Parallel Shaft Planetary Gear Train for Compact Automatic Transmission
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Solution Overview
Problem
The challenge in designing a planetary gear train for vehicles is to achieve a higher number of shift speeds while minimizing the number of components, which can lead to improved mountability, cost reduction, weight reduction, and enhanced power delivery efficiency, particularly in front-wheel drive vehicles.
Innovation Solution
The solution involves using two planetary gear sets disposed on parallel shafts with externally-meshed gears and frictional elements, including clutches and brakes, to achieve eight forward speeds and two reverse speeds, allowing for optimal gear ratio adjustment and improved power delivery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of shift speeds is increased, then fuel economy and vehicle performance are improved, but the number of components increases leading to deteriorated mountability, increased cost, increased weight, and reduced power delivery efficiency
Solution Approach 1:
The patent combines two planetary gear sets (first and second planetary gear sets) into a single integrated transmission system where rotation elements are shared and connected through externally-meshed gears. This merging approach achieves 8 forward speeds and 2 reverse speeds without proportionally increasing the number of components, as the same clutches and brakes serve multiple gear ratio functions across both planetary gear sets.
Solution Approach 2:
The clutches and brakes in the transmission system are designed with multi-functionality, where each friction element can engage different rotation elements (sun gears, planet carriers, ring gears) to achieve various gear ratios. For example, the first clutch can connect the first sun gear to the input shaft for certain gear ratios while connecting the second sun gear for other ratios, allowing a limited number of friction elements to control a large number of shift speeds.
2Productivity
If the number of shift speeds is increased, then vehicle performance is improved, but mountability is deteriorated due to increased length and component count
Solution Approach 1:
The patent employs a nested arrangement where the first and second planetary gear sets are disposed in parallel shafts with rotation elements positioned at different radial distances. The externally-meshed gears connect rotation elements between the two planetary gear sets, creating a compact nested structure that reduces the overall axial length of the transmission system while maintaining 8 forward speeds and 2 reverse speeds capability.
3Device complexity
If the number of components is reduced, then mountability and cost are improved, but achieving a higher number of shift speeds becomes more difficult
Solution Approach 1:
The transmission system uses dynamically controllable friction elements (clutches and brakes) that can selectively engage and disengage different rotation elements based on the desired gear ratio. This dynamic control allows a fixed number of physical components to generate a variable number of gear ratios (8 forward + 2 reverse), as the same clutches and brakes can be combined in different engagement patterns to achieve different speeds.
Solution Approach 2:
The externally-meshed gears serve as intermediary elements that connect rotation elements between the first and second planetary gear sets. These intermediary gears enable the sharing of rotation elements across both planetary gear sets, allowing clutches and brakes to control multiple gear ratios simultaneously and achieve a high number of shift speeds without proportionally increasing the number of friction elements.
4Productivity
If more components are used, then more shift speeds can be achieved, but power delivery efficiency is reduced
Solution Approach 1:
By merging two planetary gear sets into an integrated system with shared rotation elements and externally-meshed gear connections, the patent reduces the total number of discrete components compared to using separate planetary gear sets for each gear ratio. This consolidation minimizes the number of friction elements and meshing interfaces, thereby reducing power loss through friction and improving overall power delivery efficiency while maintaining 8 forward speeds and 2 reverse speeds.
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 reduces the length of the gear train, enhances mountability, and improves fuel economy by allowing for easier gear ratio changes, thereby improving power delivery and fuel efficiency.
Implementation Method 1
frictional elements including four clutches selectively connecting the first and second rotation elements to the first shaft and selectively connecting the first rotation element to the fourth and sixth rotation elements, and two brakes selectively connecting the first and second rotation elements to the transmission housing
Data Source
AI summary
A planetary gear train of an automatic transmission may include: a first shaft receiving engine torque; a second parallel shaft; a first planetary gear set on the first shaft including a first element engaging the first shaft and a transmission housing, a second element engaging the first shaft and the transmission housing, and a third output element; a second planetary gear set on the second shaft, and including a fourth element engaging the first element, a fifth element connected to the third element and directly connected to an output gear, and a sixth element connected to the first shaft and engaging the first element; three transfer gears; and frictional elements including four clutches connecting the first and second elements to the first shaft and connecting the first element to the fourth and sixth elements, and two brakes connecting the first and second elements to the transmission housing.