Planetary Gear Train with Four Sets for Wide Ratio Span
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Solution Overview
Problem
Conventional 8-speed automatic transmissions face limitations in achieving optimal power performance and fuel economy due to a narrow gear ratio span, which affects drivability and transmission efficiency, and increasing the number of speed stages complicates mountability, cost, and durability.
Innovation Solution
A planetary gear train with four simple planetary gear sets and seven control elements is designed to achieve at least ten forward speed stages and one reverse speed stage, with a gear ratio span greater than 10.0, ensuring linearity of step ratios and maximizing engine driving efficiency while maintaining pinion shaft durability by avoiding load on planet carriers at high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of speed stages is increased to enhance fuel economy and optimize drivability, then power performance and driving efficiency are improved, but the number of internal components increases leading to deteriorated mountability, cost, and weight
Solution Approach 1:
The patent combines four planetary gear sets into a single integrated transmission system where multiple planetary gear sets share common components such as the sun gear, planet carriers, and ring gears. This merging approach enables the achievement of 10 forward speed stages and 1 reverse speed stage without proportionally increasing the number of internal components, as shared components reduce the total component count compared to separate gear sets.
Solution Approach 2:
The planetary gear sets are designed with multi-functional components that serve multiple purposes. For example, the sun gear, planet carriers, and ring gears are shared across multiple planetary gear sets, allowing these components to fulfill multiple functions simultaneously. This universality enables the transmission to achieve high speed stage multiplication without requiring separate dedicated components for each speed stage.
2Productivity
If conventional 8-speed automatic transmission is used with gear ratio span of 6.5-7.5, then basic transmission function is achieved, but power performance and fuel economy improvement is limited
Solution Approach 1:
The patent achieves a gear ratio span greater than 10.0 by optimizing the gear ratio parameters of the four planetary gear sets. This is accomplished by carefully selecting and adjusting the number of teeth on sun gears, planet gears, and ring gears, as well as configuring the control elements to achieve optimal gear ratio distribution. The expanded gear ratio span enables better fuel economy and power performance compared to conventional 8-speed transmissions with gear ratio spans of 6.5-7.5.
3Productivity
If gear ratio span is increased to improve fuel economy, then driving efficiency is enhanced, but linearity of step ratios may be compromised affecting drivability
Solution Approach 1:
The patent achieves both expanded gear ratio span (>10.0) and linearity of step ratios by optimizing the gear ratio parameters of the four planetary gear sets. Through careful selection and adjustment of the number of teeth on sun gears, planet gears, and ring gears, along with strategic configuration of control elements, the transmission achieves gear ratios that maintain linearity across all 10 forward speed stages while expanding the overall gear ratio span, thereby improving both fuel economy and drivability.
4Power
If planet carriers are loaded at stopped states during high speed operation, then torque transmission is achieved, but durability of pinion shafts deteriorates
Solution Approach 1:
The patent employs dynamic control of the planetary gear sets through strategically placed control elements (clutches and brakes) that can selectively engage and disengage different planetary gear sets based on operating conditions. During high-speed operation, the control elements are configured to prevent load from being applied to planet carriers at stopped states, thereby protecting pinion shaft durability. The system dynamically adjusts the engagement state of control elements to optimize both torque transmission and component protection.
Data Source
AI summary
The present disclosure provides a planetary gear train of an automatic transmission for a vehicle. The planetary gear train may include: an input shaft receiving torque of an engine; an output shaft outputting changed torque; 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; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements.