Rotary Engine Side Wall Coating Stress Relief
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Solution Overview
Problem
The side walls of rotary internal combustion engines, such as Wankel engines, face challenges with high pressure and thermal loads, requiring durable coatings to prevent wear and spallation while maintaining efficient cooling and sealing performance.
Innovation Solution
A housing design with a peripheral wall and side walls featuring a core face with a cavity section and a flared abutment section, coated with a material harder than the core material, where the coating covers the cavity section and ends at a coating edge on the flared portion, avoiding contact with the end face, and a second coating on the peripheral wall for enhanced durability and reduced spallation risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a hard coating is applied on the side wall core face to resist wear and thermal loads, then the durability and wear resistance is improved, but the coating may spall off under high stress and thermal cycling
Solution Approach 1:
A stress relief groove is introduced at the boundary between the coating and the uncoated region, positioned to relieve thermal and mechanical stresses before they can cause spallation. This preliminary stress relief mechanism prevents coating failure under thermal cycling and high pressure conditions.
Solution Approach 2:
The side wall core face is designed with a curved profile instead of a flat surface, creating a gradual transition zone between the coated cavity section and the uncoated abutment section. This geometric parameter change reduces stress concentration at the coating boundary, preventing spallation while maintaining wear resistance.
2Reliability
If the coating covers the entire core face including the abutment section, then wear resistance is improved, but the coating edge contacts the end face causing spallation under pressure
Solution Approach 1:
The coating is selectively applied only to the cavity section of the core face that requires wear resistance, while the abutment section remains uncoated. This local quality differentiation ensures the coating provides protection where needed without creating stress concentration at the boundary with the end face.
Solution Approach 2:
A stress relief groove is positioned at the coating edge on the flared portion, creating a preliminary stress relief mechanism that prevents pressure transmission to the coating-end face interface, thereby avoiding spallation.
3Productivity
If the coating extends close to the end face to maximize coverage, then manufacturing efficiency is improved, but the coating edge contacts the end face under load causing failure
Solution Approach 1:
The coating is restricted to the cavity section only, with a clear boundary defined by the stress relief groove on the flared portion. This local quality approach simplifies coating application by defining a precise stop point while maintaining reliability through stress management.
Solution Approach 2:
The stress relief groove is positioned in advance on the flared portion to prevent coating edge contact with the end face under load, ensuring coating integrity without compromising application efficiency.
4Temperature
If coolant passages are placed close to combustion chambers for efficient cooling, then thermal management is improved, but the side wall structure becomes more complex and vulnerable to thermal stress
Solution Approach 1:
The side wall core face is designed with a curved profile that naturally creates stress distribution patterns favorable for accommodating coolant passages near the combustion chamber. This geometric parameter change allows efficient cooling while managing thermal stress through the curved geometry's inherent stress distribution properties.
Data Source
AI summary
A housing for a rotary engine has: a peripheral wall defining two end faces and an inner face transverse to the two end faces; two side walls sealingly engaged to the two end faces of the peripheral wall, a core of a side wall of the two side walls having a core face, the core face having a cavity section facing the rotor cavity and an abutment section annularly extending around the cavity section, the abutment section facing an end face of the two end faces, the abutment section having a flared portion flaring away from the end face; and a coating on the core face, the coating made of a material harder than a material of the core of the side wall, the coating covering the cavity section and ending at a coating edge located on the flared portion, the coating edge free of contact with the end face.