Power-Split CVT with Toroidal Variator for Wide Ratio Spread
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Solution Overview
Problem
Continuously variable transmissions (CVTs) in automotive vehicles face challenges such as inefficiency, high cost, and bulkiness due to slip and friction losses, complex actuation systems, and the need for a wide ratio spread to achieve high overdrive ratios and launch efficiency, which are difficult to achieve while maintaining compactness and low manufacturing costs.
Innovation Solution
A continuously variable transmission design incorporating a ratio varying unit with a compound epicyclic gear set and a toroidal variator, utilizing a PitchSteer mechanism for low-energy variator control, and a power-split configuration to enhance efficiency and reduce the ratio spread, allowing for a high ratio spread with improved launch efficiency and compactness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a wide ratio spread is used to achieve high overdrive ratio and launch efficiency, then transmission efficiency and launch performance are improved, but the transmission becomes bulkier and more costly
Solution Approach 1:
The patent combines a toroidal variator with a compound epicyclic gear set into a single integrated transmission unit. The variator provides continuous ratio variation while the epicyclic gear set provides fixed ratio stages, merging the advantages of both systems in one compact package that achieves wide effective ratio spread without proportionally increasing size
Solution Approach 2:
The transmission uses a dynamically controllable variator mechanism that can continuously adjust its ratio spread based on operating conditions. The PitchSteer control system dynamically modifies the variator ratio in real-time, allowing the transmission to optimize efficiency across different vehicle speeds and loads without requiring a physically larger fixed ratio spread
2Ease of operation
If complex actuation systems are used to control the variator, then ratio control precision and response are improved, but manufacturing cost and device complexity increase
Solution Approach 1:
The patent replaces complex hydraulic or electronic actuation systems with a simplified mechanical PitchSteer control mechanism. This mechanism uses a small roller that pivots on a fixed axis to directly control the variator ratio through pure mechanical advantage, eliminating the need for complex actuators while maintaining precise and responsive ratio control
Solution Approach 2:
The PitchSteer control mechanism uses simple, low-cost mechanical components including a small roller, pivot axis, and control arm. These inexpensive parts can be easily manufactured and replaced if needed, significantly reducing actuation system cost while providing sufficient control precision for variator operation
3Ease of manufacture
If belt or chain systems are used in the variator, then cost and simplicity are improved, but slip and friction losses increase reducing efficiency
Solution Approach 1:
The patent uses a toroidal (doughnut-shaped) variator design with curved friction surfaces instead of flat belt or chain systems. The toroidal geometry creates optimal contact patches between friction surfaces, distributing loads more evenly and reducing slip and friction losses while maintaining the simplicity and low cost of friction-based power transmission
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 achieves high transmission efficiency, reduced energy consumption, and lower manufacturing costs, enabling seamless gear shifts and efficient engine operation across a wide range of vehicle speeds, with peak cruise efficiencies of up to 95% and reduced emissions, making it suitable for future automotive trends including electrification and autonomous driving.
Implementation Method 1
slip and friction losses
Implementation Method 2
toroidal variator
Implementation Method 3
compound epicyclic gear set comprising a first set of planets; the first set of planets being rotationally mounted within a carrier and meshing with a sun gear
Data Source
AI summary
The invention relates to a continuously variable transmission (CVT) comprising a ratio varying unit and a compound epicyclic gear set. The ratio varying unit has a rotating first side and a rotating second side, the rotational axes of the first and second sides being coaxial. The compound epicyclic gear set comprises a first set of planets, being rotationally mounted within a carrier and meshing with a sun gear. The epicyclic gear set also has a first annulus gear and a second set of planets; the second set of planets also being rotationally mounted within the carrier and meshing with a second annulus gear. One of the first or second rotating sides of the ratio varying unit is coupled to the carrier and the other of the first or second rotating sides of the ratio varying unit is coupled to the sun gear.