion
Solution Approach 1:
The patent introduces the carrier as an intermediary structure that provides bearing boss portions to support the needle bearings, which in turn support the pinion shaft. This intermediary carrier structure assumes the burden of supporting the pinion assembly, allowing the small diameter pinion itself to be minimized without compromising support reliability.
Solution Approach 2:
The patent transitions from a radial arrangement where bearings would be positioned within the pinion diameter to an axial arrangement where the pinion shaft extends through the pinion and is supported at its ends by the carrier. This dimensional change allows the support structure to be positioned in a different spatial dimension, avoiding interference with the small pinion diameter.
3Power
If the stepped pinion structure is adopted to maintain reduction ratio, then the reduction ratio is preserved, but the radial size cannot be further reduced due to bearing accommodation requirements
Solution Approach 1:
The stepped pinion is segmented into a large diameter pinion and a small diameter pinion that are integrated on a common pinion shaft. The large diameter pinion meshes with the sun gear while the small diameter pinion meshes with the ring gear. This segmentation allows the reduction ratio to be determined by the gear ratios of these two pinions, preserving the desired power transmission characteristics.
Solution Approach 2:
The support structures (pinion shaft and needle bearings) are extracted from the interior of the stepped pinion and positioned externally on the carrier. This extraction eliminates the constraint that would otherwise prevent further reduction of the radial size of the planetary gear reducer, as the bearings are no longer limited by the internal space of the stepped pinion.
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 solution achieves a downsized transaxle with efficient lubrication, enabling a compact design without compromising performance by using needle bearings and a novel oil supply system.
Implementation Method 1
The stepped pinion is supported by needle bearings provided outside the small diameter pinion and large diameter pinion so as to be rotatable with respect to the carrier
Data Source
Figure 1
Figure 2A~2B
Figure 3~4
AI summary
A transaxle includes a planetary gear reducer (40) and a differential device (80). The planetary gear reducer (40) includes a stepped pinion, a first needle bearing, a second needle bearing, and a carrier. The stepped pinion includes a pinion shaft with which a large diameter pinion and a small diameter pinion are integrated. The first needle bearing is fitted to a part of the pinion shaft outside the large diameter pinion. The second needle bearing is fitted to a part of the pinion shaft outside the small diameter pinion. The carrier is configured to support the stepped pinion via the first needle bearing and the second needle bearing such that the stepped pinion is rotatable with respect to the carrier, and to couple the stepped pinion and the differential device (80).