Planetary Gear Train Nested Design for Compact Automatic Transmission
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Solution Overview
Problem
Current planetary gear trains in automatic transmissions face challenges in achieving a compact design and optimal power delivery performance while maintaining fuel efficiency, particularly in achieving multiple shift speeds and reducing fuel consumption.
Innovation Solution
The design incorporates three separately disposed planetary gear sets on an input and output shaft, along with three transfer gears and five frictional elements, allowing for eight forward speeds and one reverse speed, enabling improved mountability and power delivery performance by optimizing gear ratios and reducing the length of the gear train.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple planetary gear sets are combined to achieve more shift speeds, then fuel economy and performance are improved, but the length of the gear train increases, reducing mountability
Solution Approach 1:
The patent applies nesting by placing the first planetary gear set inside the second planetary gear set, with the sun gear of the first set positioned within the ring gear of the second set. This nested configuration allows multiple gear sets to occupy overlapping spatial volumes, significantly reducing the overall axial length of the transmission while maintaining the capability for multiple shift speeds and improved fuel economy
Solution Approach 2:
The patent transitions from a linear arrangement of planetary gear sets to a three-dimensional nested configuration. By utilizing radial and axial spatial dimensions simultaneously, the gear sets are arranged in a compact volumetric layout rather than extending linearly, thereby reducing the length of the gear train while preserving multiple speed ratios for fuel efficiency
2Ease of operation
If friction members are operated sequentially to shift between speeds, then speed control is achieved, but drag torque increases due to non-operational frictional elements
Solution Approach 1:
The patent extracts and eliminates unnecessary friction members from the transmission system. By carefully selecting which friction members are needed for each speed range and removing redundant ones, the design reduces the number of non-operational frictional elements that would otherwise generate drag torque, while maintaining adequate shift control through the remaining essential friction members
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 efficiency, reduces fuel consumption, and allows for easier gear ratio changes, improving low-speed driving performance and fuel economy, while minimizing non-operational frictional elements to reduce drag torque and compact design possibilities.
Implementation Method 1
a first planetary gear set including a first sun gear, a first planet carrier, and a first ring gear as rotation elements thereof; a second planetary gear set including a second sun gear, a second planet carrier, and a second ring gear as rotation elements thereof; and a third planetary gear set including a third sun gear, a third planet carrier, and a third ring gear as rotation elements thereof
Implementation Method 2
five frictional elements
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 disposed in parallel with the input shaft, a first planetary gear set including a first sun gear, a first planet carrier, and a first ring gear, a second planetary gear set including a second sun gear, a second planet carrier, and a second ring gear, and a third planetary gear set including a third sun gear, a third planet carrier, and a third ring gear. The planetary gear train may further include first, second, third and fourth clutches and a first brake.