US3824895A - Fluid ram provided with means for braking the ram piston at the end of its stroke - Google Patents

Abstract

A fluid ram, for example a hydraulic ram, is provided with means for braking the ram piston at the end of its stroke. According to the invention the piston is braked by the action of the ram working fluid, and means are provided for preventing the pressure of the working fluid becoming excessively high. In one embodiment the entire braking means is located inside the ram in order to simplify connection to the working fluid supply circuit. The invention is applicable to both single and double action rams.

Description

United States Patent n91 Martin July 23, 1974 I FLUID RAM PROVIDED WITH MEANS FOR BRAKING THE RAM PISTON AT THE END OF ITS STROKE [75] Inventor:

[73] Assignee: Societe Anonyme Poclain, Le

Plessis-Belleville (Oise), France [22] Filed: Apr. 23, 1973 [21] Appl. No.: 353,676

Louis Martin, Senlis, France [30] Foreign Application Priority Data May 3, 1972 France 72.15721 [52] US. Cl.....; 91/401, 91/422 [51] Int. Cl F15b.l5/22 [58] Field of Search 91/401, 422

[56] References Cited UNITED STATES PATENTS 7/1966 Madland et a1 91/26 3,605,409 8/1971 House 01 all. 91/401 X Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Wi|liam F. Woods Attorney, Agent, or FirmNathaniel A. Humphrics [5 7 ABSTRACT A fluid ram, for example a hydraulic ram, is provided with means for braking the ram piston at the end of its stroke. According to the invention the piston is braked by the action of the ram workingfluid, and means are provided for preventing the pressure of the working fluid becoming excessively high. In one embodiment the entire braking means is located inside the ram in order to simplify connection to the working fluid supply circuit. The invention is applicable to both single and double action rams.

5 Claims, 3 Drawing Figures PATENTEuJuLzslau sum 2 or 2 FLUID RAM PROVIDED WITH MEANS FOR BRAKING THE RAM PISTON AT THE END OF ITS STROKE BACKGROUND OF THE INVENTION The use of fluid rams, and of hydraulic rams in particular, has shown that it is necessary to limit the end of the piston stroke, so as not to damage the cylinder. Certain rams already have apparatus which enable the piston to be braked at the end of its stroke, by the action of the fluid itself.

However, in such apparatus, too high pressures must not be produced during braking, as they would finally damage the ram. In short, if the use of calibrated valves for limiting the pressure of a fluid in a chamber is known, the usual arrangement lead to the construction of additional connections outside the organ having the said chamber, and this is not very satisfactory, for it is wont to complicate'the connections and increase their number, consequently increasing the chance of leaks.

. SUMMARY OF THE INVENTION The invention provides a fluid ram comprising:

a cylinder,

a piston-piston rod assembly mounted slidably in the said cylinder,

an inlet chamber, and a delivery chamber, definedin the cylinder by the piston, separate and arranged on either side of this piston,

an inlet conduit, and a delivery conduit, connecting the inlet and delivery chambers respectively to the outside of the cylinder,

and a shock-absorption apparatus for the end-of the piston stroke having an auxiliary chamber which, when the piston is adjacent to one of the ends of the cylinder and is approaching its extreme position corresponding to the said end, is initially in communication with the delivery conduit and is then substantially isolated from the said delivery conduit,

a communication conduit which is formed in the piston-piston rod assembly and connects the inlet chamber to the delivery conduit;

a controlled valve which is arranged in the said communication conduit,

a piston for determining the opening of said controlled valve, to which this controlled valve is linked,

and an elastic organ which is linked between the controlled valve and the piston-piston rod assembly and the influence of which tends to keep the said controlled valve in its closed position and is antagonistic to the effect on the control piston of the fluid contained in the auxiliary chamber. Advantageously, the communication conduit passes through the piston for determining the opening of the controlled valve. A

Preferably, the ram also includes:

an auxiliary conduit which connects the auxiliary chamber to the delivery conduit and which is formed in the piston-piston rod assembly,

and a calibrated valve which is arranged in the auxiliary conduit so as to limit the pressure of the fluid in the auxiliary chamber to a given value, while allowing for possible passage of the fluid from the said auxiliary chamber to the delivery conduit.

with the invention;

When this ram is of the double-action type, it is may be provided with another auxiliary chamber which, when the piston is adjacent to the other end of the cylinder and is approaching its extreme position corresponding to the said other end, is initially in communication with the inlet conduit, and is then substantially isolated from the inlet conduit, and which, in this latter arrangement, is placed in at least partial communication with the communication conduit through the said controlled valve, which then acts as another calibrated valve.

