US3667223A

US3667223A - Hydraulic system having means for isolating leaking branch circuits

Info

Publication number: US3667223A
Application number: US115256A
Authority: US
Inventors: Charles T Thurston
Original assignee: McDonnell Douglas Corp
Current assignee: McDonnell Douglas Corp
Priority date: 1971-02-16
Filing date: 1971-02-16
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06

Abstract

A hydraulic system has a reservoir which contains a hydraulic fluid and includes a piston which bears against that fluid. The system also has a pump which derives fluid from the reservoir and supplies high pressure fluid to a plurality of branch circuits, each having a hydraulic motor or some other hydraulically powered device or load. The branch circuits are connected to the reservoir so that fluid after passing through the hydraulic motors is returned to the reservoir at low pressure. An isolating apparatus is interposed between the pump and branch circuits and includes a main valve for isolating each branch circuit. Each main valve is normally open, and is controlled by a pilot valve which is in turn operated by a cam follower disposed in the path of a cam which is carried by and responsive to the position and movement of the reservoir piston. Should one of the branch circuits develop a leak, the volume of the fluid in the reservoir will decrease, causing the piston to move through the reservoir and carry its cam with it. The cam, by operating the pilot valves associated with the main valves, shuts off and opens the main valves sequentially until the main valve associated with the leaking branch is closed, at which time loss of reservoir fluid terminates and further movement of the piston is merely a function of normal system operating conditions and not leakage. Once operated by the cam the pilot valve for the leaking branch circuit is pressure loaded or mechanically held in a position to isolate the branch from the remainder of the system in which case the pilot valve is independent of cam position.

Description

Thurston 1 June 6, 1972 HYDRAULIC SYSTEM HAVING IVIEANS FOR ISOLATING LEAKING BRANCH CIRCUITS [72] Inventor: Charles T. Thurston, St. Charles, Mo.

[73] Assignee: McDonnell Douglas Corporation, St.

Louis, Mo.

[22] Filed: Feb. 16, 1971 21 Appl. No.: 115,256

[52] U.S.Cl ..60/5l,60/52 HC,9l/412, 137/411, 244/85 [51] Int. Cl ..FlSb H00 [58] Field of Search ..60/52 HC, 51; 137/411, 395, 137/386; 244/85 [56] References Cited UNITED STATES PATENTS 2,396,984 3/1946 Broadston et al. ..60/52 HC 2,428,150 9/1947 Field ..60/52 l-lC UX 2,574,416 11/1951 Rose ..60/52 HC X 2,625,169 1/1953 Parrish ..137/411 X Primary Examiner-Edgar W. Geoghegan Atl0rneyGravely, Lieder & Woodruff [57] ABSTRACT A hydraulic system has a reservoir which contains a hydraulic fluid and includes a piston which bears against that fluid. The system also has a pump which derives fluid from the reservoir and supplies high pressure fluid to a plurality of branch circuits, each having a hydraulic motor or some other hydraulically powered device or load. The branch circuits are connected to the reservoir so that fluid after passing through the hydraulic motors is returned to the reservoir at low pressure. An isolating apparatus is interposed between the pump and branch circuits and includes a main valve for isolating each branch circuit. Each main valve is normally open, and is controlled by a pilot valve which is in turn operated by a cam follower disposed in the path of a cam which is carried by and responsive to the position and movement of the reservoir piston. Should one of the branch circuits develop a leak, the volume of the fluid in the reservoir will decrease, causing the piston to move through the reservoir and carry its cam with it. The cam, by operating the pilot valves associated with the main valves, shuts off and opens the main valves sequentially until the main valve associated with the leaking branch is closed, at which time loss of reservoir fluid terminates and further movement of the piston is merely a function of normal system operating conditions and not leakage. Once operated by the cam the pilot valve for the leaking branch circuit is pressure loaded or mechanically held in a position to isolate the branch from the remainder of the system in which case the pilot valve is independent of cam position.

1 1 Claims, 6 Drawing Figures PATENTEDJUH 6 I972 SHEET k [If 4 HYDRAULIC SYSTEM HAVING MEANS FOR ISOLATING LEAKING BRANCH CIRCUITS BACKGROUND OF THE INVENTION The invention relates in general to hydraulic systems and, more particularly, to an apparatus for locating and isolating leaking circuits of hydraulic systems.

Many aircraft of current manufacture utilize hydraulic motors of one type or another to operate much of the power operated equipment on board. The use of these motors is not confined to accessories, but is extended to the critical control surfaces which control the flight of the aircraft. For example, the stabilator which imparts a pitching moment to the aircraft for the purpose of changing elevation is operated by a hydraulic motor. Likewise so are the ailerons which impart roll to the aircraft. Similarly, the spoilers which increase drag and reduce lift, are also operated by hydraulic motors. The hydraulic motors for operating the stabilators, ailerons and spoilers form part of a separate hydraulic system within the aircraft, and that system is often termed the power control system.

