US2954800A - Hydraulic system - Google Patents

Description

United States Patent r`1ce HYDRAULIC SYSTEM William G. Searles and Preston M. Wright, Indianapolis, Ind., assignors to Corson Bros., Inc., Indianapolis, Ind., a `corporation of Indiana.

Filed Jan. 4, 19'60, ser. No. 276

4 claims. (c1. 'lsv- 620) This invention relates to a hydraulic system including a hydraulic motor and a valving means for controlling its operation. More particularly the invention relates to a system of the type in which the motor is` operated in one direction by pressure liquid supplied from a suitable source and in the other direction by the load imposed upon it.

A system embodying the invention in its preferred form comprises a main valve and a modulating valve. The modulating valve has a rst, or motor, port fand second and third ports connected to the motor port respectively through check valves opening toward the motor port. The main valve is operable to connect either of the second and third ports to a source of iluid under pressure While connecting the other of such ports to return. The modulating valve embodies a piston which is operable, under the inuence of pressure at the. second port, to unseat the check valve disposed between the motor port and the third port. Control of the modulating valve is effected through a. movable control member operable to force the last mentioned check valve toward closed condition against force exerted upon it by the piston.

Further features of the invention will become apparent from the following more detailed description and from the drawing, in which the single figure illustrates, in part diagrammatically, a complete system in which our invention is embodied.

The system shown in the drawing comprises a hydraulic motor connected through a conduit 11 to a motor port 12 provided in the housing 13 of a modulating valve 14. The housing 13 has two other ports, 15 p and 16, connected through conduits 17 and 18 to a main Valve 19. The valve 19, as shown, is a lfour-way valve operable to connect either of the conduits 17 and 18 to the outlet of a power-operated pump 21 while connecting the other to a return line 22 leading toa sump 23 from which the pump 21 draws liquid. The Valve 19 is conveniently of the closed-center type having a neutral position in which it blocks ow from the pump 21 to both conduits 17 and 18. The outlet of the pump 21 is shown as connected tothe return conduit 22 through a pressure-relief valve 24 to provide a path over which liquid can circulate when the valve 19 is closed.

Within the housing 13 of the modulating valve 14 passages 13' are provided connecting the motor port 12 with port through a check valve 26 and with port 16 through a check valve 27. lBoth of the check valves 26 and 27 are spring-seated and open toward the motor port 12. Also provided within the housing 13 is 'a means responsive to pressure at one of the ports 15 and 16 for unseating the check valve associated with the other of such ports. As shown, such means is responsive to pressure at `the port 15 and operates under the inuence of such pressure to unseat the check valve 27. To this end the housing 13 is provided with a bore 30 coaxial with the seat of valve 27 and in such bore there is disposed .a piston 31 having a projection 32 of reduced diameter engageable with the valve 27. The end of 'the movement of the piston toward the port 15. For a` reason which will appear hereinafter, the diameter of the piston 31 is larger than that of the seat 27 for thev valve 27.

Control means for the modulating valve 14 comprises a rod 35 slidably mounted in the housing 13 coaxiallywith the valve 27 and projecting out of the housing for operative connection to a control member, shown asa lever 36 pivotally mounted on a bracket 37 secured to the end of housing 13.

With the main valve 19 positioned as shown in the drawing, liquid delivered by the pump 21 circulates through the pressure relief valve 24 and no pressure is applied to either of the ports 15 and 16 of the modulating valve 14. Both check valves 26 and 27 are closed, thus blocking return flow-from the motor 10 and maintaining the piston of such motor in fixed position against any external load applied to it. For normal operation of the system under control of the lever 36, the valve 19 is positioned to cause pressure liquid from the pump 21 to be supplied to port 15 of the modulating valve 14 and to connect port 16 to the return line 22. If, in such circumstances the rod 35 is held in its leftward limit of movement by the control lever 36 to maintain the valve 27 seated, liquid delivered by the pump will flow by way of passage 13', port 12, and conduit 11 to the motor 10 to displace the motor piston Iagainst its load. However, if the lever 36 is operated to move the rod 35 to the right, the piston 31 will move to the right under the influence of pressure at the port 15 and will unseat the valve 27 to permit at least some of the liquid entering passage 13 through the check valve 26 to ow past Valve 27 and return to the sump via conduits 18 and 22. It may here be noted that whenever the rod 35 is retracted while pressure liquid is being supplied to the port 15 the valve 27 will always open. This follows from the facts that the diameter of the piston 31 is greater than that of the valve seat 27 and that the unit lluid pressure existing in passages 13 and acting leftwardly on the valve 27 cannot exceed that existing at port 15 and acting rightwardly on the piston 31. Of course, the amount by which the effective area of the piston 31 exceeds that of the valve seat 27 must be great enough to enable the pressure at port 15 to prevail over the spring which urges valve 27 to closed position.

