US2420052A - Control apparatus for hydraulic machines - Google Patents

Description

May 6, E947. w. P. MUIR 2,420,952

CONTROL APPARATUS FOR HYDRAULIC MACHINES Filed March 5, 1945 53 5B PILOT VALVE 7 3O -a 35 35 4 UNLOADER 9 VALVE STORAGE TQSIK 54 PlLOT VALVE 30 I w 41 J37 9 UNLOADER VALVE PILOT VALVE CONTROL SHAFT "$5 g5 PlLOT VALVE \iNLOADER 50 4137! 53 49 VALVE-* 50 mvENTOR YV-P-MUIR Patented May 6, 1,947 P P CONTROL APPARATUS FOR HYDRAULIC MACHINES William P. Muir, Hampsted, Quebec, Canada, as-

signor to Dominion Engineering Works Limited, Lachine, Quebec, Canada Application March 3, 1945, Serial No. 580,751

4 Claims.

This invention relates to control apparatus for controlling the speed and limiting the tonnage or maximum working pressure of hydraulic presses and other hydraulic machines.

The invention has, for one of its objects, to provide improved control apparatus in which stepped speed variation of a hydraulic machine is obtained by sequential operation of a series of pump unloader valves controlling the delivery of a plurality of pumps through which pressure fluid is supplied to the working cylinder or cylinders of said machine.

Another object is to provide, in connection with said improved speed controlling apparatus, means whereby the tonnage or working pressure of the hydraulic machine is prevented from rising above a predetermined maximum value.

Proceeding now to a more detailed description reference will be had to the accompanying drawing, in which the single figure is a diagrammatic illustration of what I now conceive to be the preferred embodiment of the invention.

Referring more particularly to the drawings, 5, 6 and 1 designate pumps having their pressure sides connected to a common discharge header 8 from which the pressure fluid delivered by the pumps is conducted to the working cylinder or cylinders of a hydraulic press or other hydraulic machine. Check valves 9, l and II are arranged to prevent reverse flow from the header 8 to the pumps 5, B and I. The suction sides of pumps 5, 8 and I are shown connected to individual pressure-fluid storage tanks l2, l3 and I4 by their respective inlet connections l5, l3 and I1. If desired, these individual storage tanks may be replaced by a single storage tank serving all of said pumps.

The delivery of each pump is individually controlled by a separate pump unloader valve which is connected between the discharge side of the pump and its associated storage tank so that the pump discharge may be by-passed back to said storage tank through said unloader valve. These unloader valves are respectively indicated at I9, 20 and 2|. They each comprise a valve element 23 operating in a valve casing 24 provided with an inlet port 25 connected to the discharge side of the associated pump and a discharge port 26 connected to the associated pressure-fluid storage tank. Valve element 23 closes against a seat 2'! afforded by discharge port 26. This valve element is carried by a piston 28 which is a close sliding fit in the cylindrical guide portion 29 of the valve casing and divides the latter into upper and lower pressure chambers 30 and 3|. It may 2 be noted here that the pressure-receiving area afforded by the upper surface of piston 28 is much greater than that afforded by the lower annular surface of the piston surrounding the valve element 23.

The unloader valves [9, 29 and 2| are individually controlledby separate 3-way pilot valves respectively indicated at 33, 34 and 35; Each pilot valve assembly comprises a spool valve 81 slidably mounted in a valve casing 38 provided with ports 4|, 42, 43 and 44. Valve 31 is moved in one direction by a spring 46 and in the opposite direction by a cam 41 which is fixed to a cam shaft 8 and acts against a roller 49 carried by the valve stem 52.

The ports of each pilot valve are connected in the following manner: Port 4| is connected, through line 52, to a'port 53 provided in the top casing wall of the associated pump unloader valve. Port 42 is connected, through line 54 and header 55, to an independent source of pressure fluid represented by pump 53. The ports 43 and 44 are located adjacent opposite ends of the valve casing 38 and are connected together by a'fiuid passage 58. These ports 43 and 44 are also connected to a common exhaust line 59 leading to the fluid pressure storage tank of the associated pump.

The hydraulic circuit of each pilot valve also includes a by-pass line 6| connected between the lines 52 and 54. A check valve 62, included in each by-pass line 6!, permits flow of fluid from line 52 to line 54.

The header 55 and the pressure side of pump 56 are connected, through line 59, to a weightloaded hydraulic accumulator 84 equipped with weights 35 which may be varied to adjust the pilot pressure by which the unloader valves are held closed against the normal Working pressure established in the pressure chambers 3! of the unloader valves by the main pumps 5, 6 and i.

