GB2176572A

GB2176572A - Lockable spring strut

Info

Publication number: GB2176572A
Application number: GB08614595A
Authority: GB
Inventors: William Ferguson Douglas Hart
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-06-15
Filing date: 1986-06-16
Publication date: 1986-12-31
Also published as: GB8614595D0; GB2176572B

Abstract

A spring strut has a central plunger 14 which upon compression of the strut displaced hydraulic fluid from a central chamber 16A into a concentric annular chamber 19A in which an annular piston 24 is backed by a pack 28 of disc springs. A spool valve 20 disposed between the central and annular chambers provides means for holding the members of the strut in any desired position. In a modification (Fig. 2), the central plunger is provided with a piston head and a further chamber defined on the plunger side of the piston head is in communication with the annular chamber so that when the strut is held or locked by closure of the controlling valve the resistance to extension of the strut is against the force stored in the spring pack and not atmospheric as is the case with the unmodified construction. <IMAGE>

Description

SPECIFICATION Spring loaded actuators This invention relates to spring loaded actuators.

A spring loaded actuator consists of two mutually relatively movable members which are urged towards one extreme of their range of movement by spring means incorporated on or in the actuator. Thus, the actuator is capable of performing an actuating role unidirectionally under the influence of the spring means.

This invention is concerned especially, but not exclusively, with a spring strut which is a form of spring loaded actuator.

According to the present invention, there is provided a spring loaded actuator incorporating hydrualic means adapted and arranged to displace a hydraulic fluid between mutually connected variable volume chambers in accordance with relative movement of the actuator members, and spring means applying pressure to the hydraulic fluid and arranged to urge the fluid uni-directionally from one chamber to the other.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic sectional elevation of a spring strut in accordance with one embodiment of the present invention; and Figure 2 is a sectional elevation, to a larger scale than Fig. 1, of part of a spring strut in accordance with a second embodiment of the present invention.

In Fig. 1 of the drawings, a spring strut consists of mutually telescopic members 10 and 11, each of these members being tubes of circular cross-section and the member 11 being slidably located within the member 10 by means of a low-friction bush 12 retained in the member 10 by means of a circlip 13.

The outer end of the membr 10 anchors one end of a central plunger 14 which cooperates with a bore 15 of a cylinder body 16 extending concentrically within the member 11. Thus, the plunger 14 and the cylinder body 16 mutually cooperate to define a variable volume chamber 16A. The inner end of the cylinder body 16 is located within an end piece 17 which in turn is anchored within the inner end of the member 11. An annular seal 18 is provided adjacent the inner end of the plunger 14. The outer end of the cylinder body 16 is provided with radially disposed ports 19 through which a hydraulic fluid may be displaced between the chamber 1 6A and annular chamber 19A defined around the cylinder body 16. Within the cylinder body 16, there is provided a valve means is the form of a spool valve 20 operable to open and close the ports 19 as further explained herebelow.

A stem 21 of the valve 20 is carried by an end piece 22 retained within the member 11 by means of a circlip 23. The end piece 22 is provided with annular seals engaging the valve stem 21 and also the inside surface of the member 11 for the purpose of retaining hydraulic fluid.

Within the annular space around the cylinder body 16, there is fitted a free annular piston 24 the outer end of which part-defines the second variable volume chamber 19A which is in communication with the chamber 1 6A by way of the ports 19 and valve 20. The annular piston 24 carries an annular seal 25 which slidably engages the inner surface of the member 11, and the annular piston 24 also engages a further annular seal 26 carried by the cylinder body 16. The inner end portion of the annular piston 24 is relieved from the adjacent surfaces of the member 11 and the cylinder body 16 to avoid engagement with surface which may become roughened in a matter not compatible with efficient operation of the annular piston.

The inner end of the annular piston 24 abuts a sliding washer 27 which in turn engages a mechanical spring 28 in the form of a pack of disc springs or Belville washers. The inner end of the mechanical spring 28 abuts the inner face of the end piece 17.

The end piece 22 is provided with a plugged filling port 22A for the introduction of hydraulic fluid to any desirec pre-charge pressure.

Operation of the spring strut described above is as follows. Telescopic movement between the member 10 and the member 11 to compress the strut effects travel of the central plunger 14 into the bore 15 of the cylinder body 16. This is turn effects displacement of hydraulic fluid from the central chamber 1 6A into the annular chamber 1 9A by way of the ports 19, assuming the valve 20 to be in an open condition. Displacement of fluid into the annular chamber in turn effects movement of the annular piston 24 to compress the mechanical spring 28.With the mechanical spring thus further loaded, the spring strut is capable of acting as an actuator because the energy stored in the spring may act to return hydraulic fluid from the annular chamber 19A to the central chamber 16A and thereby thrust the central plunger 14 outwards with respect to the cylinder body 16 and so extend the strut.

The members of the strut may be held at any position by closing the valve 20. With the valve 20 closed, the strut of Fig. 1 is hydraulically locked against compression and is held against extension by atmospheric pressure. It will be appreciated that the relatively high stiffness of the mechanical spring 28 is made use of in the context of a spring strut by the advantage of the ratio between the plunger 14 and the annular piston 24.

