Fluid-working machine and operating method

Abstract

A fluid-working machine has a plurality of working chambers, e.g. cylinders (11), of cyclically changing volume, a high-pressure fluid manifold (14) and a low-pressure fluid manifold (16), at least one valve (13, 15) linking each working chamber to each manifold, and electronic sequencing means (20) for operating said valves in timed relationship with the changing volume of each chamber (11), wherein the electronic sequencing means is arranged to operate the valves of each chamber in one of an idling mode, a partial mode in which only part of the usable volume of the chamber is used, and a full mode in which all of the usable volume of the chamber (11) is used, and the electronic sequencing means (20) is arranged to select the mode of each chamber on successive cycles so as to infinitely vary the time averaged effective flow rate of fluid through the machine.

Description

BACKGROUND TO THE INVENTION [0001] This invention relates to a fluid-driven (motor) and / or fluid-driving (pump) machine having a plurality of working chambers of cyclically changing volume and valve means to control the connection of each chamber to low- and high-pressure manifolds. The invention also relates to a method of operating the machine. [0002] The invention has particular reference to non-compressible fluids, but its use with gases is not ruled out. It has particular reference to machines where the at least one working chamber comprises a cylinder in which a piston is arranged to reciprocate, but its use with at least one chamber delimited by a flexible diaphragm or a rotary piston is not ruled out. [0003] With most fluid working machines the fluid chambers undergo cyclical variations in volume following a sinusoidal function. It is known to provide flow rectifying seating valves, allowing fluid to be admitted and exhausted from the working chamber, which valves are electr...

AI Technical Summary

Benefits of technology

[0019] Preferably, the working chambers comprise cylinders in which pistons are arranged to reciprocate. If so, the partial pumping mode preferably includes closing the valve linking the cylinder to the low-pressure manifold and opening the valve linking the cylinder to the high-pressure manifold a small fraction in advance of the top dead centre position of the piston. The partial motoring mode preferably includes closing the valve linking the cylinder to the high-pressure manifold and opening the valve linking the cylinder to the low-pressure manifold a small fraction after the top dead centre position of the piston.

[0020] If valve actuations are delayed in this way to almost the end of the stroke, then the rate of change of chamber volume will be at an acceptably low level to permit valve actuation. This means that a small fraction of a whole cylinder can also be selected by the controller to add to the machine's output. The range over which this is practicable is limited by stability of valve ope

Problems solved by technology

Experience shows that varying the timing of the valves, such that portions of the stroke are disabled, in order to vary machine output creates a significant amount of audible and fluid borne noise.

It was considered that delayed closure of valves, occurring during times of significant flow, such that part of the chamber displacement could be rejected, would result in extremely high rates of change of flow and pressure, which in turn would generate noise.

However, in practice it was found that whole chamber selection during times of low flow demand resulted in large flow variations, seeing as the fluid machine was idle for long instances between active chambers.

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