CVT Variator Axial Position Control at High RPM
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Solution Overview
Problem
Continuously variable transmissions (CVTs) face challenges in reducing transmission belt tension and minimizing shock loads during transmission ratio changes, especially when operating at high speeds, leading to increased forces and wear, and existing methods to limit maximum shaft rpm for axial position changing do not provide a safe driving experience while allowing full engine power usage.
Innovation Solution
Implementing the 'Maximum Axial Position Changing RPM Method' and 'Alternate Maximum Axial Position Changing RPM Method' to limit the maximum shaft rpm for axial position changing in CVTs, using adjusters and tensioning pulleys to reduce belt tension and compensate for transmission ratio change rotation, while ensuring safe driving and full engine power utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the maximum shaft rpm for axial position changing is limited to a maximum axial position changing rpm value, then the force required for axial position changing is reduced and shock loads are minimized, but the driver cannot use the full power of the engine when needed
Solution Approach 1:
The system performs preliminary actions by reducing belt tension before axial position changing occurs, and by pre-positioning the variator within an allowable range that accommodates upcoming changes. This preparation reduces the force required during the actual position change while maintaining the ability to handle high engine speeds and full power conditions.
Solution Approach 2:
The system dynamically adjusts the maximum axial position changing rpm value based on operating conditions, including engine speed, torque, and driving demands. This dynamic adjustment allows the CVT to operate at full engine power when needed while still limiting axial position changing to safe rpm ranges, resolving the contradiction between force reduction and power utilization.
2Speed
If the axial position of the variator is changed at high shaft rpm, then the transmission ratio can be adjusted quickly, but the force required increases and shock loads occur
Solution Approach 1:
The system reduces belt tension and pre-positions the variator before initiating axial position changes, even at high shaft rpm. This preliminary preparation allows quick transmission ratio adjustment while minimizing the force required and preventing shock loads that would otherwise occur at high speeds.
Solution Approach 2:
The system changes the maximum axial position changing rpm value as a controllable parameter based on operating conditions. By dynamically adjusting this parameter, the system enables axial position changing at appropriate speeds that balance quick response with reduced force requirements and minimized shock loads.
3Force
If the transmission belt tension is reduced to minimize shock loads, then the force for axial position changing decreases, but the transmission may become slack and lose efficiency
Solution Approach 1:
The system performs preliminary tension reduction only when and where needed—specifically on the slack side of the transmission belt before axial position changing. This selective preliminary action minimizes shock loads and force requirements while maintaining adequate tension on the drive side to prevent belt slackness and maintain transmission efficiency.
Solution Approach 2:
The system applies different tension levels to different sides of the transmission belt—reducing tension locally on the slack side to minimize shock loads during variator adjustment, while maintaining higher tension on the drive side to ensure reliable belt engagement and prevent slippage. This local differentiation resolves the contradiction between reducing shock loads and maintaining transmission reliability.
Data Source
AI summary
Methods that can be used to “limit the maximum shaft/spline rpm (speed) at which axial position changing of a variator mounted on it is performed to a “maximum axial position changing rpm value” for all variator mounted shafts/splines of a CVT, while still allowing a safe driving experience and also allowing the driver to use the full power of the engine when needed.