Hydraulic machines and systems

Abstract

A hydraulic system employing an electronically commutated fluid working machine having working chambers, each having one or more electronically controllable valves actively controlled by a controller to regulate the net displacement of working fluid into or out of low- and high-pressure manifolds on a cycle by cycle basis to meet an indicated demand. The high-pressure manifold has an additional outlet, regulated by a controllable outlet valve. If the demand indicated by a demand signal is expected to cause pulsatile flow or vibrations which may excite resonant modes, the controller causes the displacement of working fluid by the working chambers to exceed the demand indicated by the demand signal, and the controller simultaneously opens an electronically controllable outlet valve to allow some of the excess flow to leave, such that the net displacement of fluid meets the demanded displacement of fluid, while mitigating the pulsatile flow or undesirable vibrations.

1 . A hydraulic system comprising;
 a hydraulic machine, the hydraulic machine comprising a rotatable shaft, a low-pressure manifold and a high-pressure manifold, and one or more working chambers having a volume which varies cyclically with rotation of the rotatable shaft, each working chamber having both a low-pressure valve which regulates communication between the low-pressure manifold and the working chamber, and a high-pressure valve which regulates communication between the high-pressure manifold and the working chamber, wherein for each working chamber at least one of the respective low-pressure valve and the respective high-pressure valve is an electronically controllable working chamber valve;   the high-pressure manifold extending between the one or more said working chambers and one or more actuator ports and one or more additional outlets;   one or more hydraulic actuators which are fluidly connected to said high-pressure manifold through the one or more actuator ports and thereby hydraulically driven by the hydraulic machine;   one or more electronically controllable outlet valves which regulate the opening or closing of the one or more additional outlets; and   at least one controller configured to control the one or more electronically controllable working chamber valves and the one or more electronically controllable outlet valves;   wherein the at least one controller is operable to receive a demand signal and to regulate the one or more electronically controllable working chamber valves in phased relationship to cycles of working chamber volume to thereby regulate the net displacement of working fluid by each working chamber on each cycle of working chamber volume, and to concurrently regulate the one or more electronically controllable outlet valves, to thereby regulate the net displacement of working fluid into or out of the high-pressure manifold allowing for the flow of working fluid out of the high-pressure manifold through the one or more additional outlets, when one or more additional outlet is open, to meet a demand indicated by the demand signal.   
     
     
         2 . A hydraulic system according to  claim 1 , wherein the at least one controller is configured to control the electronically controllable working chamber valves to cause the hydraulic machine to displace working fluid in excess of the demand indicated by the demand signal and to cause one or more outlet valves to be open, the net displacement of working fluid into the high-pressure manifold from the one or more working chambers through the high-pressure valves being thereby regulated to meet the demand indicated by the demand signal after allowing for the flow of working fluid out of the high-pressure manifold through the one or more additional outlets. 
     
     
         3 . A hydraulic system according to  claim 1 , wherein one or more said outlet valve(s) is a variable flow control valve, and the at least one controller controls the variable flow control valve across a range of positions. 
     
     
         4 . A hydraulic system according to  claim 1 , wherein at least one controller is configured to open and close a said outlet valve in phased relationship to cycles of working chamber volume to reduce pressure ripples in the high-pressure manifold. 
     
     
         5 . A hydraulic system according to  claim 1 , wherein the high-pressure manifold is in communication with a higher-pressure working fluid source through an inlet valve and at least one controller is configured to close and open the inlet valve in phased relationship with cycles of working chamber volume, to reduce pressure ripple. 
     
     
         6 . A hydraulic system according to  claim 1 , wherein one or more said additional outlets extend from the high-pressure manifold to the low-pressure manifold such that one or more outlet valves regulate the flow of working fluid out of the high-pressure manifold to the low-pressure manifold through one or more said additional outlets. 
     
     
         7 . A hydraulic system according to  claim 1 , wherein one or more said additional outlets extend from the high-pressure manifold to a further manifold, such that the respective one or more outlet valves regulate the flow of working fluid out of the high-pressure manifold to the further manifold through the one or more said additional outlets. 
     
     
         8 . A hydraulic system according to  claim 7 , wherein the further manifold is a pressurised manifold in fluid communication with one or more actuators. 
     
     
         9 . A hydraulic system according to  claim 7 , wherein the high-pressure manifold is part of a closed-circuit hydraulic arrangement and the further manifold is part of an open-circuit hydraulic arrangement, or vice versa. 
     