Like other hydraulic systems in the aircraft, the power control system includes a pump and reservoir, and is a closed loop system in which the return to the pump is pressurized above external conditions to prevent pump cavitation. Furthermore, the power control system is normally divided into branch cir cuits in which the stabilators may be on one branch, the right aileron and right spoiler on another, and the left aileron and left spoiler on still another. Should anyone of these branch circuits develop a leak, the hydraulic fluid within the reservoir will eventually be depleted and the entire system will fail, notwithstanding the fact that only one branch of the system contains a defect. When this occurs the pilot must resort to his backup or redundant system which most likely is not as sensitive or responsive as the power control system.

Other hydraulic systems on aircraft, such as the utility system which operates the landing gear, canopy, and the like, are affected in the same manner by leaks in their circuits as are hydraulic systems in general.

SUMMARY OF THE INVENTION One of the principle objects of the present invention is to provide a multibranch hydraulic system with isolating means for detecting a leak in any of the branches and for isolating that branch from the remaining branches so that the remaining branches will not be rendered inoperative due to complete loss of the system fluid. Another object is to provide isolating means of the type stated which operates mechanically and is highly reliable. A further object is to provide isolating means of the type stated which is not sensitive to and is unaffected by system dynamics, flow transients, pressure surges, thermal expansion and the like. An additional object is to provide isolating means of the type stated which is ideally suited for use in the power control and other hydraulic systems of aircraft. These and other objects and advantages will become apparent hereinafter.

The present invention is embodied in a hydraulic system having a reservoir, a pump, and a plurality of branch circuits. Between the discharge side of the pump and each branch circuit the system is provided with isolating means which is responsive to the volume of the fluid in the reservoir and isolates the individual branch circuits as the fluid volume decreases. The invention also resides in the isolating means. The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form part of the specification and wherein like numerals refer to like parts wherever they occur:

FIG. 1 is a schematic view of a hydraulic system constructed in accordance with and embodying the present invention;

FIG. 2 is an elevational view, partially broken away and in section, showing a reservoir and an isolating apparatus forming part of the present invention;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2;

FIGS. 4 and 5 are sectional views taken along lines 4-4 and 5-5, respectively, of FIG. 3; and

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 2.

DETAILED

DESCRIPTION branch circuits

8, 10 or 12 and for isolating the branch circuit in which the leak exists. The pump 6 is connected to the reservoir 4 through a suction line 18 and discharges high pressure fluid into a high pressure supply line 20 which empties into the isolating apparatus 16 and further supplies fluid to the reservoir 4 for so-called bootstrap pressurization. The isolating apparatus 16, in turn distributes the high pressure fluid to the branch circuits 8, l0 and 12, each of which includes a distributor line 22 leading to its hydraulic motor 14. Each

branch cir cuit

8, 10 and 12 further includes a check valve 24 through which the hydraulic fluid from its motor 14 passes before entering a common return line 26 which is also connected to the isolating apparatus 16 and empties into the reservoir 4, thus completing the circulation of the'hydraulic fluid. The supply line 20 and return line 26 are connected through a relief valve The reservoir 4 includes (FIG. 2) acylindrical housing 30 containing an annular type of piston 32 which upon movement wipes the inwardly presented cylindrical wall of the reservoir housing 30. The front or lower face of the piston 32, that is the face presented toward the ports of the suction and

return lines

18 and 26, bears against the fluid in the reservoir 4, whereas the back face of the piston 32 is for the most part exposed to ambient pressure conditions existing externally of the system 2. Projecting axially from the back face of the piston 32 is a hollow piston rod 34, the cylindrical inside face of which is wiped by a fixed piston 36 mounted on a fluid supply tube 38 which extends axially through the center of the housing 30. The supply tube 38 projects through the main body of the piston 32 so that the outside face is wiped by the piston 32. At its opposite end the supply tube 38 is secured to the housing 30 where it is connected with the high pressure supply line 20. Near the fixed piston 36 the interior of the supply tube 38 communicates with the interior of the hollow piston rod 34 through a radial port 40, and this port is located intermediate the movable piston 32 and the fixed piston 36. Thus, the interior of that much of the piston rod 34 located between the

pistons

32 and 36 is at the pressure of the high pressure supply line 20, and the high pressure exerts force on a limited area along the backside of the movable piston 32, that area being annular and located between the piston rod 34 and the supply tube 38. Accordingly, the high pressure fluid in the piston rod 34 forces the piston 32 downwardly in the housing 30 against the main body of fluid therein, and this pressurizes the fluid within the housing 30, although not to nearly the pressure of the fluid leaving the discharge port of pump 6. Since the fluid within the housing 30 is pressurized, so is the fluid within the return line 26 and suction line 18, and this prevents the pump 6 from cavitating.

The disposition of the piston rod 34 in the housing 30 is dependent on the amount of fluid in the housing 30, and should the quantity of fluid decrease, the piston 32 will move or drop closer to the base of the housing 30, carrying the piston rod 34 with it. Thus, when a leak develops in the system 2, the volume of fluid in the reservoir housing 30 will decrease and the piston rod 34 will retract into the housing 30. At its outwardly presented end the piston rod 34 is encircled by a flange-like camming surface 42 which projects radially outwardly from the outer surface of the rod 34 and is in effect composed of two beveled surfaces.

