US2971536A

US2971536A - Hydraulic control valve throttling mechanism

Info

Publication number: US2971536A
Application number: US744721A
Authority: US
Inventors: John A Junck; James E Scheidt
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1958-06-26
Filing date: 1958-06-26
Publication date: 1961-02-14
Anticipated expiration: 1978-02-14

Description

Feb. 14, 1961 J, JUNCK ETAL HYDRAULIC CONTROL VALVE THROTTLING MECHANiESM Filed June 26, 1958 INVENTORS JbH/v A. Jim/ck BY JZMESEScHE/DT TTORNEYS United States Patent HYDRAULIC CONTROL VALVE THROTTLING MECHANISM This invention relates to hydraulic control valves and particularly to the throttling mechanism therefor which is the means included in the valve structure to permit slow or gradual control of the mechanism controlled by the valve.

Many forms of hydraulic control valves include a shouldered spool reciprocable in a ported cylinder. As the spool is reciprocated in the cylinder, selected ports are opened and closed in order to direct fluid under pressure to desired places such as to a fluid motor or jack. Since the action of opening or closing a port with a simple spool shoulder is relatively abrupt, it is common practice to slot or notch the spool shoulders to obtain a slow throttling or metering effect and thus a desired gradual or smooth action of the fluid motor or jack. Commonly used designs of such throttling notches are found to create a dynamic force from the jet flow or turbulence which tends to urge the spool in the same direction as the. operator induced motion. Hence heavy spring pressure is required to effect return of the spool to a normal or neutral position.

It is the object of the present invention to provide a spool type valve with improved throttling notches and more specifically with notches which will eliminate any reactionary force exerted axially on the valve spool in the direction away from neutral position and permit return of the spool with a lighter spring. This also reduces the overall operator effort in actuating the valve since the operator works against a lighter spring load.

The invention is described herein in its application to a hydraulic control valve employed with a double acting hydraulic jack. It is not intended, however, to limit the scope of the invention to the particular valve illustrated and its adaptability to many forms of control valves, par ticularly of the spool type, will be apparent from the ensuing description.

Further objects and advantages of the invention will appear from an understanding of the following specification wherein reference is made to the accompanying draw- In the drawing:

Fig. 1 is a central sectional view through a spool valve illustrating the throttling means of the present invention and diagrammatically showing a source of fluid under pressure and a hydraulic jack to be actuated by the valve;

Fig. 2 is an-enlarged fragmentary section to illustrate the eifect of improved throttling means; and

Fig. 3 is an enlarged section similar to Fig. 2 but illustrating a conventional type of throttling means.

In the system illustrated in Fig. 1, a double acting hydraulic jack is illustrated at and is adapted to be actuated in either direction by fluid under pressure from a pump 11 which withdraws fluid from a reservoir 12. A return line 13 also leads to the reservoir and a relief valve of conventional design illustrated at 14 is employed in the usual manner in such a system. Control of fluid under pressure, which is directed to the jack 10 ice as well as control of the return circuit, is accomplished through a valve, the body of which is illustrated at 15. The valve 15 may be considered as typical of many valves used for this general purpose and the following brief description of the manner in which it operates will enable a ready understanding of the advantages of the throttling mechanism of the present invention.

The valve 15 has a cylindrical bore for the reception of a reciprocable valve spool 16 having grooves and land portions which cooperate with ports opening into the cylindrical bore to control direction of fluid flow through the valve. Fig. 1 shows a valve spool 16 in a neutral position in which it is balanced as by a spring 17 exerting pressure against the valve spool in one direction, as through a collar member 18, and reacting against the valve housing 15 in the opposite direction by means of a shouldered sleeve 19. With this arrangement, the spool is normally held in the position shown and may be moved in one direction or another through actuating leverage (not shown) which is connected to one extreme end 20 of the spool.

In the neutral position shown in Fig. l, fluid from the pump 11, which may be considered as continuously operating, is directed into an inlet port 21 and. is free to pass through the valve cylinder to

ports

22 and 23 and out through an exhaust port 24 and to the return line 13 without having effected the position of the jack 10.