The pilot Valve operating cams 47 are fixed to control shaft 48 in diiierent positions of relative angular displacement and the angular setting of these cams determines the sequence of operatie-n of the pilot valves. The cams are shaped and arranged so that all the pumps 5, 6 and l are loaded at one limit of cam travel and are by passed at the other limit of cam travel. The

control shaft 48' is equipped with an operating lever $6 which may be operated either manually or automatically. in the case of automatic operation lever 63 is interconnected by suitable linkage 61 with valve restoring mechanism or other operating parts or control elements of the hydraulic machine.

In the present drawings the valve spool 31 of the uppermost pilot valve 33 is shown moved to the right by its operating spring 46 so that port 4| is uncovered. This permits the pressure fluid previously supplied to the upper pressure chamber 30 of unloader valve I 9 to be exhausted to storage tank [2 via line 52, pilot valve ports 4| and 43 and exhaust line 49. Pressure fluid trapped between valve spool 31 and the right hand end of cylinder 38 is also exhausted by way of pilot valve port 44, passage 58 and exhaust line 59. With the pressure chamber 311 of the pilot valve l9 connected to exhaust as-herein described the main pump pressure established in the lower pressure chamber I'llv ofunloader valve I9 is efiective to raise the piston 28 and valve 23' to uncover discharge port 26 and thereby permit the discharge of pump 5- to be by-passed back to storage tank l2. through chamber 31 of unloader valve [9.

Thevalve spool 31 of pilot valve 34, is shown in a neutral position in which the left hand end of the valve spool is blocking the port 41. The pressure fluid thus trapped in the pressure chamber 30 of unloader valve 20 is effective to hold the valve element 23 of thisunloader valve closed against the normal working pressure established in the pressure chamber 3| by the main pumps 5; Band 1. If the working pressure-established in the pressure chamber 3,! of unloader valve 20 bythe main: pum s 5, 6V and 1, hould increase beyond normal limitwhile, the valve spool 31 of pilot valve 34 is in the neutral position shown there: would\ be an undesirable, intensification of the pilot pressure in. the pressurecham er 3.0 and line 52 of unloader valve 20'. According to my invention this is takencare of by the provision oftheiby p s line 61 ahdcheck Valve 62. From this it will be apparent that at, all times the main purnppressure acting against the valve operating piston of each unloader valve is limited to a value equal to some multiple of the opposing pilot pressure a ting on said piston, dependent on the'ratio of the lower annular pressure receiving area of the piston to the whole areaof the upper surface of the piston, In this connection it will also be apparent that the pilot pressure should be maintained' at a constant" value that will limit the discharge of the main pumps 5, 6 and 1 to the required pressure. In the present instance this is accomplished by the provision of the weightloaded hydraulic accumulator 64 but it will' be understood that various other arrangements may be provided for adjusting the pilot pressure.

The main pump pressure acting on the lower annular pressure receiving areas of the valve operating pistons 28 of the several unloader valves is shown on a pressure gauge while the pilot pressure applied to the upper pressure receiving areas of said pistons to hold the unloader valves closed is shown bya pressure gauge 1|.

From the foregoing description and from a study of the drawings it will be apparent that the flow of fluid from the main pumps 5, 6 and 1 to the header 8- is decreased when the control lever 66 is swung to the left and is increased when said lever is swung to the right. In this connection it will be apparent that movement of lever 68 to the left from the position shown will turn the control cams 41 of the pilot valves 33, 3.4 and 35' in a, direction to permit the valve spools 31 of these pilot valves tobermoved to the right by the valve operating springs 45 a distance dependent on the extent to which the lever 66 is moved. In this connection it will be seen that even a relatively slight movement of the lever 66 to the left will result in the spool valve 31 of pilot valve 34 being moved to a position in which it at least partially uncovers the port 4|. of, said pilot valve-tothereby permit exhaust of fluid from the: pressure chamber 30 of unloader valve 20 with resulting opening of the valve 23 of this unloader valve to provide a bypass connection for the pump 6. If the move- 7 ment of the lever 66 to the left is continued a condition will be reached in which the pressure chambers 30 0f all the unloader valves are connected' totexhaust to permit the valve elements 23 or thesaunloader valves to be opened to unload all the main pumps 5, 6 and 1. When the lever 66 is moved to the right the spool valves 31 of the pilot valves 33, 34 and 35 will be shifted to the left in sequence against the resistance of the springs 46 to throttle or close. of: the la -Pas aff rded. by said pilot'valves. and their. pipe con.- nec ions,

Having thus described what I. now conceive'to be the preferred: embodiment ofthis invention it will: be understood that variou modifications may be resorted fro-within; the'scQlJe and spirit of the invention, asdefined. by the appended; claims.