The isolating apparatus 16 includes (FIGS. 3-5) a valve block 44 which is formed integral with or bolted to the reservoir housing 30 adjacent to the outwardly projecting portion of the piston rod 34. The valve block 44 contains three

main valves

46, 48 and 50 (FIG. 1) which control the flow of high pressure fluid to the branch circuits 8, and 12, respectively. Each

main valve

46, 48 and 50 (FIGS. 3 and 4) is housed within a valve bore 52 formed in the valve block 44, and each valve bore 52 near its inner end is surrounded by an annular relief 56 which opens into a single supply channel 58 (FIG. 4) leading from an inlet port 60. Thus, the supply channel 58 is common to the annular reliefs 56 of all the

valves

46, 48 and 50. The high pressure supply line 20 connects with the inlet port 60 so that the annular relief 56 of each

valve

46, 48 and 50 is supplied with high pressure hydraulic fluid. Axially beyond its annular relief 56 each valve bore 52 is encircled by another annular relief 62, and the reliefs 62 of the individual valve bores 52,'in contrast to the reliefs 56, are separated from each other and open into individual distributor channels 64 (FIG. 3). In other words, the valve block 50 contains three individual and separate annular reliefs 62, and likewise three individual and separate distributor channels 64. The distributor channels 64 terminate at distributor ports 66, and each port 66 is connected to the distributor line 22 of a different branch circuit 8, l0 and 12. Finally, near their outer ends the valve bores 52 are encircled by still more annular reliefs 68, and each of these annular reliefs 68 opens into an override channel 70 (FIG. 4) which is common to all of the reliefs 68. Thus, each valve bore 52is surrounded by three

annular reliefs

56, 62 and 68 arranged in that order from the inner end of the valve bore 52.

The

main valves

46, 48 and 50 are identical in construction and operation, and by reason of this fact only the valve 46 associated with the branch circuit 8 will be described in detail. That main valve 46 includes (FIGS. 3 and 4) a valve sleeve 78 and a valve spool 80 which is housed within the sleeve 78 and is free to shift axially to and fro therein. In one position the valve spool 80 blocks the interior of the valve sleeve 78 between the

annular reliefs

56 and 62, and hence the valve 46 is considered closed when the spool 80 is so disposed, while in the opposite position the valve spool 80 allows fluid to flow through the interior of the sleeve 78 from the annular relief 56 to the annular relief 62, and accordingly the valve 46 is considered open when spool 80 is disposed in that other position. More specifically, the valve sleeve 78 at its innennost end possesses an end cylinder 82 which at its one end opens into the end of the main valve bore 52 through an end cap 84. At its opposite end the end cylinder 82 opens into an enlarged valve chamber 86 which is disposed inwardly from and is encircled by the annular relief 56 and indeed opens into the annular relief 56 through radial ports 88 in the sleeve 78. The valve chamber 86 in turn opens into a reduced intermediate cylinder 90 at a shoulder-like valve seat 92. The intermediate cylinder 90 is disposed at the annular relief 62, and intermediate its' ends it empties into the annular relief 62 through radial ports 94 in the sleeve 78. Beyond the intermediate cylinder 90 the valve sleeve 78 is provided with another enlarged chamber 96 which is disposed at the annular relief 68 and communicates with the annular relief 68 through radial ports 98 in the sleeve 78. Finally, at its outer end the sleeve 78 is retained in position by an end cap 79 provided with a centrally disposed reduced bore 100 which extends from the end of the enlarged chamber 96 to the outer end face of the end cap 79.

The valve spool 80 includes (FIGS. 3 and 4) an operating piston 106 which is positioned in and engaged with the walls of the end cylinder 82, and extending from the piston 106 is a stem 108 which projects axially through enlarged valve chamber 86 into which the radial ports 88 open. The stem 108 in turn merges into a poppet 110 having a beveled face 112 which moves toward and away from the valve seat 92 when the spool shifts. When the beveled face 112 engages the seat 92 the spool 80 is in its closed position, and conversely when the beveled face 112 is away from the seat 92 the spool 80 is in its open position. At the reduced end of the beveled face 112 the poppet merges into another and longer stem 114 which extends through the intermediate cylinder 90 to beyond the radial ports 94 which empty into the annular relief 62 where it is joined with a return piston 116 which wipes the walls of the intermediate cylinder 90. The piston 116 is at its opposite end engaged by a return shaft 1 18 which extends axially through the enlarged end chamber 96 and is urged toward the valve seat 92 by a coil-type compression spring 120 which encircles it. The return shaft 118 merges into an indicator pin 122 which projects through the reduced bore 100 and aligns with an actuator 124 of a limit switch 126 mounted on the valve block 50 by means of a bracket 128. When the valve spool 80 is in its open position the end of the indicator pin 122 remains spaced from the switch actuator 124, but when the spool 80 shifts to its closed position the indicator pin 122 depresses the switch actuator 124, and this closes the circuit in which the switch 126 is located.