This other auxiliary chamber is preferably defined by an auxiliary piston, which is hollowed out, is arranged in the inlet chamber, and is mounted slidably relative to the ram piston. A non-return valve is inserted between this other auxiliary chamber and the inlet chamber so as to allow passage of fluid from the inlet chamber to the said other auxiliary chamber.

A better understanding of the invention will be obtained and secondary features and their advantages will become apparent in the course of the description of the embodiments presented below by way of example.

It will be understood that the description and drawings are only for guidance and are not limiting.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an axial section of a first ram in accordance FIG. 2 is an axial section of a second rain in accordance with the invention;

FIG. 3 shows a third embodiment, in axial section.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Theram shown in FIG. 1 consists of a cylinder 1 and a piston 2 having two faces 20 and 2b, to which is linked a piston rod 3. Seals 4 are inserted between piston 2 and cylinder 1 and between the piston rod 3 and cylinder 1. Piston 2 is mounted slidably in cylinder 1 and, with the said cylinder, defines with its face 2a a chamber 5, known as the delivery chamber, and with its face 2b a chamber 6, known as the inlet chamber. Moreover, at this point it will be noted that, when the ram is of the double-action type, the pressurised fluid is selectively admitted to a first of these two chambers, the second of these two chambers itself being placed in communication with a discharge reservoir. The terms used for chambers 5 and 6 are, therefore, only for convenience, but do not necessarily describe the function of the corresponding chamber.

Piston rod 3 in unitarily connected to the piston 2 at a radially extending surface 7 defining one end of a first portion of the piston 2 having a relatively small diameter of such dimension as to be matingly insertable in a first portion 8 of cylinder 1 which is also of relatively small diameter. Additionally, the end portion of piston 2 opposite the connection to rod 3 comprises a second portion of the piston which is of larger diameter dimensioned to be matingly received in a larger diameter portion of the casing 1 extending to the right of a radial surface 8a as illustrated in FIG. 1. Consequently, when the piston moves to the left to the dotted line position 7a illustrated in FIGS. 1 and 2, a first auxiliary chamber 9 is formed. It is to be noted that during intermediate movement of the piston from right to left as viewed in FIG. I, the fluid in the auxiliary chamber 9 is forced outwardly into the first or smaller diameter portion of the cylinder but that upon the piston arriving at the position 7a, the fluid in chamber 9 cannot, due to the position of the piston, continue to flow in the latter manner.

It will be noticed that a conduit, known as delivery conduit 10, connects the first portion 8 of the cylinder 1 to the exterior ofthe cylinder 1. A cavity 13 is formed in the piston 2 and the piston rod 3. A withdrawable closure has been provided for cavity 13. In this way, it has been possible to introduce into housing 13 a control piston 14 for determining the opening of a valve 15. A conduit 16, formed in piston rod 3, connects the first auxiliary chamber 9 to piston 14, at least in posi tion 16a which it occupies, when chamber 9is effectively formed. Valve is arranged in a conduit 17, which connects face 2b of piston 2 to chamber 33 defined by one end 14a of control piston 14. Moreover, valve 15 is slidably guided by guides 18 bearing on a cylindrical surface 19. Furthermore, conduits 19a pass through piston 14, and connect its two faces 14a and 14b. They run into a chamber 20 which, when the first auxiliary chamber 9 is formed, opens through a conduit 21 into housing 8. In fact, conduits 17, 19a and 21 together constitute a communication conduit, which connects faces 2a and 2b of piston 2. A spring 22 tends to hold valve 15 against its seat and its influence is in a direction opposite the direction of the force on the control piston 14 created by the pressure of fluid in the first auxiliary chamber 9. I

It will be noted that conduit 16 connects the first auxiliary chamber 9 to a chamber 20a defined by a portion of face 14a of piston 14. Moreover, a conduit 11a connects the said chamber 20a to chamber 20. Conduit 11a runs into chamber 20 through a bore 34. A valve 12a, guided axially in bore 34, has a calibrated spring, which tends to close it against the antagonistic influences of the pressure of the fluid contained in chamber 20a. In this way, a passage is formed between auxiliary chamber 9 and housing 8, through conduits 16, 11a and 21, bore 34 and valve 12a.

