Cycloid Rotor Engine Sealing Grid Design
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Solution Overview
Problem
Rotary engines face challenges in sealing working fluid during compression, combustion, and expansion strokes due to manufacturing tolerances and thermal expansion, leading to high leakage, low efficiency, and high emissions, particularly in gerotor-based designs like the Wankel engine.
Innovation Solution
The cycloid rotor engine design features a rotor with Z1 lobes rotating within a fixed housing, utilizing a cycloidal geometry that ensures continuous contact with peak seals, minimizing gaps and enhancing sealing efficiency through a unique seal grid system that includes face and peak seals, which are radially biased and lubricated directly, reducing oil consumption and emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a gerotor-based rotary engine design is used to achieve high power density and low part count, then the engine structure becomes simpler with fewer moving parts, but sealing of working fluid becomes difficult due to manufacturing tolerances and thermal expansion
Solution Approach 1:
Rollers are introduced as intermediary elements between the inner and outer rotors. These rollers form the displacement chambers and enable sealing through their contact with both rotors, solving the sealing problem while maintaining the simplicity of the gerotor design
Solution Approach 2:
A flexible seal ring is used to accommodate manufacturing tolerances and thermal expansion while maintaining sealing effectiveness. The flexibility of the seal ring allows it to adapt to dimensional changes without compromising the seal
2Reliability
If the gap between inner rotor and outer rotor is increased to accommodate manufacturing tolerances and thermal expansion, then the engine becomes more reliable, but leakage increases and sealing efficiency decreases
Solution Approach 1:
A flexible seal ring is employed that can deform to maintain contact with the rotors even when gaps vary due to tolerances or thermal expansion. This flexibility allows the seal to adapt to dimensional changes while preventing leakage
Solution Approach 2:
The seal system is designed to self-adjust through the elastic deformation of the seal ring, which automatically compensates for gap variations without requiring external adjustment mechanisms
3Reliability
If apex seals are used in a Wankel-style engine to seal the combustion chamber, then the combustion chamber is enclosed, but oil must be metered into the working chamber for lubrication causing emission problems
Solution Approach 1:
The sealing function is extracted from the combustion chamber environment and placed in the non-combustion areas. The seal ring operates outside the combustion chamber, eliminating the need for oil lubrication in the working fluid path and preventing oil-related emissions
4Power
If a high surface to volume ratio combustion chamber is used in a rotary engine, then the engine achieves high power density, but thermal losses increase due to the large exposed surface area
Solution Approach 1:
The flexible seal ring creates an efficient combustion chamber geometry that reduces the surface area in contact with hot gases while maintaining compact dimensions, thereby reducing thermal losses without sacrificing power density
Data Source
Figure 1(a)~1(d)
Figure 2(a)~2(c)
Figure 3(a)~3(f)
AI summary
A rotary engine has a cycloid rotor and a sealing grid including a face seal that rotates with the rotor, and including other seals that do not rotate with the rotor. As the rotor rotates within a housing, the rotor, housing and seal grid form at least one working chamber between them, the chamber undergoing a change from initial volume V1 to V2, which is less than V1, thus compressing a working medium, and subsequently expanding to volume V3, which may be larger than V1, such that the chamber volume is a smooth and continuous function of rotor's rotational angle.