In addition to the three

main valves

46, 48 and 50, the valve block 44 further contains three

pilot valves

136, 138 and (FIGS. 3 and 5). The pilot valve 136 operates and is located directly beyond the end of the main valve 46, while the pilot valve 138 operates and is located directly beyond the main valve 48. Similarly, the pilot valve 140 is located directly beyond and operates the main valve 50. Each

pilot valve

136, 138 and 140 fits into a pilot valve bore 142 in the valve block 44 and the axes of these bores 142 extend radially with respect to the axis of the piston rod 34. Inasmuch as the

pilot valves

136, 138 and 140 are identical in construction and operation, only the pilot valve 136 will be described in detail.

The pilot valve 136 includes (FIGS. 3 and 5) a valve sleeve 144 which fits into the pilot valve bore 142 and is retained therein by an end cap 145. The valve sleeve 144 has an elongated spool cylinder 146 which at its rear end, that is the end furthest from the piston rod 34, opens into an enlarged end chamber 147. The spool cylinder 146 is surrounded by three

annular reliefs

148, 150 and 152 which exist in the valve block 44 or valve sleeve 144 or both. The annular relief 148 opens into the spool cylinder 146 through radial ports 154 and communicates with the inner end of the valve bore 52in which the main valve 46 is contained by means of a connecting channel 156 (FIG. 3). The next annular relief 150 opens into the midportion of the spool cylinder 146 through radial ports 158 and is further connected with the high pressure supply channel 58 through a supply duct 160 (FIG. 5). The annular relief 150 similarly opens into the spool cylinder 146 through apertures 162 and like the annular relief 148 is connected to the inner end of the valve bore 52 for the main valve 36, the connection being through an oblique connecting duct 164 (FIG. 3). On the other hand, the enlarged end chamber 147 near its juncture with the spool cylinder 146 is surrounded by an annular relief 166 formed in the valve block 44 and the end cap 145, and this relief 166 opens into the enlarged end chamber 147 through radial ports 168. The annular relief 168 further empties into a low pressure return connecting duct 170 (FIGS. 4 and 5) which in turn discharges into a lower pressure return channel 172 (FIG. 4) located in the valve block 44 adjacent to the high pressure supply channel 58. The return channel 172 terminates at a discharge port 174 in the block 44 and that port 174 is connected to the return line 26. i

The spool cylinder 146 and the enlarged end chamber 147 in the valve sleeve 144 of the pilot valve 136 contain a valve spool 176 (FIGS. 3 and 5) which shifts axially between an actuating position in which it allows high pressure fluid to flow through the cylinder 146 to the end of the main valve bore 52 of the main valve 46 so as to close the valve 46, to a non-actuating position in which it blocks flow from the spool cylinder 146 and does not allow further high pressure fluid to flow to the inner end of the main valve bore 52. In particular, the

valve spool 176 includes a pair of spaced

pistons

178 and 180 which wipe the walls of the spool cylinder 146 and are connected by a reduced connecting rod 182. The length of the rod 182 is such that it spaces the

pistons

178 and 180 apart a distance slightly greater than the spacing between the radial ports 154 and 158 opening into the

annular reliefs

148 and 150, respectively. When the pilot valve 136 is in its actuating position the radial ports 154 and 158 are located opposite the connecting rod 182, in which case the

pistons

178 and 180 will be disposed on opposite sides of the radial ports 154 and 158, respectively, thus allowing high pressure fluid to flow from the annular relief 150 through the spool cylinder 146 to the annular relief 148, and thence through the connecting duct 164 to the main valve bore 52 where it moves the main valve spool 80 therein to its closed position. The piston 178 merges into another rod 184 joined to a stop 186, and the stop 186 is in turn connected with an end rod 188 encircled by a coiled compression spring 190 which urges the pilot valve spool 176 to its non-actuating position. The end rod 188 projects through the end of the valve sleeve 144, and beyond the rear end face of the sleeve 144 it is fitted with a knob 192.

At the opposite or front end of the valve sleeve 144, the piston 180 (FIGS. 3 and 5) merges into a short stern 194 which in turn merges into an operating rod 196 the diameter of which is smaller than the piston 180. The operating rod 196 projects through the end of the sleeve 144 and likewise beyond the adjacent face of the valve block 44. Between the operating rod 196 and the sleeve 144 is a gap which when the pilot valve spool 176 is in its actuating position allows fluid to enter the spool cylinder 146, providing a force to hold the spool 176 in its actuated position.

Bolted against the front face of the valve block. 44, that is against the face presented toward the piston rod 34, is an actuating mechanism 200 (FIGS. 3, 5 and 6) for successively driving the spools 146 of the

pilot valves

136, 138 and 140 inwardly to their actuating positions as the camming surface 42 on the end of the piston rod 34 passesopposite to those

pilot valves

136, 138 and 140. The actuating mechanism 200 includes a base plate 202 having three plunger bores 204 (FIG. 5) which align with the front ends of the pilot valve bores 142. The plunger bores 204 receive cam plungers 206 having rearwardly opening sockets 208 into which the operating rods 196 of the valve spools 176 are fitted. The cam plungers 206 are attached to the operating rods 196 by set screws 210. At their forward or outwardly presented ends, the plungers 206 are fitted with cross pins 212 on which roller followers 214 are journaled. When any one of the pilot spools 176 is in its nonactuating position, the roller followers 214 associated with that spool 176 will lie in the path of the camming surface 42 on the piston rod 34 so that when the camming surface 42 engages the outwardly projecting roller follower 214, it will drive the plunger 206 associated with that follower 214 inwardly and move the valve spool 176 connected thereto to its actuating position.

