Cushioning Device For Hydraulic Cylinders

Abstract

A cushioning device for the reciprocable piston of a hydraulic cylinder having a valve associated with the piston to be automatically shiftable by fluid flow and pressure fluctuations to progressively restrict flow from the cylinder as the piston reaches the end of its retraction stroke, but to allow substantially unrestricted fluid flow into the cylinder to move the piston in the opposite direction.

Description

BACKGROUND OF THE INVENTION

It is frequently desirable to provide a cushioning mechanism in a hydraulic cylinder for decelerating piston movement in a controlled manner as the piston approaches the end of its stroke. Many such cushioning devices are used commercially, but in most cases they are unduly complex and costly to manufacture.

SUMMARY AND OBJECTS OF THE INVENTION

Accordingly, it is an object of the present invention to provide an efficient, non-complex and inexpensive cushioning device for use in hydraulic cylinders.

Another object is to provide an improved cushioning device readily adaptable to progressively restrict the flow of fluid out of a hydraulic cylinder during its retraction stroke, particularly as the piston nears the end of such stroke, and yet provide substantially unrestricted fluid flow into the cylinder during its extension stroke.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a portion of a hydraulic cylinder utilizing the cushioning device of the present invention therein;

FIG. 2 is a sectional view of the cylinder taken along line II--II in FIG. 1; and

FIG. 3 is a cross sectional view similar to FIG. 1, but illustrating an alternative embodiment of the cushioning device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing, a cushioning means 10 is attached to a piston 12 of a hydraulic cylinder 13. The piston is reciprocally mounted in a bore 14 of a tubular housing 16 of the cylinder. The housing has an inlet-outlet port means 18 formed through a sidewall thereof which communicates with a conduit 20, adapted to selectively communicate with a source of pressurized hydraulic fluid or a sump via conventional control means (not shown). The port means is located closely adjacent to a closed end 22 of the cylinder.

The piston is secured to a rod 24 by a lock nut 26 and is provided with a reduced diameter section 28 to further provide a shoulder of the piston. The section is provided with an annular groove 30 which seats a snap ring 32 therein. An expansible chamber 34 is defined between the piston, the closed end of the cylinder and the housing to communicate with port means 18 and conduit 20.

Cushioning means 10 comprises a valve member constructed in the form of a cup-shaped annular member comprising a ring 36 and a radially inwardly extending flange 38. A central opening 40 of the flange has a substantially larger diameter than the outer diameter of section 28 of the piston. Flange 38 is retained axially by retention means comprising a shoulder of piston 12 and an annular washer 42 which abuts snap ring 32. Ring 36 has a plurality of annular grooves 44 formed on its outer periphery. As best shown in FIG. 2, the ring has an outer diameter substantially smaller than the inner diameter of bore 14.

OPERATION

FIG. 1 illustrates piston 12 at the end of its retraction stroke wherein the piston has moved leftwardly to exhaust fluid from chamber 34, through port 18 and into conduit 20. When ring 36 starts to cover the port, a pressure drop occurs across the port to force the ring upwardly. As shown in FIG. 2, substantial surface portions of the ring, along an arcuate segment thereof, move into substantial abutment with sidewall portions of the housing adjacent to the port.

In this manner, fluid flow out of the port is progressively restricted as the ring covers the port to decelerate the piston as it approaches the end of its retraction stroke. In order to prevent complete blockage of the port, annular grooves 44 are machined externally on the ring to provide an orifice affording limited continuous communication between chamber 34 and conduit 20.

During the extension stroke of cylinder operation, pressurized fluid from conduit 20 forces ring 36 radially inwardly to provide unrestricted fluid flow from port 18 to chamber 34.

FIG. 3 is a cross sectional view similar to FIG. 1, but illustrating a modified cushioning device. Like numerals are used to depict corresponding constructions with such numerals appearing in FIG. 3 being accompanied by an "a."

A cushioning means 10a is attached to a piston 12a of a hydraulic cylinder 13a. The piston is reciprocally mounted in a bore 14a defined in a tubular housing 16a having an inlet-outlet port means 18a formed through a sidewall thereof to communicate with a conduit 20a. Although the cushioning means is employed at the rod end of the cylinder, it could readily be adapted for use at the head end thereof, as suggested by FIG. 1.