When it is desired to extend the jack 10 by admission of fluid under pressure to its left end as illustrated in Fig. 1, the spool 16 is moved toward the right against resistance of the spring 17 until a land 26 on the valve closes communication to the port 23 in the manner shown in Fig. 2 and a land 27 on the spool closes communication to the port 22 except in the area of notches 28 formed in the land 27 and capable of being gradually closed by further movement toward the right for throttling purposes. This restriction of flow causes a build up of pressure in the inlet chamber 21 which is communicated to and opens a check valve 30 normally urged to a closed position by a spring 31. Opening of the check valve 30 admits fluid under pressure to a chamber 31 which enters the valve cylinder and surrounds the valve spool therein and, since the spool has been moved toward the right, the fluid is admitted to a chamber 32 through throttling notches illustrated in dotted lines at 33. The chamber 32 also communicates, through a port indicated in dotted lines at 34 and a conduit 35, with the letthand end of the jack 10 as shown. In the same position of the valve, fluid necessarily exhausted from the righthand end of the jack 10 flows through line 36 and port 37 into a chamber 38 now in communication, through throttling slots, with port 22 and outlet 24 where it is directed through conduit 13 back to the reservoir 12.

Actuation of the jack in the opposite direction is effected by movement of the spool 16 oppositely or to the left where throttling slots 40 shown in Fig. 2 control the flow of oil through port 23 to outlet 24. The course of fluid flowing to and returning from the jack is the reverse of that hereinabove described, the exhaust from the lefthand end of the jack flowing through conduit 35, chamber 32 and toward the exhaust port 24 through an outlet 42.

Operation of the valve spool 16 in either direction from the neutral position shown in Fig. 1 is resisted by compression of the spring 17 which is relied upon to return the spool to its neutral position when the operator releases the control lever. Heretofore throttling slots have been of the design shown at 28a and 40a in Fig. 3, and this design produced a turbulence and force reaction which tended to move the valve spool in the same direction that it was being moved by the operator. A heavy spring in place of that shown at 17 was required to overcome these forces and return the spool to its neutral position so that the effort expended by the operator in moving the spool was relatively great. One previously used design of these slots is shown at 28:1 and 46a, respectively, in Fig.3, where the slot is produced by a circular milling cutter like that employedfor cutting a keyway in a shaft. The fluid flow during throttling, as in a position illustrated in Fig. 3, is indicated by the arrow leaving thespool approximately tangent to the curved surfaces of slots 280. Due to the unbalance in forces caused by the change in velocity of oil jetting from slot 23a, a force is created to urge spool 16 to the right as indicated by arrow 45, which is away from the neutral position. In the present invention, the throttling notches shown at 28 and 40 in Fig. 2 are formed by cutting with an end mill or the like directed radially inwardly and at a slight angle with respect to spool 16 to provide shallow cylindrical pockets which capture the fluid and redirect it substantially radially from spool 16, as may be seen from the direction arrows in Fig. 2. At the same time, by virtue of the sharp turn in the direction of fluid fiow at the corner of the pockets, a secondary force is reacted axially on spool 16 in the same direction as spring 17 urging the valve to neutral position. This enables the use of the lighter spring shown and reduces the operator effort in overcoming the force of the spring each time that the valve is actuated.

We claim:

1. In a control valve having a spool reciprocable in a cylinder and having a land for opening and closing a port in the cylinder upon movement of the spool in one direction and a spring urging the spool in the opposite direction, the improvement which comprises a shallow throttling notch intercepting an edge of said land and forming a pocket wherein reaction of fluid passing through the notch will urge the spool in the same direction as the spring.

2. In a control valve having a spool reciprocable in a cylinder and having a land for opening and closing a port in the cylinder upon movement of the spool in one direction and a spring urging the spool in the opposite direction, the improvement which comprises a shallow cylindrical throttling notch'intercepting an edge of said land and forminga cylindrical pocket with the axis of the cylinder disposed radially inwardly of the spool.

3. In a control valve having a spool reciprocable in a cylinder and having a land for opening and .closing a port in the cylinder upon movement of the spool in one direction and .a spring urging thespool in the opposite direction, the improvementwhich comprises a throttling notch intercepting an edge of said land and forming a cylindrical pocket with the axis of the cylinder disposed radially inwardly ofthe spool and inclined in the direction of the springforce against the spool.

4. In a valve having a spring centered spool reciprocable in a cylinder and having lands for opening and closing ports in the cylinder wall, the improvement which comprises throttling slots intercepting the edges of the lands and including twoangularly related surfaces converging in the direction of fluid flow and spring force to react theforce of fluid passing through them and create a tendency to move the spool toward a neutral position.

References Cited in the file of this patent UNITED STATESPATENTS 2,480,403 Ferris Aug. 30, 1949 2,812,775 Hodgson Nov. 12, 19 57 FOREIGN PATENTS 589,937 Germany Sept. 8, 1 932