Nested Planetary Gear Train for Compact Automatic Transmission
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Solution Overview
Problem
Conventional automatic transmissions with increased speed stages face challenges in installability, power flow efficiency, and production cost due to the increased number of internal components, particularly planetary gear sets, which also affect fuel economy and drivability.
Innovation Solution
A planetary gear train for automatic transmissions that achieves nine forward speed stages and one reverse speed stage using a combination of four simple planetary gear sets and six control elements, including clutches and brakes, to optimize power delivery and fuel economy while minimizing component count and length, thereby improving silent driving at low engine speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of speed stages is increased to enhance fuel economy, then fuel economy is improved, but the number of internal components (planetary gear sets) increases, leading to increased transmission length and deteriorated installability
Solution Approach 1:
The patent applies nesting by placing one planetary gear set inside another planetary gear set, specifically positioning the second planetary gear set within the first planetary gear set. This nested configuration allows multiple gear sets to occupy the same spatial envelope, achieving 8-speed multiplication with compact dimensions and avoiding the linear length increase that would result from sequential arrangement of gear sets.
2Use of energy by moving object
If the number of speed stages is increased to enhance fuel economy, then fuel economy is improved, but the number of planetary gear sets increases, leading to increased weight
Solution Approach 1:
The nested planetary gear set configuration allows two gear sets to share the same physical space, effectively halving the material required compared to sequential arrangement. The second planetary gear set is positioned within the first, reducing overall transmission volume and weight while maintaining 8-speed functionality.
Solution Approach 2:
The patent makes the fourth shaft serve multiple functions by connecting it to both the fifth rotation element and the twelfth rotation element, and making it selectively connectable to both the second shaft and the third shaft. This multi-functionality reduces the total number of shafts and components required, thereby reducing weight.
3Use of energy by moving object
If the number of speed stages is increased to enhance fuel economy, then fuel economy is improved, but the number of planetary gear sets increases, leading to increased production cost
Solution Approach 1:
The nested configuration of planetary gear sets reduces the total component count and assembly complexity. By positioning the second planetary gear set within the first, the patent minimizes the number of separate housings, mounting points, and alignment procedures required, thereby reducing manufacturing and assembly costs.
Solution Approach 2:
The fourth shaft is designed to perform multiple functions: connecting to the fifth rotation element, connecting to the twelfth rotation element, and being selectively connectable to both the second shaft and the third shaft. This multi-functionality reduces the total component count, simplifying manufacturing and assembly processes.
4Speed
If conventional planetary gear sets are disposed one above another to achieve multiple speed stages, then speed multiplication is achieved, but the transmission length increases and mountability deteriorates
Solution Approach 1:
Instead of arranging planetary gear sets in a sequential linear fashion (one above another), the patent nests the second planetary gear set within the first planetary gear set. This three-dimensional nested arrangement achieves the same speed multiplication effect while minimizing the transmission's overall length and improving mountability.
5Device complexity
If dog clutches are used instead of wet-type control elements to reduce component count, then component count is reduced, but shift feel deteriorates
Solution Approach 1:
The patent employs friction-based control elements (clutches and brakes) that operate as consumable friction interfaces rather than permanent mechanical locks. These elements provide progressive engagement and disengagement characteristics that deliver superior shift feel compared to dog clutches, while the patent minimizes their number through efficient arrangement.
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 outputting torque, a first planetary gear set, a second planetary gear set, a third planetary gear set, a fourth planetary gear set, a first shaft, a second shaft, a third shaft, a fourth shaft, a fifth shaft selectively connectable to at least one of the second shaft and the third shaft, and directly connected to the input shaft, a sixth shaft connected to the ninth rotation element, a seventh shaft connected to the tenth rotation element, and an eighth shaft connected to the eleventh rotation element, selectively connectable to the sixth shaft, and directly connected to the output shaft.