CVT Pulley Clamp Force Control via Transmission Ratio
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Solution Overview
Problem
Existing CVT systems face inefficiencies due to unclear relationships between clamp force and slip ratio, making it difficult to determine the optimal clamp force without high-performance sensors, leading to energy wastage and reduced fuel efficiency.
Innovation Solution
A method that fixes the clamp force of one pulley and gradually decreases the clamp force of the other pulley in predetermined steps, determining the optimal clamp force by minimizing transmission ratio changes without relying on additional sensors, by using two reduction forces and limiting values to find the section where the safety coefficient is 1.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high hydraulic pressure is supplied to increase clamp force, then slip between pulleys and belt is prevented, but energy is wasted and CVT efficiency decreases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the clamp force parameter based on operating conditions. The control unit modifies hydraulic pressure to the pulley clamps according to transmission ratio, engine load, and vehicle speed, optimizing the clamp force to prevent slip while minimizing energy waste. This resolves the contradiction by finding the optimal clamp force level rather than maintaining excessively high pressure.
2Loss of energy
If clamp force is decreased to improve energy efficiency, then fuel efficiency improves, but slip between belt and pulleys may be generated
Solution Approach 1:
The patent implements feedback control by continuously monitoring transmission ratio changes and using this information to adjust clamp force. The control unit calculates transmission ratio from rotational speeds of driving and driven pulleys, and when slip is detected (abnormal transmission ratio change), it increases clamp force to prevent slip. This feedback mechanism ensures slip prevention while allowing clamp force to be minimized for energy efficiency under normal conditions.
3Measurement precision
If high-performance sensors are added to detect slip for precise clamp force control, then optimal clamp force can be determined, but device complexity increases
Solution Approach 1:
The patent uses transmission ratio as an intermediary parameter to detect slip conditions. Instead of directly measuring slip with complex sensors, the system calculates transmission ratio from easily obtainable rotational speed data of the driving and driven pulleys. This intermediary approach provides sufficient slip detection capability without requiring high-performance sensors, thus resolving the contradiction between measurement precision and device complexity.
4Loss of energy
If clamp force is reduced to a theoretical minimum with safety coefficient of 1, then energy efficiency is maximized, but the relationship between clamp force and slip is unclear making precise control difficult
Solution Approach 1:
The patent replaces direct mechanical measurement of slip with a calculation-based approach using transmission ratio. By substituting the mechanical slip detection system with a computational method that uses rotational speed sensors and mathematical calculations, the system achieves precise control at the theoretical minimum clamp force without the complexity of direct slip measurement. This resolves the contradiction by making the clamp force-slip relationship controllable through calculation rather than direct measurement.
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 approach allows for improved CVT efficiency and fuel efficiency by determining the optimal clamp force between pulleys and belt, ensuring maximum efficiency without the need for high-performance sensors, thereby enhancing vehicle performance.
Implementation Method 1
CVTs composed of a belt and pulleys can continuously control a transmission ratio by controlling hydraulic pressure applied to a driving pulley and a driven pulley
Data Source
AI summary
A clamp force control method for a continuous variable transmission may include a first process that fixes clamp force of any one of a driving pulley and a driven pulley, and a second process that finds a section where a transmission ratio may be the minimum while gradually decreasing the clamp force from a current clamp force of the other pulley of which the clamp force may not be fixed in the first process and sets the clamp force in the section where the transmission ratio may be the minimum as the clamp force of the other pulley, which may not be fixed.