FIG. 2 shows a simplified, equivalent embodiment of the assembly of conduits 16, 11a and 21 and valve 12a. The existence will be noted of an auxiliary conduit 11, which connects the first auxiliary chamber 9 to the smaller diameter portion 8, being formed in piston rod 3. A calibrated valve 12, consisting of a ball-bearing and a spring for holding this ball-bearing in position, is arranged in auxiliary conduit 11 and allows passage of fluid from the first auxiliary chamber 9 to delivery conduit 10.

Finally, with reference to FIG. 3, a ram is shown which is similar to the ram of FIG. 2, while being provided with the following complementary apparatus.

Piston 2 has a cylindrical portion 23 adjacent to its face 2b, or which an auxiliary piston 24 is slidably mounted.

Piston 24 has an internal cavity 25 which, in cooperation with conduit 17, forms a second auxiliary chamber 26. A spring 27 returns piston 24 to a position which gives the maximum volume to chamber 26, while a stop 28 limits the clearance of the said piston 24.

A non-return valve 29 is arranged on the base 32 of I. piston 24 and connects the second auxiliary chamber 26 to chamber 6 of the ram. The latter chamber is deconduit 31, known as an inlet conduit, connects chamber 6 to the outside of cylinder 1.

The following description of methods of using the rams described above, will lead to a better understanding of the advantages which are obtained from them.

With the ram of FIG. 1, the case in question is one in which the pressurised fluid is admitted to chamber 6 and acts on face 2b of piston 2, in the direction caus ing a decreace in the value of the volume of chamber 5. The fluid contained in this chamber 5 is delivered but of cylinder 1 through conduit 10. Shoulder 7 then reaches 7a, which causes a considerable deceleration of the piston 2, the fluid contained in chamber 9 only being able to escape, in principle, through the passage of small cross section between shoulder 7a and the bore of housing 8. It will be noted in the first place that, when piston 2 is moved until the'pressure of the fluid contained inchamber 9 undergoes a considerable increase, the said fluid is conveyed by conduit 16 (or 16a) to act on piston 14, against the influence of spring 22. When the value of the pressure is sufficiently high, it pushes back piston 14. The pressure of the fluid contained in chamber 6 then allows valve 15 to open, which enables the said fluid (which is-the fluid which has caused the movement of piston 2) to escape back to the fluid reservoir, through conduits 17, 19a and 21. As a result, the influence of the fluid in chamber 6 on piston 2 is nullified. I

Furthermore, it could happen that the deceleration of the piston 2 would be so considerable that the pressure of the fluid in chamber 9 would exceed a critical value, beyond which there is a considerable risk of permanent distortion of cylinder 1. To avoid this result, the spring of valve 12a is so selected that the valve opens under the influence of the pressure of the fluid in chamber 9, when the said pressure reaches the above-mentioned critical value. Opening of valve 12a therefore enables the fluid in chamber 9 to escape through conduits 16, 11a and 21 into conduit 10 and avoids any risk of excess pressure.

The arrangement of conduits 16, llaand 21 and valve 12a in piston rod 3 itself, in addition to providing a compact ram and satisfactory protection of the valve, also completely eliminates the possibility of any leak due to the presence of valve 12a.

The embodiment illustrated in FIG. 3 comprises a double-acting cylinder in which the piston 2 is further modified to provide means for cushioning the stroke of the piston as it approaches the head 30 of the cylinder. This result provides cushioning for the end of the piston stroke at both ends of the cylinder and is achieved by the provision of a second auxiliary chamber 26 formed in the interior of a hollow auxiliary piston 24 and communicating with a normally closed valve 15 on its inner end.

