Pulley Drive System with Controlled Slip for Noise Reduction
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Solution Overview
Problem
Pulley drive systems in electrically powered lawn care devices face issues with high reduction ratios, short center distances, and harsh impact noises due to high power requirements, leading to potential damage and noise during start-up, especially with universal electric motors.
Innovation Solution
A pulley drive system using a toothed belt with a tensioning arrangement that allows for controlled slip between the belt and the driven pulley upon start-up, featuring a smooth or partially toothed pulley with partial teeth that mesh with the belt, and a tensioning mechanism to manage torque and prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed centre distance between driving pinion and driven pulley is used, then the structure is simple, but only a few teeth of the driving pinion engage with the belt making high reduction ratio impossible
Solution Approach 1:
The patent introduces a movable idler pulley that can change its position dynamically along the belt path. This allows the centre distance between the driving pinion and driven pulley to be adjusted, enabling high reduction ratios while maintaining adequate tooth engagement. The idler pulley moves to accommodate different operational requirements, transforming a static structure into a dynamic one that adapts to varying reduction ratio needs.
2Adaptability or versatility
If the distance between centres of driving and driven pulleys is made adjustable, then high reduction ratio is possible, but additional assembly costs and extra packaging space are required
Solution Approach 1:
The idler pulley serves multiple functions: it maintains belt tension, enables centre distance adjustment for high reduction ratios, and guides the belt path. By combining these functions into a single component, the patent avoids the need for separate tensioning mechanisms and adjustment devices, thereby reducing assembly complexity and packaging space requirements while achieving the desired adaptability.
3Power
If high power is required or there is a large degree of inertia in the system, then maximum drive torque is delivered on initial start up, but harsh impact noises occur and damage to the belt and pinion can result
Solution Approach 1:
The patent employs a rubber-coated driven pulley that acts as a cushioning element between the belt and the pulley surface. The rubber layer absorbs and dampens the harsh impact forces and noises that occur during startup when maximum drive torque is delivered. This beforehand cushioning protects both the belt and pinion from damage while allowing the system to utilize the full power capability of the motor.
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
The system reduces noise and prevents damage by allowing controlled, momentary slip during high-torque situations, ensuring the belt remains under tension and operates within a predetermined torque range, preventing motor stall and maintaining system integrity.
Implementation Method 1
The tensioning arrangement is set to tension the toothed belt so that slip will occur between the toothed belt and the driven pulley upon start-up of the drive system before the drive pinion and the driven pulley reach synchronous rotational speeds
Data Source
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Figure 3~4
AI summary
A pulley drive system such as for an electric motor drive (3), comprising an endless belt (5) trained around a driving pinion (1) and a driven pulley (4, 104). A tensioning arrangement (9) is provided for acting on a stretch of the belt (5) between the driving pinion (1) and the driven pulley (4, 104) to increase the tension in the belt (5). The driven pulley is arranged without full meshing engagement with the section of the toothed belt (5) in contact therewith, whereby slip can occur between the belt (5) and the driven pulley (4, 104) upon start-up of the drive system before the drive pinion (1) and the driven pulley (4, 104) reach synchronous rotational speeds.