Power-Split CVT with Nested Planetary Gears for Low-Load Starting
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Solution Overview
Problem
Existing continuously variable transmission (CVT) systems face limitations in configuration complexity and design compactness, with high variator load and transmission losses, particularly when implementing power-splitting structures for vehicle starting without additional clutches.
Innovation Solution
A power-split continuously variable transmission device featuring three planetary gear sets and a variator unit with specific shift elements, allowing for infinitely variable power transmission between input and output shafts through a compact design, reducing variator load and transmission losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a power-split transmission structure with variator is used to enable vehicle starting from standstill, then the gear ratio spread is expanded and starting process is enabled, but the variator load increases and transmission losses increase
Solution Approach 1:
The transmission device segments the power flow into multiple independent paths: one path through the variator for continuous ratio adjustment, and additional paths through planetary gear sets for direct mechanical power transmission. This segmentation allows the system to bypass the variator during high-load conditions, reducing transmission losses while maintaining starting capability.
Solution Approach 2:
Planetary gear sets are introduced as intermediary mechanisms between the input and output shafts. These intermediaries provide alternative power transmission routes that can engage when the variator load becomes excessive, effectively mediating the power flow to reduce losses during critical operating conditions.
2Loss of energy
If multiple planetary gear sets and shift elements are added to reduce variator load, then transmission losses are reduced, but the device complexity increases
Solution Approach 1:
Multiple planetary gear sets are merged into a compact coaxial arrangement where they share common input and output shafts. This merging approach consolidates what would otherwise be separate complex subsystems into an integrated unit, reducing overall device complexity while maintaining the multiple power path functionality needed to reduce transmission losses.
Solution Approach 2:
The planetary gear sets serve multiple functions: they provide alternative power transmission paths to reduce variator load, enable direct mechanical power transmission, and work cooperatively with the variator across different operating conditions. This multi-functionality reduces the need for additional dedicated components, thereby controlling device complexity.
3Volume of moving object
If three planetary gear sets are arranged coaxially with the variator, then the design compactness is improved, but the manufacturing complexity increases
Solution Approach 1:
The three planetary gear sets are nested coaxially within the variator housing, with each gear set arranged along the same central axis. This nesting arrangement maximizes space utilization and achieves compact design by placing components in concentric layers, reducing the overall transmission device volume while maintaining manufacturability through standardized coaxial mounting procedures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a simple, compact transmission device with low component loads and efficient power transmission, enabling vehicle starting from standstill without additional clutches, suitable for front-transverse or rear-transverse arrangements, and suitable for motor vehicle drive trains.
Implementation Method 1
The power transmission takes place, without conversion of the form of energy, in a force-locking manner, by way of the friction-locking contact of two or more contact bodies which are moving relative to each other
Data Source
AI summary
A variator unit is fixed to a rotationally fixed component and has a secondary side rotationally fixed to an input shaft and a primary side rotationally fixed to a first element of a first planetary gear set. The input shaft is rotationally fixable via a second shift element to a second element of a second planetary gear set, which is fixable to the rotationally fixed component via a first shift element, and is rotationally fixed to a first element of a third planetary gear set. A second element of the first planetary gear set is fixed to the rotationally fixed component. A first element of the second planetary gear set is rotationally fixed to a third element of the third planetary gear set. A third element of the first planetary gear set is rotationally fixed to a third element of the second planetary gear set.