     
         10 . A hydraulic system according to  claim 9 , wherein the hydraulic system comprises a prime mover coupled to the hydraulic machine to provide power to cause the hydraulic machine to pump working fluid from the low-pressure manifold to the high-pressure manifold and wherein the hydraulic system further comprises a second hydraulic machine driven by the prime mover, or one or more further working chambers of the hydraulic machine configured to pump working fluid from the or another low-pressure manifold, to the further manifold, such that the prime mover powers both the open-circuit and closed-circuit hydraulic arrangements. 
     
     
         11 . A hydraulic system according to  claim 1 , which is a hydraulic vehicle, for example a fork lift truck. 
     
     
         12 . A method of operating a hydraulic system, the hydraulic system comprising;
 a hydraulic machine, the hydraulic machine comprising a rotatable shaft, a low-pressure manifold and a high-pressure manifold, and one or more working chambers having a volume which varies cyclically with rotation of the rotatable shaft, each working chamber having a low-pressure valve which regulates communication between the low-pressure manifold and the working chamber and a high-pressure valve which regulates communication between the high-pressure manifold and the working chamber, wherein for each working chamber at least one of the respective low-pressure valve and high-pressure valve is an electronically controllable working chamber valve;   the high-pressure manifold extending between the one or more said working chambers and one or more actuator ports and one or more additional outlets;   one or more hydraulic actuators which are fluidly connected to said high-pressure manifold through one or more said actuator ports and thereby hydraulically driven by the hydraulic machine,   one or more electronically controllable outlet valves which regulate the opening or closing of the one or more additional outlets; and   the method comprising receiving a demand signal and, responsive thereto, regulating the one or more electronically controllable working chamber valves in phased relationship to cycles of working chamber volume to thereby regulate the net displacement of working fluid by each working chamber on each cycle of working chamber volume, and concurrently regulating the one or more electronically controllable outlet valves, to thereby regulate the net displacement of working fluid into or out of the high-pressure manifold allowing for the flow of working fluid out of the high-pressure manifold through the one or more additional outlets, when one or more additional outlet is open, to meet a demand indicated by the demand signal.   
     
     
         13 . A method according to  claim 12 , wherein the electronically controllable working chamber valves are controlled to cause the hydraulic machine to displace working fluid in excess of the demand indicated by the demand signal and one or more electronically controllable outlet valves is controlled to be open, such that the net displacement of working fluid into the high-pressure manifold from the one or more working chambers is regulated to meet the demand indicated by the demand signal after allowing for the flow of working fluid out of the high-pressure manifold through the one or more additional outlets. 
     
     
         14 . A method according to  claim 13 , wherein when the demand is below a threshold, the electronically controllable working chamber valves are controlled to cause the hydraulic machine to displace working fluid at a predetermined minimum fraction of maximum displacement, or in a predetermined pattern of working chambers carrying out active or inactive cycles of working chamber volume,
 and wherein the one or more outlet valves are controlled to cause hydraulic fluid to flow out of the high-pressure manifold such that the overall displacement of working fluid into the high-pressure manifold meets the demand.   
     
     
         15 . A method according to  claim 13 , wherein under at least some circumstances the electronically controllable working chamber valves are controlled to cause the hydraulic machine to displace working fluid at one of a plurality of discrete fractions of maximum displacement, or in one of a plurality of predetermined patterns of working chambers carrying out active or inactive cycles of working chamber volume,
 wherein the electronically controllable working chamber valves are controlled to cause the working chambers to displace one of the plurality of discrete fractions of maximum displacement in excess of the displacement required to meet the demand indicated by the received demand signal, or to carry out one of the plurality of predetermined patterns which causes the combined displacement of the one or more working chambers to exceed the displacement required to meet the demand,   and wherein the one or more outlet valves are controlled to cause hydraulic fluid to flow out of the high-pressure manifold such that the overall displacement of working fluid into the high-pressure manifold meets the demand.   
     
     
         16 . A method according to  claim 13 , wherein the electronically controllable working chamber valves are controlled to cause the hydraulic machine to displace working fluid in excess of the flow required to meet the demand indicated by the demand signal and to cause one or more of the outlet valves to be open, responsive to determination that the demand is such that if,
 i) the one or more additional outlets were closed, and   ii) demand was met only using working fluid displaced by the one or more working chambers,   there would be an undesirable response from the system arising from the pattern of selection of working chambers to carry out active or inactive cycles to meet the demand.   
     
     
         17 . A method according to  claim 13 , comprising measuring or calculating a current rate of flow of working fluid through one or more said additional outlets, optionally comprising measuring the pressure in the high-pressure manifold.