FLUID CONTROL DEVICES

Abstract: A fluid control device of the sliding spool type having pilot control wherein a control profile (20) is located in a longitudinal bore through the spool (4) and has radial clearance (22) in said bore. The control profile (20) separates respective control chambers (12, 14) which extend to the main bore in which the spool is located and an orifice arrangement (5) in the wall of said spool (20) directs secondary fluid flow from a pressure port (10) onto said control profile and into said chambers (12, 14) whereby an imbalance in the chamber pressures will cause sliding movement of the spool. Further respective orifices (6, 8) allow said secondary flow to return to the low pressure side of a fluid supply. The control profile (20) is arranged on a rod which extends externally of the body of the device and sliding movement of the rod causes imbalance of a hydraulic Wheatstone bridge formed by the orifices (5, 6, 8) in combination with the control profile (20) whereby the bridge tends towards equilibrium causing the spool (4) to follow movement of said control profile (20) in a force feedback gain manner. The device has a position feedback ratio of 1:1.

Description: _ _ This invention relates to fluid " control device such as hydraulic or pneumatic controls-valves, servovalv and position control devices and in particular relates to such devices of the sliding spool type which are pilot operated to facilitate better response, control of large flow capacities and/or control from remote controlling means. The remote controlling means may be mechanical, electromechanical, electrohydraulic, fluidic or electroni or any combination-thereo , be it proportional control, analogue, digital, mark/space ratio or otherwise. Various forms of pilot operated valves are well known and by far the most common has a sliding spool pilo valve perched on top of the main control valve in a "piggy-back" fashion. The pilot spool has also been placed insi bore of the main control valve spool. An inherent proble or disadvantage with sliding spool type valves is the high degree of accuracy required in manufacture due to th fine tolerances required between the sealing lands of the spool and the bore in which the spool is adapted to slide. These fine tolerances render spool type valves expensive to manufacture and furthermore, the spool is a delicate piece of apparatus which must be handled with extreme care and replaced if damage or wear affects the fine tolerances. The aforementioned problems are compounded when the pilot valve is also of the spool type as the same criticality of tolerances applies to the pilot valve. Other types of pilot valves such as slide valves, flapper valves, nozzle-jets or variations of each are well known and have various different charac- teristics which render them suitable in some situations and not in others. However, the fine tolerances required with these other types of pilot valves requires at least the same high degree of accuracy in manufacture as with spool type valves and thus' there are no real gains to be made from a cost consideration as between the various alternatives. The choice thus usually depends on the particular requirements of the control^" be it on-off control, proportional control or servo-control, for example, and whatever the choice the cost of such control is -relatively expensive. The object of this invention is to provide an improved control arrangement for a spool type control valve which is more economical to manufacture than existing arrangements. It is a further object to provide.an improved control arrangement for a spool type control valve which facilitates on-off, proportional and/or servo-control of a fluid medium. It should be noted that these latter two types of control'are not conveniently achievable with spool type pilot valves. Accordingly the invention provides a fluid control device of the sliding spool type wherein a spool having various lands is adapted to slide within the bore of a body part to facilitate primary fluid flow between various main ports in said body part dependent upon the position of said spool, said spool having a longitudinal bore extending therethrough and means within said spool bore to facilitate fluid controlled movement of said spool, characterized in that, said means comprises a con- trol profile having radial clearance in said spool bore and separating respective control chambers, each control chamber includes part of the bore of said body part whereby pressurized fluid in said control chambers exerts forces or respective endsof said spool, a first or arrangement is provided in said spool to facilitate second ary fluid flow from a pressure port of said main ports, through the wall of said spool and onto said control profile whereby said secondary flow is directed into respective said control chambers and, via further respec- tive orifice arrangements, back to -the low pressure side of a fluid supply such that said device is caused _ _ . _ to act as a Wheatstone bridge tending towards equilibriu whereby said spool follows movement of