Support for axial reciprocation of the hollow auxiliary piston 24 with respect to the piston 2 is provided by a slide support means 23 extending axially from the face 2b of piston 2. A radial lug 28 on the outer end of the slide support means 23 provides a stop for limiting the movement of the hollow auxiliary piston 24 to the right as viewed in FIG. 3. The second auxiliary chamber 26 provided on the interior of piston 24 is connected by a non-return valve 29 to the chamber 6 so as to allow the passage of fluid from the chamber 6 to the second auxiliary chamber 26. It should be noted that a coil compression spring 27 acts upon piston 24 to move the piston to its extreme righthand position illustrated in FIG. 3 in which position the auxiliary chamber 26 has its largest possible volume. Fluid within the chamber is prevented from exiting therefrom bythe nonreturn valve 29. Movement of the end 32 of the auxiliary piston against the cylinder end 30, as the piston approaches the end of its stroke moving to the right in FIG. 3, causes the piston,24 to move to the left to compress fluid within chamber 26 to decelerate piston 2. However, upon the pressure in chamber 26 reaching a predetermined value, valve opens to vent chamber 26 via passages 33, 19a, 20, 21 etc. in an obvious manner. Therefore, it will be appreciated that valve 15 serves to limit the maximum pressure in chamber 26 in essentially the same manner as valve 12 operates to vent pressure from the chamber 9 of the first embodiment. Consequently, valve 15 provides controlled communication with the high pressure side of the cylinder for cushioning the piston movement.

It will have been noticed that the different elements are all contained in cylinder 1 and are even arranged on the piston 2 of the ram. Here again, a well protected and leak-free arrangement is obtained. The extreme compactness and simplicity of the proposed solutions will be noted.

The invention is not limited to its embodiments which have been presented, but, on the contrary, covers all the modifications which could be made to them without departing from their scope or spirit.

What is claimed is: i a

1. A hydraulic ram comprising a cylinder having a first end portion and a second end portion, said second end portion being of a larger diameter than said first end portion, a piston mounted in said cylinder, said piston comprising a first piston portion of relatively small diameter dimensioned to matingly fit in the first end portion of said cylinder and a second piston portion of larger diameter dimensioned to matingly fit in the second end portion of said cylinder, piston rod means extending from said first end portion and being of a smaller diameter than said first piston portion, said piston rod means extending from said cylinder outward through seal means in an end wall of said cylinder, a delivery conduit extending through said cylinder wall and having an inner end defining an inlet communicating with outermost end portions of said first end portion of said cylinder, an auxiliary conduit extending through a portion of the piston rod and the piston providing communication between the outer periphery of the first piston portion and the outer periphery of a portion of the piston rod spaced from said piston in communication with said first cylinder portion as the piston moves toward the first end of the cylinder and calibrated valve means mounted in said auxiliary conduit for permitting fluid from the second cylinder portion on the side of the piston to which the piston rod is connected to flow through the auxiliary conduit in response to the pressure of said fluid in said auxiliary conduit reaching a predetermined value.

2. A fluid ram comprising a cylinder, a piston-piston rod assembly slidably mounted in said cylinder, an inlet chamber and a delivery chamber in the cylinder each respectively constituting the portions of the cylinder on opposite sides of the piston, an inlet conduit, a delivery conduit, said inlet conduit and said delivery conduit each being respectively connected to first and second opposite end portions of the cylinder for communication with the inlet and delivery chambers, shock absorbing means including an auxiliary chamber in said cylinder operable as the piston moves through an intermediate position in communication with said delivery conduit so that movement of the piston moves fluid from the auxiliary chamber to the delivery conduit with subsequent movement of the piston toward its extreme end position in the first end of the cylinder terminating communication of the auxiliary chamber with the delivery conduit to substantially isolate the auxiliary chamber, a communication conduit formed in the pistonpiston rod assembly extending between and connecting said inlet chamber to said delivery conduit, a control valve mounted in said communication conduit, an auxiliary conduit formed in the piston-piston rod assembly connecting the auxiliary chamber and the delivery conduit, a pressure actuated calibrated valve in the auxiliary chamber which opens upon the pressure in the auxiliary chamber reaching a predetermined value, a control piston connected to the control valve for adjusting the opening of said control valve in accordance with pressure applied to the control piston from said auxili-' ary chamber, and elastic biassing means positioned in and engaging the piston-piston rod assembly and also engaging the control piston for exerting force on the control piston which tends to keep the control valve in its closed position and opposes the force on the control piston caused by the pressure of the fluid contained in the auxiliary chamber.

3. The invention of claim 2 wherein the control piston for adjusting the opening of the control valve is mounted in a cylindrical portion of the auxiliary conduit.

