US2977932A

US2977932A - Hydraulic actuator

Info

Publication number: US2977932A
Application number: US566657A
Authority: US
Inventors: Towler Frank Hathorn
Original assignee: Electraulic Presses Ltd
Current assignee: Electraulic Presses Ltd
Priority date: 1955-03-12
Filing date: 1956-02-20
Publication date: 1961-04-04
Anticipated expiration: 1978-04-04

Description

April 4, 1961 TWLER 2,977,932

HYDRAULIC ACTUATOR Fi led Feb. 20, 1956 2 Sheets$heet 1 /N VENTOR JOHN MAURHZE TowLER oeceasrs.

K i-RANK nxrnoml TOWER Exam-ran A TTORNE Y5 APril 1961 J. M. TOWLER 2,977,932

HYDRAULIC ACTUATOR Filed Feb. 20, 1956 2 Sheets-Sheet 2 2 57 i 2 fig 7 FROM PUMP l/Vl/E/VTOA By JOHN MAURICE TOM LE1? DECL'ASED FRANK HATfi/OR/V TOIa/LER, EXECUTOR HTTORIVE \S' United States Patent O7 HYDRAULIC ACTUATOR John Maurice Towler, deceased, late of Mayfair, London, England, by Frank Hathorn Towler, executor,

" Dob Park, Otley, England, assignor to Electraullc Presses Limited, Rodley, near Leeds, England, a hm ited-liability company of Great Britain 7 Filed Feb. 20, 1956, Ser. No. 566,657

Claims priority, application Great Britain Mar. 12, 1955 1 Claim; (Cl. 121-38) This invention relates to hydraulic actuating pistons and cylinders such as may be used to move the spindle of a hydraulic valve or other device.

One object of this invention is to provide an actuating piston and cylinder directly supplied with pressure liquid from a pump of known capacity and so constructed that only a portion of the pump capacity is used to move the actuating piston, the balance of the pump capacity being discharged to exhaust, such that the actuating piston is moved at a pre-determined speed. Another object of this invention is to provide an actuating piston and cylinder which may be supplied with pressure liquid from any source at a very high rate of flow and so constructed that the piston may be moved almost instantaneously without causing undue shock in the supply line to the actuating cylinder.

. Broadly the present invention consists in hydraulic actuating means comprising a piston in a cylinder which cylinder has an inlet for pressure liquid for moving the piston when efiecting its pressure stroke and an outlet for carrying away said pressure liquid during said pressure stroke, the arrangement being such that said inlet and outlet are connected so that pressure liquid is free to escape through said outlet at a controlled rate until the piston has completed its pressure stroke when said outlet is automatically isolated from said inlet and the flow of pressure liquid through said outlet is stopped.

In hydraulic actuating means according to a preferred embodiment of the invention a restricted orifice of predetermined area is provided in the connection between the pressure liquid inlet and outlet also valve means which closes said connection automatically when the piston reaches the end of its pressure stroke. A further restricted orifice is also provided in the passage which connects the pressure liquid inlet to the area of the piston against which it acts to perform the pressure stroke of the piston.

An embodiment as above although suitable for use in all cases where a hydraulic actuator is required the piston of which moves at a controlled rate is particularly suitable for use as the actuating means for opening the prefill-exhaust valve of a hydraulic press.

In order that the invention may be clearly understood and carried into effect a hydraulic actuator according to the above embodiment will now be described, by way of example, by aid of the accompanying drawings of which:

Fig. 1 shows a preferred embodiment of the actuator in sectional elevation through its actuating piston and cylinder.

Fig. 2 is a diagrammatic view showing the actuator in relation to a conventional press.

Fig. 3 is a fragmentary sectional view showing a modified form of orifice defining means. I

Fig. 4 is a fragmentary sectional view showing another modified orifice defining means.

The hydraulic actuating means shown in the drawing comprises an actuating'piston 1 and reciprocable in a cylinder defined by a casing 2 which cylinder is closed Patented Apr. 4, 1961 at the upper end by a cover 17. The actuating piston has a piston head 5 which is a close sliding fit in the cylinder bore and it has a stem 6 with a central bore 7 and orifice 8 opening into a central bore 3 in the piston and the latter is in communication with exhaust by the radial passages 9 in the piston head and radial passages 4 in the cylinder end. It will be noted that the piston head 5 has a valvesurface 14 which engages a seating surface 15 on the cylinder end when the piston is in its extreme downward position looking at the drawing. Consequently, whenthe piston 1 is in its extreme downward position, the radial passages 9 are isolated from exhaust by the seating of the

surfaces

14, 15. Pressure liquid is supplied to the piston by the connection 12 in the manifold block 13 which is attached to the cover 17. A loose washer 10 is provided as a sliding fit on the stem 6 and this washer'has a number of orifice holes 11. Thus, when liquid is supplied to the connection 12, it passes down the passage 16 and through the orifices 11 to the top of the piston head 5 in order to move the piston 1 downwards; and at the same time excess pressure liquid is spilled through the bore 7, orifice 8 and radial passages 9 and 4 to exhaust, until the piston 1 reaches the end of its downward stroke and the said radial passages 9 and 4 are closed to exhaust, when full pressure may be built up in the space above the piston head without further loss to exhaust. Then, when the connection 12 is connected to exhaust by means of a valve not shown, the piston 1 may be made to return by means of a spring 18 acting through a pressure plate 19 as shown in Fig. 2 and liquid above the piston head Swill lift the sliding washer 10 and pass freely to exhaust up passage 16 and out of the connection 12. Thus it will be seen that the speed of the downward stroke is restricted by the orifices 11 but that the return stroke is not so restricted since the washer 10 is free to lift.

