Title:
PREFILL VALVE FOR HYDRAULIC CLAMPING DEVICES
United States Patent 3599534


Abstract:
A prefill valve for providing a large quantity of relatively low-pressure hydraulic fluid to fill the space behind a moving piston for a portion of its operating cycle and thereafter sealing off the low-pressure source and providing communication between that space and a separate, high-pressure fluid source. The valve includes a slidable sleeve having a double-acting piston at one end and a face at its other end which cooperates with the valve body to effect closing of the low-pressure fluid source. The valve is actuated by one or more hydraulically actuated auxiliary pistons which move the slidable sleeve to the closed position and interconnect the high-pressure fluid source with the space behind the piston.



Inventors:
PURCHON RICHARD
Application Number:
05/007600
Publication Date:
08/17/1971
Filing Date:
02/02/1970
Assignee:
CINCINNATI MILACRON INC.
Primary Class:
Other Classes:
60/429, 91/519
International Classes:
F15B11/08; (IPC1-7): F15B11/00
Field of Search:
60/52HF,97H 91
View Patent Images:
US Patent References:
2614539Fluid pressure actuated reversing valve for hydraulic rams1952-10-21Ernst
2544731Prefill valve1951-03-13Sedgwick
2490625Transfer molding press1949-12-06Hall



Foreign References:
FR836400A
Primary Examiner:
Geoghegan, Edgar W.
Claims:
What I claim is

1. In a fluid-operated press having a relatively small diameter piston to provide rapid movement of a ram member to a predetermined position and a relatively large diameter piston to provide a large force, a valve member including an end wall and a valve body attached thereto, said valve member having at least a pair of fluid inlets and a pair of fluid outlets, each of said fluid outlets being adapted to communicate with one of said pistons, one of said fluid inlets being in communication with a source of relatively low-pressure fluid and the other of said fluid inlets being in communication with a source of relatively high-pressure fluid, a generally annular closure member slidably positioned within said valve body in fluidtight relationship therewith and incorporating a double-acting piston adapted to selectively open or close said low-pressure fluid inlet between said source of relatively low-pressure fluid and one of said actuating pistons, said closure member being biased to a position to permit flow from said low-pressure source and said actuating piston, the improvement comprising:

2. The valve member of claim 1 wherein said high-pressure source is in communication with said small diameter piston and said low-pressure source is in communication initially with said large diameter piston but upon actuation of said closure member to close said low-pressure fluid inlet said large diameter piston is put into communication with said high-pressure source.

3. The valve member of claim 1 wherein the effective area of the face of the piston of said annular closure member opposite the side against which the auxiliary pistons bear is greater than the effective area of the outermost faces of said auxiliary pistons.

4. The valve member of claim 1 wherein said high-pressure hydraulic fluid is conveyed to said auxiliary pistons by means of substantially radial passageways interconnecting the bores of said pistons with said high-pressure source.

5. The valve member of claim 1 wherein said radial passageways in said auxiliary pistons are positioned substantially at the ends of the internal bore of the auxiliary pistons.

6. The valve member of claim 1 wherein the communication between the opposite ends of said annular closure member takes place along the inner cylindrical surface thereof.

Description:
BACKGROUND OF THE INVENTION

This invention relates generally to flow control valves for hydraulic systems and, more particularly, to a prefill valve which permits the flow of a relatively large volume of low-pressure hydraulic fluid from a low-pressure source to a clamping device, and thereafter isolates that source and provides communication between the clamping device and a source of high-pressure hydraulic fluid.

In hydraulically operated clamping devices, it frequently is desirable to rapidly traverse the moving portion of the clamping device, which can be a large clamping piston, for example, to a particular point in order to reduce the cycle time. This is generally accomplished by providing a separate, small area piston which is in communication with a relatively high-pressure source to provide a rapid travel of the clamping system while at the same time utilizing only a small volume of hydraulic fluid. When the small area, traversing piston and the large area clamping piston are coaxially arranged with the smaller traversing piston positioned within the larger, clamping piston, it is necessary that hydraulic fluid be provided behind the large diameter clamping piston while it is moving so that when the high clamping force is required, the clamping piston can be quickly put into communication with a source of high-pressure fluid. Otherwise a time delay would be necessary until the space behind the large diameter piston is filled with fluid. Preferably, the fluid behind the large diameter piston is provided from a relatively low-pressure source to reduce the size, and thus the cost, of the hydraulic high-pressure pump required.

In order to permit the operation above described, it is necessary that a suitable valve be provided to permit the flow of hydraulic fluid from the low-pressure source to the clamping piston during the rapid traverse portion of the cycle and thereafter isolate the low-pressure fluid source and provide communication between the clamping piston and a source of high-pressure fluid. It is an object of the present invention to provide such a valve which, because of its construction, is relatively simple to assemble and has a long service life.

