US 3602102 A
Description (OCR text may contain errors)
United States Patent Inventor Thomas S. Fenari Baltimore. Md. Appl. No. 21.011 Filed Mar. 19, 1970 Patented Aug. 31,1971 Assignee Westinghouse Electric Corporation Pittsburgh, Pa.
FLUID PRESSURE ACTUATOR APPARATUS 4 Claims, 4 Drawing Figs.
RETURN SUMP FLUID l2 PRESSURE SUPPLY SOURCE FLOW CONTROL SERVO VALVE 2,893,356 7/1959 Murray r 91/438 X 2,995,014 8/1961 Horky et a1.... 91/438 X 3,011,482 12/1961 Elmeretal. 91/438X 3,398,649 8/1968 McMillen 91/438 X Primary Examiner Martin P. Schwadron Assistant Examiner-lrwin C. Cohen Atlorneys- F. H. Henson, E. P. Klipfel and D. F. Straitiff ABSTRACT: An improved fluid-pressure actuator apparatus of the type comprising a fluid-pressure supply source, a fluidpressure-operated actuator, a pivotal work member driven angularly by such actuator, a flow control servo valve device between source and actuator, andoverload-preventing means having a relief valve means for bleeding off actuator pressure above a certain release value. The improvement resides in the use ofa relief-valve means having a release pressure that is significantly below the source pressure, and in the inclusion ofa relief-valve interlock means to render the relief-valve means nonresponsive during flow of fluid under pressure to the actuator.
PRIOR ART DEVICE fit.
luv: 8 mu 1b PATENTED AUG31 I971 3,602,102
SHEET 1 OF 2 RETURN SUMP FLUID l2 PRESSURE SUPPLY SOURCE FIG. fl PRIOR ART FLOWVCONTROL ,u
SERVO VALVE DEVICE RETURN SUMP .4-
FLUID l2 PRESSURE SUPPLY SOURCE FLOW CONTROL H SERVO VALVE DEVICE PAIENIEDIUG3I 19?: 3,602,102
SHEET 2 UF 2 TO FLOW CONTROL SERVO VALVE DEVICE II VIA A i LINE I3 TO AN END OFACTUATOR CYLINDER 9 VIA A LINE l9 FIG. 3
l TOA RELIEF VALVE I8 WITNESSES INVENTOR Thomas S. Fenori FLUID PRESSURE ACTUATOR APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention Fluid-pressure actuator systems which include an overload preventing actuator pressure relief-valve means.
2. Description of the Prior Art Where fluid-pressure actuators, hydraulic or pneumatic, linear or rotary, are employed to actuate devices, linkages, etc., such as manipulator arms on undersea vehicles, digging arms on construction equipment, etc., which may experience externally applied loads in excess of normal workloads, such asmay be caused by obstruction, striking forces, or arrestedmovement inertia forces, a relief-valve means is often em-- ployed to release actuator pressures above a selected value in behalf of preventing overloading of such equipment beyond its strength capabilities. Since the usual actuator and driven member system has a transmission efficiency less than 100 percent, a given externally applied force at the end of the arm delivered to the actuator reversely corresponds to a higher actuator pressure than that required to create such force by the actuator. Accordingly, it has been the practice to employ a re lief valve having a pressure-release threshold value above that of the supply source pressure, in behalf making available the maximum performance potential represented by such supply source pressure; This necessitates, however, use of actuator and driven members which are strong enough to withstand the high level stresses imposed by the external load forces that must be tolerated as a result of the relatively high-pressure release value. Under such circumstances, the actuator and driven members must be capable of withstanding external load-force stresses that are significantly greater than the maximum driving-force stresses created by the actuator mechanism. Where minimal weight of the apparatus is desira ble, such excessive external load-resisting requirements introduces an undesirable weight factor as a result of the increased size necessitated by the increased strength.
