Planetary Gear Train for Nine-Stage Automatic Transmission
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Solution Overview
Problem
Current automatic transmissions with multiple speed-stages face challenges in improving fuel efficiency and power delivery performance due to increased parts count, which also affects installability, production cost, and weight, while maintaining a limited gear shift ratio span, resulting in suboptimal driving efficiency and drivability.
Innovation Solution
A planetary gear train design that achieves nine forward speed stages and one reverse speed stage using a minimum number of components by combining four single-pinion planetary gear sets with six control elements, ensuring a gear shift ratio span of 9.0 or more, thereby enhancing engine driving efficiency and maintaining linearity between step ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of speed stages is increased to improve fuel efficiency, then fuel consumption is reduced, but the number of parts increases which deteriorates installability and increases production cost and weight
Solution Approach 1:
The patent combines multiple planetary gear sets into a unified structure where gear sets share common components. Specifically, the first and second planetary gear sets share a sun gear, and the third and fourth planetary gear sets share a sun gear, allowing multiple speed stages to be achieved with fewer independent parts.
Solution Approach 2:
Individual components perform multiple functions across different speed stages. The control elements (clutches and brakes) are designed to selectively engage different gear sets for various forward and reverse speed stages, making each component multi-functional rather than dedicated to a single purpose.
2Use of energy by moving object
If the gear shift ratio span is increased to improve fuel efficiency, then fuel consumption is reduced, but linearity of step ratios deteriorates which affects drivability
Solution Approach 1:
The patent optimizes the gear ratio parameters across different speed stages to achieve a span of 9.0 or more while maintaining linearity. The specific gear ratios are carefully calculated and adjusted to balance the extended span with smooth transitions between stages, ensuring both fuel efficiency and drivability.
3Productivity
If the number of planetary gear sets is increased to achieve more speed stages, then the number of forward speed stages is increased, but the weight of the transmission increases
Solution Approach 1:
The planetary gear sets are arranged in a nested configuration where inner gear sets are positioned within or alongside outer gear sets. This nested layout allows multiple gear sets to occupy shared spatial volume, reducing the overall transmission weight compared to a linear arrangement of separate gear sets.
4Productivity
If the number of control elements is increased to enable more speed stages, then the number of available speed stages is increased, but the device complexity increases
Solution Approach 1:
Each control element (clutch or brake) is designed to control multiple planetary gear sets simultaneously or to provide multiple control functions. For example, a single clutch may engage to control torque transmission across several gear sets, reducing the total number of control elements needed while maintaining the capability for multiple speed stages.
Data Source
AI summary
A planetary gear train of an automatic transmission for vehicle may include an input shaft receiving power of an engine, an output shaft outputting shifted power of the engine, a first planetary gear set including a first rotation element, a second rotation element, and a third rotation element, a second planetary gear set including a fourth rotation element, a fifth rotation element, and a sixth rotation element, a third planetary gear set including a seventh rotation element, an eighth rotation element, and a ninth rotation element, a fourth planetary gear set including a tenth rotation element, an eleventh rotation element, and a twelfth rotation element, and six control elements disposed at positions selectively connecting the rotation elements to each other or at positions selectively connecting the rotation elements and a transmission housing.