The present invention provides a fluid system (99) comprising a source of hydraulic fluid under pressure supplying a hydraulic fluid consumer (103) together with a valve passing fluid between said source and said fluid consumer (102). A first fluid compliance (105) is situated between said source (1
The present invention provides a fluid system (99) comprising a source of hydraulic fluid under pressure supplying a hydraulic fluid consumer (103) together with a valve passing fluid between said source and said fluid consumer (102). A first fluid compliance (105) is situated between said source (100) and said valve (102) and a variable restrictor (110) is provided for varying the cross sectional area available for flow of fluid through said valve (102) and is movable between a first position (A) with a larger said area and a second position (B) with a smaller said area. A bias means (117) biases said restrictor (110) towards said second position while an opening means (Fa) urges said restrictor (110) against said bias (117) when fluid flows through said valve (102) and a damping means (126) damps movement of said restrictor between said first and second positions and provides a resistance which increases with the velocity of displacement of said restrictor (110).
대표청구항▼
1. A fluid system comprising: a. a source of hydraulic fluid under pressure, said source producing in use a varying flow comprising a plurality of local flow maxima and local flow minima, wherein adjacent maxima and minima are separated by at least a minimum time (Ta);b. a controller for controlling
1. A fluid system comprising: a. a source of hydraulic fluid under pressure, said source producing in use a varying flow comprising a plurality of local flow maxima and local flow minima, wherein adjacent maxima and minima are separated by at least a minimum time (Ta);b. a controller for controlling said source;c. a hydraulic fluid consumer;d. a valve passing fluid between said source and said fluid consumer, wherein the valve comprises a valve body having an aperture and an edge portion and a spool axially displaceable within said aperture;e. a first fluid compliance between said source and said valve;f. the spool being a variable restrictor for smoothly and continuously varying a cross sectional area available for flow of fluid through said valve and movable between a first position with a larger said area and a second position with a smaller said area, said spool having a tapered portion including a plurality of tapered fluted segments each having a tapered opening forming an orifice between itself and the edge portion of the body and each orifice having a cross-sectional area which varies according to the axial displacement of the spool;g. a bias means for biasing said restrictor towards said second position, said bias means providing a substantially constant biasing force;h. an opening means for urging said restrictor against said bias means when fluid flows through said valve, such that under steady flow, a pressure drop across said valve is low and varies little with changing flow; andi. a damping means for damping movement of said restrictor between said first and second positions and providing a resistance which increases with a velocity of displacement of said restrictor, characterized in that a time constant (Tr) of the damped movement of said restrictor is longer than said minimum time (Ta). 2. The fluid system of claim 1, wherein said source comprises a plurality of working chambers connectable to and isolatable from said valve, thereby to cause said source to produce a varying flow comprising a plurality of local flow maxima and local flow minima, wherein said controller is operable to add working chambers to and delete working chambers from a set of working chambers connected to said valve no more frequently than an interval (Td), characterized in that the time constant (Tr) of the damped movement of said restrictor is longer than said interval (Td). 3. The fluid system of claim 1, wherein said source comprises a plurality of working chambers which produce flow pulses separated by a non-zero minimum time (Tp), characterized in that the time constant (Tr) of the damped movement of said restrictor is longer than said non-zero minimum time (Tp). 4. The fluid system of claim 1, wherein said source produces a varying flow comprising a plurality of local flow maxima and local flow minima formed by a summation of flow pulses, each of said flow pulses having a maximum length (Tc), characterized in that the time constant (Tr) of the damped movement of said restrictor is longer than said maximum length (Tc). 5. The fluid system of claim 1, wherein said source is a pulsative flow source producing in use a varying flow comprising a plurality of local flow maxima and local flow minima, and producing in use one or more short repeating flow patterns, each having the same average flow and having a maximum period (Tf), characterized in that the time constant (Tr) of the damped movement of said restrictor is longer than said maximum period (Tf). 6. The fluid system of claim 1, wherein at least one local flow minimum is substantially zero. 7. The fluid system of claim 1, wherein said source is a variable flow source producing in use a time-averaged output flow, said time averaged output flow following a demand signal and having a maximum bandwidth (1/Ts), wherein the time constant (Tr) of the damped movement of said restrictor is less than said maximum bandwidth (Ts). 8. The fluid system of claim 1, wherein said fluid consumer comprises one or more motors or actuators. 9. The fluid system of claim 1, further comprising a second fluid compliance between said valve and said fluid consumer. 10. The fluid system of claim 9, wherein said first and second fluid compliances each comprise an accumulator. 11. The fluid system of claim 1, wherein said spool comprises a first, flow confronting surface of fixed cross-sectional area and a variable outlet area at a second end thereof, the area of which depends upon the axial position of said spool relative to the valve body, thereby to create a variable pressure drop across said valve. 12. The fluid system of claim 1, wherein said biasing means comprises a spring. 13. The fluid system of claim 1, wherein any of said biasing means, said damping means, or said opening means comprises an electronically controlled actuator, a solenoid/electromagnetic actuator, a piezoelectric actuator, an electrorheological device, or a hydraulic amplifier. 14. The fluid system of claim 1, wherein said valve is a dual-mode valve operable at least some of the time to control the flow of fluid therethrough, and wherein said dual-mode valve is connected to said hydraulic consumer. 15. The fluid system of claim 1, wherein said source comprises a plurality of working chambers of cyclically varying volume controlled on a stroke-by-stroke basis by said controller, by means of high-speed commutating valves associated with each working chamber and controlled so as to vary the time-averaged proportion of working chambers which provide fluid to or from said valve. 16. The fluid system of claim 1, wherein said resistance decreases or remains substantially the same when a pressure difference between two volumes of fluid within the valve reaches or exceeds a threshold. 17. The fluid system of claim 1, further comprising at least one pressure transducer providing a pressure measurement to said controller, wherein said controller is arranged to create an estimation of the pressure drop across said valve and to use said estimation in conjunction with said pressure measurement to adjust an output of said source.
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