CVT Pulley Screw Actuation for Precise Gear Ratio Control
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Solution Overview
Problem
Existing continuously variable transmissions for motor vehicles face challenges in effectively transmitting motion from the actuator to the movable half-pulley, leading to inefficiencies in gear ratio control.
Innovation Solution
A continuously variable transmission system featuring a mechanical connection device with a variable length member comprising a first hollow threaded member and a second threaded member, where the first hollow threaded member is rotated by the actuator to lengthen or shorten the mechanical connection, allowing precise axial movement of the movable half-pulley relative to the fixed half-pulley, thereby adjusting the gear ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mechanical connection device with threaded members is used to connect the actuator to the movable half-pulley, then the transmission of motion efficiency is improved, but the device complexity increases
Solution Approach 1:
The first hollow threaded member is designed as a hollow structure that can be nested within or around the second threaded member. This nesting arrangement allows the mechanical connection device to achieve compact integration while maintaining the screw mechanism's motion transmission capability, thereby improving efficiency without proportionally increasing complexity
Solution Approach 2:
The mechanical connection device acts as an intermediary mechanism between the actuator and the movable half-pulley. The threaded members provide a controlled interface that translates actuator rotation into precise axial movement of the half-pulley, improving motion transmission efficiency while isolating the complexity within a dedicated connection component
2Measurement precision
If the first hollow threaded member is rotated to lengthen or shorten the mechanical connection, then the precision of axial movement control is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The mechanical connection device is segmented into two separate threaded members (first hollow threaded member and second threaded member) that can be manufactured and assembled independently. This segmentation allows each threaded member to be produced with standard threading tolerances, reducing overall manufacturing precision requirements while maintaining control precision through the combined mechanism
Solution Approach 2:
The threaded members are designed to work dynamically through relative rotation, where the conversion of rotational motion to axial motion provides inherent mechanical advantage and precision control. The dynamic screw mechanism amplifies small rotational movements into precise axial displacements, achieving high control precision without requiring extremely tight manufacturing tolerances
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 solution enhances the transmission of motion from the actuator to the movable half-pulley, improving the efficiency and precision of gear ratio control, reducing axial thrusts on the drive shaft and allowing for easier integration with existing transmission units.
Implementation Method 1
The mechanical connection device comprises a variable length member including a first hollow threaded member and a second threaded member, screwed together and coaxial with the first shaft. The first hollow threaded member is adapted to be rotated by the actuator relative to the second threaded member, that is prevented from rotating, so that the rotation of a threaded member relative to the other causes the lengthening and/or shortening of the mechanical member constituted by the two threaded members.
Data Source
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AI summary
The continuously variable transmission comprises a housing (9), inside which a primary pulley (19) is provided mounted on a drive shaft (15) and comprising a V- shaped groove (23) of variable size to house a drive belt (25). Inside the housing (9), a secondary pulley (21) is also provided mounted on a driven shaft (17) and comprising a V-shaped groove for the drive belt (25). Each of said primary pulley (19) and secondary pulley (21) comprises an axially fixed half-pulley (19A; 21B) and an axially movable half-pulley (19B; 21A) movable relative to the respective drive shaft (15) and driven shaft (17), to move towards and away from each other. An actuator (11) associated with one of said pulleys controls the axial movement of the respective movable half-pulley (19B; 21A) relative to the fixed half-pulley (19A; 21B). The actuator (11) is connected to the movable half-pulley (19B) by means of a mechanical connection device (69) axially extending through the fixed half-pulley (19A).