SUMMARY OF THE INVENTION

Briefly stated, in accordance with one aspect of the present invention, a prefill valve for hydraulic clamping devices is provided which includes a pair of fluid inlets, one connected to a source of relatively low-pressure hydraulic fluid and the other connected to a source of relatively high-pressure hydraulic fluid. The valve also includes a pair of outlets, one in communication with a piston-cylinder arrangement wherein the piston has a relatively small area and requires only a small quantity of hydraulic fluid, and the other of which is in communication with a relatively large piston-cylinder arrangement which requires a high volume of hydraulic fluid. The valve incorporates a slideable sleeve which is adapted to selectively permit or prevent communication between the relatively low-pressure fluid source and the large diameter, high-volume piston-cylinder arrangement. The sleeve incorporates a double-acting piston at the end opposite the end which provides the closure between the low-pressure fluid source and the high-volume piston-cylinder arrangement and is biased to the open position to provide the communication between the low-pressure fluid source and the large diameter, high-volume piston-cylinder arrangement. The sleeve is moved to the position whereby the source of relatively low-pressure hydraulic fluid is closed by means of one or more auxiliary pistons which bear against the opposite face of the sleeve. The auxiliary pistons are hydraulically actuated and move the sleeve laterally whereupon communication between the source of relatively high-pressure hydraulic fluid and the large diameter high-volume clamping piston-cylinder arrangement is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary cross-sectional view of a portion of a hydraulic clamping device showing the valve structure of the present invention in its operative environment.

FIG. 2 is a view of the left end of the device shown in FIG. 1.

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 2 and shows the sleeve member in the open position in the upper portion of the figure and in the closed position in the lower half of the figure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings and particularly to FIG. 1 thereof, there is shown a hydraulic clamping device 10 incorporating a ram 11 which is slidably positioned in a cylinder 12 adapted to provide the desired clamping pressure. Such clamping devices can be employed in diecasting and injection-molding machines to hold a movable mold half and a stationary mold half tightly together against the high separating forces imposed by the molten material injected in to the mold cavity under high pressure. Other applications for clamping devices of the character herein described include hydraulic presses of various types.

Ram 11 includes a large, double-acting clamping piston 13 at the end opposite the ram surface 14 to permit the ram to be moved in either of two directions by pressurized hydraulic fluid brought into communication with one of the faces of piston 13. Concentrically positioned within ram 11 is a bore 15 within which a piston 16 having a diameter smaller than that of piston 13 is positioned. Although ram 11 is capable of axial movement within cylinder 12 piston 16 can be stationary and can be affixed to a tubular element 17 which extends through piston 16 and provides communication between a cylindrical space 18 within ram 11 and a source of high-pressure hydraulic fluid (not shown).

Tubular member 17 is supported at its opposite end by a valve member 19 which is in communication with a source of relatively low-pressure hydraulic fluid, such as, for example, reservoir 20 and is also in communication with a source of high-pressure hydraulic fluid (not shown). The source of relatively low-pressure hydraulic fluid or reservoir 20, can be positioned above valve member 19 as shown in FIG. 1 so that the fluid can flow into and through the device by means of gravity. Under those conditions, the fluid can be at substantially ambient pressure. Alternatively, however, the source of relatively low-pressure hydraulic fluid can be positioned below valve member 19, but under those conditions it would be necessary that some pressure be applied to the fluid to cause it to flow up to the valve.

Valve member 19 constitutes a prefill valve which comprises a valve housing 21 an inlet port 22 to permit communication between the low-pressure fluid source and piston 13 through a chamber 23 and an annular passageway 24. A tubular sleeve 25 is slidably positioned within valve housing 21 to effect closure of inlet port 22. The closure is effected by the end 26 of sleeve 25 which is adapted to cooperate with an annular abutment 27 provided in valve housing 21 and thus preclude flow from inlet port 22 to annular passageway 24. Axial travel of sleeve 25 is limited in one direction by abutment 27 and in the other direction by an end wall 28 attached to valve housing 21 and by means of bolts 29, and through which the high-pressure hydraulic fluid is supplied as will be hereinafter explained.

The internal structure of valve member 19 is shown in greater detail in FIG. 3, which is a cross-sectional view of the valve wherein the upper half shows the valve in the open position, permitting flow from chamber 23 to annular passageway 24, while the lower half shows the valve in the closed position. As therein shown, sleeve 25 is of annular conformation, slidably positioned within valve housing 21, and incorporates a double-acting piston 30 at the end opposite closure end 26. Piston 30 on sleeve 25 can be axially moved within a bore 31 while the body portion 32 of sleeve 25 is carried within bore 33, which is of somewhat smaller diameter than bore 31. Additionally, the inner diameter of sleeve 25 is greater than the outer diameter of tubular member 17, for reasons which will subsequently be explained. Sleeve 25 is normally in the open position shown in the upper half of FIG. 3 and is biased into that position by means of pressurized hydraulic fluid supplied to the rear face 34 of piston 30 through a radial passageway 35 in valve housing 21.

When the parts of valve member 19 are in the position shown in FIG. 1 and in the upper half of FIG. 3, the high-pressure fluid is supplied through tubular element 17 to cylindrical space 18 to rapidly traverse ram 11 while the space behind large diameter piston 13 is in communication with the relatively low-pressure fluid in reservoir 20 and thus as ram 11 moves outwardly, or to the right as seen in FIG. 1, the reduced pressure behind large piston 13 as it moves outwardly causes the hydraulic fluid in the reservoir to flow through valve member 19 and into cylinder 12, thus filling the space within cylinder 12 behind piston 13 and also the space within annular passageway 24.

