GB2151306A

GB2151306A - Actuator gland construction

Info

Publication number: GB2151306A
Application number: GB08430573A
Authority: GB
Inventors: Philip Earle Barnes; John Edly Horr
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1983-12-16
Filing date: 1984-12-04
Publication date: 1985-07-17
Also published as: FR2556789B1; IT8424097A0; SE8406358D0; GB2151306B; SE8406358L; IT8424097A1; GB8430573D0; FR2556789A1; JPS60143206A; IT1177435B; DE3445999A1; IL73760A0

Abstract

An improved hydraulic actuator structure includes a gland (80) integral with the sidewall (15) of the actuator cylinder. The integral land is provided with rod bearing lands (85) coated with a nongalling material (90) such as silver, indium, copper, lead, tin or a combination of such materials. <IMAGE>

Description

SPECIFICATION Actuator gland construction Technical Field This invention relates generally to actuators and more particularly to a novel bearing construction for the cylinders of hydraulic actuators.

Background Art Current hydraulic actuators such as those employed for positioning a device such as an aircraft control surface, typically comprise a cylinder having a piston slidably disposed therewithin and mounted on a rod which connects to the actuated device. Selected pressurization and draining of the cylinder adjusts the longitudinal position of the piston within the cylinder and hence the position of the rod on which the piston is mounted, thereby adjusting the position of the connected device.

Typically, the actuator cylinders are sealed with a removable gland secured to the cylinder by any suitable means such as a nut or similar threaded fastener. In aircraft actuators, the cylinder is usually formed from stainless steel and the gland, from bronze. The gland usually includes a plurlaity of circumferential grooves formed in the interior and exterior surfaces thereof, the grooves accommodating seals which seal the gland to both the cylinder and rod to minimize the leakage of hydraulic fluid from the interior of the cylinder. Lands defined by the internal seal grooves provide bearings on which the rod is slidably supported as it moves with the piston.

Those skilled in the art will appreciate that to allow free movement of the rod through the gland while sealing the gland to the rod involves adherence to very strict manufacturing tolerances in both the eccentricities of the gland and cylinder as well as the clearances therebetween and between the gland and the rod. Exaggerated clearances and overly eccentric component parts risk not only malfunctioning of the actuator, but also premature wear of the bearings and seals, and hence intolerable leakage of fluid from the actuator.

Disclosure of Invention It is therefore a principal object of the present invention to provide an improved hydraulic actuator gland structure.

It is another object of the present invention to provide such a structure characterized by a minimal number of component parts for minimizing the criticality of component part eccentricities and clearances therebetween.

These and other objects which will become more apparent from the following detailed description taken in connection with the appended claims and accompanying drawings are achieved by the actuator of the present invention wherein a cylinder gland is formed integrally with the cylinder and is provided with rod bearing lands coated with a nongalling material such as silver. The material may be coated on the lands by such processes as electroplating, vapor deposition or flame spraying. The integral lands coated with the nongalling bearing material reduce the number of separate component parts required in the actuator or gland structure and hence the adverse effects of excessive eccentricities of such parts and improper clearances therebetween.In the preferred embodiment, the bearing material comprises a layer of silver coated on a backing layer of copper which is coated directly on the integral lands, although other materials are contemplated and disclosed in detail in the following description.

Brief Description of Drawings Fig. 1 is a fragmentary sectional elevation of a prior art hydraulic actuator gland structure; Fig. 2 is a fragmentary sectional elevation of the actuator gland structure of the present invention; and Fig. 3 is an enlarged fragmentary view of a portion of the gland structure of the present invention showing the accommodation by the structure of a misalignment between a piston rod and bearings therefor.

Best Mode for Carrying Out The Invention and Industrial Applicability Thereof Referring to Fig. 1, an end portion of a prior art hydraulic actuator 10 is shown. Actuator 10 comprises a cylinder, typically of stainless steel or similar material of suitable strength and hardness within which a piston 20 is slidably received. Piston 20 is fixed to output rod 25 typically of chrome plated steel such that selected pressurization and draining of the cylinder cause the piston and rod to move longitudinally thereby moving an actuated device (not shown) connected to rod 25 for operation by the actuator. To provide bearing surfaces for the rod and to seal the cylinder against the leakage of hydraulic fluid therefrom, cylinder 1 5 is provided with a gland 30 typically of bronze disposed in an annular recess located in the cylinder wall.

The gland is compressively held in place by a locknut 35 threaded into the end of the cylinder. As shown, gland 30 is provided with a pluarlity of grooves formed in the interior and exterior surfaces thereof. Grooves 40 accommodate seal rings 45 and backing rings 50 for sealing the gland to the outer surface of rod 25 while groove 55 receives seal ring 60 and backing rings 65 therewithin for sealing the gland to the interior surface of cylinder 1 5. Grooves 40 define three lands 70 which function as bearings to radially support rod 25 and allow the rod to slide through the gland in the normal reciprocal movement of the rod.

