GB2095753A

GB2095753A - Apparatus for damping the end stroke of a piston in a hydraulic cylinder

Info

Publication number: GB2095753A
Application number: GB8204184A
Authority: GB
Original assignee: VAGGERYDS MEK VERK
Current assignee: VAGGERYDS MEK VERK
Priority date: 1981-02-17
Filing date: 1982-02-12
Publication date: 1982-10-06
Also published as: SE8101054L; DE3204358A1; FI820505L; NO820482L

Abstract

A cylindrical section which functions as a damping body 29 is connected to piston 4 which travels inside cylinder tube 1. In the vicinity of an end stroke position, damping body 29 which may have axial grooves 31 enters with some play, an outlet channel for the fluid under pressure and penetrates through a ring-like throttle body 9 which, with axial play, is installed in a ring-like cavity 27 in the outlet channel. The throttle body 9 has a cross section which can not be deformed and is equipped with axial slots or grooves 28 at its outer periphery. The cavity 27 is closed off at its outer periphery from the space toward the piston side by means of a removable lock ring 20 e.g. a so-called Seeger ring or circlip, with larger inner diameter than the smallest groove diameter of the throttle body 9. Damping sleeve 10 engages a similar throttle body and damping arrangement at the other end of the cylinder tube 1. <IMAGE>

Description

SPECIFICATION Apparatus for damping the end stroke of a piston in a hydraulic cylinder This invention concerns apparatus for damping the end stroke of a piston, and parts attached thereto, in a hydraulic cylinder in the end position of the piston. Such apparatus has previously been proposed e.g. in Swedish published patent specifications Nos. 437 046 and 416 1 57 respectively, which describe two constructions, in which achievement of a satisfactory damping at the end position of a stroke has been attempted by means of a cylindrical dampting body located on the piston, which damping body, in the vicinity of the end positions, penetrates a channel with certain play and throttles the fluid leaving it. A ringlike cavity is incorporated into said channel, which cavity receives a likewise ring-like throttle body with axial play.When the piston approaches the end position of its stroke, the ring-like throttle body, under the influence of the pressure of the fluid, is placed against the lateral wall of the cavity which is farthest away from the piston and in this position exerts additional throttling of the fluid, e.g. oil, theroby increasing retardation of the piston movement, which of course is desirable in order to avoid extremely great stresses, which easily arise, when the piston approaches an end position.

In order to obtain a desired retardation cycle which is suited to the operation of the hydraulic cylinder, the apparatus described in patent specification No. 416 1 57 has axial grooves in the mantle surface of the damping body, which grooves can vary with regard to depth and or width. These grooves will in this case come into engagement with the throttle body to form leakage walls for the fluid and consequently, depending on the length or distance of the piston in end position, result in a throttle of the out flow of the liquid from the pressure side of the piston and thus a suitable retardation.

When the piston subsequently returns due to a change of direction of fluid flow, the throttle body will immediately leave its contact against the above stated lateral wall so that the fluid immediately obtains full access to the corresponding piston side during the entire succeeding drive of the piston in this new direction.

According to patent specification 347 046 and according to the present invention, a ring-like throttle body with a cross section which can not be deformed, is used, but it is slotted and bears with certain elastic pressure against one of the sides of the outlet channel, therefore extra channels 14 must be incorporated in the wall, against which the throttle body does not bear.

The slotted section is necessary for installation and removal of the throttle body from the cavity.

This apparatus is very complicated and expensive to manufacture and to service.

Even the apparatus according to patent specification 416 157 is marred by considerable disadvantages. Here, among other components, a ring-like guide body with spring loaded cross section is used so as to be capable of insertion in and removal from the cavity and it is equipped with grooves distributed around the perimeter, through which grooves the fluid passes during the return stroke. This construction requires great precision in manufacture and the throttle body is relatively easily damaged and is easily subjected to wear, which effects its product life and function.

An advantage of the apparatus according to the present invention is that the throttle body by being capable of being locked into the cavity in a simple manner by means of a lock ring or internal circlip, which when needed can be removed and reinstalled, may be constructed extremely sturdily with a cross section which can not be deformed and without having to be slotted. Installation and dismantling, i.e. replacement, of the throttle body is therefore a very simple and quick operation.

This is a great advantage, because these throttle bodies can become greatly worn in a short period of time during intensive operation, even if this does not occur so quickly in the apparatus according to this invention. Furthermore the manufacture of the cavity according to this invention is particularly simple, since the cavity has a very simple form.

