US3500865A - Hydraulically operable control valve - Google Patents

Description

LGI-:REER ETAL.

HYDRAULICALLY OPERBLE CONTROL VALVE Filed April 8, 196s March 17, 1970 United States Patent Olhce 3,500,865 Patented Mar. 17, 1970 t. Int. Cl. F16k 11/06; G05-d 1]/035 U.S. CI. 137-6256 5 Claims ABSTRACT 0F THE DISCLOSURE A valve system comprising a hydraulically operable main control valve, and a manually adjustable servovalve for controlling said main control valve, in which said main control valve in addition to a reciprocable main valve spool includes at each end of said main valve spool an auxiliary piston and a return spring, both return springs tending to hold said main valve spool in its neutral position, and in which the adjustment of the servovalve spool, which has an annular shoulder communicating with a conduit for feeding oil under pressure to said main control valve, is elfected by a manually operable push rod through the intervention of a control spring preloaded by a screw and a spring dish.

The present invention relates to a hydraulically operable control valve with a control piston, the stroke of Iwhich is dependent on the actuating stroke of a servovalve. v

It is known hydraulically to adjust control valves of major nominal width and to hold such valves in their neutral central position by means of springs. In this connection, centering springs are employed which have as steep a characteristic as possible in order by means of pressure dependent manually operable servo-valves to obtain a position of the main control valve which is proportional to the manual stroke on the servo-valve, thereby assuring a fine control of the consumer connected thereto. Thus, tine or iinest controls are employed, for instance, in order to prevent a too sudden discharge of a heavy material carrying loading shovel or loading bucket in a vehicle, thereby preventing damage. The fact that with increasing diameter of the control piston, the services actuated by the servo-pressure circuit increase with the fourth power makes it mandatory that very strong springs are employed l"which have high tolerances and can be mounted in a housing of customary size only under considerable difiiculties or not at all. The fine sensitive adjustment of the control piston as it is required for a iine control is no longer assured.

It is, therefore, an object of the present invention to provide a hydraulically operable control valve which will overcome the above mentioned drawbacks.

It is another object of this invention to provide an arrangement for no longer manually operable control valves of vhydraulic installations, according to which the main control valve will be able by means of a manually operable servo-valve to pass through a txed fine control area and control the remaining portions of the stroke, i.e. in a fast traverse movement.

'I'hese and other objects and advantages of the invention will appear more clearly from the following speeltication, in connection with the accompanying drawings, in which:

FIGURE 1 is a longitudinal section through a main control valve for an arrangement according to the present invention.

FIGURE 2 is a section through a servo-valve for use characterized primarily, in that the main control valve t has associated therewith auxiliary pistons and return springs, and that the adjustment of `the piston of the servo-valve, which piston is designed as a step piston, is t effected by a push rodthrough theintervention of a control spring which is preloaded by awscrew and a spring dish.

The arrangement is furthermore characterized in that the annular surface of the said stepped piston faces the connection for the control oil.

Referring now to the drawings in detail, the arrangement shown therein comprises a main valve 2 (FIG. 1) associated with a Working cylinder 1, for instance, the cylinder of a loading bucket, and furthermore comprises a servo-valve 3 (FIG. 2). The said cylinders 2 and 3, are interconnected through hydraulic conduits 4, 4a, while the main control valve 2 is connected with the working cylinder 1 through conduits 7 and 8. The oil under pressure for actuating the working piston 1a for cylinder 1 is delivered by a pump 9. The oil under pressure for adjusting the control spool 13 is delivered by a servopump 21. The oil under pressure not required for the Iworking cylinder 1 and the servo-pumps 9 and 21 is discharged to the oil reservoirs 10i and 11, respectively, through check valves 32 and 32a, respectively. The valve spool 13 is displaceably arranged in the housing 12 of the main control valve 2. The housing 12 is closed at both ends by covers 14 and 14a, respectively. Within said covers .14 and ,14a are respectively mounted bushings 15 and 15a which serve for guiding the auxiliary pistons 16 and 16a, respectively. Springs 17 and 17a respectively located in said covers 14 and 14a rest on one hand against the surfaces 14 and 14" of the covers 14 and 14a, respectively, while the other end of said springs rests upon a pot- shaped spring dish 18 and 18a, respectively, which are placed over extensions 43 and 43a, respectively, of bushings 15 and 15a. In this way the spring force exerted by the springs 17 and 17a is conveyed through the members 18 and 18a, bushings 15 and 15a, and servo-pistons 16 and 16a to the two end faces of the main valve spool 13 which, in this way, is held by said springs 17 and 17a in its central position. Oil under pressure is passed through passages 19 and 19a to the servo-pistons 16 and 16a. The oil under pressure is conveyed to the interior of the covers 14 and 14a through conduits 4 and 4a, respectively.

The servo-valve 3 comprises a housing 20 which receives oil under pressure from the servo-pump 21. Re-

ciprocably mounted in said housing 20 is a stepped valve spool 22 provided with an annular surface 25. A screw 27 is Screwed into that end face 26 of the valve spool 22 which faces toward the push rod 23. The head 28 of said screw 27 extends into a pot-shaped spring dish 29. It will thus be appreciated that the tension of the spring 6 which is clamped between the end face 26 and the surface 30 facing said screw head 28 can be adjusted by means of said screw 27. The push rod 23 is guided in a closing bushing 31 which is screwed into the housing 20.