As those skilled in the art will appreciate, proper operation of actuator 10 depends not only on the precision of the fit of piston 20 within cylinder 15, but also the precision of the fit between the gland and the cylinder as well as between the piston rod and bearing lands. Thus, it will be understood that eccentricities in the cylinder, the gland, or the piston rod must be minimized to assure proper operation of the actuator without premature wear of the seal rings and excessive leakage from the cylinder. Similarly, clearances between the piston rod and gland as well as between the gland and the cylinder must be precisely controlled to ensure proper operation of the actuator and to avoid premature wear of the seals.

In accordance with the present invention, as illustrated in Fig. 2 of the drawings, the actuator gland is formed integrally with the cylinder whereby the eccentricities of the outer surface of the gland and the clearance between the gland and the cylinder are eliminated. As shown in Fig. 2, cylinder 1 5 is provided with an integral gland 80 comprising a shoulder portion of the cylinder extending radially inwardly therefrom. Gland 80 is provided with grooves 40 which accept seal rings 45 and backup rings 50 and, like gland 30, the grooves in gland 80 define a plurality of bearing lands 85 for radial support of piston rod 25.

As noted hereinabove, hydraulic actuators employed in aerospace applications typically employ stainless steel cylinders and chrome plated piston rods. Inasmuch as gland 80 is integrally formed with cylinder 15, the bearing lands 85 are formed from the same material as the cylinder. When this material comprises stainless steel, to prevent galling and/or fretting of the lands and piston rod, the lands are coated with at least one layer of a nongalling (nonfretting) bearing material. In the preferred embodiment, the bearing material comprises a cold flowing metal such as tin, indium, lead, copper, silver or a combination thereof. As shown in Fig. 2, two layers of the nongalling material are contemplated, inner layer 90 comprising a thin (0.001 inch), inner coating of silver on a somewhat thicker (0.005 inch) outer coating of copper.The bearing materials may be applied to the lands by such techniques as electroplating, flame spraying or vapor deposition. While it has been determined that silver performs somewhat better than copper as a bearing material when used in conjunction with a chrome plated piston rod, it has also been determined that a layer of silver as thick as the combined thickness of the silver and copper layers could flow off the lands when rubbed by the surface of the piston rod in the normal operation of the actuator.

Referring to Fig. 3, it is seen that the provision of nongalling, cold flowing bearing material on lands 80 allows the actuator bearings to accommodate misalignments between the cylinder and piston shaft. As shown in Fig. 3, a misalignment of these two members results in excessive radial loading of the end of the bearing land, thereby cold flowing the bearing material longitudinally outwardly, the material conforming to the shape of the misaligned piston rod without jamming the actuator or causing excessive leagage of fluid there- from.

Therefore, it will be seen that with the integral glands and rod bearings of the present invention, the dependency of proper actuator operation and the dependency of the integrity of the actuator seals on strict eccentricity and clearance tolerances are reduced.

The reduction in the number of separate component parts inherent in the present invention also enhances the economy of structure as well as the ease of assembly of the actuators.

Alignment between the piston rod and cylinder is also enhanced, thereby extending seal life as well.

While a particular embodiment of the present invention has been shown and described, it will be appreciated by those skilled in the art that various modifications will, from the description herein, suggest themselves to those skilled in the art and it is intended by the following claims to cover such modifications as fall within the true spirit and scope of this invention.

Having thus described the invention, what

Claims

is claimed is: CLAIMS

1. In an actuator comprising a cylinder and an output rod slidably disposed therewithin, the improvement characterized by: said cylinder being provided with an integral gland, including an output rod bearing land; said land being coated with at least one layer of a nongalling bearing material adapted for slidable contact with an outer surface of said output rod; and said coated land providing an integral bearing for radial support of said output rod by said integral cylinder gland.

2. The actuator of Claim 1 characterized by said bearing material being a nonfretting material.

3. In an actuator comprising a cylinder and an output rod slidably disposed therewithin, the improvement characterized by: said cylinder being provided with an integral gland, said gland having at least one groove formed therein, said groove being adapted to carry a seal ring and defining in part, an adjacent land; said land being coated with at least one layer of a cold flowing bearing material adapted for slidable contact with an outer surface of said output rod; and said coated land providing an integral cylinder bearing for radial support of said output rod by said integral cylinder gland.

4. The actuator of Claims 1 or 3 characterized by said bearing material comprising at least one metal selected from the group consisting of tin, indium, lead, copper and silver or a combination thereof.

5. The actuator of Claims 1 or 2 characterized by said bearing material comprising an outer layer of copper coated on said land and an inner, concentric layer of silver coated on said copper.

6. The actuator of Claim 4 characterized by said copper layer being approximately 0.005 inch in thickness.

7. The actuator of Claim 4 characterized by said silver layer being approximately 0.001 inch in thickness.

8. The actuator of Claim 4 characterized by said copper and silver layers being electroplated on said cylinder land.

9. The actuator of Claim 4 characterized by said coppper and silver layers being vapor deposited on said cylinder land.

1 0. The actuator of Claim 4 characterized by said copper and silver layers being flame sprayed on said cylinder land.