Radial Piston Hydraulic Machine Asymmetric Orifice Noise Reduction
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Solution Overview
Problem
Hydraulic machines with radial pistons experience significant sound emissions due to harmonic excitation at a narrow fundamental frequency, leading to unpleasant whining noises, which existing technologies have not adequately addressed.
Innovation Solution
The implementation of a hydraulic machine design where the switchovers between fluid feed and discharge occur at a non-uniform rate, with isolation stages offset relative to each other, broadening the frequency range of fundamental excitations and reducing the intensity of sound emissions by avoiding pure fundamental frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the communication orifices are offset randomly or in alternation, then the pressure shocks are reduced, but the harmonic excitation at a narrow fundamental frequency is not adequately addressed
Solution Approach 1:
The patent applies asymmetry by intentionally creating non-uniform angular spacing between communication orifices in the cylinder block. Specifically, the orifices are positioned at angles that are not equal multiples of 360/n degrees, where n is the number of pistons. This asymmetric arrangement prevents the system from operating at a narrow fundamental frequency, thereby reducing harmonic excitation and the associated whining noise while maintaining relatively simple manufacturing processes.
2Object-affected harmful factors
If the switchovers occur at a uniform rate, then the machine operation is simplified, but a narrow fundamental frequency is generated causing unpleasant whining noise
Solution Approach 1:
The patent introduces dynamic variation in the switchover timing by offsetting the communication orifices angularly. This creates a non-uniform switching pattern where the timing of connections between cylinders and main ducts varies dynamically throughout the rotation cycle. The dynamic effect broadens the frequency spectrum of the fundamental excitation, preventing concentration at a single narrow frequency and thereby reducing the whining noise characteristic of uniform switching.
3Object-affected harmful factors
If pressure-compensating volume is provided at the edges of distribution orifices, then pressure shocks are avoided, but harmonic excitations from the fundamental frequency are not reduced
Solution Approach 1:
The patent changes the geometric parameter of the communication orifices by offsetting them from uniform angular spacing. This parameter change fundamentally alters the switching pattern of the hydraulic system. Instead of synchronized switching that generates strong harmonic content, the offset arrangement creates a more distributed switching pattern that reduces both pressure shocks and harmonic excitations simultaneously, addressing both harmful effects through a single design modification.
Data Source
AI summary
The hydraulic machine includes a cam and a cylinder block with pistons co-operating with cam lobes, each of which has two ramps extending between top and bottom dead center arcs. The cylinders are connected in alternation to a feed and to a discharge, in sequences separated by switchover stages including an isolation stage during which they are isolated relative to the feed and discharge main ducts. The angular position of the start or of the end of at least one first isolation stage relative to the corresponding dead center arc is different from the angular position of the start or of the end of at least one second isolation stage relative to its corresponding dead center arc, both of these dead center arcs being top dead center arcs or both of them being bottom dead center arcs.