Automatic Transmission Double Pinion Gear Configuration
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Solution Overview
Problem
Increasing the number of planetary gear sets in automatic transmissions to improve fuel efficiency leads to an unwanted increase in the overall size of the transmission, as more force is applied to the gears to generate the same torque, necessitating thicker and wider gears.
Innovation Solution
The automatic transmission is configured with four planetary gear sets, including a double pinion type, where the output is driven by the fourth ring gear with a larger radius, reducing the force applied to the gears and avoiding the need for increased module, thickness, and width of the gears, thus minimizing the transmission's size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of planetary gear sets is increased to provide more gears, then fuel efficiency is improved, but the overall size of the automatic transmission increases
Solution Approach 1:
The patent employs multiple planetary gear sets nested within a single transmission case, where each planetary gear set is compactly arranged and shares common structural elements. The first through fourth planetary gear sets are integrated in a nested configuration that allows them to occupy overlapping spatial volumes, thereby increasing the number of gears without proportionally increasing the overall transmission size.
Solution Approach 2:
The patent utilizes the radial dimension by having the output shaft extend in the radial direction from the input shaft, and arranges planetary gear sets at different radial positions and orientations. This multi-dimensional arrangement allows compact packing of four planetary gear sets within a constrained volume, enabling more gears without linearly increasing the transmission's overall dimensions.
2Device complexity
If the output is driven by a carrier of a planetary gear set, then the transmission can be configured with fewer components, but greater force is applied to the gears requiring increased module, thickness, and width
Solution Approach 1:
The patent applies different driving configurations to different planetary gear sets based on their local functional requirements. Specifically, the fourth planetary gear set drives the output through its ring gear rather than its carrier, while other planetary gear sets may use carrier driving. This localized optimization reduces the force on individual gears in the fourth planetary gear set without compromising the overall transmission configuration.
3Force
If the automatic transmission is modified to drive the output by a ring gear of a planetary gear set, then the force on gears is reduced, but the engagement relations between planetary gear sets, clutches, and brakes must be entirely changed
Solution Approach 1:
The patent employs a dynamic control system with five frictional engagement elements (clutches and brakes) that can selectively engage and disengage different planetary gear sets and their components. This dynamic engagement system allows the transmission to flexibly switch between different power transmission paths and gear configurations, accommodating the ring gear driving arrangement while maintaining adaptability for various gear ratios and operational modes.
Data Source
AI summary
An automatic transmission (1) includes, in a transmission case (2), an input shaft (3), first to third planetary gear sets (PL1-PL3) of a single pinion type, a fourth planetary gear set (PL4) of a double pinion type, five frictional engagement elements (CL1, CL2, and B1-B3), and outputs (7, 8). The outputs (7, 8) are always engaged with a fourth ring gear (R4).