The three valve plungers 206 are arranged in a row (FIGS. 5 and 6), and intermediate the plunger bores 204 into which the plungers 206 fit the base plate 202 has fulcrum elements 216 secured to it. Mounted on and pivoted aboutthe fulcrum elements 216 are connecting links 218 having bifurcated ends, the furcations 220 of which extend behind the cross pins 212 at the ends of the cam plungers 206. In this connection, it should be noted that each cross pin 212 projects beyond the sides of the cam plunger 206 which carries it so that when the furcations 220 swing forwardly with the pivoting of the link 218 on which they are carried, those furcations 220 will engage the cross pin 212 adjacent to them and drive the cam plunger 206 outwardly. Conversely, when the camming surface 42 on the piston rod 34 engages a roller follower 214 and drives it and its cam plunger 206 inwardly, the furcations 220 located adjacent to the ends of the cross pin 212 on that plunger 206 will be driven inwardly toward the valve block 44, in which case the furcations on the opposite end of the connecting link 218 will be driven outwardly. Thus, when one cam plunger 206 is driven inwardly to a depressed or actuating position, the adjacent cam plungers 206 will be forced outwardly to their withdrawn or non-actuating positions. Where two links 218 are operated by a single plunger 206, as is the case with the centermost plunger 206, that is the plunger 206 associated with the pilot valve 138, the furcations 220 on one of the links 218 are spaced apart a distance sufficient to accommodate the furcations 220 on the other link 218 (FIG. 6).

The valve block 44 further contains an override valve 230 (FIG. 4) for overriding all of the

pilot valves

136, 138 and 140 so as to maintain each

main valve

46, 48 and 50 in its open position, irrespective of the position of the reservoir piston rod 34. The override valve 230 includes a valve sleeve 232 which is fitted into an outwardly opening bore 234 in the valve block 44 and retained therein by an end cap 235. The sleeve 232 is surrounded by five

annular reliefs

236, 238, 240, 242 and 244. The center relief 2A0 opens into the override channel 70 leading to the annular reliefs 68 encircling the three

main valves

46, 48 and 50. The two

end reliefs

236 and 244 are also connected to the override channel 70 through ducts 246. The annular relief 242 is connected to the high pressure supply duct leading from the high pressure supply channel 58 and accordingly is always maintained at the high or supply pressure. The remaining annular relief 238, on the other hand, opens into and forms the upstream end of the low pressure return channel 172 which temiinates at the discharge port 174 where it empties into the return line 26. Thus, the relief 238 is maintained continually at the low or return pressure for the system 2.

The override valve sleeve 232 has a spool cylinder 248 and the

annular reliefs

238, 240, 242, 244 and 246 communicate with this cylinder 248 through radial ports 250 in the sleeve 232. Disposed within the cylinder 248 is a spool 252 having two

pistons

254 and 256 which are spaced apart by a connecting stern 258. The spool 252 moves axially between an override position in which it allows high pressure fluid from the annular relief 242 to pass through the spool cylinder 248 to the override channel 70 to a normal position in which the piston 256 blocks the apertures 250 leading from the annular relief 242 in which the high pressure fluid is contained. More specifically, when the spool 252 is in its normal position, the piston 256 thereon is disposed opposite and covers the apertures 250 leading from the annular relief 242, while the other piston 254 is positioned intermediate the apertures 250 leading to the endmost annular relief 236 and the annular 238 located adjacent thereto. In this position, the override channel 70 is vented to the return channel 172 and return line 26 through the spool cylinder 248.

The override spool 252 further has an operating rod 260 which extends completely through the end of the valve sleeve 232, beyond which it is connected to a solenoid 262 mounted on the valve block 44. When energized the solenoid 262 draws the spool 252 outwardly to its override position. Within spool cylinder 248 the operating rod 260 is encircled by a coil-type compression spring 264 which urges the override spool 252 to its normal position, that is the position in which the apertures 250 leading from the annular high pressure I relief 242 are blocked.

The solenoid 262 is wired to an electrical energy source through a switch 266. Each limit switch 126 is wired in series with warning lamps 268, and the limit switches 126 and lamps 268 are likewise placed across the electrical energy source.

