Planetary Gear Train for Nine-Speed Automatic Transmission
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Solution Overview
Problem
Automatic transmissions face challenges in achieving efficient power delivery and fuel economy with increasing transmission steps due to the rise in internal components, which can lead to mountability, cost, weight, and efficiency issues, while maintaining silent driving and engine performance.
Innovation Solution
A planetary gear train design that combines four simple planetary gear sets with six friction elements to achieve nine forward speed stages and one reverse speed stage using a minimal number of components, enhancing power delivery and fuel efficiency by selectively operating these elements to optimize engine rotation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of transmission steps is increased to improve fuel efficiency, then fuel economy is improved, but the number of internal components increases causing deterioration in mountability, cost, weight, and transmission efficiency
Solution Approach 1:
The patent employs nested planetary gear sets where multiple gear sets are arranged concentrically around a common input/output shaft. Each planetary gear set contains sun gears, planet gears, and ring gears that are nested within each other, allowing multiple transmission ratios to be achieved within a compact structure. This nesting principle enables 9 forward speed stages without proportionally increasing the overall size or component count.
Solution Approach 2:
The friction elements (clutches and brakes) are designed to serve multiple functions by selectively engaging different planetary gear sets. The same friction elements can lock different components depending on the desired transmission ratio, allowing a single set of friction elements to control multiple speed stages. This multi-functionality reduces the need for dedicated components for each transmission step.
2Use of energy by moving object
If the number of transmission steps is increased to improve fuel efficiency, then fuel economy is improved, but weight increases
Solution Approach 1:
The planetary gear sets are arranged in a nested configuration where multiple gear sets share common mounting structures and support elements. The concentric arrangement allows gear sets to be stacked radially around the input/output shaft, minimizing the transmission's overall footprint and weight. This nested structure achieves 9 forward speed stages without requiring separate housing and support structures for each gear set.
3Device complexity
If the number of friction elements is reduced to simplify the structure, then device complexity is reduced, but the ability to achieve multiple speed stages may be compromised
Solution Approach 1:
Each friction element is designed as a multi-functional component that can engage different planetary gear components (sun gears, ring gears, planet carriers) depending on the selected transmission ratio. The control system selectively activates specific friction elements to lock different combinations of gears, enabling 9 forward speed stages and reverse gear with a limited number of friction elements. This universal design allows each friction element to control multiple transmission states.
Solution Approach 2:
The patent combines the functions of multiple friction elements by having them work in combination rather than independently. Multiple friction elements can be engaged simultaneously to achieve compound gear ratios, and the same friction elements are reused across different speed stages. This merging of functions allows a small number of friction elements to control a large number of transmission steps through coordinated engagement patterns.
Data Source
AI summary
Nine or more forward speeds and at least one reverse speed is achieved by a planetary gear train of an automatic transmission for a vehicle including an input shaft, an output shaft, four planetary gear sets respectively having three rotation elements, and six control elements for selectively interconnecting the rotation elements.