Referring once again to FIG. 3, end wall 28 of valve member 19 includes a passageway 36 which provides communication between the interior of tubular member 17 and the source of relatively high hydraulic fluid pressure (not shown). Tubular member 17 is connected to end wall 28 in fluidtight relationship. Positioned parallel to passageway 36 and spaced radially therefrom are a pair of axial bores 37, 38 within which sleeves 39, 40, respectively are retained, as by means of a press fit, for example. Auxiliary pistons 41, 42, are positioned in sliding and substantially fluidtight relationships within sleeves 39, 40, respectively, and are adapted to have one end thereof in direct contact with the front face 43 of piston 30 on sleeve 25. Auxiliary pistons 41, 42 each include a central bore 44, 45, respectively, which are closed at each end thereof and which include radially positioned apertures 46, 47, and 48, 49 near each of the ends of the bores 44, 45, respectively. The apertures 46, 47, 48, and 49 can extend through both sides of pistons 41, 42 as shown, or they can extend through only one side, if desired. Additionally, intermediate apertures 50, 51 can be positioned between apertures 46, 47 and 48, 49, respectively, for reasons to be hereinafter described.

One of the ends of each of the auxiliary pistons can be closed by means of plugs 52, 53, and the other ends are closed by virtue of the fact that the bores 44, 45 do not extend throughout the length of pistons 41, 42, respectively.

Bores 37, 38 are sealed by means of plugs 54, 55, respectively. The outer portions of bores 37, 38 between plugs 54, 55, and sleeves 39, 40, respectively, are interconnected by means of a passageway 56 (see also FIG. 2) which extends to the periphery of end wall 28 and is connected to the source of high fluid pressure to impose an axial thrust on auxiliary pistons 41, 42, and thus cause them forcefully to bear against the front face 43 of piston 30. Since rear face 34 of piston 30 is also in communication with the source of high fluid pressure, in order for the sleeve 25 to remain in the open position as shown in the upper half of FIG. 3, it is necessary that the effective area of rear face 34 of piston 30 be greater than the sum of the effective areas of auxiliary pistons 41, 42 at the ends within which plugs 52, 53, respectively, are positioned.

Extending radially from passageway 36 are a pair of passageways 57, 58 which communicate with apertures 39a, 40a in sleeves 39, 40, respectively, within which auxiliary pistons 41, 42 travel. Passageways 57, 58 are plugged at their outer ends by means of plugs 59, 60, respectively, and provide communication between the source of high fluid pressure and sleeves 39, 40.

In operation, valve member 19 is initially in the position shown in the upper half of FIG. 3 wherein tubular sleeve 25 is in its retracted position. When high-pressure hydraulic fluid is caused to flow within passageway 36 and into tubular element 17 at the end of which piston 16 is positioned to define cylindrical space 18 in ram 11, the resulting unbalanced force causes ram 11 to move to the right as the parts are shown in FIG. 1. As ram 11 moves to the right, the space within cylinder 12 behind large piston 13 is at lower pressure than the pressure of the fluid within the relatively low-pressure fluid reservoir and thus fluid is caused to flow behind the large piston 13 and fill the space in the left side of cylinder 12.

When ram 11 has reached a predetermined point in its path of travel, the flow of high-pressure fluid to cylindrical space 18 is stopped. The pressure on rear face 34 of piston 30 is then relieved, resulting in an unbalanced force on piston 30 caused by the pressure on rear face 34 being lower than the pressure acting on the outermost ends of auxiliary pistons 41, 42 and against plugs 52, 53, respectively, which unbalanced force causes sleeve 25 to move to the right to assume the position shown in the lower half of FIG. 3. In that position, closure end 26 of sleeve 25 contacts annular abutment 27 in valve housing 21 and thus closes off the source of relatively low-pressure fluid from the area behind large piston 13. After auxiliary pistons 41, 42 are fully extended to cause sleeve 25 to seal inlet port 22 from annular passageway 24, apertures 46, 48 is pistons 41, 42, respectively, are brought into registry with apertures 39a, 40a in sleeves 39, 40, respectively, and thus permit the high-pressure fluid which is present in passageway 36 to flow through radial passageways 57, 58 and into central bores 44, 45 of auxiliary pistons 41, 42 and out through apertures 47, 49 at the opposite ends of auxiliary pistons 41, 42, respectively, to flow into the space vacated by front face 43 of piston 30 and thus pressurize that area. Since the inner surface of sleeve 25 is spaced from the outer surface of tubular member 17, the high-pressure hydraulic fluid also fills the annular space between sleeve 25 and tubular member 17 and thus pressurizes the space within cylinder 12 and behind large piston 13, thereby causing the latter to move toward the right as seen in FIG. 1 the desired distance. Thus, the high fluid pressure is communicated to the surface of large piston 13, causing the same to act with a very high force.

While particular embodiments of the invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention and it is intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.