US3516445A - Hydraulic actuating systems - Google Patents

Description

June 23, 1970 R. E. J. SKEATES 3,516,445

HYDRAULIC ACTUATING SYSTEMS Filed Feb. 4!, 1969 2 Sheets-Sheet 1 June 23, 1970 R. E. J. SKEATES 3,515,445

HYDRAULIC ACTUATING SYSTEMS Filed Feb. 4, 1969 2 Sheets-Sheet 2 United States Patent O 3,516,445 HYDRAULIC ACTUA'HNG SYSTEMS Ronald E. J. Skeates, Ilford, England, assignor to The Plessey Company Limited, Iiford, England, a British company Filed Feb. 4, 1969, Ser. No. 796,345 Claims priority, application Great Britain, Feb. 7, 1968, 6,024/ 68 Int. Cl. F16k 11/07, 11/10, 23/00 US. Cl. 137-62567 3 Claims ABSTRACT OF THE DISCLOSURE A hydraulic actuating arrangement in which a spool valve comprises a spool slidable in a bore in the body of the actuator, the spool being provided with a peripheral groove which, at least in the neutral position of the spool is trained so that leakage between the spool and said bore is intercepted by said groove and prevented from reaching the associated actuator (not shown). Such an arrangement may be conveniently used in digger or loading equipment to prevent creepage of the associated actuator members.

This invention relates to hydraulic actuating systems of the kind in which a single positive-displacement hydraulic power source is made available for the selective utilisation in a number of hydraulic services, each having a separate spool valve by inter-connecting these spool valves by a transfer passage which passes from a pressure inlet in series through a port of each spool valve which is open when the valve spool is in an inoperative position, to reach a lowpressure return port, so that when each spool valve is in its inoperative position, the pressure source is unloaded via the transfer passage, while the transfer passage is closed to cause a pressure build-up when any spool is moved to an operative position, each spool valve having a pressure port communicating with the said pressure inlet via a nonreturn valve, one or more service ports, and one or more return ports communicating with a point at low pressure, the high-pressure, service, and low pressure ports of each valve being isolated by lands of the valve spool when the latter is in its inoperative position.

It will be readily appreciated that when any one of the valve spools is in an operative position, the pressure ports of all valves will be pressurised, and therefore if the unit controlled by this one spool operates against a high pressure, pressure is liable to leak in the other valves past the intervening lands of their respective valve spools towards the service ports of these other valves, and that if there is any asymmetry of this leakage, this may lead to creeping of a service whose valve spool is in its inoperative position. In many applications such creepage is objectionable, one example being loader equipment and digger equipment respectively mounted on the front and rear of a vehicle, an arrangement in which it is usual to employ the loader to anchor the vehicle during digging operations.

The present invention has for an object to provide a safeguard against such creeping of non-selected services. According to the invention in the valve assembly of hydraulic actuating systems of the kind specified, the valve spool of a service to be protected against creepage is provided with a peripheral groove which in the inoperative position of the valve spool faces the land separating the pressure port and the service port of the valve housing for the service controlled by the valve spool in question, this groove being, at least in the inoperative position of the spool, drained to a point at low pressure so that leakage from the pressure port towards the service port of the valve is intercepted by the groove and thus prevented from reaching the service port of the valve.

Patented June 23, 1970 "ice One embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic plan view showing part of the hydraulic equipment and including a section of the valve assembly, and

FIG. 2 is an elevation, partly in section on line A-A of FIG. 1.