OPERATION Normally, the cylindrical housing 30 of the reservoir 4 contains enough fluid to position the reservoir piston 32 such that the camming surface 42 at the end of its piston rod 34 is presented beyond roller follower 214 for the pilot valve 136, which is the pilot valve located furthest from the cylindrical housing 30. Thus, all of the

pilot valves

136, 138 and 140 remain in their nonactuating positions, or more specifically the spools 176 of those valves are urged to their nonactuating positions by the compression springs 190 therein. The

main valves

46, 48 and 50, on the other hand, will remain in their open positions, that is the compression springs 120 therein will urge and maintain the poppets 110 away from their corresponding seats 92. The

main valves

46, 48 and 50 are primarily held in their open positions by the differential force resulting from the high pressure fluid in the chamber 86 and low pressure fluid in the bore 52. The override valve 230, of course, remains in its normal position, that is the position in which the annular reliefs 68 at the enlarged chambers 96 of the

main valves

46, 48 and 50 are all vented to the return line When the pump 6 is energized, high pressure fluid is introduced into the supply line 20, thus causing the pressure in the supply line 20 and likewise the supply tube 38 of the reservoir 4 to rise. This in turn elevates the pressure within the hollow piston rod 34 (FIG. 2), creating a force on the backside of the piston 32. The force so induced pressurizes the main body of fluid within the cylindrical reservoir housing 30, although the pressure to which that fluid is elevated is considerably less than the pressure at the discharge side of the pump 6. Since the reservoir fluid is maintained at a pressure greater than the ambient pressure external to the system, so is the fluid in the suction line 18 and return line 26 as well in various cavities and passageways of the valve block 44 which are connected directly with the return line 26. In aircraft hydraulic systems the supply pressure is normally about 3,000 psi, while the return pressure is normally about 50 psi.

To operate any one of the hydraulic motors 14, a valve (not shown) at the end of the distributor line 22 (FIG. 1) leading to that motor 14 is opened, allowing fluid to flow to the motor 14. Assuming that the motor 14 in the branch circuit 8 is actuated, then fluid will flow from the high pressure supply line 20 into the valve block 44 through the inlet port 60 therein. Within the valve block 44 the fluid flows through the supply channel 58 (FIG. 4) to the annular relief 56 of the main valve 46. The fluid in the relief 56 in turn flows into the enlarged valve chamber 86 of the valve sleeve 78 through the radial port 88. Since the valve spool 80 of the main valve 46 is in its open position, the poppet 110 will be off or away from the valve seat 92 and high pressure fluid will flow through the intermediate cylinder 90 to the ports 94 which open into the annular relief 62. From the relief 62, the fluid flows through the distributor channel 64 (FIG/3) to the outlet port 66 and thence into the distributor line20 of the branch circuit 8. After passing through the motor 14 and energizing the same, the fluid flows through the check valve 24 and then into the return line 26 through which it is returned to the reservoir 4. The motors 14in the branch circuits and 12 operate in a similar manner, only the fluid passing through them comes from the

main valves

48 and 50, respectively.

Should a leak develop in the branch circuit 8, the hydraulic system 2 will lose fluid and the volume of fluid in the housing 30 of the reservoir 4 will decrease, causing the piston 32 to move further into the housing 30. This, of course, causes the piston rod 34 to partially retract into the housing 30. In time the forward end of the spool cylinder 146 in the pilot valve 136, and this increase in pressure acts against the forward face of the piston 180 and drives it to its fully actuated position, in which case the roller follower 214 will leave the camming sur face 42. As the pilot spool 176 moves it will, of course, cornthe piston 106 and thereby moves the entire spool 80 against both the force exerted upon it by the compression spring 120 at the opposite end of the valve bore-52 and the force unbalance resulting from the diflerence in areas between the

pistons

116 and 106. The spool 80 shifts axially until the beveled face 112 of the poppet 110 engages the valve seat 92, and when this occurs high pressure fluid can no longer flow through the intermediate cylinder 90 of the main valve 46. In other words, the poppet 1 10 blocks the flow of high pressure fluid from the supply line 20 and supply channel 58 on one hand to the distributor channel 64 and distributor line 22 of the branch circuit 8 on the other.

The closing of the main valve 46 isolates the branch circuit 8 and no more fluid leaks therefrom or from the system 2. Consequently, the volumn of the fluid in the reservoir 4 decreases no further, except for normal system operational changes, and the camming surface 42 on the reservoir piston rod 34 remains generally opposite the roller follower 214 for the pilot valve 136. The piston rod 34 will move about this point as normal system operation demands.

When the branch circuit 8 is isolated a back-up systemmay be utilized to operate the component normally operated by the hydraulic motor 14 of that circuit 8. For example, if the hydraulic system 2 constitutes the power control system of an aircraft and the motor 14 of the branch circuit 8 operates the stabilators of that aircraft, a back-up hydraulic system (not shown) may be used to operate those stabilators. In any event, no further fluid is lost from the reservoir 4 so that the remaining branches 10 and 12 of the hydraulic system 2 remain in the camming surface 42 will engage the roller follower 214 (FIG. 3) on the cam plunger 206 located at the end of the pilot valve 136, and will urge that follower 214 and likewise the plunger 206 and spool 176 of the pilot valve 136 inwardly. After the spool 176 moves a short distance in its valve bore 142, its piston 178 will pass beyond the radial ports 154 leading to the annular relief 148. When this occurs, high pressure fluid will flow from the high pressure supply duct 160 (FIG. 5) into the annular relief 150'and thence into the spool cylinder 146 through the radial ports 158. The fluid will further flow through the spool cylinder 146 and into the annular relief 148 through the radial ports 154. From the relief 148 the high pressure fluid is directed through the connecting channel 156 (FIG. 3) to the inner end of the main valve bore 52 for the main valve 46. The increase in pressure at the inner end of the main valve bore 52 is transmitted through the oblique connecting duct 164, annular relief 152, and radial ports 162 to operation in the usual manner. In other words, a leak in the branch circuit 8, or for that matter the other branch circuits l0 and 12, will not cause the eventual failure of the entire hydraulic system 2 through the depletion of its hydraulic fluid.