said control prof along said spool bore in a force feedback gain manner du to imbalance of pressures in respective said control chambers. In order that the invention may be more readil understood a particular embodiment of a hydraulic control valve will now be described with reference to the accompa ing drawings wherein: FIG. 1 is a sectional side elevation of the hydraulic control valve taken in a . longitudinal direction through the valv body, FIG. 2 is a part sectional view taken on the lines A-A of FIG. 1, FIG. 3 is a part sectional view similar to FIG. 1, showing fluid pressures and flo with the control element in the neutral position, FIG. 4 is similar to FIG. 3 showing the fluid pressures and forces acting on the spoo when the 'control element is in the neut position, and FIG. 5 is similar to FIGS. 3 and 4 showing the fluid pressures and forces acting on th spool when the control element is displ from the neutral position. -Referring now to the drawings, it can be seen that the control valve consists essentially of a valve bo 2 and a control spool 4 which slides within a central bor through the body 2. The control spool 4 has a series of lands around the outer surface thereof and a central bore 3 which extends longitudinally through the spool. Five ports are arranged in the body 2 and communicate with various chambers which surround ' the spool. These ports comprise a pressure port 10, two tank ports 16 and outlet ports 35 and 37. The control valve as described to date is essentially the same as any number of conventional directional control valves and servo valves. The valve body 2 has respective end plates 28,3 which seal the respective ends of the central bore of the valve body and a control rod 18 passes through a suitable aperture in each end plate 28,30 and is sealed therein by a suitable"O"ring 32 at each end plate. The control spoo 4 has an orifice 5 extending through the wall thereof on both sides of the central bore 3. The orifice 5 is arran midway between the ends of the control spool 4. Identica orifices 6 and 8 are arranged towards respective ends of the control spool 4. Each orifice 6 and 8 extends throug the wall of the control spool 4 on opposite sides of the central bore 3. The orifices 6 and 8 are smaller in diameter than the orifice 5 and all three exte radially. The orifice 5 is termed an inlet control orifice and the orifices 6 and 8 are termed outle control orifices. The inlet control orifice 5 connects at all times -to pressure port 10 and each outlet control orifice 6 and 8 communicate with respective tank ports 16 at all times. The inlet control orifice 5 and " the outlet control orifices 6 and 8 thus provide a continuous flow o hydraulic fluid into, and out of, the respective control chambers 12 and 14 within the central bore 3 of the spool 4. The control chambers 12 and 14 are separated by a control profile 20 located on the control rod 18 and form integrally therewith or suitably attached thereto. A radial clearance 22 exists between the contro profile 20 and the internal surface of central bore 3 of the control spool 4. The clearance 22 allows continual secondary flow of fluid from the pressure port 10 through - the inlet orifice 5 to control chambers 12 and 14 respect and finally through each outlet control orifice 6,8 to th tank ports 16. ' OMP - 5 - The sizes and numbers of orifices 5, 6 and 8, the amount of radial clearance 22, and,the shape of prof 20, are chosen so as to maintain suitable fluid pressure in control chambers 12 and 14 and such pressures are designated P, and P_ respectively as shown in FIG. 3. Pressure P, acts at all times on face 24 of the control spool 4 and pressure P acts at all times on face 26 of the spool 4. hen the control spool 4 is at rest within body 2, the pressures P, and P~ and any flow forces are equilibrium. When the equilibrium is upset by changes i pressures P, and P~ or -flow forces, the control spool 4 will move to restore the equilibrium. The resistance to secondary fluid flow due to the shape of the control profile 20 and the shape and position of the orifices 5, 6 and 8 causes the valve to act as .a hydraulic Wheatston bridge tending always towards equilibrium. Control input to the control rod 18 is provid by a suitable externally mounted transducer 34, which ma take any of various known formssuch as manual, mechanica electromechanical, electrohydraulic, electronic, fluidic or a combination thereof. In use the device operates as follows. High pressure fluid is supplied to pressure port 10 and flows through the inlet control orifice 5 to the control chamb 12 and 14 on respective sides of the control profile 20. The fluid then flows through the outlet control orifices 6 and 8 to the tank ports 16. Due to the small size of the orifices 5, 6 and 8, in comparison with the main passages of the control valve, the fluid flow rates thro the control chambers 12 and 14 are only a fraction of- th fluid flow rates through the control valve main ports 35, 37, 10 and 16. Referring to FIG. 4, when the control profile 20 is held in position symmetrically opposite to