Metal working – Method of mechanical manufacture – Assembling or joining
Reexamination Certificate
1999-10-27
2001-07-24
Oberleitner, Robert J. (Department: 3613)
Metal working
Method of mechanical manufacture
Assembling or joining
C267S064140, C267S064250, C267S064280
Reexamination Certificate
active
06263556
ABSTRACT:
TECHNICAL FIELD
This invention relates to improvements in automatic temperature compensated gas spring struts that achieve quicker, easier, and safer assembly, as well as provide temperature compensation over a wider operating temperature range, along with selectable variable damping.
BACKGROUND OF THE INVENTION
A gas spring strut is essentially a sealed cylinder containing a near ideal gas (usually nitrogen under a high pressure, typically about 1000-2000 psi) with a piston in contact with the gas to force movement of a piston rod extending from one end of the cylinder. The use of gas struts as a spring element offers many advantages, but has a major drawback in that as the ambient temperature falls, the pressure of nitrogen, which follows the ideal gas law, drops by about 26% from +8° C. to −40° C., reducing the movement force of the piston rod by the same amount. Thus, gas spring struts have the disadvantage that the force with which they expand is a function of ambient temperature. If used as an automotive liftgate strut, the rate at which the strut will lift will slow as the temperature falls, and in very cold weather, the strut may not be able to lift the liftgate completely. Attempting to fix this problem by using higher force struts may only cause the liftgate to open too rapidly at high temperatures.
U.S. Pat. No. 4,613,115 proposes a gas spring strut that has two distinctly different high pressure gas volumes separated by the seal of the piston. One of the gases is considered primary and is constituted of nitrogen, the other is a secondary gas (such as freon) that changes pressure at a faster rate with temperature than does nitrogen. The secondary gas produces a force opposing the lifting force of the nitrogen so that the net lifting force is the difference in the two forces. The pressure of the secondary gas changes with temperature in such a way that the net lifting force can remain relatively constant; the secondary gas is selected in this patent to exert an opposing force that is the vapor pressure of the system; the secondary gas must be a gas which provides a continuous two-phase gas system in which the liquid and vapor phases are in equilibrium over the temperature range of −30° C. to +80° C. Patent '115 demonstrates only three gases that remain as a two-phase system within such temperature range, namely, ammonia, freon-12, and sulfur hexafluoride. Other gases suggested were not proven to be operable in such range (such as acetylene, ethane, propane, propadiene, perfluoride propane, dimethyl ether, n-butane, hydrogen bromide, and hydrogen iodide). It is noted that the patent concept has never been offered commercially because of the difficulty of assembling the different high pressure gases into their respective volume chambers while preventing the gases from mixing by bypassing the piston seal that separates the different volume chambers. Because of this, it is also noted that the patented concept had difficulty in achieving essentially constant net operating force for the piston rod with varying temperature.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an automatic temperature compensating device for gas springs that is benign, safe, and employs an economical secondary gas assembled at ambient conditions in a solid form.
It is also an object of this invention to provide an automatic temperature compensating device that ratios the pressure surfaces for the primary and secondary gases so that the net force is constant over a greater operating temperature range than that achievable by the prior art.
A further object of this invention is to provide an automatic temperature compensating device that employs a cylinder housing separate from the gas spring to alleviate the need for complex or unreliable sealing structures between the spring gas and the compensating gas.
A first aspect of this invention is a method of making an automatic temperature compensating gas spring strut, comprising: (i) providing an outer cylinder having opposite ends with one end closed and the other end apertured to permit movement of the strut therethrough; (ii) nesting an inner cylinder within the outer cylinder with radial space therebetween, the inner cylinder being apertured at opposite ends; (iii) partitioning the space between said cylinders into a first chamber adjacent the closed end of the outer cylinder and a second chamber remote from such closed end; (iv) inserting a piston in sliding, sealing relation with the interior of the inner cylinder, the piston having a piston rod extending from said piston and sealingly out through the aperture of the inner cylinder; (v) after injecting a high pressure, non-condensing gas in the first chamber, inserting a measured quantity of solid carbon dioxide (“dry ice”) in the second chamber at ambient conditions which dry ice sublimes to a condensable high pressure gas within the second chamber that is effective in balancing the pressure on opposite sides of the piston to create a relatively constant net force acting on the piston rod over a greater operable temperature range.
The invention, in a second aspect, is a force providing assembly having a temperature compensating device, the assembly comprising: (a) first and second cylinders nested with the second cylinder within the first cylinder and having their interior volumes interconnected; (b) means movably dividing the interconnected volumes to define at least one closed but variable volume chamber; (c) a two-phase condensing gas in the chamber comprised of CO
2
; (d) a force providing element remote from said cylinders; and (e) a mechanical linkage between the force providing element and said movable dividing means to transfer a net force relatively independent of ambient temperature conditions within the range of −40° C. to +80° C.
REFERENCES:
patent: 3751023 (1973-08-01), Thomas
patent: 4597565 (1986-07-01), Smith
patent: 4613115 (1986-09-01), Smith
patent: 4646884 (1987-03-01), Yang
patent: 4854554 (1989-08-01), Ludwig
patent: 5161786 (1992-11-01), Cohen
patent: 5839719 (1998-11-01), Hosan et al.
Baack David Gerald
Stephan Craig Hammann
Ford Global Technologies Inc.
Kramer Devon
Malleck Joseph W.
Oberleitner Robert J.
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