Parallel Shaft Planetary Gear Train for Compact Automatic Transmission
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Solution Overview
Problem
The challenge in automatic transmissions is to achieve a higher number of shift speeds while minimizing the number of components to improve mountability, reduce weight, and enhance power delivery efficiency, which is particularly difficult for front-wheel drive vehicles.
Innovation Solution
A planetary gear train design with two planetary gear sets disposed on parallel shafts, connected through externally-meshed gears and frictional elements, allowing for eight forward speeds and one reverse speed, optimizing gear ratios and power delivery performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of shift-speeds is increased to improve fuel mileage and performance, then the number of components in the automatic transmission increases, but mountability, cost, weight and power delivery efficiency deteriorate
Solution Approach 1:
The planetary gear train is divided into two separate planetary gear sets (first and second planetary gear sets) disposed on different shafts (first shaft and second shaft). This segmentation allows each gear set to have fewer components while achieving multiple shift speeds through their combined operation with externally-meshed gears, resolving the contradiction between high shift-speed count and component complexity
Solution Approach 2:
The patent transitions from a conventional single-shaft planetary gear arrangement to a dual-shaft configuration where planetary gear sets are disposed on parallel shafts. This dimensional change in the mechanical layout enables more efficient component utilization and reduces the total number of components needed to achieve 8 forward speeds and 1 reverse speed
2Device complexity
If the number of components is reduced to improve mountability in front wheel drive vehicles, then the number of shift speeds decreases, but fuel economy and performance are compromised
Solution Approach 1:
The externally-meshed gears connecting the two planetary gear sets serve multiple functions: they transmit power between shafts, provide additional gear ratio steps, and enable the system to achieve 8 forward speeds and 1 reverse speed with fewer total components. This multi-functionality resolves the contradiction by maintaining high shift-speed capability while reducing component count
Solution Approach 2:
The patent merges the functions of two planetary gear sets with externally-meshed gears into a unified transmission system. By combining these elements on parallel shafts, the system achieves complex gear ratios and multiple shift speeds without requiring a proportional increase in total component count, thus improving mountability while maintaining performance
3Productivity
If a conventional planetary gear train is used to achieve multiple shift speeds, then the length and mounting space requirements increase, but mountability in compact front wheel drive vehicles is improved
Solution Approach 1:
By disposing planetary gear sets on parallel shafts rather than in a single-line configuration, the patent creates a more compact three-dimensional layout. This dimensional reorganization reduces the overall length of the planetary gear train while maintaining the capability to achieve multiple shift speeds through the coordinated operation of the two gear sets
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 design improves mountability, power delivery performance, and fuel economy by reducing the number of components and enabling flexible gear ratio adjustments, potentially replacing the torque converter with a start-up clutch.
Implementation Method 1
connecting rotation elements of the planetary gear sets through a plurality of externally-meshed gears
Implementation Method 2
frictional elements including clutches selectively connecting the first shaft to rotation elements of the first and second planetary gear sets and brakes selectively connecting rotation elements of the first and second planetary gear sets to the transmission housing
Data Source
AI summary
A planetary gear train of an automatic transmission may include: a first shaft; a second shaft parallel with the first shaft; a first gear set on the first shaft including a first element selectively connected to the first shaft, a second element selectively connected to the first shaft and a transmission housing, and a third element; a second gear set on the second shaft including a fourth element operably connected to the first element and selectively connected to the first shaft, a fifth element connected to the third element and directly connected to an output gear, and a sixth element selectively connected to the first shaft and selectively connected to the housing; three transfer gears; and frictional elements including clutches selectively connecting the first shaft to elements of the first and second gear sets and brakes selectively connecting elements of the first and second gear sets to the housing.