The present invention, in providing a relief valve having its release value set well below the supply source pressure, preferably at a value that creates no more back stress on the actuator and driven members than that created by its driving force at maximum supply pressure, enables the strength and weight of the actuator mechanism and of work members driven thereby to be determined solely by the driving requirements, since its backloading strength need not exceed such driving-load strength. At the same time, by the inclusion of an interlock or disabling means which prevents operation of the relief-valve means during operation of the actuator mechanism, such actuator mechanism is capable of accepting even the full supply source pressure to enjoy the potential benefits of reduction in size requirement at the higher operating pressures for a given output force.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic representation of a typical prior art fluid-pressure actuator apparatus as employing relief-valve means responsive to actuator pressure to prevent overload of the apparatus during backloading;
FIG. 2 is a schematic representation of a similar type of fluid-pressure actuator apparatus embodying the improvement of the present invention;
FIG. 3 is a cross-sectional view of an exemplified form of an interlock means embodied in the improvement included in the F10. 2 apparatus; and
FIG. 4 is another exemplification of a fluid-pressure actuator apparatus embodying the improvement of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 there is exemplified a typical prior art fluid-pressure actuator apparatus comprising a member 5 such an arm or arm part adapted to be turned by such a pinion 6 driven by a rack 7 to turn about the axis of a drive shaft 8 to perform an arcuate movement of the projecting arm end and/or deliver a tangential force, indicated by arrows F, by such end; as in performing lifting and lowering operations, for example. The rack 7 is formed as part of a piston rod attached to a piston 8 disposed in a double-acting hollow fluid-pressure cylinder 9; the cylinder 9, piston 8, rack 7 and pinion 6 constituting a rotary actuator which may take other well-known forms such as a rotary-vane device, not shown. The rack 7 and pinion 6 is by way of exemplifying a rotary gear system which often includes other gear elements and which typically may possess a forcetransmissive efficiency in the neighborhood of percent for example. A dummy piston rod 10, the same size as that including the rack 7, may be employed to equate the cylinder volumes at opposite sides of the piston 8.
For controlling fluid-pressure operation of piston 8 in the double-acting cylinder 9 for actuation of and/or delivery of a linear force to the rack '7, hence exertion of an input torque on the pinion 6 and arm 5, the usual flow control servo valve ill is provided, which often is electrically controlled and torque motor operated in the case of hydraulic fluid, and which operates in well-known manner to effect such piston operation by opening and closing opposite ends of the cylinder 9 selectively via fluid-pressure servo valve output lines 13 to supply and return sump lines 12 and 14, to permit supply of fluid under pressure to one end and release from the other end. The fluid-pressure supply source 12, in accord with common practice is automatically maintained within small tolerance limits at a nominal supply pressure. In the case of undersea manipulator arm apparatus, for example, using hydraulic fluid, such supply pressure often is in the realm of thousands of p.s.i., in behalf of taking advantage of the smaller actuator piston sizes made possible at the higher pressures; a significant weight and size-reducing factor when considering that each such manipulator arm comprises a number of articulated sections at each joint of which is carried a respective rotary actuator.
In view of the foregoing remarks, it usually is desired to provide the maximum lifting force for the arm 5 that is potentially available by pressurization of the cylinder 9 via valve 11 to full supply source pressure, while at the same time preventing excessive loading of the arm such as can tend to be experienced as a result of shock-loading due to an object bumping the end of the arm, inertia-loading upon halts in arm motion at sudden servo valve [1 supply cutoffs, etc. In such cases it has been the practice to provide respective pressure-relief valves 15 in the from of spring-loaded check valves that are constantly connected between the servo valve output lines 13, thereby between opposite ends of cylinder 9 to permit actuator pressure in excess of full supply source pressure to bleed off from one side of the piston 8 to the other. However, due to the fact that the arm 5 and rotary actuator assemblage including piston b, rack 7, and pinion 6, as exemplified, has a transmission efficiency less than percent, the piston thrust required to develop the aforesaid maximum lifting force is significantly less than the potential piston thrust developed by the same force working backward. For example, in terms of a transmission efficiency (e), a lift force F on the end of the arm 5, a piston thrust forwardly FT and a piston thrust backwardly PT,,, the backward-to-forward piston thrusts at a given force F bear the relationship of PTB=PTF e Assuming an efficiency e of 70 percent for example, the reverse piston thrust for a given lift force will be merely 49 percent of the forward piston thrust required to create such lift force. Accordingly, the reverse piston thrust acting on hydraulic fluid behind the piston 8 will not create sufficient pressure in the cylinder 9 to open relief valves 15 until such back load force on the arm 5 is nearly double the maximum forward lift force. This then requires the actuator and arm assemblage to be designed for the increased strength required to tolerate such overload condition; thus contributing undesirably to increased weight of such assemblage, which inturn creates a need for a larger sized actuator, which in turn, tends to increase the arm strength required to support the larger actuator, etc., with the result that the arm tends to become much heavier and bulkier than is required merely to develop the desired maximum lift force.
Referring to FIG. 2, the improvement of the present invention is shown schematically as embodied in a hydraulic actuator apparatus of the prior art type exemplified in FIG. 1; identical components in the two showings bearing the same reference numerals. In accord with the present invention, communication between the servo valve device 11 and opposite ends of the double-acting cylinder 9 occurs by way of respective interlock devices 17 each of which operates:
to permit fluid pressure communication between a respective flow-control servo valve output line 13 and a respective end of the actuator cylinder 9 via a respective fluid-pressure line 19 while such line is connected via the servo valve device 1 1 to either the supply line 12 or the release line 14;
to isolate its respective line 19, hence the corresponding end of the actuator cylinder 9, from a respective spring-loaded pressure-relief valve 18 during flow of fluid under pressure to the actuator cylinder 9; and
to interconnect the lines 19 via a respective relief valve 18 upon cessation of such flow.