In Fig. 2 of the drawings, parts correspond ing generally with parts shown in Fig. 1 are given the reference numerals used in relation to Fig. 1. The spring strut of Fig. 2 is of construction generally similar to that of Fig. 1, but with modifications as will appear from the following description.

In Fig. 2, the cylinder body 16 comprises mutually concentric hollow cylinders 30 and 31 which are spaced to define therebetween an annular duct 32. The outer end of the inner cylinder 30 is centrally located on an inwardly projecting part 22B of the end piece 22, and the upper end of the cylinder 31 is centrally located by means of a centring member 33 fitted within the strut member 11 in abutment with the inside face of the end piece 22. The valve means 20 comprises a valve spool shiftable by means of the valve stem 21 and ported to provide communication between the chamber 16A and ports 34 through the inner cylinder 30 and opening into the annular duct 32.The outer end portion of the outer cylinder 31 is provided with radial ports 35 placing the annular duct 32 in communication with the interior of the centring member 33 which in turn is provided with ports 36 opening into the annular chamber 19A.

In Fig. 2, the spring pack 28 is represented by chain dotted lines and engages an annular piston and pressure seal of which the seal is indicated by reference numeral 37.

The inner end of the inner cylinder 30 is centrally located on a centring member and plunger guide 38 accommodated centrally within the end piece 17 together with the inner end of the outer cylinder 31. In this embodiment, the plunger 14 is provided with a piston 14A, and the chamber 39 on the plunger side of the piston 14A is in communication with the annular duct 32 by way of radial ports 40 provided adjacent the inner end of the inner cylinder 30. Thus, the inner cylinder 30 together with the plunger 14 and piston 1 4A constitute a piston-and-plunger pump configuration of which the chamber 16A is the larger chamber and the chamber 39 is the smaller chamber having regard to the differential displacement attributable to the difference in diameter between the piston 14A and the plunger 14.

In this embodiment, the end piece 22 is provided with diametrically opposed filling ports 22A each of which has an inner conical seat engaged by a valve ball 41. The centring member 33 is provided with an annular recess 42 for accommodating unseating movement of the valve balls 41.

Operation of the strut of Fig. 2 is as follows. The strut is preferably charged with hydraulic fluid up to a pressure of the order of 2,000 pounds per square inch whereby the spring pack 28 is pre-loaded. In the precharging and filling procedure, the strut is conveniently disposed on its side and hydraulic fluid introduced through the lower of the filling ports 22A whilst the valve ball 41 of the other filling port is held off its seat by means of an inserted implement to permit escape of air. With the spool of the valve means 20 positioned with the spool porting in registration with the ports 34, compression of the strut displaces hydraulic fluid from the chamber 1 6A through the valve spool and ports 34 into the annular duct 32. At this point, the hydraulic flow divides so that only the differential reaches the annular chamber 19A, the balance being returned to the smaller chamber 39 on the plunger side of the piston 14A.

Thus, in this embodiment , with the valve means 20 in the closed condition the strut is locked against further compression and is held against extension by the force stored in the spring pack 28 which is transmitted to the plunger side of the piston 1 4A through the ports 36, 35, annular duct 32 and ports 40.

Thus, in this embodiment, the strut is effectively locked in both directions by closure of the valve means 20.

Claims

1. A spring loaded actuator incorporating hydraulic means adapted and arranged to displace a hydraulic fluid between mutually connected variable-volume chambers in accordance with relative movement of the actuator members, and spring means applying pressure to the hydraulic fluid and arranged to urge the fluid uni-directionally from one chamber to the other.

2. A spring loaded actuator to claim 1, wherein the said spring means comprises a mechanical spring.

3. A spring loaded actuator according to claim 2, wherein the said mechanical spring comprises a pack of disc springs or Belville washers.

4. A spring loaded actuator according to any one of claims 1 to 3, including valve means operable to open and close said connection between the said chambers to flow of hydraulic fluid.

5. A spring loaded actuator according to claim 4, wherein the said other chamber is the larger chamber in a piston-and-plunger pump configuration of which the smaller chamber is hydraulically in communication with said one chamber independently of said valve means.

6. A spring loaded actuator according to any one of the preceding claims, wherein the actuator is a spring strut, the said one chamber is disposed within one member of the strut and is of volume variable by means of a free annular piston acted upon by the spring means, and said other chamber is concentric with said one and is of volume variable by a piston or plunger operable by the other member of the strut.

7. A spring loaded actuator according to claim 6 when dependent from claim 5, wherein said smaller chamber is hydraulically in communication with said one chamber by way of a duct extending in wall means defining a cylinder body of said piston-and-plunger pump configuration.

8. A spring loaded actuator according to claim 7, wherein said cylinder body comprises mutually concentric and mutually spaced hollow cylinders, and said duct is defined by an annular space between said hollow cylinders.

9. A spring loaded actuator substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.