CVT Pulley Friction Control for Shifting Efficiency
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Solution Overview
Problem
Existing belt type continuously variable transmission systems face challenges in minimizing axial thrust during gear shifting, leading to increased durability issues and hydraulic pump load, particularly due to the inability to accurately measure tangential friction coefficients on the radially outer pulley surfaces.
Innovation Solution
A transmission control method that estimates the relationship between tangential friction coefficients and gear ratios for both pulleys, calculates transmission torque, and adjusts axial thrust to suppress slippage, allowing for gear shifting by reducing axial thrust on the non-slippage side pulley without increasing thrust on the slippage side, and differentiates axial thrust reduction control based on gear ratio regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the friction coefficient of the radially outer portion of the pulley V surface is reduced, then gear shifting efficiency is improved, but slippage control becomes difficult
Solution Approach 1:
The pulley V surface is designed with different generatrix shapes for different radial portions: the radially inner portion has a straight line generatrix to provide high friction coefficient and prevent slippage, while the radially outer portion has a curved line generatrix to reduce friction coefficient and enable smooth gear shifting. This local differentiation resolves the contradiction between slippage prevention and shifting efficiency.
2Reliability
If axial thrust of the drive pulley is increased to prevent slippage, then slippage is suppressed, but durability of the pulley or metal belt deteriorates
Solution Approach 1:
By differentiating the friction characteristics of different radial portions of the pulley V surface, the system can achieve slippage suppression at the radially inner portion without requiring excessive axial thrust, thereby reducing the overall axial thrust needed and improving component durability.
3Reliability
If axial thrust of the driven pulley is increased to prevent slippage, then slippage is suppressed, but load of the hydraulic pump increases
Solution Approach 1:
The differentiated friction characteristics allow the system to achieve adequate slippage suppression with reduced axial thrust, thereby reducing the hydraulic pump load required to generate the necessary thrust forces.
4Duration of action of stationary object
If axial thrust is minimized during gear shifting, then durability is enhanced and hydraulic pump load is reduced, but slippage control precision deteriorates
Solution Approach 1:
The radially inner portion with straight line generatrix provides high friction coefficient for precise slippage control, while the radially outer portion with curved line generatrix allows smooth belt engagement. This local differentiation enables effective slippage control even with minimized axial thrust.
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
This method enables efficient gear shifting while minimizing axial thrust, enhancing pulley and belt durability and reducing hydraulic pump load by accurately estimating tangential friction coefficients and optimizing axial thrust distribution across the entire gear ratio range.
Implementation Method 1
a large friction coefficient can be secured by making a shape of a generatrix of the radially inner portion of the pulley V surface into a straight line, and thus slippage is prevented
Data Source
AI summary
In a first process, a tangential friction coefficient of a non-slippage side pulley of a drive pulley and a driven pulley is estimated from a tangential friction coefficient and a winding diameter of a slippage side pulley. In a second process, torque transmitted by a metal belt is calculated from the tangential friction coefficient and the winding diameter. In a third process, a required axial thrust of the non-slippage side pulley is calculated from the torque and the winding diameter. In a fourth process, the gear ratio is changed by reducing a ratio holding axial thrust of the non-slippage side pulley toward the required axial thrust. Therefore, the gear shifting can be performed merely by reducing the axial thrust of the non-slippage side pulley, and thus it is possible to improve the durability of the pulleys or the metal belt and to reduce a load of a hydraulic pump.