Planetary Gear Train for Automatic Transmission with Nested Configuration
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Solution Overview
Problem
Existing automatic transmissions with eight or more shift stages are cumbersome due to numerous components, affecting installability, production cost, and power flow efficiency, while striving to enhance fuel efficiency and drivability.
Innovation Solution
A planetary gear train configuration utilizing four planetary gear sets, two external gears, and six control elements to achieve at least nine forward speeds and one reverse speed, reducing length and improving power delivery and fuel efficiency by allowing a wide range of gear teeth variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of components is increased to achieve more shift stages, then the fuel efficiency and drivability are improved, but the installability deteriorates and the transmission becomes lengthy
Solution Approach 1:
The patent employs nested planetary gear sets where smaller planetary gear sets are positioned within or alongside larger ones, allowing multiple gear reduction stages to be compacted into a shorter axial length. The first and second planetary gear sets are arranged such that their rotational elements share common mounting structures, achieving nested configuration that reduces overall transmission length while maintaining multiple shift stages.
Solution Approach 2:
The patent transitions from a traditional single-row planetary gear arrangement to a multi-dimensional configuration by placing planetary gear sets at different radial positions and using transfer gears to connect rotational elements across different planes. This spatial reorganization allows power flow through multiple gear stages without increasing axial length proportionally.
2Productivity
If the number of components is increased to achieve more shift stages, then the fuel efficiency and drivability are improved, but the device complexity increases
Solution Approach 1:
The patent designs rotational elements to serve multiple functions: the first rotational element of each planetary gear set acts as both a sun gear for its own planet gears and as a ring gear for transfer gears from adjacent gear sets. The second rotational elements serve as planet carriers that can be selectively connected to different shafts. This multi-functionality reduces the need for separate dedicated components for each gear stage.
Solution Approach 2:
The patent combines multiple planetary gear sets into a single integrated transmission assembly where control elements selectively connect rotational elements of different gear sets to common shafts. The first and second planetary gear sets are merged through shared mounting structures and common power flow paths, reducing overall component count compared to separate gear train assemblies.
3Productivity
If the number of components is increased to achieve more shift stages, then the fuel efficiency and drivability are improved, but the production cost increases
Solution Approach 1:
The patent divides the transmission into modular planetary gear sets that can be manufactured and assembled separately. Each planetary gear set (first and second) can be produced as an independent module with standardized components, allowing for economies of scale and reduced manufacturing complexity compared to a monolithic gear train design.
4Productivity
If the number of components is increased to achieve more shift stages, then the fuel efficiency and drivability are improved, but the power flow efficiency deteriorates
Solution Approach 1:
The patent establishes continuous power flow paths through the planetary gear sets where torque is transmitted through engaged gear teeth without interruption. The control elements enable smooth transitions between different gear ratios by selectively engaging clutch packs, maintaining continuous torque transmission and minimizing power losses during shift operations.
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, fuel consumption, and installability by achieving a gear ratio span of over 8.7, ensuring linear step ratios for efficient shift staging and improved drivability.
Implementation Method 1
a first planetary gear set having first, second, and third rotational elements, a second planetary gear set having fourth, fifth, and sixth rotational elements, a third planetary gear set having seventh, eighth, and ninth rotational elements, and a fourth planetary gear set having tenth, eleventh, and twelfth rotational elements
Data Source
AI summary
The present disclosure provides nine forward speeds and one reverse speed. They are achieved by a planetary gear train of an automatic transmission that includes a main shifting portion having three planetary gear sets arranged on an input shaft, an auxiliary shifting portion having one planetary gear set arranged on an output shaft, nine shafts respectively connected with corresponding rotational elements of the four planetary gear sets, and two transfer gears respectively forming external gear-engagement between the main and auxiliary shifting portions.