The present invention provides apparatus for damping the end stroke of a piston, which comprises a piston rod and other components, in a hydraulic cylinder, in which a cylindrical damping body situated adjacent and firmly joined to the piston, has a plurality of axial grooves in its perimeter, the depth and/or width of said grooves diminishing in a direction towards the piston, which grooves during a damping cycle penetrate with a certain amount of play into an outlet channel in a cylinder end cap or in a member adjacent to the cylinder end, which channel forms an outlet for fluid subjected to pressure in the space inside the cylinder in front of the piston, and in which a cavity extends in the wall at the opening of the outlet channel facing the piston, around the damping body at its engagement in the channel, in which cavity a ring-like throttle body is installed with axial play such that during the damping cycle the damping body is able to slide through the throttle body which is firstly pressed by the fluid toward the lateral wall of the cavity that is the wall situated farthest away from the piston so as to limit throttling of the fluid in the fluid outlet to the openings, formed between the throttle body and the grooves of the damping body, and during the return stroke of the piston, the throttle body is able to move toward the open section of the cavity and thereby free the fluid for passage in the opposite direction to the piston, characterised in that the ring-like throttle body is formed with a cross section which can not be deformed and has a number of axially extending grooves in its outer perimeter, which grooves give free passage to the hydraulic fluid and in that in the wall of the cavity nearest to the piston there is a groove wherein is inserted a removable lock ring e.g. a so-called Seeger ring or circlip, which prevents the throttle body from leaving the cavity and whose inner diameter is larger than the smallest diameter of the grooves of the throttle body thereby ensuring a free supply of the fluid to the piston during its return motion, and in that the throttle body after removal of the lock ring can be removed from or respectively inserted in the cavity.

The damping body preferably comprises a sleeve which is formed with a bevelled end and which encloses the piston rod. However, the damping body at the other end of the piston may be constructed as a cylindrical section of the piston rod itself, but still formed with a bevelled end.

The invention will be explained further, by way of example, with reference to an embodiment illustrated in the accompanying drawings, in which: Fig. 1 is a side elevation, partially in crosssection, of one end of a hydraulic cylinder equipped with an embodiment of apparatus according to the present invention; and Fig. 2 is a side elevation, partially in crosssection of the other end of the hydraulic cylinder shown in Fig. 1.

The following numerical designations have been used in the drawings.

1. Cylinder tube 2. Piston rod 3. Cylinder tube lug including end cap 4. Piston 5. Piston rod guide 6. Guide washer 7. Damping member 8. Throttle body 9. Throttle body 10. Sleeve for damping, damping body 11. Piston seal 12. Piston rod seal 1 3. Deflector 14. O-ring 1 5. Support ring 16. O-ring 17. Support ring 18. O-ring 1 9. Tension pin 20. Lockring or circlip 21. Lockring orcirclip 22. Index bolt 23. Washer 24. Link bearing 25. Latch ring 26. Lube nipple 27. Cavity 28. Groove 29. Damping body 30. Damping groove 31. Damping groove As shown in Figs. 1 and 2, a hydraulic cylinder comprises a cylinder tube 1 having inlet/outlet ports A and B and enclosing a piston 4 connected to a piston rod 2.In its end position, as shown in Fig. 1, the piston abuts a cylinder tube lug including an end cap, designated as a whole by reference numeral 3, which is held in place in the end of the tube 1 by washers 23 and bolt 22. An annular recess in the tube lug 3 accommodates a support ring 1 5 and an O-ring 14. At the other end of the tube 1 (Fig. 2) is located a damping member 7 adjacent a piston rod guide 5 and a guide washer 6 which is held against the end of the tube by washers 23 and bolts 22. An annular recess in the piston rod guide 5 also accommodates a support ring 1 5 and an O-ring 14. The piston 4 is sealed against the tube wall by a piston seal 11 accommodated in an annular recess in the piston 4 and the piston rod 2 is sealed against the piston rod guide 5 by a piston rod seal 12 in a recess in the guide 5.

A damping body 29 extends from the side of the piston 4 opposite the piston rod 2. A second damping body in the form of a sleeve 10 is located around the piston rod 2 adjacent the piston 4. These damping bodies 29 and 10 each have bevelled ends and grooves 31, 30, respectively. Ring-like throttle bodies 8, 9 respectively each having grooves 28 are provided at respective ends of rye tube 1 in cavities 27 in the damping member 7 and lug 3 respectively.

Lock rings 20, 21 respectively, in the form of socalled Seeger rings or circlips are located adjacent throttle bodies 9, 8 respectively in respective grooves in a wall of each cavity 27.