4. The invention of claim 2 wherein said ram is of the double-action type and additionally including a second auxiliary chamber which, when the piston is adjacent to the second end portion of the cylinder and is closely approaching its extreme possible position in the second end portion of the cylinder, is initially in communication with the inlet conduit and is subsequently isolated from the inlet conduit by a portion of the cylinder and valve means providing at least partial communication of said second auxiliary chamber with the communication conduit through said control valve.

5. The invention of claim 4 wherein said second auxiliary chamber is formed in a hollow auxiliary piston mounted in said inlet chamber and additionally including slide support means on said piston slidably supporting said auxiliary piston and a non-return valve connected between said second auxiliary chamber and the inlet chamber so as to allow passage of fluid from the inlet chamber to said second auxiliary chamber.

Claims (5)

1. A hydraulic ram comprising a cylinder having a first end portion and a second end portion, said second end portion being of a larger diameter than saId first end portion, a piston mounted in said cylinder, said piston comprising a first piston portion of relatively small diameter dimensioned to matingly fit in the first end portion of said cylinder and a second piston portion of larger diameter dimensioned to matingly fit in the second end portion of said cylinder, piston rod means extending from said first end portion and being of a smaller diameter than said first piston portion, said piston rod means extending from said cylinder outward through seal means in an end wall of said cylinder, a delivery conduit extending through said cylinder wall and having an inner end defining an inlet communicating with outermost end portions of said first end portion of said cylinder, an auxiliary conduit extending through a portion of the piston rod and the piston providing communication between the outer periphery of the first piston portion and the outer periphery of a portion of the piston rod spaced from said piston in communication with said first cylinder portion as the piston moves toward the first end of the cylinder and calibrated valve means mounted in said auxiliary conduit for permitting fluid from the second cylinder portion on the side of the piston to which the piston rod is connected to flow through the auxiliary conduit in response to the pressure of said fluid in said auxiliary conduit reaching a predetermined value.

2. A fluid ram comprising a cylinder, a piston-piston rod assembly slidably mounted in said cylinder, an inlet chamber and a delivery chamber in the cylinder each respectively constituting the portions of the cylinder on opposite sides of the piston, an inlet conduit, a delivery conduit, said inlet conduit and said delivery conduit each being respectively connected to first and second opposite end portions of the cylinder for communication with the inlet and delivery chambers, shock absorbing means including an auxiliary chamber in said cylinder operable as the piston moves through an intermediate position in communication with said delivery conduit so that movement of the piston moves fluid from the auxiliary chamber to the delivery conduit with subsequent movement of the piston toward its extreme end position in the first end of the cylinder terminating communication of the auxiliary chamber with the delivery conduit to substantially isolate the auxiliary chamber, a communication conduit formed in the piston-piston rod assembly extending between and connecting said inlet chamber to said delivery conduit, a control valve mounted in said communication conduit, an auxiliary conduit formed in the piston-piston rod assembly connecting the auxiliary chamber and the delivery conduit, a pressure actuated calibrated valve in the auxiliary chamber which opens upon the pressure in the auxiliary chamber reaching a predetermined value, a control piston connected to the control valve for adjusting the opening of said control valve in accordance with pressure applied to the control piston from said auxiliary chamber, and elastic biassing means positioned in and engaging the piston-piston rod assembly and also engaging the control piston for exerting force on the control piston which tends to keep the control valve in its closed position and opposes the force on the control piston caused by the pressure of the fluid contained in the auxiliary chamber.

3. The invention of claim 2 wherein the control piston for adjusting the opening of the control valve is mounted in a cylindrical portion of the auxiliary conduit.

4. The invention of claim 2 wherein said ram is of the double-action type and additionally including a second auxiliary chamber which, when the piston is adjacent to the second end portion of the cylinder and is closely approaching its extreme possible position in the second end portion of the cylinder, is initially in communication with the inlet conduit and is subsequently isolated from the inlet conduit by a portion of the cylinder and valve means providing at least partial communication of said second aUxiliary chamber with the communication conduit through said control valve.

5. The invention of claim 4 wherein said second auxiliary chamber is formed in a hollow auxiliary piston mounted in said inlet chamber and additionally including slide support means on said piston slidably supporting said auxiliary piston and a non-return valve connected between said second auxiliary chamber and the inlet chamber so as to allow passage of fluid from the inlet chamber to said second auxiliary chamber.

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