Piston Stress Reducing Portion for Hydraulic Rotator
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Solution Overview
Problem
Conventional pistons for liquid-pressure rotating devices suffer from reduced fatigue strength due to stress concentration at welded corners, leading to shortened lifespan and decreased performance in terms of weight, energy conversion efficiency, and maximum rotating speed.
Innovation Solution
Incorporating an annular concave stress reducing portion on the inner peripheral surface of the piston's peripheral wall main body portion, which reduces stress on the welded end portion and prevents corner angle formation, thereby enhancing fatigue strength and extending piston life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the piston is made hollow for weight reduction, then the weight of the piston decreases, but the dead volume increases causing larger compression loss
Solution Approach 1:
The piston utilizes a hollow structure with strategic openings and sealed portions that create controlled internal cavities. The hollow portion with opening portion and sealed section creates a porous-like configuration that reduces weight while managing fluid dynamics to minimize compression loss during operation.
Solution Approach 2:
The piston applies local quality by having different structural characteristics in different regions: the hollow portion for weight reduction, the opening portion for fluid communication, and the sealed portion for maintaining pressure. This localized structural differentiation allows the piston to simultaneously achieve weight reduction and minimize dead volume effects.
2Ease of manufacture
If the lid portion is welded to the peripheral wall main body portion at a right angle corner, then the manufacturing is simplified, but stress concentrates at the welded end portion reducing fatigue strength
Solution Approach 1:
The invention replaces the right angle corner configuration with a curved transition surface where the lid portion meets the peripheral wall main body portion. This curved configuration eliminates the sharp corner that causes stress concentration, distributing stress more evenly across the welded joint and improving fatigue strength while maintaining manufacturing feasibility.
3Loss of energy
If the hollow portion is sealed to reduce dead volume, then the compression loss decreases, but the welded portion becomes subject to high stress reducing reliability
Solution Approach 1:
The curved transition surface at the welded joint eliminates stress concentration points that would otherwise compromise the reliability of the sealed hollow structure. This allows the hollow portion to be effectively sealed for reducing dead volume and compression loss while maintaining the structural integrity and reliability of the welded connection under high stress conditions.
Solution Approach 2:
The piston structure implements local quality by creating a curved transition zone specifically at the welded portion where stress concentration occurs. This localized geometric modification targets the critical stress area without affecting the overall sealing function of the hollow portion, thereby simultaneously achieving reduced compression loss and improved reliability.
Data Source
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AI summary
A piston 61 is included in a liquid-pressure rotating device 72 in which a plurality of pistons 61 including the piston 61 are arranged at a cylinder block 9 in a circumferential direction of the cylinder block 9, the cylinder block 9 being configured to rotate together with a rotating shaft 5, the liquid-pressure rotating device 72 being used as a pump or a motor. The piston 61 includes: a cylindrical peripheral wall main body portion 62 including a hollow portion 62b, an opening portion 64 being formed at one end of the peripheral wall main body portion 62 and communicating with the hollow portion 62b; a lid portion 63 welded to an inner peripheral surface of the opening portion 64 to seal the hollow portion 62b and including an outer surface formed as a pressure receiving surface 63 a which receives liquid pressure; and a stress reducing portion 65 provided on an inner peripheral surface of the peripheral wall main body portion 62, the inner peripheral surface being in contact with or close to an end portion 68a of a welded portion 68 formed between the opening portion 64 and the lid portion 63, the end portion being located at the hollow portion 62b side, the stress reducing portion being configured to reduce stress acting on the end portion 68a of the welded portion 68.