Since the' diversion of high pressure fluid through the oblique connecting duct 164 interposed between the main valve 46 and its pilot valve 136 causes the pilot spool 176 to shift to its fully actuated position, in which case the roller follower 214 is away from the camming surface 42, the pilot valve 136 once actuated is not sensitive to flow transients, pressure surges, thermal expansion and the like in the system 2. In this connection, it should be noted that the spacing between the roller followers 214 of the

pilot valves

136, 138, 140, is such that normal reservoir level changes do not move the piston 32 and camming surface 42 enough to trip an adjacent pilot valve.

Assuming now that the leak is not in the branch circuit 8, but is instead in the branch circuit 10, then after the pilot valve 136 is moved to its actuated position and the main valve 46 associated therewith is closed, the hydraulic system 2 will still lose fluid and the volume of fluid in the reservoir 4 will continue to decrease. Thus, the camming surface 42 after engaging and depressing the roller follower 214 at the end of the pilot valve 136 will continue to advance toward the reservoir 30 and in time will engage and depress the cam follower 214 at the end of the next pilot valve 138. This not only has the effect of moving the next pilot valve 138 to its actuating position and thereby closing the main valve 48 associated therewith, but it also rocks the connecting link 218 between the cam plungers 206 for the pilot valves 136 and 138 (FIG. 5). In other words, the cam surface 42 by driving the cam plunger 206 at the end of the pilot valve 138 inwardly, moves the opposite end of the link 218 outwardly, thereby drawing the cam plunger 206 at the end of the pilot valve 136 outwardly and moving the pilot valve 138 to its non-actuating position. More specifically, as the plunger 206 draws the spool 176 of the pilot valve 136 forwardly through its spool cylinder 146 the piston 178 thereon eventually comes to a position between the ports 154 and 158 leading to the

annular reliefs

148 and 150, respectively. This isolates the inner end of the valve bore 52 for the main valve 46 from the high pressure fluid in the supply duct 160 and vents the inner end of the valve bore 52 to the lower pressure duct 170 which opens into the enlarged end chamber 147 through annular relief 166 and radial ports 168. With the decrease in pressure at the inner end of the valve bore 52 for the main valve 46, the spring 120 moves the main valve spool 80 back to its open position and allows high pressure fluid to again flow through the spool cylinder 146 to the distributor channel 64 and thence to the distributor line 22 of the branch circuit 8. Thus, when the next pilot valve 138 is moved to its actuating position, the pilot valve 136 will be forced back to its nonactuating position and will allow the main valve 46 associated therewith to return to its open position so as to restore the branch circuit 8 to normal operation.

Of course, when the pilot valve 138 is in its actuating position and the main valve 48 associated therewith is closed, the branch circuit 10 associated therewith will be isolated and no further fluid will leak therefrom. Consequently, the piston 32 will advance no further into the reservoir housing and the main valve 48 will remain closed while the other

main valves

46 and 50 will be open.

Assuming now that both the

branch circuits

8 and 10 are free of leaks and that the leak is in the branch circuit 12, then the piston rod 34 will continue to retract into the reservoir housing 30 and eventually its camming surface 42 will engage and depress the cam follower 214 at the end of the pilot valve 140. This, of course, moves the pilot valve 140 to its actuating position which in turn results in the closure of the main valve 50, thereby isolating the branch circuit 12. As the pilot valve 140 moves to its actuating position, the connecting link 218 between the

pilot valves

138 and 140 forces the pilot valve 138 to its nonactuating position, and this allows the spring 120 of the main valve 48 to restore that valve to its open position, thus reactivating the formerly isolated branch circuit 10.

Should one desire to open any one of the

main valves

46, 48 or 50 if closed, he need only close the override switch 266. This energizes the solenoid 262 which draws the spool 252 (FIG. 4) in the override valve 230 to its open position, allowing high pressure fluid to flow from the duct 160 to the annular relief 242 and thence into the spool cylinder 248 through the radial ports 250 associated with that relief 242. The high pressure fluid flows from the spool cylinder 248 to the override channel 70, and since the override channel 70 communicates with the annular relief 68 of the

main valves

46, 48 and 50, the fluid in those reliefs 68 and likewise in the enlarged chambers 96 will be elevated to the pressure of the fluid in the high pressure supply line 20. Any valve spool 80 in its closed position will accordingly be driven to its open position so that all branch circuits will operate off the pump 6 and reservoir 4. If the system 2 constitutes the power control system of an aircraft it may be desirable to override the power control system when executing a critical maneuver such as landing, for the short time during which the formerly closed valve is open and the leaking circuit is in operation will most likely not deplete the reservoir of its hydraulic fluid.

Similarly, a mechanic who desires to check the operation of the

main valves

46, 48 and 50 and the

pilot valves

136, 138 and 140 can do so by pulling the knobs 192 on the latter outwardly away from the valve block 44.