When the main valve 19 has been positioned tn supply pressure liquid to the port 15 and the opened valve 27 permits return ow of liquid through port 16 and conduit 18, the unit fluid pressure existing at motor port 12 and transmitted to the motor will essentially equal the pressure drop across the valve 27. If that unit pressure is suicient to overcome the load on the motor 10, the motor will extend against the load. However, if such unit pressure is insufficient to overcome the load on the motor, the load will force the motor piston downwardly and displace liquid which, entering the passages 13', will join that supplied by the pump and ow to return past Valve 27. Since the pressure-drop across the valve 27 depends upon the extent to which it is closed, the lever 36 can be manipulated to cause the motor piston to be raised, be lowered, or remain in any fixed position of adjustment.

If the main valve 19 is reversed to connect port 16 of the modulating valve to the pump and port 15 to return, the piston 31 will move to the left against the shoulder 33 and the liquid supplied by the pump lwill tend to -ow past valve 27 to the motor 10 to raise the Patented Oct. 4, 1960 t 3 piston'thereof; and unlessthe rod *35 is held in its extreme leftward position by a force great enough to overcome the fluid pressure acting rightwardly on the valve 27, liquid will so flow to the motor 10. In this connection, it maybe noted that the eiect of iluid pres-I surein urging the valve 27 toward open position can be greater when thepressure fluid is supplied to the port 16 than when it is supplied to the port 15; since in the former case the pressure is effective over the area of the valve seat 27' while in the latter it is effective only over the increment by which the area of the piston 31 exceeds that of the valve seat. It is therefore possible to impose on the rod 35 and control lever 36 a frictional resistance to movement which will be suicient to retain them in `any position of adjustment When port 15 is connected to the pump but which will be insutlicient tovhold the valve 27 seated when port 16 is connected to the pump. thejmain valve 19 to the condition in which it directs pressure liquid to port 16 can be employed as an overriding control Which Will cause extension of the motor to its limit irrespective of the position occupied by the control lever 36 at the time the valve 19 was adjusted.

It will be-understood that the precise construction i1- lustrated and above described is set forth merely oy Way of example and that our invention is not limited thereto.

We claim as our invention: y

-1. In a hydraulic system having a motor, a source of liquid under pressure, and a return, means for controlling the oW of liquid to and from the motor, said means comprising a modulating valve having a motor port connected to `the motor and first and second additional ports, said modulating valve including passages connecting said motor port to said additional ports and including 4iirst and second check valves opening toward In such an arrangement, adjustment of.

the motor port,'means for connecting said first additional port to the source of liquid under pressure and said second additional port to the return, means responsive to pressure at said iirst additional port for urging said second check valve to open position, and adjustable control means for limiting opening of said second check valve under the influence of said pressure-responsive means.

2. A system as set forth insclaim l with the addition that said connecting means comprises `a.fou-r-way valve adjustable to connect either of said additional ports to the source of liquid under pressure andthe other ofs'uch additional ports to the return.

3. A modulating valve for use in controlling ahydraulic motor, 'comprising a 'housing having a bore, a motor port, and passages connecting opposite ends of said bore with said motor port, said housing having two additional ports communicating respectively with opposite ends of said bore, said passages being provided respectively with check valves opening toward the motor port, a pistony in said bore, means operativeby movement of said piston in response to pressure at oneend of ysaid bore for moving toward open position the check valve in thepassage connected to the opposite end of the bore, and an adjustable control means for limiting opening of the latter check valve.

4. A valve as set forth in claim 3 with` the addition that the last mentioned check valve includes a seat aligned With said bore and a Valve member engageable with the outerside ofy such seat, said piston-operated means including a member of lesser diameter than the valve seat and secured to the piston in position to ex-k No references cited.

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