Spring devices – Vehicle – Comprising compressible fluid
Reexamination Certificate
1998-09-18
2001-02-27
Graham, Matthew C. (Department: 3613)
Spring devices
Vehicle
Comprising compressible fluid
C267S064260
Reexamination Certificate
active
06193223
ABSTRACT:
BACKGROUND OF THE INVENTION
Hydraulic struts have been used for many years for opening and holding open a door or other closure. Generally, a strut includes two telescoping members and is moveable between a compressed position when the door is closed and an extended position when the door is open. Some struts also provide for locking in the open or extended position.
The speed at which a conventional hydraulic strut extends or compresses is governed by the speed at which hydraulic fluid can enter a chamber and either apply pressure to a moveable piston or fill a vacuum created by the motion of the piston. This fluid flow is created from either the suction action of the retracting piston in a sealed strut, or by an injection system external to the strut.
One disadvantage of conventional hydraulic struts is that the rate of speed at which the strut extends and compresses is the same.
Applications exist where it is desirable to have a strut which opens at one predetermined rate of speed and closes at another. One example is a door which provides access to the personnel carrying area of an aircraft. Doors that can both open rapidly and close slowly allow for rapid and easy exit from the vehicle when the door opens and avoid injuring personnel or damaging items when closing the door. It is also desirable that the strut provide for a mechanism to lock it in the extended or open position.
There exist struts which have variable expansion and compression speeds. These are achieved by using variable flow rate valves which allow for fluid flow at two different speeds, depending on the direction of flow. Rapid opening struts operate by pressurized injection of hydraulic fluid into the strut from an outside source or an injection device. When the strut is compressed, the injected hydraulic fluid is returned to the outside source or discharged from the strut system. A disadvantage of this type of strut is that, because the strut is not sealed and self contained, the hydraulic fluid can become contaminated or leak onto surrounding structures. Another disadvantage is that the addition of an injection device makes the strut system bulkier and more cumbersome than conventional struts.
In view of the above, it should be appreciated that there is still a need for a dampening strut that can open and close at different speeds; is compact, sealed, and self-contained; and can automatically lock in an open position. The present invention satisfies these and other needs and provides further related advantages.
SUMMARY OF THE INVENTION
The present invention is embodied in a hydraulic strut which can open and close at different speeds; is compact, sealed, and self-contained; and can automatically lock in an open position. The hydraulic strut includes an outer telescoping member and an inner telescoping member. The strut has mounts on opposing ends so that it may be attached to a fixed structure and a pivotable door or closure attached to the fixed structure.
A feature of the present invention is that it includes both a second hydraulic reservoir, which is defined by an inner tubular metal cylinder, and a first hydraulic reservoir, which is defined by an outer tubular metal cylinder that circumferentially surrounds the inner cylinder. Thus, the first hydraulic reservoir surrounds the main hydraulic chamber, as opposed to being laterally or longitudinally situated from it. A valve connects the second hydraulic reservoir and the first hydraulic reservoir. Two distinct chambers, connected by a variable rate valve, avoids the need for an injection device and allows the strut to have a predetermined opening rate and a different predetermined closure rate, in a strut which is a self-contained, sealed unit. Furthermore, the struts are shorter and more compact than if the chambers were disposed laterally or longitudinally from one another. This is a significant advantage in areas where space is limited, such as, in aircraft passenger compartments. This feature also increases the strength of the strut.
Another feature is that the first hydraulic reservoir contains an auxiliary piston and the second hydraulic reservoir contains a main piston. The auxiliary piston creates hydraulic pressure which serves as a counter-force against which the main piston presses when the strut is compressing. The counter-force prevents a slippage or a jolt when the strut begins moving from a locked and extended position toward a compressed position, as would normally occur if no counter-force were present. This feature also reduces the volume of the first hydraulic reservoir as the strut extends and hydraulic fluid is drawn from the auxiliary hydraulic chamber into the second hydraulic reservoir by the movement of a main piston. By reducing the volume of the first hydraulic reservoir, the auxiliary piston prevents a suction force from building in the first hydraulic reservoir which would slow the transfer of hydraulic fluid and consequently slow the expansion rate of the strut.
The present invention also includes a unique and advantageous self-locking mechanism. A locking sleeve moveably retains a plurality of locking balls in the shaft of the main piston. The locking sleeve circumferentially surrounds the piston shaft and is spring biased to expose the locking balls when the strut reaches its fully extended position. The piston shaft includes an outer shaft, which is tubular, and an inner shaft, which is a solid rod and is moveably retained within the outer shaft. A trapezoidal shaped annular groove is formed in the inner shaft. A plurality of apertures are formed in the outer shaft. When the strut is not in an extended, locked position, the inner shaft and outer shaft are positioned so that the trapezoidal shaped annular groove is lined up with the plurality of apertures. Located within the space formed by the aligned inner and outer shafts is the plurality of locking balls. In this same position, the locking balls are retained by the spring biased locking sleeve.
A release sleeve circumferentially surrounds the outer shaft, and is accessible by hand from the outside of the strut. A connector pin attaches the release sleeve to the inner shaft and passes through opposed slots in the outer shaft. The release sleeve is spring biased such that when the strut reaches its fully extended position, the release sleeve moves the inner shaft to drive the locking balls into a plurality of spherical depressions formed in a portion of the outer telescoping member. In this position, the locking balls are in contact with both the inner telescoping member and the outer telescoping member, and effectively prevent movement of one relative to the other. To release the strut, an operator moves the release sleeve, and consequently the inner shaft, to a position which allows the locking balls to leave the spherical depressions and return to a retained position.
Several advantages of this release mechanism are that it automatically locks when the strut reaches the extended position, it minimizes the profile of the strut, and it reduces the danger of an accidental release of the lock.
Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.
REFERENCES:
patent: 3963101 (1976-06-01), Stadelmann et al.
patent: 4993522 (1991-02-01), Wagner
patent: 4997150 (1991-03-01), Mardollo
patent: 5115723 (1992-05-01), Wang
patent: 5263674 (1993-11-01), Huang
Engineering Drawing, Strut Assy, Dampening, HA333 (3 Sheets).
Engineering Drawing, Strut, Dampening, SDHA613, Oct. 1996.
Graham Matthew C.
Hartwell Corporation
Pretty & Schroeder, P.C.
Rodriguez Pamela J.
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