Helical Compression Spring Coating for Oil Scraper Rings
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Solution Overview
Problem
The helical compression spring in two-part oil scraper rings of internal combustion engines experiences secondary wear and reduced tangential force due to relative movements, impairing the scraping action and friction performance, especially under conditions of insufficient lubrication.
Innovation Solution
A multi-layer coating comprising alternating plies of CrN and a-C:H:Me layers, with a metal-free DLC layer as the outermost layer for improved running-in behavior and wear resistance, applied using PVD and PA-CVD processes, is used to enhance the friction and wear properties of the helical compression spring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer DLC coating is applied to the helical compression spring, then wear resistance is improved, but internal stresses increase and layer stability deteriorates
Solution Approach 1:
The coating is divided into multiple alternating layers of CrN and a-C:H:Me, where each layer type compensates for the internal stresses of the other. This segmented structure prevents stress accumulation and delamination while maintaining wear resistance.
Solution Approach 2:
The patent uses a composite coating system combining CrN (a hard, stress-resistant ceramic coating) and a-C:H:Me (a wear-resistant DLC coating with metal additives). The composite structure leverages the complementary properties of both materials to achieve both low wear and stable adhesion.
2Reliability
If the helical compression spring operates under insufficient lubrication, then friction increases and wear accelerates, but the spring must maintain scraping function
Solution Approach 1:
The coating changes the surface properties of the spring by introducing low-friction DLC layers with metal additives that maintain lubricity even under insufficient lubrication conditions. This parameter change in surface chemistry allows the spring to maintain scraping function while reducing friction and wear.
Solution Approach 2:
The a-C:H:Me layers provide localized low-friction properties at the contact surfaces where scraping occurs, while the CrN layers provide hard, wear-resistant properties in regions experiencing higher contact pressures. This spatial differentiation of coating properties optimizes performance under varying lubrication conditions.
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 coating significantly extends the lifetime of the helical compression spring, maintains good friction properties even under insufficient lubrication, and improves running-in behavior by balancing internal stresses and providing enhanced wear resistance.
Implementation Method 1
applied using PVD and PA-CVD processes
Implementation Method 2
applied using PVD and PA-CVD processes
Implementation Method 3
the internal stresses, which are higher in the case of DLC as compared with CrN, can be equalised in the coating as a whole by the CrN plies
Implementation Method 4
Both the a-C:H:Me and the a-C:H layer mentioned below are DLC layers and ensure comparatively low wear and good friction properties
Data Source
AI summary
A helical compression spring, preferably of steel, in particular CrSi steel or CrNi steel, comprises a coating which has at least one a-C: H: Me coating or a plurality of layers of CrN (16) and a-C: H: Me coatings (14) alternately. In a method for coating a helical compression spring, preferably of steel, a plurality of layers of CrN and a-C: H: Me coatings are applied alternately.