It should be noted that the term hydraulic motor as used herein includes not only hydraulic cylinders, but also any type of hydraulically operated device or load.

This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A hydraulic system comprising a reservoir having a chamber in which a hydraulic fluid is contained and a member associated with the chamber and bearing against the fluid therein so that the position of the member relative to the chamber is dependent on the volume of fluid in the chamber, a plurality of branch circuits connected with the reservoir, each branch circuit having at least one hydraulically powered device which is operated by fluid passing through the branch circuit, means for causing fluid to flow from the reservoir to the branch circuits, isolating means connected between the reservoir and the branch circuits and responsive to the position of the member relative to the reservoir chamber for blocking the flow of fluid to the branch circuits individually when the volume of the fluid in the chamber decreases and for isolating a branch circuit having a leak therein, whereby the reservoir will not be depleted of fluid and the remaining branch circuits will remain operational.

2. A hydraulic system according to claim 1 wherein the means for causing fluid to flow from the reservoir to the branch circuits is a pump located between the reservoir and the isolating means; and wherein the isolating means sequentially blocks the branch circuits until a leaking branch circuit is blocked, at which time the isolating means continues to block and isolate the leaking branch circuit.

3. A hydraulic system according to claim 2 wherein the isolating means comprises a different main valve interposed between each branch circuit and the pump, each main valve having an open position wherein it allows high pressure fluid from the pump to flow into the branch circuit associated therewith and a closed position wherein it blocks the flow of fluid to the branch circuit associated therewith, and operating means positioned between the reservoir piston and main valves for closing each main valve when the member reaches a different position relative to the reservoir chamber.

4. A hydraulic system according to claim 3 wherein the member is a piston in the reservoir chamber; wherein the piston carries a camming surface; and wherein the operating means includes cam followers which are engaged and shifted by the camming surface and operate the main valves when shifted.

5. A hydraulic system according to claim 4 wherein the operating means further comprises pilot valves which are operated by the cam followers and control the main valves.

6. A hydraulic system according to claim 3 wherein the operating means includes means for opening the preceding main valve when a subsequent main is closed.

7. A hydraulic system according to claim 4 wherein the cam followers are arranged one after another in the direction of movement for the camming surface; and wherein the operating means includes connecting links pivoted intermediate adjacent cam followers such that when one cam follower is engaged and shifted to close the main valve associated therewith, the adjacent cam followers will be moved to and held in a position in which the main valves associated therewith are open, whereby only one branch circuit is isolated at a time.

8. A hydraulic system according to claim 4 wherein the isolating means further comprises override means for holding all of the main valves open irrespective of the position of the reservoir piston.

9. A hydraulic system according to claim 4 wherein high pressure fluid discharged from the pump is diverted to a limited area on the backside of the reservoir piston so that the piston is forced against the fluid in the chamber and causes the piston to retract into the chamber as the volume of reservoir fluid decreases.

10. A hydraulic system comprising a reservoir having a chamber in which a hydraulic fluid is contained, a pump connected with the reservoir, a plurality of main valves connected to the discharge side of the pump, a branch circuit connected to each main valve and to the reservoir, each branch circuit having a hydraulically powered device which is operated by high pressure hydraulic fluid admitted to the branch circuit through the main valve associated therewith, movable means shifting in response to changes in the volume of the fluid in the reservoir chamber due to a leak in one of the branch circuits, and operating means engageable by the movable means for closing the main valves individually and in sequence as the movable means shifts in response to changes in the reservoir fluid volume and until the main valve associated with the leaking branch circuit is closed, whereby the leaking branch circuit is isolated.

11. An apparatus for locating and isolating leaking branch circuits in a multibranch hydraulic system having a pump and a reservoir connected to the pump and to the circuit branches and provided with a movable means which bears against the fluid in the reservoir and changes position in response to changes in the volume of the fluid in the reservoir so that the piston will move as the leaking circuit loses fluid; said apparatus comprising a main valve interposed between the pump and each branch circuit and, operating means for movingeach main valve from an open position wherein it admits high pressure fluid to the branch circuit associated therewith to a closed position wherein it blocks the flow of fluid to and isolates that branch circuit, the operatingmeans being sequentially engaged and mechanically shifted by the movable means as the movable means shifis in response to the change of volume of the reservoir fluid, whereby the individual branches are sequentially isolated until the leaking circuit is isolated.

ll 4 IF i i

Claims

11. An apparatus for locating and isolating leaking branch circuits in a multibranch hydraulic system having a pump and a reservoir connected to the pump and to the circuit branches and provided with a movable means which bears against the fluid in the reservoir and changes position in response to changes in the volume of the fluid in the reservoir so that the piston will move as the leaking circuit loses fluid; said apparatus comprising a main valve interposed between the pump and each branch circuit and, operating means for moving each main valve from an open position wherein it admits high pressure fluid to the branch circuit associated therewith to a closed position wherein it blocks the flow of fluid to and isolates that branch circuit, the operating means being sequentially engaged and mechanically shifted by the movable means as the movable means shifts in response to the change of volume of the reservoir fluid, whereby the individual branches are sequentially isolated until the leaking circuit is isolated.