Multi-Speed Transmission Fast Reverse Gear Design
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Solution Overview
Problem
Conventional automatic transmissions face challenges in achieving a fast reverse gear ratio and a close gear step between first and second forward gears, leading to inefficiencies in transmission efficiency, fuel economy, and increased heat generation.
Innovation Solution
The implementation of a multi-planetary gearset arrangement with additional stationary and rotating torque-transferring mechanisms, allowing for the establishment of seven forward speed ratios and two reverse speed ratios, with a gear step between the first and second forward speed ratios of 1.5 or less, enabling faster reverse speeds and efficient shifts with the torque converter clutch applied.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional planetary gearset arrangement is used, then the transmission can achieve different gear ratios, but the reverse gear ratio is numerically too large to obtain the required reverse speed
Solution Approach 1:
The transmission system is divided into multiple independent planetary gearsets (first, second, third, and fourth planetary gearsets), each capable of providing different gear ratios. This segmentation allows the reverse gear function to be distributed across multiple gearsets rather than relying on a single gearset, enabling achievement of faster reverse speeds through selective engagement of specific gearsets for reverse operation
Solution Approach 2:
Each planetary gearset is designed to serve multiple functions - can be engaged for forward gear ratios or reverse gear ratios depending on which clutches and brakes are applied. The gearsets are configured with multiple torque paths that allow the same physical components to achieve different gear ratios and operational modes, providing universal functionality across forward and reverse operations
2Reliability
If conventional gear schemes are used, then the transmission can operate in different gears, but the gear step between first and second forward gears is too large to permit shifts with torque converter clutch applied
Solution Approach 1:
The gear ratios are specifically designed and optimized to achieve a small gear step (ratio of approximately 1.5 or less) between first and second forward gears. This parameter optimization of the gear ratios enables the transmission to perform shifts with the torque converter clutch applied, improving both shift smoothness and transmission efficiency during normal operating conditions
Solution Approach 2:
The transmission system incorporates multiple torque paths through the planetary gearsets that allow dynamic selection of engagement sequences. The system can dynamically engage or disengage specific clutches and brakes to achieve smooth transitions between gears, particularly enabling shifts between first and second forward gears to occur with the torque converter clutch applied, thereby maintaining dynamic operational flexibility
3Loss of energy
If conventional gear arrangements are used, then the transmission can provide basic gear ratios, but transmission heat generation increases and fuel economy decreases
Solution Approach 1:
The multiple planetary gearsets are configured to provide continuous and smooth torque transfer paths through the transmission system. The overlapping torque paths and carefully designed gear ratios minimize abrupt shifts and energy losses, allowing for continuous useful action of torque transmission with reduced heat generation. The system maintains efficient torque transfer across all gear ranges, improving fuel economy despite the increased number of gearsets
Data Source
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AI summary
The present disclosure provides an automatic transmission having an input adapted to couple to a torque-generating mechanism and an output coupled to the input. The transmission also includes a first rotating torque-transferring mechanism disposed along a first torque path and coupled to the input. A second rotating torque-transferring mechanism is disposed along a second torque path and is coupled to the input independent of the first torque-transferring mechanism. The transmission includes a plurality of stationary torque-transferring mechanisms, each of which is disposed between the input and output. The transmission includes a first planetary gearset, a second planetary gearset, a third planetary gearset, and a fourth planetary gearset, where each gearset includes a sun gear, a ring gear, and a carrier assembly. Moreover, the ring gear of the third planetary gearset is coupled to the carrier assembly of the second planetary gearset and the carrier assembly of the fourth planetary gearset.