Planetary Gear Train Nested Configuration for 8-Speed Transmission
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Solution Overview
Problem
Conventional 8-speed automatic transmissions face challenges with increased length, weight, cost, and reduced transmission efficiency due to multiple planetary gear sets and control elements, which affect mountability, fuel economy, and drivability, especially with larger gear ratio spans that compromise linearity of step ratios.
Innovation Solution
A planetary gear train configuration that combines four planetary gear sets with seven control elements to achieve ten forward speed stages and one reverse speed stage, securing a gear ratio span greater than 10.01, thereby enhancing engine driving efficiency and drivability by minimizing component count and optimizing gear ratio linearity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of speed stages is increased to enhance fuel economy and optimize drivability, then fuel economy and drivability are improved, but the number of internal components (particularly planetary gear sets) increases, which leads to increased transmission length, deteriorating mountability, cost, weight, and transmission efficiency
Solution Approach 1:
The patent employs nested planetary gear sets where planetary gear sets are arranged concentrically around a common input/output shaft. The second planetary gear set is positioned inside the first planetary gear set, allowing multiple gear reduction stages to be achieved within a compact radial space, thereby reducing the overall transmission length while maintaining multiple speed stages for improved fuel economy
2Speed
If conventional 8-speed automatic transmissions use three to four planetary gear sets and five to seven control elements, then more speed stages are achieved, but the length of the automatic transmission increases, deteriorating mountability
Solution Approach 1:
The patent merges multiple planetary gear sets into a compact configuration where they share common shafts and housing space. The nested arrangement allows the first and second planetary gear sets to occupy overlapping radial spaces, effectively combining their functional volumes and reducing the overall transmission length while achieving 8-speed capability
Solution Approach 2:
The patent transitions from a linear arrangement of planetary gear sets to a radial/nested configuration. By organizing gear sets concentrically around a central shaft rather than in series along the shaft length, the design achieves multiple speed stages in a compact radial footprint, reducing the axial length of the transmission
3Device complexity
If 8-speed automatic transmissions have gear ratio spans of 6.5-7.5, then transmission design is simplified, but improvement of fuel economy may not be great
Solution Approach 1:
The patent optimizes the gear ratio parameters across the 8-speed range to achieve a gear ratio span greater than 9.0. By carefully selecting and adjusting the gear ratios of each speed stage, the design achieves superior fuel economy while maintaining acceptable linearity of step ratios, demonstrating that parameter optimization can decouple the trade-off between complexity and performance
4Productivity
If 8-speed automatic transmissions have gear ratio spans larger than 9.0, then fuel economy is improved, but it may be difficult to secure linearity of step ratios, deteriorating driving efficiency of an engine and drivability of a vehicle
Solution Approach 1:
The patent carefully optimizes the gear ratio parameters to achieve a balance between large gear ratio span (>9.0) for fuel economy and acceptable linearity of step ratios for drivability. By adjusting the individual gear ratios within the transmission, the design minimizes the deterioration of drivability while maintaining the fuel economy benefits of a large overall gear ratio span
Data Source
AI summary
A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting an output torque, a first planetary gear set including first, second, and third rotational elements, a second planetary gear set including fourth, fifth, and sixth rotational elements, a third planetary gear set including seventh, eighth, and ninth rotational elements, and a fourth planetary gear set including tenth, eleventh, and twelfth rotational elements.