Asymmetric MF Expander Spring for Oil Ring Groove Jamming
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Solution Overview
Problem
Conventional MF springs in three-part oil scattering rings can jam in the piston ring groove due to thermal expansion from hot combustion gases, leading to excessive wear and operational issues, especially in engines with high compression ratios and combustion chamber pressures.
Innovation Solution
An MF expander spring with an axial trapezoidal or diamond-shaped steel strip design, featuring sharp and blunt angles to allow for axial and circumferential expansion without jamming, and an S-shaped wavy steel strip configuration to enhance elasticity and prevent jamming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a conventional MF spring with trapezoidal wave structure is used, then the spring can exert radial and axial forces to press the oil scattering rings against the cylinder inner wall, but the spring can jam in the piston ring groove due to thermal expansion from hot combustion gases
Solution Approach 1:
The spring profile is changed from a symmetric trapezoidal wave to an asymmetric sawtooth wave with different flank angles. The inclined flanks have angles between 5° and 15° relative to the axial direction, while the return flanks have angles between 75° and 85°. This asymmetric geometry allows the spring to expand preferentially in the axial direction when heated, preventing radial jamming in the piston ring groove while maintaining pressing force
Solution Approach 2:
The spring geometry parameters are specifically optimized with inclined flanks at 5°-15° angles to control thermal expansion behavior. This parameter change ensures that when the spring is heated by combustion gases, it expands primarily in the axial direction rather than radially, preventing jamming while maintaining functional pressing force
2Strength
If the spring expands thermally due to hot combustion gases, then the spring can maintain elasticity, but the spring expands in the circumferential direction and jams in the piston ring groove
Solution Approach 1:
The asymmetric sawtooth profile with differently angled flanks directs thermal expansion preferentially in the axial direction. The inclined flanks (5°-15°) allow greater axial compliance while the steep return flanks (75°-85°) constrain radial expansion, preventing circumferential jamming even when the spring is heated and maintains elasticity
Solution Approach 2:
The spring design actively utilizes thermal expansion by shaping it to expand preferentially in the axial direction when heated. The asymmetric geometry converts what would be a harmful radial expansion into a controlled axial expansion, maintaining elasticity while preventing jamming in the piston ring groove
3Length of moving object
If the spring is designed with oblique parts to provide axial elasticity, then the spring can move axially, but the spring cannot dodge in the axial direction and jams when the oil scattering ring height exceeds the groove width
Solution Approach 1:
The asymmetric sawtooth profile with shallow inclined flanks (5°-15°) provides smooth axial movement capability while the steep return flanks (75°-85°) prevent excessive axial displacement. This geometry allows the spring to accommodate axial movements within the groove width constraints, preventing jamming even when oil scattering ring heights vary
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 new spring design prevents jamming and reduces wear on the oil scattering rings and piston ring grooves by allowing for controlled expansion and maintaining the necessary axial and radial distances, ensuring smooth operation even under high thermal loads.
Implementation Method 1
excessive heating by hot combustion chamber gases can occur that the spring expands and jammed both in the radial direction and in the axial direction
Implementation Method 2
The spring offers good elasticity in the radial direction, but only a limited elasticity in the axial direction
Data Source
Figure 1~2B
Figure 3A~4B
AI summary
The invention relates to an MF expander spring (20) for a three-part oil scraper ring (2, 4, 6, 8). This comprises a steel strip that is corrugated in a trapezium- or diamond-shape in the axial direction, wherein the MF expander spring (20) has axial protrusions (30, 32) which are intended to each rest against an upper or lower scraper ring (34, 36) in the radial direction from the inside, in order to press these outwards against an inner surface of a cylinder, and wherein the MF expander comprises: upper flat sections (24) which are intended to rest on an upper scraper ring (34, 36) of a three-part oil scraper ring (2, 4, 6, 8) in the axial direction; lower flat sections (23) which are intended to rest on a lower scraper ring (34) of the three-part oil scraper ring (2, 4, 6, 8) in the axial direction; and side sections (26, 28) extending between the upper flat sections (24) and the lower flat sections (22). At least every second side section (26) forms an acute angle (α) with the associated upper or lower flat sections (22, 24).