Operation The arrangement according to the present invention operates as follows:

The servo-pump 21 conveys oil under pressure into the reservoir 11 against the maximum pressure adjusted by the check valve 32a. The bore 33 in housing 20 of the servo-valve 3 communicates through line 4 with the chamber 34a (FIG. l) of the closure 14a of the control valve 2. The bore 33 communicates with the oil reservoir 11 through the bore 35 in the stepped valve spool 22,

transverse bore 35a, chamber 35h, and bore 35C. A cori responding arrangement is provided for the chamber 34 in the cover 14. If now, the push rod 23 of the servo-valve 3 is depressed to a certain extent, first by means of the control edges 36 and 36a, the connection to the oil reservoir 11 is interruped, and thereupon by means of the control edges 37 and 38 of the stepped valve spool 22 ir' housing 20, and conduit 4, the connection between the servo-pump 21 and the chamber 34a is established. The now flowing oil flow displaces the piston 16a against the thrust of spring 17. The chamber 34 still remains in communication with the oil reservoir 11. The farther the spring 17 is compressed, the greater becomes the force, and consequently, the oil pressure required in the servocontrol circuit. This pressure acts upon the annular surface 25 and displaces the stepped valve spool 22 against the thrust of spring 6. In this connection it is assumed that the operator holds the push rod 23 in its initially selected position. As a result, the control edges 37 and 38 close the connection between the servo-pump 21 and chamber 34a. The control edges 36 and 36a likewise remain closed during this operation so that the piston 13 of the main control valve 2 will occupy a position which is proportional to the stroke of the push rod 23. The piston 13 moves on only when the push rod 23 is depressed further. When the pressure produced by the spring 17, which pressure acts upon the annular surface 2S, exceeds the maximum force of spring 6 a mechanical connection is, by means of the spring dish 29, established between push rod 23 and the stepped valve spool 22. The control edges 37 and 38 cannot move into their closing position without the operator desiring so, so that the valve spool 13 of the main control valve 2 will, due to the fact that it is actuated by the servo-piston 16a, move against the abutment 39, and the servo-pump 21 will overcome the pressure adjusted on the check valve 32a, and will feed to the oil reservoirs 11.

In order to exclude any undesirable reaction by the leakage oil collecting in the chambers 40 and 40a, the said chambers 40 and 40a are through bores 41 and 41a and annular passages 42 and 42a connected to the oil reservoir 11.

As will be seen from the above, with the arrangement according to the present invention which excels by its compact construction and small spring dimensions, the main control spool passes through a very narrow fine control range.

What we claim is:

1. A valve system comprising a fluid operable main control valve, and a manually adjustable servo-valve for controlling said main control valve, in which said main control valve includes a reciprocable lmain valve spool and has adjacent each end of said main valve spool a fluid operable plunger for acting upon said main valve spool and a return spring operable to act upon the respective adjacent plunger, both return springs being operable through said plungers to return said main valve spool to a neutral position, and in which said servo-valve includes rst conduit means for connection with a source of pressure fluid, second conduit means for conveying uid to one of said plungers, a reciprocable servo-valve spool for controlling the communication between said first and second conduit means, said servo-valve spool having an annular shoulder in fluid communication with said second conduit means, manually adjustable means, spring dish means connected to the manually adjustable means, a first spring interposed between said spring dish means and the adjacent end of said servo-valve spool, a second spring continuously acting upon the other end of said servo-valve spool in a direction counter to the direction of action of said first spring, and means for variably pre-loading said first spring.

2. A valve system according to claim 1, which includes two bushings respectively associated with said plungers for guiding the same, one side of each bushing facing in the direction toward said main valve spool and being provided with a recess with a surface forming an abutment for said main valve spool, housing means respectively surrounding said bushings, two spring dishes respectively resting on that side of the respective bushing which is opposite to said one bushing side, said return springs respectively being interposed between and resting on the respective spring dish and the adjacent housing means.

3. A valve system according to claim 2, which includes conduit means leading from said recesses to the outside of said main control valve for conveying leakage oil to an oil reservoir.

4. A valve system according to claim 3, which includes sealing means in said housing means for sealing the latter relative to said bushings.

5. A hydraulically operable valve system which in eludes: main valve means, and servo-valve means hydraulically connected to said main valve means; said main valve means comprising a reciprocable main valve spool controlling the ow of actuating uid to and from a cylinder piston system to be controlled, two plunger means respectively arranged on opposite ends of said main valve spool and respectively operable by pressure fluid to respectively move in one direction and the opposite direction to thereby move said main valve spool in said one or the other direction, and return spring means continuously urging said main valve spool to a neutral position in which fluid communication of said main valve means with a cylinder piston system to be controlled is interrupted; said servo-valve means including a reciprocable stepped servo-valve spool with an annular shoulder surface operable to be acted upon by pressure fluid conveyed through said servo-valve means to said main control valve means, a manually operable control member arranged in axial alignment with and in axially spaced relationship to said servo-valve spool, spring dish means coaxially arranged with regard to said manually operable member and located in spaced relationship to the respective adjacent end face of said servo-valve spool, iirst spring means interposed between said spring dish means and the respective adjacent end of said servo-valve spool, said first spring means continuously urging said servo-valve spool to move in one direction from one end position of said servo-valve spool, second spring means associated with the opposite end of said servo-valve spool and together with said first spring means urging said servo-valve spool to occupy its neutral position, said annular shoulder surface facing away from said first spring means.

References Cited UNITED STATES PATENTS 2,751,182 6/1956 Snyder. 2,870,789 1/1959 Bilaisis 137-6256 3,200,845 8/ 1965 Nakazima et al 137-6256 3,304,953 2/1967 Wickline et al. IS7- 625.6 3,340,897 9/1967 Nevulis IS7-625.6

FOREIGN PATENTS 1,333,554 6/1963 France.

720,966 12/ 1954 Great Britain.

HENRY T. KLINKSIEK, Primary Examiner U,S. Cl. XR, 137-1165 l

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