Pulley Coil Spring Geometry for Torsional Durability
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Solution Overview
Problem
Pulley structures for alternators face durability issues due to excessive torsional deformation of coil springs, leading to potential cracks and wear, especially during engine startup and shutdown, and existing solutions increase pulley size or reduce torque transmission efficiency.
Innovation Solution
A pulley structure with a trapezoidal-shaped coil spring that restricts further torsional deformation, functions as a one-way clutch, and has a neutral axis closer to the inner surface to reduce bending stress, incorporating a lock mechanism to prevent diameter expansion deformation and maintain torque transmission without increasing size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the coil spring is allowed to undergo excessive torsional deformation to absorb rotational fluctuation, then the ability to accommodate engine rotation fluctuation is improved, but cracks or breakages are generated on the coil spring surface due to bending stress
Solution Approach 1:
The patent changes the geometric parameters of the coil spring by giving the spring wire a trapezoidal cross-section instead of a circular one. The longer side of the trapezoid is positioned on the inner circumferential surface, which alters the stress distribution characteristics and reduces maximum bending stress during torsional deformation
Solution Approach 2:
The patent introduces asymmetry in the coil spring's cross-sectional shape. The trapezoidal cross-section with unequal sides creates an asymmetric stress distribution that favors reduced stress concentration on the inner circumferential surface where tensile stress acts during diameter expansion
2Force
If the coil spring diameter is expanded to increase torque transmission capacity, then the torque transmission ability is improved, but the lock mechanism is triggered restricting further deformation
Solution Approach 1:
The patent modifies the physical parameters of the coil spring by using a trapezoidal cross-section, which changes the relationship between diameter expansion and torque transmission. This allows the spring to achieve higher torque capacity before triggering the lock mechanism, effectively increasing the operational range
3Reliability
If the coil spring is designed with higher torsional strength to prevent breakage, then the durability is improved, but the bending stress concentration on the inner surface increases
Solution Approach 1:
The patent creates a composite cross-sectional geometry by combining different side lengths in the trapezoidal shape. This geometric composition allows the spring wire to achieve higher overall torsional strength while the specific configuration (longer side on inner surface) reduces stress concentration, creating a beneficial composite effect
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
Enhances durability and reduces wear on the pulley components by minimizing bending stress and maintaining torque transmission efficiency without enlarging the pulley structure, even under high torsional loads and frequent engine cycles.
Implementation Method 1
the torque is transmitted or blocked between the outer rotating body and the inner rotating body due to diameter expansion or reduction deformation of the coil spring
Implementation Method 2
the coil spring of these pulley structures functions as a one-way clutch (coli spring clutch) which transmits or blocks the torque in one direction between the outer rotating body and the inner rotating body
Implementation Method 3
these pulley structures include a mechanism (hereinafter, referred to as a lock mechanism) in which further diameter expansion deformation of the coil spring is restricted and two rotating bodies rotate integrally with the coil spring when the outer circumferential surface of a free part of the coil spring abuts against the outer rotary body
Data Source
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AI summary
The present invention pertains to a pulley structure (1) equipped with an outer rotating body (2), an inner rotating body (3), and a coil spring (4), said pulley structure 1 characterized in that a cross section of the spring wire of the coil spring (4) along a direction running along the rotational axis and parallel to the rotational axis is a trapezoidal shape, the length Ti [mm] of an inner-diameter-side portion in the rotational axis direction in the cross section is greater than the length To [mm] of an outer-diameter-side portion in the rotational axis direction in the cross section, and when the number of windings of the coil spring (4) is N, expression (1) is satisfied. N×Ti-To/2<1