CVT Pulley Surface Geometry for Stick-Slip Noise Reduction
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Solution Overview
Problem
Belt-type continuously variable transmissions (CVTs) with grooved pulleys often produce uncomfortable stick-slip sounds due to tangling and deformation of resin blocks, leading to reduced contact pressures and increased noise, especially at maximum reduction ratios and low engine speeds.
Innovation Solution
The design reduces contact areas between the driven pulley and resin blocks at maximum reduction ratios by shaping the pulley surfaces to increase contact pressure, and sets the transmission to a low speed state, inhibiting stick-slip sounds and rider discomfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If grooves are formed on the surface of each pulley to reduce V-belt abrasion, then the duration of the CVT is prolonged, but stick-slip sounds are produced when the V-belt is released from the pulley
Solution Approach 1:
The patent applies different surface treatments to different regions of the pulley. The groove portions maintain their grooved structure for abrasion reduction, while the non-groove portions (where the V-belt contacts during release) are given a different surface treatment to prevent stick-slip sounds. This local differentiation resolves the contradiction by allowing each region to optimize for its specific function.
2Area of moving object
If the V-belt is wrapped around the driven pulley at maximum reduction ratio, then the contact length between V-belt and pulley surface is increased, but contact pressure is reduced and stick-slip sounds are produced
Solution Approach 1:
The patent differentiates the surface properties of groove portions versus non-groove portions. The non-groove portions are specifically designed with surface treatments that maintain high contact pressure and prevent stick-slip sounds, even when the contact area is large at maximum reduction ratio. This local quality differentiation allows the system to handle both large contact areas and high contact pressure requirements.
3Power
If the CVT operates at maximum reduction ratio with low engine speed, then torque transmission is optimized, but stick-slip sounds are more likely to be heard by the rider
Solution Approach 1:
The patent applies specific surface treatments to the non-groove portions of the pulley that are active during low-speed, high-torque operation. These surface treatments are designed to prevent stick-slip sounds while maintaining effective torque transmission, allowing the CVT to operate quietly at maximum reduction ratio without compromising power transmission capability.
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 effectively minimizes stick-slip sounds and rider discomfort by increasing contact pressure between the pulley and resin blocks, even at maximum reduction ratios and low engine speeds, ensuring smooth operation and reliable torque transmission.
Implementation Method 1
the contact areas are reduced between the surfaces of the driven pulley and the resin blocks of the V-belt at the maximum reduction ratio. Accordingly, contact pressure is increased between the surfaces of the driven pulley and the resin blocks.
Implementation Method 2
Stick-slip sounds are produced when friction thus occurs between the resin blocks and the surfaces of the pulleys.
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
In the continuously variable transmission, a slanted angle θ2 (θ4) of a surface of a first (second) outer peripheral portion 42b (43b) with respect to a plane perpendicular to an axis of an immovable (movable) pulley member 42 (43) is greater than a slanted angle θ1 (θ3) of a surface of a first inner peripheral portion 42a (43a) with respect to the plane perpendicular to the axis of the immovable (movable) pulley member 42 (43). Further, at the maximum reduction ratio, a first lateral surface 39a of a V-belt 39 makes contact with the first inner peripheral portion 42a without making contact with the first outer peripheral portion 42b, whereas a second lateral surface 39b of the V-belt 39 makes contact with the second inner peripheral portion 43a without making contact with the second outer peripheral portion 43b.