Referring now to the drawings, hydraulic liquid from a reservoir T is pumped via a positive-displacement pump P to a transfer passage 1, which is sub-divided by lands 6a, 6b and 60, respectively co-operating with valve spools 3a, 3b and 3c, into series-connected portions 1a, 1b, 1c and 1d, the latter being drained to the reservoir T by a return line 4, which also communicates with two low-pressure ports 21 for each spool valve 3a, 3b and 30 respectively arranged at each side of the transfer passage 1. The inlet of the transfer passage 1 further communicates with a pressure gallery 9, see FIG. 2, which is connected to a pair of annular pressure ports 12 for each valve spool via a check valve 10 and branch passage 11. Arranged at each side of the transfer passage, about half-way between the pressure port 12 and the return port 21 for each valve spool 3, is a service port 14 and 24 respectively, each service port 14 and 24 being faced by an annular port 16 or 26 respectively in the valve spool which, as the valve spool is moved to one or the other side from its illustrated inoperative central position, connects the service port with either the pressure port 12 or the low-pressure port 21 in a well known manner so that displacement of a spool 3 towards the left will connect its right-hand service port 14 to the associated pressure port 12 while venting the left-hand service port 24 to a low-pressure port 21 and vice versa thus causing operation of the associated service in one direction or the other according to the direction in which the valve spool has been displaced. In the illustrated embodiment it has been assumed that while slight creepage of the service controlled by valve spool 3a is not particu larly objectionable, such creepage cannot be permitted in the case of the service controlled by valves 3b and 30 respectively. In order to prevent such creepage in each of the last-mentioned valves along the lands 7 and 8 which, in cooperation with lands 15 and 25 of the valve housing 2 isolates, in the inoperative position of these valves, their pressure ports 12 from their service ports 14 and 24, a circumferential groove 17 is provided in each of the lands 7 and 8 of these valve spools at a point of their length which, when the valve spool is in its inoperative position, faces the land 15 or 25 of the valve housing which separates the pressure port 12 from the service port 14 or 24, and each of these grooves communicates, by radial bores 18 and a longitudinal bore 19 extending along the axis of the spool, with radial bores 20 which when the valve is in this inoperative position, open into one of the low-pressure ports 21, so that any liquid which may leak from one of the pressure ports 12 along one of the lands 7 or 8 of either valve spool 3b or 3c towards the adjacent service port 14 or 24 will be intercepted by the groove 17 and is via the low-pressure port 21 returned to the reservoir tank T.

This arrangement is clearly of particular advantage in cases in which one of the services, for example that controlled by valve spool 3a, is liable to require a very high operating pressure while one or more other services, for example those controlled by spools 3b and 3c, are normally required to be held, during the operation of this highpressure service, in a preset position to effect a holding operation which is unlikely to produce high pressures in their operating units.

The disposition position of the radial bores 18 and 20 has been so chosen as to prevent the creation of a shortcircuit bleed through these bores and the axial bore 19,

between the service ports 14, 24 and their respectively associated pressure and return ports 12 and 21. Thus it will be seen that when a valve spool is moved to the right of FIG. 1, its bores 20, which in the neutral position communicate with the low-pressure port 21, will be blanked off by the land 23 of the valve housing which separates this port from the adjacent service port 24 before the groove 17 reaches the associated pressure port 12, While when the valve is moved to the left, the groove 17 in land 8 will remain in co-operation with the land 25 that separates service port 24 from pressure port 12, until the radial bores 20 at the left-hand side of the spool become isolated from lowpressure port 21 by the land 27 provided beyond that port. The same arrangements apply to the right-hand side of each of the spools 3b and 30 when the spool is moved to the left and to the right respectively.

What is claimed is:

1. A valve assembly for hydraulic actuating equipment of the kind hereinabove specified, wherein the valve spool of a service to be protected against creepage is provided with a peripheral groove which in the inoperative position of the valve spool faces the land separating the pressure port and the service port of the valve housing for the service controlled 'by the valve spool in question, and means for connecting said groove to a point at low pres sure so that leakage from the pressure port towards the service port of the valve is intercepted by the groove and thus prevented from reaching the service port of the valve.

2. A valve assembly as claimed in claim 1, wherein said valve spool has an inoperative position and at least one operative position, said means for connecting said groove being so constructed as to be operative only when the valve spool is in said inoperative position.

3. A valve assembly as claimed in claim 1, including a valve housing having a bore in which the valve spool slides, at least one land forming a wall portion of said bore, at least one low-pressure port and at least two further ports including at least one pressure port and at least one service port, all said ports opening into said bore, wherein the valve spool is provided with an axial passage and with two axially spaced radial bores intersecting said passage and respectively leading to the groove and to a point at the surface of the spool which faces such low-pressure port when the spool is in its inoperative position but faces, and is blanked oil? by, such land when the groove is open to such further pressure port of the valve housing.

References Cited UNITED STATES PATENTS 2,486,087 10/1949 Wright 137-596.13 3,262,467 7/1966 Stacey 137625.69 XR 3,429,341 2/ 1969 Sochting 137-625.68

HENRY T. KLINKSIEK, Primary Examiner US. Cl. X.R. 1373l2

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