orifice 5, the resistance to flow into chamber 12 is equal to th _ .. OM resistance to flow into chamber 14. Thus, the pressures P.. and P are equal and the control spool 4 will be at rest. In practice, the actual rest position of the control spool 4 will be dependent on manuf cturing tolerances and forces due to fluid flow through the con¬ trol valve, that is flow forces. Thus the position of th control profile 20 will be such that forces f, and f due to pressures P-, and P_ and flow forces acting on control spool 4 will be in equilibrium. The pressure area of the control rod 18 is equal to the difference between the cross-sectional area of the control profile 20 and the cross-sectional area of the control rod 18 and if the pressure area on each side of the control profile 20 is equal the force f is-zero. Referring now to FIG. 5, the control profile 2 is shown displaced in relation to the orifice 5. The resistance to flow into chamber 12 is larger than the resistance to flow into chamber 14 and thus pressure P, in control chamber 12 is less than pressure P„ in control chamber 14. The force 2 acting on the control spool 4 due to pressure P_ is thus larger than force f, due to pressure P, and the control spool 4 will therefore move to a position whereby the orifice 5 is centrally located relative to the control profile 20. In other words, the control spool 4 will move to re-establish equilibrium of forces f, and f- and equilibrium of the flow forces. The speed of response of the control spool 4 to the positional change of control rod 18 and thus the position of control profile 20, is a function of the sizes of the r arious orifices and the shape of the control ' profile 20. It should be evident from the description here¬ inabove that the fluid control device according to the present invention provides an improved arrangement which allows the operation of large flow capacity valves which require considerable force to shift the controlled member (control spool) . The device according to this invention is convenient to manufacture because fihere are no critic tolerances as between the control profile 20 and the inn surface of the bore through the control spool 4. Moveme of the control rod 18 does not require a significant for in relation to the forces required to move the control spool 4 and thus the rod may be moved by any convenient transducer means 34 adapted to provide the necessary control to operate the spool 4 in the manner required. In other words, the valve has a high gain force feedback The control spool 4 has various land.s which are arranged in relation to the inlet and outlet ports to provide whatever necessary control is required at some remote machine location. The invention thus provides a low cos and simple two stage operation of valves and position control devices and eliminates the conventional pilot spool controls with their inherent disadvantages. It should be noted that the control valve described provides a- 1:1 ratio position feedback and can be readily adapted to provide on-off control, proportional control and/or servo control as required. The valve described may be conveniently adapted for continuous control in an automat manner such that continuous control of proportion control valves, servo valves and position control devices is readily attainable. Clearly various modifications may be readily provided without departing from the spirit or .scope of the invention. The orifices 5, 6 and 8 may in fact compr a series of radially disposed orifices in order to achiev a particular fluid flow. Conveniently, the control rod 18 may be cut short at one end so as not to extend throug the end plate 30. The broken line 38 in FIG. 4 shows a convenient place for ending the rod 18 and the resulting force in chamber 14 acting on the end of rod 18 will prov a force sufficient to return the rod 18 to a particular start position which may be to the extreme left-hand side - 8 - - .- ' as shown in FIG. 4. This avoids the use of a spring ret in situations where the valve is required to have some b back to a neutral or start position. similar result can be achieved by using a rod which has different diame on opposite sides of the control profile 20 such that th pressure area on opposite sides of the control profile 20 is unequal and a net force results. In a further modification outlet control orifi 6 and 8 are arranged in the valve body 2 rather than in wall of the spool 4 and thus connect the chambers 12 and 14 directly with the low pressure side of the hydraulic supply. With this modification the control orifices 6 an 8 may be made adjustable " in size externally of the body part whereby the characteristics of the control valve, s as a response time for example, may be readily adjusted. According to a still further modification the control spool 4 is directly connected to operate external machinery. In other -words, instead of the control valve being used to operate equipment such as a hydraulic ram, for example, which in turn actuates some mechanical move- ment, the control valve may, in some circumstances, be us to directly actuate the mechanical movement. It should also be noted that the control profi 20 which is shown in the described embodiment as being symmetrical in the longitudinal direction about a central transverse plane may, according to a modification, be asymmetrical in order to provide different characteristic for the opposite directions of movement of the control spool 4. The different characteristics may relate to response time or force, for example. OM