I claim;

l.- Apparatus for controlling the; operating p ed f a ydrauliomachinc. comprisinaaseries of pumps, means for conducting pressure fluid from. the pressure sides of all on said' pumpsto a working cylinder of, the machine. aseparate by-passfor eachpumn-throueh, which: the pump discharge, is diverted:tQ'decrease-theflow otprcsur flu d t sa d cy inder; a separate. unloader alve controlling the bi -pass: oi eachpump and a ap d to. close against. the pump pre sure; a separate pilot valve for-controlling the,- operation of each unloader valve, reach: pilotevalve: including a casing provided, with a. series ofports including a pressure fluid. intake. port connected, to a' pressure line in which a predetermined pressure is maintained independently of said, pumps. 3 dc:- liveryport connected tothe valve casing of. the associated, unloader valve by at pressure fluid transfer line-and. an exhaustport, avalvemovahleinthe pilotvalve casing toa pumploading position in which said. valve: establishes communication between said intake and delivery ports and blocks, communication. between, said Ports and the exhaust port or to av valve. unloading position in, which; said, valve: establishes commuv nication between the deliveryport and the exhaust port and. blocks communication between said ports and the intake port, each, movable pilot valve element servin in its.pump. loading P sition, to. permit. flow. oi pressure. fluid to.- the alve casing of the associatedtunloader valve to hereby l se said; unloader valve againstthe pump pressure, said movable valve element, of each. ilot .valve also, servin ,v in its Dump. unload;- in position, to permit thevalve. closing.v fluid pressure. previous y supplied to. the casing of the associated unloader.w valve. to be exhausted, tram said casingto, thereby permit openins ot the unload r va ve y he Pump Pr ssure. acting thereaeains a hydrauliapressure accumulator onnected; to the fluid. pre sure. line. serving; the intake, por s 0.1? said pilo valves. andmeansfor V successively operating, said. pilot valves preconnected to each of the transfer lines interconnecting the casings of the associated pilot and unloader valves to prevent undesirable intensiflcation of the fluid pressure holding the unloading valves closed when the pilot valves are in their neutral position.

3. Apparatus for controlling the operating speed of a hydraulic machine comprising a series of pumps, means for conducting pressure fluid from the pressure sides of all of said pumps to a working cylinder of the machine, a separate by-pass connected to each pump and through which the pump discharge may be diverted to decrease the flow of pressure fluid to said cylinder, a pump unloader valve included in each bypass and adapted to close against the pump pressure, a separate pilot valve for controlling the loading and unloading of each pump, each of said pilot valves being operable to a pump loading position establishing connections through which pressure fluid is supplied to the associated pump unloader valve to close said valve and being also operable to a pump unloading position establishing connections through which the closing pressure previously applied to the associated pump unloader valve is exhausted to permit the unloader valve to be opened by the pump pressure acting thereon and mechanism for operating said valves in a predetermined sequence comprising a shaft and a plurality of pilot valve actuating cams fixed to said shaft in different positions of angular adjustment.

4. Apparatus for controlling the operating speed of a hydraulic machine comprising a series of pumps, means for conducting pressure fluid from the pressure sides of all of said pumps to a working cylinder of the machine, a separate by-pass connected to each pump and through which the pump discharge may be diverted to decrease the flow of pressure fluid to said cylinder, a pump unloader valve included in each bypass and adapted to close against the pump pressure, a separate pilot valve for controlling the loading and unloading of each pump, each of said pilot valves being operable to a pump loading position establishing connections through which pressure fluid is supplied to the associated pump unloader valve to close said valve and being also operable to a pump unloading position establishing connections through which the closing pressure previously applied to the associated pump unloader valve is exhausted to permit the unloader valve to be opened by the pump pressure acting thereon and mechanism for operating said valves in a predetermined sequence comprising a separate spring for operating each pilot valve in one direction, a separate cam for operating each pilot valve in the opposite direction against the resistance of said spring and means for simultaneously operating all of said cams, the setting of said cams being such as to operate the several pilot valves in predetermined sequence.

WILLIAM P. MUIR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,408,942 Holdsworth Mar. 7, 1922 1,607,531 Haight Nov. 16, 1926 1,612,638 Metzgar Dec. 28, 1926 1,649,297 Nelson Nov. 15, 1927 ,1 38 Noble July 11, 1939

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