Piston Shoe Interface Lubrication via Segmented Pockets
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Solution Overview
Problem
Axial piston pumps and motors face insufficient lubrication at the piston-to-shoe interface under high-load conditions, leading to wear and increased axial endplay, particularly during the intake portion of the operational cycle where pressure is minimal.
Innovation Solution
The method involves forming pockets on the outer surface of the piston's rounded end and the inner surface of the piston shoe, allowing liquid to be selectively supplied to and from these pockets during the cyclic movement of pistons, creating a dynamic hydrostatic bearing at the piston-to-shoe interface to maintain consistent lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid is supplied through the internal channel to the feed port at the apex of the rounded head, then lubrication is provided to the piston shoe-to-cam plate interface, but insufficient lubrication occurs at the piston-to-shoe interface under high-load conditions
Solution Approach 1:
The invention segments the lubrication delivery system by adding multiple feed ports distributed around the rounded head surface, rather than relying on a single apex feed port. This segmentation allows lubricant to be delivered to multiple locations simultaneously, ensuring adequate coverage across the entire piston-to-shoe interface even under high-load conditions where pressure may be minimal at certain locations.
Solution Approach 2:
The invention applies local quality by positioning feed ports at specific locations around the rounded head where lubrication is most needed. Each feed port delivers lubricant locally to its corresponding region of the piston-to-shoe interface, ensuring that high-load areas receive adequate lubrication regardless of the overall pressure conditions in the system.
2Force
If pressure at the feed port is minimal during the intake portion of the operational cycle, then lubrication can be supplied to the piston shoe-to-cam plate interface, but little or no driving force exists to drive lubricant into the piston-to-shoe interface
Solution Approach 1:
By segmenting the lubrication delivery into multiple feed ports located at different positions around the rounded head, the system ensures that at least some feed ports experience adequate pressure during all phases of the operational cycle. This segmentation compensates for pressure variations at any single location, maintaining consistent lubricant delivery force to the piston-to-shoe interface throughout the intake and discharge portions of the cycle.
Solution Approach 2:
The feed ports are positioned to receive lubricant before it reaches the apex feed port, ensuring that lubrication is established at the piston-to-shoe interface in advance of high-load conditions. This preliminary action of lubricant delivery at strategically positioned feed ports ensures that the interface is protected before maximum contact loads occur.
3Strength
If materials are selected and processed to achieve wear resistance at the piston-to-shoe interface, then wear resistance is improved, but lubrication may still be needed to prevent wear and maintain operational reliability
Solution Approach 1:
The invention merges two protective mechanisms: material wear resistance and hydrostatic lubrication. By combining the inherent wear resistance of selected materials with the additional protection from multi-location lubricant delivery through distributed feed ports, the system achieves enhanced operational reliability that neither mechanism could provide alone, especially under high-load conditions.
Solution Approach 2:
The distributed feed ports provide beforehand cushioning by delivering lubricant to the piston-to-shoe interface in advance of high-load contact conditions. This prior cushioning of lubricant presence protects the wear-resistant materials from direct metal-to-metal contact during subsequent high-load operations, maintaining operational reliability.
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
This approach ensures continuous and even lubrication distribution across the piston-to-shoe interface, reducing wear and maintaining the hydrostatic bearing, even at points of varying contact and pressure, thereby enhancing the operational reliability of axial piston machines.
Implementation Method 1
liquid is supplied to each piston-to-shoe interface to form a hydrostatic bearing at each piston-to-shoe interface
Data Source
AI summary
Methods and apparatus are provided for lubricating a piston-to-shoe interface in a hydraulic motor or pump. Piston assemblies are installed in a housing that are each adapted to receive a reciprocating drive force and are each configured, in response thereto, to cyclically move between an intake direction and a discharge direction. Each piston assembly includes a piston and a piston shoe, and the piston, the piston shoe, or both have a plurality of pockets formed in a surface that defines a piston-to-shoe interface. When the pistons cyclically move, liquid is supplied to each piston-to-shoe interface to form a hydrostatic bearing at each piston-to-shoe interface. A portion of the liquid that is supplied to each piston-to-shoe interface is selectively supplied to and from one or more of the plurality of pockets.