Valves and valve actuation – Mechanical movement actuator – Screw
Reexamination Certificate
1999-04-20
2001-08-14
Kaufman, Joseph A. (Department: 3754)
Valves and valve actuation
Mechanical movement actuator
Screw
C137S901000, C251S216000, C251S264000, C251S274000, C251S285000, C251S339000
Reexamination Certificate
active
06273398
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved vent valve for a gas strut, and to a gas strut incorporating such a vent valve.
2. The Prior Art
Gas struts are extensively used for the purpose of applying a force between mutually moveable components of a structure. A typical use of gas struts is to balance, at least partially, the weight of a lid, cover or door to assist manual raising of a lid, cover or door.
In many applications, particularly where the struts are to be used in mass produced products such as automobiles, the force which a particular strut is required to produce will be known at the time when the strut is manufactured, and the strut can accordingly be charged, at the time of manufacture, with the correct gas pressure to produce the required force. With such struts there is no requirement for subsequent adjustment of the force exerted by the strut.
In some applications, however, it is desirable to be able to adjust the force exerted by the strut after manufacture. In order to achieve this, it is known to charge struts, during manufacture, with a higher gas pressure than will ultimately be required when the strut is in use, and to provide the strut with a vent valve which enables some of the gas charge in the strut to be vented subsequent to manufacture in order to tune the force which the strut produces to the particular application for which it is being used. A gas strut having such a vent valve is described in GB-A-2168453.
Whilst the gas strut of GB-A-2168453 discloses the principle of a vent to enable the gas pressure within the strut to be selectively decreased subsequent to manufacture, the particular arrangement proposed in GB-A-2168453 suffers from two significant disadvantages.
Firstly, it will be appreciated that after the adjustment of the gas pressure within the strut has been effected it is imperative that the vent valve seals absolutely the vent passage to prevent further escape of gas. The total charge of gas within the gas strut is quite small, and the gas is confined at a high pressure. Any leakage of gas will result in a decrease in the force which the strut is capable of applying, and this is highly undesirable. In this context, it must be remembered that a strut may be required to have a service life of ten years or more. With the vent valve arrangement disclosed in GB-A-2168453 the use of a screw having a conical point which seals, in use, with a conical seat makes achieving the necessary seal difficult. Considerable care must be exercised in the manufacture of the seat and the conical end of the screw to ensure an absolutely gas tight seal.
The second problem associated with GB-A-2168453 is that the venting of excess pressure which occurs when the vent valve is open is difficult to control. As soon as the conical face of the control screw moves out of engagement with its corresponding conical seat a relatively large area is available for gas flow, and this may produce an excessively fast release of gas pressure. Further, since gas pressure in the case of GB-A-2168453 is vented via a drilled passage in the vent valve body the release of gas pressure may produce a blast of gas which may impinge on the hands or face of the worker adjusting the gas pressure. Since the venting gas may be very cold as a result of the adiabatic expansion which occurs when it leaves the gas strut, it is highly undesirable that the venting gas should be directed, as a blast, at any part of the body of the person adjusting the gas pressure.
We have now devised an improved vent valve which substantially eliminates the problem outlined above.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a vent valve for a gas strut comprises a body which, in use, sealingly closes an end of the cylinder of a gas strut; a valve seat defined in the body; a first passage in the body extending from one side of the valve seat to a surface of the body which, in use, is exposed to the interior of the gas strut; a second passage in the body extending from the other side of the valve seat to a surface of the body which, in use, is exposed to the exterior of the gas strut, the second passage being screw-threaded; a screw in screw-threaded engagement with the screw threads of the second passage; and a ball located between the screw and the valve seat whereby tightening of the screw will force the ball into engagement with the valve seat to prevent the flow of the gas from the first passage to the second passage.
Preferably, the screw is a grub screw and is located wholly or substantially wholly within the second passage. This significantly improves the appearance of the gas strut and reduces the weight thereof as compared with the use of a cap screw as illustrated in GB-A-2168453.
Preferably, the second passage provides the sole communication between the valve seat and the exterior of the gas strut. Accordingly, high pressure gas exiting the gas strut via the valve seat will be forced to flow via the clearance between the screw and the screw threads of the second passage. Since the clearance between the screw threads of the screw and the second passage will be relatively small, the fact that the gas is forced to flow through this clearance space will substantially limit the rate at which gas may escape. This significantly assists the controlled venting of gas from the gas strut. Also, as the gas flows through the clearance space it will be defused and as a result no blast of escaping gas can impinge of the personnel adjusting the gas strut.
In a particularly preferred embodiment of the invention the ball is of a hard material, for example hardened steel and the body is of a relatively soft material, for example brass. Hardened steel balls which are accurately spherical and which have a fine surface finish are readily available at low cost. Such a ball will form an adequate seal with a conical seat provided in a brass body even if the seat is finished only to standard commercial machining tolerances. Accordingly, the use of a hardened steel ball and a seat of relatively soft metal eliminates the problem of providing an adequate seal, as outlined above.
The particular configuration of vent valve according to the preferred embodiment of the invention offers the significant advantage that it facilitates adjusting of the gas content of the gas strut when the gas strut is in situ. The proposed position of the vent valve, coupled with the fact that the vent valve can be operated by means of a key of relatively small proportions greatly facilitates the adjustment of the gas content of the strut without removing the strut from its final use position.
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Arvin Motion Control Limited
Dykema Gossett PLLC
Kaufman Joseph A.
Keasel Eric
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