Variable Displacement Pump Wear-Resistant Guide
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Solution Overview
Problem
Variable displacement pumps face issues with wear of the piston accommodation portion and deterioration of fatigue strength due to the displacement of contact points between the roll and piston portion, leading to increased wear and reduced fatigue strength when attempting to harden the housing material.
Innovation Solution
A variable displacement pump design featuring a hollow cylindrical guide portion with higher wear resistance than the housing, interposed between the piston accommodation portion and the piston portion, formed from a harder material than the housing, which enhances wear resistance and maintains higher fatigue strength in the housing by using materials like gray cast iron for the guide and ductile cast iron for the housing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the hardness of the housing is increased to suppress wear of the piston accommodation portion, then wear resistance is improved, but fatigue strength deteriorates
Solution Approach 1:
The housing structure is segmented into two distinct parts: the main housing body and the guide portion. Each part is made from materials optimized for its specific function - the housing body uses material with high fatigue strength while the guide portion uses material with high wear resistance. This segmentation allows both requirements to be satisfied simultaneously without compromise.
Solution Approach 2:
Different material properties are applied to different locations within the housing structure. The guide portion, which experiences sliding contact and wear, is made from harder material (gray cast iron) specifically where wear resistance is needed. The main housing body retains material with superior fatigue strength for structural integrity. This local differentiation of material quality resolves the contradiction between wear resistance and fatigue strength.
2Reliability
If a harder material is used for the guide portion to protect the piston accommodation portion, then wear resistance is improved, but the overall structure becomes more complex
Solution Approach 1:
The guide portion is merged with the housing to form an integrated structure. Rather than being a separate detachable component, the guide portion is formed as an integral part of the housing, reducing the number of parts and simplifying assembly while still providing the necessary wear resistance through material selection.
Solution Approach 2:
The housing structure utilizes composite construction by combining different cast iron materials in a single integrated component. The guide portion and housing body are formed as one piece using materials with different properties (gray cast iron for wear resistance, ductile cast iron for fatigue strength), achieving composite material benefits without the complexity of assembling separate components.
Data Source
Figure 1
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AI summary
Provided is a variable displacement pump which includes a cylinder block including a plurality of cylinder bores formed in a rotation shaft in a circumferential direction and rotating together with the rotation shaft, a piston provided inside each of the plurality of cylinder bores to be slidable, and a swash plate supported to be tiltable with respect to the rotation shaft while a distal end portion of the piston is slidable thereon and which sucks and discharges a working fluid by moving the piston in a reciprocating manner with a stroke in accordance with an inclination angle of the swash plate, the variable displacement pump including: a control piston which includes a piston portion pressing the swash plate and controls the inclination angle of the swash plate; a piston accommodation portion which is formed in the housing and accommodates the piston portion; and a hollow cylindrical guide portion which is disposed between the piston accommodation portion and the piston portion and includes an inner peripheral surface supporting the piston portion to be slidable thereon, in which the housing is formed of a material having higher fatigue strength than the guide portion and the guide portion is formed of a material harder than the housing.