The damping apparatus according to the invention functions in the following manner: Through port A hydraulic fluid flows in and causes a movement of the piston 4 and the other components attached thereto in direction of the arrow.

When damping sleeve 10 reaches the throttle body 8, a throttling of the oil flow arises. As a result of the difference in pressure between the sides of the throttle body 8, said body 8 is shifted in the direction of the arrow until it reaches a sealing surface on the damping member 7, i.e.

until it butts against a lateral wall of the cavity 27 which is situated nearest to the outlet port B.

When this position is reached, the remaining quantity of oil must be forced or pressed out into a cleft between the throttle body 8 and the damping sleeve 10. This renders an effective damping (retardation) of the stroke. Grooves 30 in the sleeve 10 are milled so that an increasing throttling arises resulting in a soft braking action.

When the direction of flow of the hydraulic fluid is changed and pressure is applied through the port B, the piston 4 and the piston rod 2 are influenced in a direction contrary to that of the arrow. When this occurs, the throttle body 8 is shifted toward the lock ring 21 thereby opening a passage for the hydraulic fluid. The throttle body 8 has a number of milled (or similarly provided) grooves 28 which give free passage to the hydraulic fluid immediately the throttle body 8, leaves the sealing surface of the member 7, i.e.

the surface in the cavity 27. The damping apparatus at the other end (Fig. 1) functions substantially in the same way.

The present invention also provides other improved apparatus by means of which, without extra valves (overflow valves and non-return valves), it is possible to achieve a damping of the end stroke. Owing to the construction and arrangement of the damping body and the throttle body, the damping or retardation increases to a maximum at the end positions. Also the cylinder has full compressive force immediately upon starting off from the damping or end position of the previous stroke. Therefore no disturbing throttling of the hydraulic fluid arises during starting off from each damped position.

It should however be appreciated that the invention is not limited only to that which is revealed by the above described embodiment but that other alternatives are within the scope of the invention to the degree that they can be understood by the claims or can be considered to be equivalent to these.

Claims

1. Apparatus for damping the end stroke of a piston, which comprises a piston rod and other components, in a hydraulic cylinder, in which a cylindrical damping body situated adjacent and firmly joined to the piston, has a plurality of axial grooves in its perimeter, the depth and/or width of said grooves diminishing in a direction towards the piston, which grooves during a damping cycle penetrate with a certain amount of play into an outlet channel in a cylinder end cap or in a member adjacent to the cylinder end, which channel forms an outlet for fluid subjected to pressure in the space inside the cylinder in front of the piston, and in which a cavity extends in the wall at the opening of the outlet channel facing the piston, around the damping body at its engagement in the channel, in which cavity a ring-like throttle body is installed with axial play such that during the damping cycle the damping body is able to slide through the throttle body which is firstly pressed by the fluid toward the lateral wall of the cavity that is the wall situated farthest away from the piston so as to limit throttling of the fluid in the fluid outlet to the openings, formed between the throttle body and the grooves of the damping body and during the return stroke of the piston the throttle body is able to move toward the open section of the cavity and thereby free the fluid for passage in the opposite direction to the piston, characterised in that the ring-like throttle body is formed with a cross section which can not be deformed and has a number of axially extending grooves in its outer perimeter, which grooves give free passage to the hydraulic fluid and in that in the wall of the cavity nearest to the piston there is a groove wherein is inserted a removable lock ring e.g. a so-called Seeger ring or circlip, which prevents the throttle body from leaving the cavity and whose inner diameter is larger than the smallest diameter of the grooves of the throttle body thereby ensuring a free supply of the fluid to the piston during its return motion and in that the throttle body after removal of the lock ring can be removed from or respectively inserted in the cavity.

2. Apparatus as claimed in claim 1, characterised in that the damping body adjacent to the piston comprises a sleeve which is formed with a bevelled end and which encloses the piston rod.

3. Apparatus as claimed in claim 1 or 2, characterised in that another damping body at the other end of the piston is constructed as a cylindrical section of the piston rod itself, and is formed with a bevelled end.

4. Apparatus as claimed in any preceding claim, characterised in that the opening encircled by the lock ring constitutes the only channel for the passage of fluid to or from the space adjacent to the respective side of the piston and that this opening is capable of engaging or is in alignment with the grooves in the throttling body and the grooves in the damping body, the grooves in the throttling body making it possible during the return movement of the piston for the fluid to exert full compressive force on the piston as soon as the throttling body has left contact with the lateral wall of the cavity which faces towards a connection port i.e. an inlet/outlet port for the fluid.

5. Apparatus for damping the end stroke of a piston substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.