8-Speed Automatic Transmission Gear Train Using Nested Planetary Sets
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Solution Overview
Problem
Current automatic transmissions with fewer shift speeds face limitations in optimizing fuel mileage and performance, and existing gear train designs for higher speeds are complex and inefficient, particularly in utilizing space and hydraulic control efficiency.
Innovation Solution
A gear train configuration combining two simple planetary gear sets and one compound planetary gear set with two clutches and four brakes, allowing for eight forward speeds and two reverse speeds, optimizing power delivery and reducing fuel consumption by leveraging a Ravigneaux planetary gear set and selective connections via clutches and brakes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of planetary gear sets is increased to achieve more shift speeds, then the number of forward speeds increases, but the device complexity increases
Solution Approach 1:
The patent combines two simple planetary gear sets and one compound planetary gear set into a single integrated gear train system. The compound planetary gear set integrates multiple planetary gear mechanisms sharing common elements (sun gear, ring gear, planet carriers), allowing multiple speed ratios to be achieved through a unified structure rather than separate gear sets, thus reducing overall device complexity while maintaining high adaptability for multiple forward speeds.
Solution Approach 2:
The planetary gear sets are designed with multi-functional rotational elements that can serve different purposes in different operating modes. For example, the sun gear, ring gear, and planet carriers can alternately function as input, output, or fixed elements depending on which clutch or brake is engaged, enabling a single gear set to provide multiple speed ratios and reducing the need for additional specialized components.
2Adaptability or versatility
If more clutches and brakes are used to control more shift speeds, then the number of forward speeds increases, but the hydraulic control efficiency decreases
Solution Approach 1:
The patent merges the functions of multiple clutches and brakes into a coordinated control system where two clutches and four brakes work in combination to control three planetary gear sets. This integrated approach allows multiple speed ratios to be achieved through coordinated engagement of fewer friction elements compared to traditional designs, reducing hydraulic control complexity and improving efficiency.
Solution Approach 2:
The gear train design allows certain rotational elements to automatically assume different functional roles (input, output, or fixed) based on which clutch or brake is engaged, reducing the need for complex external control mechanisms. The system self-regulates its configuration through the selective engagement of friction elements, improving hydraulic control efficiency.
3Adaptability or versatility
If a larger number of friction elements are used to achieve more shift speeds, then the number of forward speeds increases, but the brake volume increases
Solution Approach 1:
The patent combines multiple friction control functions into a compact arrangement where four brakes control three planetary gear sets through strategic placement and shared control mechanisms. This merged configuration achieves eight forward speeds and two reverse speeds with reduced total brake volume compared to traditional designs that would require separate brakes for each gear set.
Solution Approach 2:
The compound planetary gear set employs a nested structure where multiple planetary mechanisms are arranged concentrically, sharing common sun gears, ring gears, and planet carriers. This nesting allows friction elements to be positioned more efficiently in three-dimensional space, reducing the overall volume required for brake components while maintaining the capability for multiple speed ratios.
4Loss of energy
If the gear train is designed for more shift speeds, then fuel consumption is reduced, but the space utilization within the transmission decreases
Solution Approach 1:
The compound planetary gear set uses a nested concentric arrangement where multiple planetary mechanisms share common rotational elements and are arranged in overlapping configurations. This nesting maximizes space utilization by allowing gear components to occupy the same radial space at different axial positions, enabling eight forward speeds to be achieved within a compact transmission housing that would otherwise be too small for traditional multi-speed designs.
Solution Approach 2:
The patent transitions from two-dimensional planar gear arrangements to three-dimensional spatial configurations, utilizing axial stacking and radial nesting of planetary mechanisms. This dimensional change allows multiple gear sets to coexist in a compact volume by exploiting the third dimension (axial direction), thereby achieving high speed ratios within limited transmission space while optimizing fuel efficiency.
Data Source
AI summary
A gear train of an automatic transmission for vehicles is provided to improve power delivery performance and reduce fuel consumption as a consequence of realizing eight forward speeds and two reverse speeds by combining two simple planetary gear sets and one compound planetary gear set with two clutches and four brakes.