Power-Split CVT with Speed Summer to Cut Meshing Losses
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Solution Overview
Problem
Continuously variable transmissions (CVT's) are less efficient than gear-based transmissions due to friction-based drive interfaces, leading to inefficiencies in power transmission across various speed and torque changes, necessitating a means to achieve CVT functionality with high transmission efficiency.
Innovation Solution
The implementation of power splitting technology, utilizing a torque junction and a speed summer to split power into a parallel path and remerge it, minimizing gear meshing losses and optimizing gear ratios, thereby enhancing efficiency across a wide range of operational conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If friction-based drive interface is used in CVT, then infinite gear ratios are achieved, but transmission efficiency deteriorates
Solution Approach 1:
The power flow is segmented into multiple paths: a primary path with high efficiency gear meshes and a secondary path with variable ratio mechanism. This allows the system to achieve continuous variable ratios while maintaining high efficiency by keeping the majority of power in the efficient gear mesh path.
Solution Approach 2:
The patent merges the advantages of fixed gear transmissions (high efficiency through meshing) with the flexibility of CVT (infinite ratios). The combined system uses both gear-based power transmission and friction-based variable ratio mechanisms in parallel to achieve both efficiency and adaptability.
2Use of energy by moving object
If number of forward ratios is increased from 3-4 to 6-12, then engine operating efficiency is improved, but transmission complexity increases
Solution Approach 1:
The variable ratio mechanism serves multiple functions: it provides continuous ratio adjustment, enables infinite gear ratios, and maintains high transmission efficiency through the combined power paths. This multi-functionality reduces the need for separate mechanisms for each function.
Solution Approach 2:
The transmission system dynamically adjusts the power distribution between the primary and secondary paths based on operating conditions. The variable ratio mechanism continuously adapts the gear ratios to keep the engine in its optimal efficiency range across varying vehicle speeds and loads.
3Adaptability or versatility
If friction-based CVT interface is used, then continuous variable ratios are achieved, but power transmission efficiency deteriorates
Solution Approach 1:
The patent introduces a friction-based element as an intermediary that selectively couples or decouples the variable ratio mechanism from the power flow. This intermediary allows the system to engage the CVT function only when needed while maintaining the high-efficiency gear mesh path as the primary power transmission route.
Data Source
AI summary
A power split continuously variable transmission (CVT) technology in which efficiency improvements are obtained by elimination of gear meshing at the 1:1 ratio point. A family of power split transmissions are defined using variable displacement hydraulic devices as the variator and employing rotary couplings as speed summers. Input coupled, output coupled and compound coupled systems are described along with impact of and avoidance of power circulation (aka recirculation). Multiple and bidirectional mechanical channel inputs to the speed summer and clutching mechanisms are described enabling transmissions to reach forward gear ratio ranges with a speed of up to 23× with workable efficiencies throughout which can result in improvement in overall efficiency such as in ICE powertrains as well as permitting CVT function in heavy-duty EV powertrains during acceleration or high-grade conditions where otherwise extremely high torque and sustained low speed operations may induce highly inefficient or drive motor overheat conditions.