Planetary Gear Train for Wide Ratio Span and Linearity
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Solution Overview
Problem
Conventional automatic transmissions face challenges in achieving a wide gear ratio span and securing linearity of step ratios, which affects power delivery performance and fuel economy, especially when trying to implement more than eight forward speed stages without increasing the number of internal components, leading to deteriorated mountability, cost, weight, and transmission efficiency.
Innovation Solution
A planetary gear train design that combines four single pinion planetary gear sets with six control elements, including clutches and brakes, to achieve at least nine forward speed stages and one reverse speed stage, while maintaining a minimal number of components, thereby widening the gear ratio span and ensuring linearity of step ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of speed stages is increased to improve power delivery performance and fuel economy, then the gear ratio span and linearity of step ratios are improved, but the number of internal components increases leading to deteriorated mountability, cost, weight, and transmission efficiency
Solution Approach 1:
The patent combines four planetary gear sets into a single integrated transmission system where multiple gear sets share common components such as the sun gear, planet carrier, and ring gear. This merging approach allows the achievement of nine forward speed stages and one reverse speed stage without proportionally increasing the number of internal components, as each planetary gear set is configured to share elements with adjacent sets, thereby improving power delivery performance while controlling device complexity.
Solution Approach 2:
The planetary gear sets are designed with multi-functional capability where the same physical components (sun gear, planet carrier, ring gear) serve multiple functions across different speed stages. By configuring the control elements to engage and disengage specific components, the system achieves nine forward speed stages and one reverse speed stage using a minimal number of internal components, thus improving fuel economy and power delivery without proportionally increasing component count.
2Use of energy by moving object
If the number of speed stages is increased to achieve wider gear ratio span, then fuel economy is improved, but the transmission efficiency deteriorates due to increased number of components
Solution Approach 1:
The patent merges four planetary gear sets into an integrated configuration where components are shared across multiple gear sets. This reduces the total number of internal components that would otherwise be required to achieve nine forward speed stages and one reverse speed stage. By minimizing the number of meshing interfaces and moving parts, the design reduces energy losses through friction and mechanical inefficiency, thereby maintaining high transmission efficiency while achieving wide gear ratio span for improved fuel economy.
3Productivity
If conventional planetary gear sets are used to achieve nine forward speed stages, then the gear ratio span exceeds 9.3, but the linearity of step ratios cannot be secured
Solution Approach 1:
The patent applies local quality by optimizing the gear ratio of each individual planetary gear set to contribute specifically to the overall linearity of step ratios. Each planetary gear set is configured with specific tooth counts and geometric parameters tailored to its position in the transmission system. This localized optimization ensures that the cumulative gear ratio span exceeds 9.3 while maintaining linearity of step ratios, as each local configuration is designed to compensate for variations in the overall gear train.
4Productivity
If the number of internal components is increased to achieve more speed stages, then the speed stages increase, but the mountability deteriorates
Solution Approach 1:
The patent merges four planetary gear sets into a compact integrated unit where components are shared and spatially optimized. This configuration achieves nine forward speed stages and one reverse speed stage without proportionally increasing the physical size or component count. The merged design allows for better packaging and mounting within the transmission housing, as the shared components reduce the overall footprint and simplify the assembly process, thereby improving mountability while maintaining the required number of speed stages.
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 changed torque of the engine, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a third planetary gear set including seventh, eighth, and ninth rotation elements, and a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements, in which the input shaft is directly connected to the second rotational element and the sixth rotational element, the output shaft is directly connected to the third rotational element and the eleventh rotational element, the fourth rotational element is directly connected to the eighth rotational element and is selectively connected to the first rotational element, and the seventh rotational element is directly connected to the tenth rotational element.