Planetary Gear Train Nested Configuration for Compact Automatic Transmission
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Solution Overview
Problem
Current planetary gear trains for automatic transmissions face challenges in achieving a compact design and optimal power delivery performance while maintaining fuel efficiency, particularly in achieving a higher number of shift speeds and efficient operation of frictional elements.
Innovation Solution
The design incorporates three planetary gear sets and five frictional elements, along with externally-meshing gears, to achieve eight forward speeds and one reverse speed, allowing for improved mountability and reduced fuel consumption by optimizing the arrangement of rotation elements and frictional elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple planetary gear sets are combined to achieve more shift speeds, then power delivery performance is improved, but the length and complexity of the gear train increases
Solution Approach 1:
The patent employs nested planetary gear sets where a second planetary gear set is positioned inside a first planetary gear set, and a third planetary gear set is positioned inside the second. This nested configuration allows multiple gear sets to occupy overlapping spatial volumes, achieving 8 forward speeds and 1 reverse speed without proportionally increasing the overall length of the transmission assembly.
Solution Approach 2:
The invention transitions from a linear arrangement of planetary gear sets to a three-dimensional nested structure. By utilizing radial and axial spacing within the nested configuration, the patent achieves multiple speed ratios without extending the transmission length in the primary direction, effectively using dimensional optimization to resolve the space-power delivery contradiction.
2Adaptability or versatility
If more frictional elements are added to control shift speeds, then shift control capability is improved, but device complexity increases
Solution Approach 1:
The patent designs frictional elements (clutches and brakes) that can serve multiple functions across different shift speeds. For example, the first clutch C1 and second clutch C2 are configured to engage different planetary gear sets at different speeds, allowing a limited number of frictional elements to control all 8 forward speeds and 1 reverse speed. This multi-functionality reduces the total number of frictional elements needed compared to conventional designs.
Solution Approach 2:
The invention merges the control functions of multiple frictional elements into a coordinated system where clutches and brakes work in combination. The patent shows that at each shift speed, a specific combination of frictional elements is engaged to achieve the desired gear ratio, allowing the system to achieve high adaptability with fewer individual components through synergistic operation.
3Volume of moving object
If planetary gear sets are arranged in a compact configuration, then mountability is improved, but power delivery efficiency may be compromised
Solution Approach 1:
The nested arrangement of planetary gear sets allows the patent to achieve a compact transmission assembly volume while maintaining adequate spacing between gear sets for proper power transmission. The first, second, and third planetary gear sets are nested concentrically, utilizing radial and axial clearance to prevent interference while enabling efficient torque transfer through each stage.
Solution Approach 2:
The patent optimizes the local configuration of each planetary gear set within the nested structure, ensuring that meshing gears and carriers are positioned to maximize power transmission efficiency at each stage. The carrier gears and planet gears are arranged with appropriate clearances and alignment to minimize power losses despite the compact overall volume.
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 configuration enhances power delivery performance, reduces fuel consumption, and minimizes drag torque by allowing three frictional elements to operate at each shift-speed, resulting in improved mountability and efficiency.
Implementation Method 1
frictional elements selectively interconnecting the rotation elements or selectively connecting the rotation element to a transmission housing
Data Source
AI summary
A planetary gear train of an automatic transmission may include a first shaft receiving engine torque, a second shaft disposed in parallel to the first shaft, a first planetary gear set on the first shaft including a first element operated as a fixed element, a second element directly connected to the first shaft, and a third element, a compound planetary gear set formed by combining a second planetary gear set and a third planetary gear set including a fourth element selectively connected to the first shaft and the third element, a fifth element connected to an output gear, a sixth element selectively connected to the first element, and a seventh element selectively connected to the third element through a gear.