In accord with the present invention, the relief valves 18 have pressure-release valves below the supply source pressure, preferably at a value such that a backload F on the member or arm 5, while the flow control servo valve device 11 is closed, will be substantially no greater than the forward force F created by piston 9 during flow of fluid under pressure from such servo valve device to the cylinder 9 at one side or the other of such piston. Where, for example, if supply source pressure were 3,000 p.s.i. and the transmission efficiency, 2, of the arm and rotary actuator assemblage 6, 7 and 8, were 71 percent then the desired pressure-release setting for the reliefvalve manes 18 preferably would be no greater than the product of e times the supply pressure, or about one-half of supply pressure, which would be 1,500 p.s.i., in accord with the chosen example.
Referring to H0. 3, an exemplified construction of each of the interlock devices comprises a multipart hollow casing means 23 having a port 20 for connection to a respective line 13 extending to and from the flow-control servo valve device 11, a port 22 for connection to a respective line 19 extending to and from a respective end of the actuator cylinder 9, and a port 24 for connection to a respective relief valve 18 in a respective line 21 leading to a branch of the opposite line 19. A bore 25 extends between the ports 20 and 24, and the port 22 opens radially inward through the wall of such bore 25 near the port 24 end thereof. An isolation valve 27 in the form of a ball is disposed within bore 25 near the port 24 for seating cooperation with an annular tapered seat 28 encircling the port 24, to effect the desired isolation of the respective relief valve 18 from the respective end of the actuator cylinder 9 via the ports 22 and 24. To effect the desired operation of isolation valve 27 when fluid under pressure from the servo valve device 11 is flowing from port 20 to the actuator cylinder 9 via port 22, device 17 includes a piston assemblage 29 which is in slidable sealing cooperation with the wall of the bore 25 and is urged by a helical compression spring 30 acting on its one end toward a repose position in the direction of the port 20, in which position it is shown in the drawing. Piston assemblage 29 includes a hollow elongated piston member 31 which is closed at its end nearest to port 20 by a poppet valve 32 when the assemblage is in such repose position. A helical compression spring 34, caged within piston member 31, lightly biases valve 32 toward seating engagement around an adjacent end of a cylindrical opening 36 extending axially through the center of such piston member. The assemblage also includes a fluted stem 38 which is attached to the valve 32 and extends slidably through the opening 36 into the interior of the bore at the port 24 end in operative attachment with and support of the isolation valve 27; there being a self-aligning connecting means 40 adjoining valve 27 to the end of stem 38.
In operation of piston assemblage 29, as fluid under pressure is supplied from servo valve device 11 to one side of the actuator cylinder 9, it first appears at port 20 of the respective interlock device 17 and acts on such piston assemblage to cause same to move, against the bias of spring 30, and first seat the isolation valve 27 in closure of port 24 leading to the respective relief valve 18, whereafter, the piston member 1 continues to move while the poppet valve 32 becomes arrested by the seated isolation valve 27 at one end of the fluted stem 38, and such valve 32 is thereby opened to permit flow of such fluid under pressure to reach the cylinder device 9 via the interior of such piston member, the interior of bore 36, the port 22, and the respective line 19 connected thereto, while the seated isolation valve 27 prevents access of such fluid flow to the actuator from reaching the respective relief valve 18. Thus, in accord with the present invention, the respective end of the actuator cylinder 9 may become pressurized up to full supply source pressure while being isolated from its respective relief valve 18 which has a release pressure lower than such supply source pressure.
In behalf of rendering the respective relief valve 18 effective to relieve an actuator backload condition as previously discussed herein, as soon as flow to the respective end of the cylinder 9 via the device 17 as described above ceases, as brought about by closure of the servo valve device 11, the spring 30 returns the piston member 31 to its repose position, after first reseating the poppet valve 32 and thereafter unseating the isolation valve 27 to establish the required communication between the respective end of the cylinder 9 and the respective relief valve 18 via the port 22, the interior of bore 25, and the now open port 24. A small bleed port 42, assures sufficient bypass of fluid through the piston assemblage 29 sufflcient to assure its return to the repose position in which it is shown in FIG. 3. 1
At any time that the servo valve device 11 calls for release of fluid from a respective end of the cylinder 9, which occurs correspondingly with supply to the other cylinder end, such releasing fluid will enter port 22 of the respective device 17, pass through the bore 25 and into the opening 36 of piston member 31, as permitted by the fluted stem 38, and cause the valve 32 to unseat against the light bias of spring 34, and leave via the port 20 en route to such servo valve device.