'A piston and cylinder such as described above may be used to operate the prefill exhaust valve 20 of a hydraulic press such as that shown in Fig. 2, connection 12 being in communication with the return rams 21 of the hydraulic press so that when pressure is directed from the pushback or return rams to connection 12, the piston 1 will be moved downwards at a comparatively low pressure suflicient to open the prefill and exhaust valve, and when it is fully open, the

seating surfaces

14, 15 will be in contact, closing further communication with exhaust so that full pressure may then be built up in the pushback rams without any loss of pressure through connection 12 to the actuating piston and cylinder. Thus, if a pump of known capacity is connected to the return rams and connection 12, the actuating piston will be moved at a predetermined speed according to the number and size of orifices 11 and, when the actuating piston reaches the end of its stroke, thereby opening the prefill-exhaust valve, full pressure will be available to effect the return stroke of the press ram. It will be under stood that the function of orifice 8 in association with orifices 11 is to ensure suflicient pressure to move the piston 1 at the said predetermined speed. Another function of orifice 8 is to prevent a violent pressure surge in the pipe line to connection 12 when it is suddenly supplied with pressure liquid at a high rate of flow, That is to say that pressure liquid spills to exhaust through orifice 8 at the same time as pressure is building up on top of piston head 5 to start moving piston 1; whereas, without orifice 8, the build-up of pressure would be very sudden indeed.

Another embodiment of this invention as shown in Fig. 3 consists of a hydraulic actuating piston and cylinder generally as described in the previous embodiment, excepting that the washer 10 is replaced by a plain washer 22 concentrically guided in the cover 17 through the medium of radially projecting lugs 23 on the washer. The washer has a central bore 24 of larger diameter than the stem 6 such as to provide an annular orifice serving the same purpose as the orifices 11 described in the previous embodiment. Furthermore, the stem 6 may be tapered or varied in diameter along its length in order to vary the area of the orifice during the downward strokeof the piston, thereby varying the speed of the piston during the downward stroke.

If a suitable clearance is provided between the piston head 5 and the wall of the cylinder 2, for example a clearance of two to three thousandths of an inch for a piston having a diameter of approximately three inches, the stem 6 and passages 7, 3 and 9 may be dispensed with as such clearance has the same function as these passages. In such an alternative construction the reduced orifice or choke 8 can be accommodated in the passage 16 in the manner according to our co-pending U.S. application Serial No. 566,658, filed February 20, 1956, now Patent No. 2,904,074, which shows the same in the form of a fixed choke through which the pressure liquid flows to and from the head 5 of the piston 1.

Instead of using a fixed choke through which the pressure liquid to and from the piston 1 has to pass, an orifice 25 corresponding to the orifice 8 is formed in a piston associated with which is a movable valve member 26 functioning similarly to the valve washer 10. The member 26 also acts as a valve so as to perform the same function as the valve washer 10, by lifting on the return motion of the piston 1 to allow pressure liquid to pass freely to the connection 12 through passages provided in the aforesaid valve piston which passages by-pass the choke or orifice through which the liquid has to pass when the said valve piston is in its closed position and the piston 1 is moving in the opposite direction.

What is claimed is:

A hydraulically operated actuating device comprising, in combination, a casing defining an operating cylinder and a manifold connected to receive fluid under pressure, a cover member closing one end of said cylinder and having an opening affording communication between said manifold and said one end of the cylinder, said cylinder having an outlet to exhaust at its other end, a piston reciprocable in said cylinder, an orifice defining element dimensioned to extend over the opening in said cover member and operative to restrict fluid flow from said manifold to said cylinder, said element having a central aperture, a stem rigid with said piston positioned to extend through the opening in said cover member and through the aperture in said element to retain the element in alinement with the opening, and a restricted passage extending through said stem and said piston effective to by-pass a portion of the fluid supplied from said manifold to the outlet at the other end of said cylinder during the pressure stroke of said piston and in cooperation with said element in controlling the rate of advance of said piston, said orifice element being slidable on said stem away from the opening in said cover plate to afford substantially unrestricted flow of fluid from the cylinder in the return stroke of the piston.

References Cited in the file of this patent UNITED STATES PATENTS 236,151 Furney Jan. 4, 1881 713,788 Nethery Nov. 18, 1902 880,030 Leavitt Feb. 25, 1908 1,956,758 Ernst May 1, 1934 2,185,402 Dinzl Jan. 2, 1940 2,190,755 Dinzl Feb. 20, 1940 2,307,949 Phillips Jan. 12, 1943 2,324,697 Harrington July 20, 1943 2,583,295 Greer Jan. 22, 1952 2,656,855 Booth Oct. 27, 1953 2,664,106 Livers "1,, Dec. 29, 1953 2,676,661 Crooke Apr. 27, 1954 2,865,397 Chenault Dec. 23, 1958