Isolating Decoupler With Progressive Wrap Spring Clamping
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Solution Overview
Problem
Diesel and gasoline engine accessory drive systems experience increased crankshaft vibrations and belt chirp noise due to higher acceleration/deceleration rates and alternator inertia, leading to reduced belt operating life and noise issues.
Innovation Solution
An isolating decoupler with a torsion spring having a major and minor diameter section, where the minor section is radially outboard of a wrap spring, allowing it to clamp the wrap spring to a shaft during load conditions, thereby increasing torque bearing capacity and preventing damage from overtorque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional isolator decoupler with uniform diameter torsion spring is used, then the structure is simple, but the torque bearing capacity is insufficient under high load conditions
Solution Approach 1:
The torsion spring is divided into two distinct sections: a first section with a first diameter and a second section with a second diameter that is less than the first diameter. This segmentation allows the spring to have different functional zones - the larger first section provides initial torque absorption while the smaller second section engages to provide additional clamping force on the wrap spring under high load conditions, thereby increasing overall torque bearing capacity.
Solution Approach 2:
The torsion spring features non-uniform diameter distribution with a larger first diameter section and a smaller second diameter section. This local quality variation optimizes the spring's performance by concentrating clamping force where needed - the smaller second diameter section is positioned to clamp the wrap spring against the pulley bore, providing enhanced local pressure and friction under high torque conditions without compromising the overall spring structure.
2Object-affected harmful factors
If the wrap spring is loosely fitted on the shaft, then installation is easy, but belt chirp noise increases due to belt slip under high vibration
Solution Approach 1:
The decoupler employs a dynamic clamping mechanism where the torsion spring's second section moves radially under torque load to progressively clamp the wrap spring against the pulley bore. This dynamic adjustment allows the system to maintain optimal friction force between the wrap spring and shaft under varying load conditions, preventing belt slip and chirp noise during high vibration while allowing easy installation when not under load.
Solution Approach 2:
The system changes the clamping force parameter dynamically through the torsion spring's deformation under load. As torque increases, the torsion spring compresses and the second diameter section moves to increase the clamping force on the wrap spring, thereby increasing the friction force between the wrap spring and shaft to prevent belt slip and reduce chirp noise during high vibration conditions.
3Reliability
If a rigid connection between pulley and shaft is used, then torque transmission is efficient, but vibration and overtorque damage the belt and accessories
Solution Approach 1:
The wrap spring acts as an intermediary frictional connection between the pulley and shaft, replacing a rigid mechanical connection. This intermediary allows torque to be transmitted through friction while providing slip protection - when overtorque occurs, the wrap spring can slip on the shaft, protecting the belt and accessories from damage while maintaining sufficient torque transmission efficiency during normal operation through optimized friction force.
Solution Approach 2:
The torsion spring with its two-diameter configuration provides beforehand cushioning by progressively engaging the smaller second diameter section to clamp the wrap spring under increasing load. This progressive clamping action cushions the system against sudden torque spikes and overtorque conditions, preventing damage to the belt and accessories before they occur while maintaining efficient torque transmission during normal operation.
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 solution effectively reduces belt chirp noise and extends belt life by progressively clamping the wrap spring to the shaft, enhancing the decoupler's torque bearing capacity and protecting against overtorque damage.
Implementation Method 1
a torsion spring having a first section having a major diameter and a second section having a minor diameter
Implementation Method 2
a wrap spring having an inner diameter less than an outer surface outer diameter, the wrap spring frictionally engaging the outer surface
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An isolating decoupler comprising a shaft having an outer surface, a pulley rotationally engaged about the shaft, a torsion spring having a first section having a major diameter and a second section having a minor diameter, the major diameter is greater than the minor diameter, the torsion spring engaged with the pulley, a wrap spring having an inner diameter less than an outer surface outer diameter, the wrap spring frictionally engaging the outer surface, the torsion spring having an end fixedly connected to the wrap spring, the torsion spring loaded in a winding direction whereby the diameter of each coil of the torsion spring decreases in a progressive sequence as a load increases, the second section is disposed radially outboard of the wrap spring such that the second section moves radially inward to clamp the wrap spring during a load condition, and the pulley comprising a member disposed to progressively release the wrap spring from the shaft outer surface upon occurrence of a predetermined load condition.