Apparatus embodying the principles of the present invention has been employed successfully in a hydraulically operated undersea manipulator-arm system.
The construction of the relief valve devices 18 per se may take the usual form as including a poppet-type valve unseatable by fluid pressure against the bias of a force-adjustable helical compression spring.
Referring to FIG. 4, where a double-acting cylinder 9 not having a dummy piston rod 10, as in FIGS. 1 and 2, is employed in a hydraulic actuator system, the displacement and effective piston areas at opposite sides of the piston 8 will be different to the extent of the volume and projected area occupied by the piston rod 7 on the one side. The different effective piston areas can be compensated for as to desired reliefpressure differences by suitable adjustment of the spring force in the relief valve 18. To compensate for the different displacement volumes, the excess amount of release fluid from the larger-sized side b, releasing from corresponding relief valve 18b, that can't be accommodated by the smaller-sized side a, is accommodated by spillover via a check valve 44 to a branch of return sump line 14. In the reverse situation, the deficient amount of fluid releasing via relief valve from the smaller-sized side a to side b, can be furnished from the sump line 14 via a check valve 47.
Where the apparatus may involve only a single-acting actuator device, having a spring-returned piston, for example, it will be appreciated that only one relief-valve means 18 and interlock device 17 will be required, and the servo valve device 11 will be single acting rather than double as in the case of the apparatus of FIGS. 1, 2 and 4.
Where the apparatus may be pneumatically actuated, the compliance of the compressed air in such systems may afford a degree of yieldability that tends to afford the backload-relief protection sought after under the present invention, however, it appears reasonable that the improvement of the present invention will function as set forth in the foregoing description either with pneumatic or hydraulic fluid under pressure, even though only the latter has been proven by actual use. In the case of pneumatic apparatus, the relief valves 13 may vent directly to the atmosphere where the compressed air supply source is open-ended, and the servo valve device 11 also vents to the atmosphere during release from the actuator cylinder.
Still further, in accord with the improvement of the present invention, where the forward or driving efficiency of the actuator and driven member system, which may be expressed as ef, is significantly different than the backload or driven efficiency of such system, eb, the preferred release pressure value, rpfor the release valve means 18 would be that which can be expressed as the product of supply source pressure, ps, and the two efficiencies, or r,,=p,(e,) e
1. An improved fluid-pressure actuator apparatus comprising:
a source of fluid at supply pressure,
an assemblage including fluid-pressure actuator means and pivotal work member means actuable angularly,
said assemblage having a transmission efficiency in driven and backload states,
an on-off-type valve means for controlling supply and release of fluid under pressure to and from said actuator means, and
overload-preventing means including a relief-valve means for bleeding off actuator pressure above a certain releasepressure value;
wherein the improvement resides,
in said relief-valve means having a release-pressure value below said supply-pressure value, and
in the inclusion of an interlock means operative to render said relief-valve means ineffective and effective responsively to flow and cessation of flow, respectively, to said actuator means.
2. The improved actuator apparatus of claim 1, wherein:
the release-pressure value for said relief-valve means is substantially no greater than the product of the supply pressure and the square of the transmission efficiency.
3. The improved actuator apparatus of claim ll, wherein:
said actuator means is double-acting, and
said relief-valve means functions to bleed off fluid from one pressure side to the other in said actuator means.
4. The improved actuator apparatus of claim 1, wherein:
said interlock means comprises,
casing means having inlet-port means open to said on-offtype valve means, an outlet-port means open to said rotary actuator means, and a relief-port means open to said relief valve means,
an isolation-valve means actuable to seated and unseated positions to open and close said relief-port means to said outlet-port means,
a piston means having a central opening extending axially therethrough,
a spring-biased check valve means normally closing an inletport-adjacent end of said central opening and having a fluted stem extending therethrough in interconnection with said isolation-valve means at its projecting end,
a return-spring means urging said piston means toward a repose position in the direction. of said inlet-port means, and
bleed-port means establishing restricted communication between said inlet-port means and said outlet-port means while said check valve means is closed;
the aforesaid being so constructed and arranged that:
flow of fluid under pressure supplied to said inlet-port means en route to said outlet-port means first moves said piston means, check valve means and isolationwalve means in unison until the latter becomes seated, thereafter continuation of such flow effects continued movement of said piston means relative to said check valve means and isolation-valve means, thereby, permitting such flow to continue to said outlet-port means via the unseated check valve means and the interior of said piston means;
upon cessation of such flow, said returnspring means will move said piston means toward its repose position, first reseating said check valve means and unseating said isolation-valve means, and
in such repose position, release of fluid under pressure from said outlet-port means can transpire to said relief-port means and/or to said inlet port via said check valve means according to relative pressure and flow conditions established therein.