Longitudinal Leaf Spring with Varying Cross-Section for S-Curvature Compensation
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Solution Overview
Problem
Existing leaf springs in motor vehicle axles, particularly those made of fiber composite materials, face challenges with durability and service life due to stress changes and S-impact during braking, leading to potential permanent damage and reduced service life.
Innovation Solution
A motor vehicle axle suspension featuring a longitudinal leaf spring with varying cross-sectional sizes along its central axis and a clamping device offset from the center, which compensates for S-curvature by having a larger rear branch cross-sectional size than the front branch, reducing shear stresses and enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a longitudinal leaf spring is used to absorb forces in X, Y and Z directions, then the suspension capability is improved, but the spring experiences S-impact during braking leading to increased stress and reduced service life
Solution Approach 1:
The leaf spring is designed with varying cross-sectional dimensions along its length, with the rear branch having a larger cross-section than the front branch. This local variation in geometry concentrates structural reinforcement exactly where the S-impact generates highest stresses during braking, allowing the spring to withstand multi-directional forces while resisting damage from braking-induced stress concentrations.
2Weight of moving object
If the leaf spring is made of fiber composite material to reduce weight, then the specific weight is reduced, but shear stresses between layers can cause fiber strands to tear or break
Solution Approach 1:
The invention employs fiber composite material construction for the leaf spring, utilizing multiple layers of fiber-reinforced composites. The varying cross-sectional design works synergistically with the composite material structure to distribute shear stresses across the layered construction, preventing delamination and fiber strand failure while maintaining the lightweight advantage of composite materials.
Solution Approach 2:
The rear branch is designed with a larger cross-sectional size compared to the front branch, creating localized reinforcement in the region most susceptible to S-impact during braking. This geometric variation optimizes the distribution of shear stresses within the fiber composite layers, preventing stress concentrations that would otherwise cause inter-laminar failure or fiber strand tearing.
3Strength
If the cross-sectional geometry is changed to increase spring rigidity, then the movement of differential housing is restricted, but the weight remains constant compared to conventional springs
Solution Approach 1:
The leaf spring features a non-uniform cross-sectional geometry where the rear branch has a larger cross-section than the front branch. This localized geometric variation increases rigidity precisely in the region subjected to highest braking loads, while the front branch maintains a smaller cross-section that allows greater flexibility for differential housing movement during normal suspension 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 design results in a weight-optimized, more durable leaf spring with improved braking behavior and reduced peak stresses, maintaining driving comfort and safety while extending the service life.
Implementation Method 1
the longitudinal leaf spring again has an essentially rectilinear course. Due to the compression or rebound due to the dynamic wheel forces, the course then changes during rebound into a curved course or during compression, especially in the case of strong compression, into a course that is opposite to the originally curved course
Implementation Method 2
When the stress conditions change, shear stresses occur within the leaf spring, which can lead to a weakening of the leaf spring between the individual layers
Data Source
Figure 1a~1c
Figure 2a~2b
Figure 3a~3b
AI summary
The present invention relates to a longitudinal leaf spring designed to optimize stress distribution for the specific case of S-shaped movement during braking. For this purpose, the longitudinal leaf spring has a longitudinally extending cross-sectional area of varying dimensions, which is particularly larger in a central connection area 5 than in the branches 6 extending from the connection area 5.