Claims: CLAIMS : 1. A fluid control device of the sliding spool ty wherein a spool having various lands is adapted to slide within the bore of a body part to facilitate primary flu flow between various main ports in said body part depend upon the position of said spool, said spool having a longitudinal bore extending therethrough and means withi said spool bore to facilitate fluid controlled movement of said spool, characterized in that, said means compris a control profile having radial clearance in said spool bore and separating respective control -chambers, each control chamber includes part of the bore of said body p whereby pressurized fluid in said control chambers exert a force on respective ends of said spool, a first orific arrangement is provided in said spool to facilitate seco ary fluid flow from a pressure port of said main ports, through the wall of said spool and onto said control pro whereby said secondary flow is directed into respective said control chambers and, via further respective orifice arrangements, back to the low pressure side of a fluid supply such that said device is caused to act as a Wheats bridge tending towards equilibrium whereby said spool follows movement of said control profile along said spool bore in a force feedback gain manner due to imbalance of pressures in respective said control chambers. 2. A fluid control device as defi in claim 1, characterized in that said control profil __s arranged on a control rod which extends to the outside of said body part for controlled movement from a transducer. 3. A fluid control device as defined in- claim 2, characterized in that said control rod extends through opposite end plates of said body part and said control profile is arranged between the ends thereof. - 1.0 - - .- 4. A fluid control device as defined in claim 2, characterized in that, said control roj3 extends through a end plate of said body part and through one said control chamber and said control profile is arranged towards a free end of said rod, which free end is located in the ot said control chamber whereby fluid pressure on said free end is adapted to provide a restoring force to restore sa control profile to a start or neutral position. 5.. A fluid control device as defined in claim 2, characterized in that, said control rod extends through opposite end plates of said body part and said control profile is arranged between the ends thereof, the diamete of said rod on one side of said control profile being larger than the diameter of said rod on the other side of said control profile. 6. A fluid control device as defined in claim 1, characterized in that, said further orifice arrangements are provided in said spool on opposite sides of said firs orifice arrangement in the .axial direction of said spool, to facilitate said secondary flow from said respective control chambers, through the wall of said spool to respective tank ports of said main ports and thereby back to said low pressure side of said fluid supply. 7. A fluid control device as defined in claim 1, characterized in that said f rther orifice arrangements are provided in said body part at opposite ends of said spool to facilitate said secondary flow from said respect control chambers, through the wall of said body part and back to said low pressure side of said fluid supply. 8. A fluid control device as defined in claim 7, characterized in that each said further orifice arrangeme is adjustable to allow variation of the flow rate of said ( OMPI secondary fluid flow whereby the operating characteristi of said spool may be varied to suit different applicatio of said device. 9. A fluid control device as defined in claim 1, characterized in that, said control profile is symmetric in the axial direction of said spool, whereby operating characteristics of said spool are the same in both direc tions of movement. 10. A fluid control device as .defined in claim 1, characterized in that, said control profile is asymmetri in the axial direction of said spool, whereby operating characteristics of said spool are different for opposite directions of movement. 11. A fluid control device as defined in claim 1, characterized in that, said spool is adapted for connect through an end plate of said body part, to actuate appar by virtue of the sliding movement of said spool. OMP

Inventors: JOHNSON GARRICK ROSS, STECKI JACEK STANISLAV, JOHNSON, GARRICK, ROSS, STECKI, JACEK, STANISLAV
Applicants: JOHNSON GARRICK ROSS, SCALZO JOSEPH, STECKI JACEK STANISLAV, JOHNSON, GARRICK, ROSS, SCALZO, JOSEPH, STECKI, JACEK, STANISLAV
Application year: 1983
Main classification: F16K11
IPC codes: F15B13, F16K11, F16K27