The piston is secured to a rod 24a by lock nut 26a. An annular washer 27 is press-fitted (e.g., 0.0005-0.00015 in. press-fit) or otherwise suitably secured on rod 24a to abut piston 12a. The washer comprises an annular recess forming a circumferentially extending reduced diameter section or ledge portion 28a and a radially extending flange 29. Cushioning means 10a comprises a cup-shaped valve means or member comprising a ring 36a, having smooth and uninterrupted radially outer surface portions, and a radially inwardly extending flange 38a.

A central opening 40a of the flange has a larger diameter than the outer diameter of ledge portion 28a of washer 27. The flange is retained axially by retention means comprising an annular slot defined between radial portion 29 of the washer and piston 28a. In addition, ring 36a has a diameter which is less than the inside diameter of bore 14a to permit limited radial movements of the valve member.

OPERATION

FIG. 3 illustrates piston 12a at the end of its extension stroke to exhaust fluid from the rod end of the cylinder. When ring 36a begins to cover port 18a at its leading, frusto-conically shaped free end 31 remote from flange 38a, fluid forces generated by fluid flow and the resulting pressure drop occasioned across the ring function to move outer surface portions of the ring into masking relationship with port 18a. Fluid flow out of conduit 20a is thus progressively restricted to dampen the retraction stroke.

Such restriction creates a pressure build-up in the head end of the cylinder whereupon a suitably calibrated pump relief valve (not shown) will open to reduce the flow to such head end and the linear speed of the piston will be reduced. Since the outer diameter of ring 36a is slightly smaller than the inner diameter of bore 14a, port 18a will not become fully blocked in its FIG. 3 position. During retraction of piston 12a, leftwardly in FIG. 3, pressurized fluid from conduit 20 will force ring 36a radially upwardly away from inlet port 18a to provide substantially unrestricted fluid flow into expansible chamber 34a.

Claims

What is claimed is:

1. A hydraulic cylinder comprising a tubular housing, a piston reciprocally mounted on a rod in said housing to define an expansible chamber therewith, port means formed through a sidewall of said housing, adjacent to a closed end thereof, for communicating a pressurized fluid to said chamber and cushioning means solely responsive to fluid flow between said chamber and said port means for gradually restricting fluid flow from said chamber to said port means when said piston moves axially toward said port means and for permitting substantially unrestricted fluid flow from said port means to said chamber when said piston moves axially away from said port means, said cushioning means comprising an annular member of cup shape having a ring with an outside diameter which is substantially smaller than the inside diameter of said housing positioned to move radially outwardly into abutment with said sidewall solely in response to exhaust fluid flow to at least substantially cover said port means and an integral, radially inwardly extending flange and annular retention means comprising a washer secured to said rod abutting said piston and defining a shoulder of reduced diameter and a radial portion of greater diameter to define an annular slot capturing said flange between said radial portion and said piston for guiding radial movement of said ring relative to said port means.

2. The invention of claim 1 wherein radially outer surface portions of said ring are smooth and uninterrupted and terminate at a frusto-conically shaped free end of said ring, remote from said flange.

3. A cushioning device in combination with a piston disposed on a rod in a hydraulic cylinder having a fluid inlet-outlet port formed through a housing thereof, said cushioning device comprising valve means loosely disposed within said housing and being positionable by the piston into radial alignment with said port during retraction of the piston and being shiftable radially outwardly solely by fluid discharged from the cylinder to move into masked relationship over said port, said valve means comprising an annular ring member with an outside diameter which is substantially smaller than the inside diameter of said housing positioned to move radially outwardly into abutment with said housing to at least substantially cover said port and having a radially inwardly extending flange secured thereto, and retention means comprising a washer secured to said rod abutting said piston and defining a shoulder of reduced diameter and a radial portion of greater diameter to define an annular slot capturing said flange between said radial portion and said piston for guiding radial movement of said ring relative to said port.

4. The invention of claim 3 wherein said valve means cooperates with said housing to form flow restricting means gradually providing a restricted passage for fluid discharged to said port to decelerate piston movement by causing a pressure drop across said port to maintain the ring of said valve means in said masked relationship and being movable radially inwardly out of said masking relationship in response to fluid flow from said port to said cylinder to permit substantially unrestricted fluid flow thereby.