Variable capacity vehicle-mounted cryogenic storage vessels and method of making same

A vehicle-mounted double-walled ellipsoidal cryogenic storage vessel includes an inner vessel enclosed by an outer shell to form an insulation chamber therebetween. Both the inner vessel and the outer shell are formed in the same manner. An elliptical pressure head of circular cross-section is cut along a diameter to form two end halves. An end wall is secured between the two end halves to form an end, which is secured to an end of a wall like cross-section. This process is repeated with another pressure head to form the other end of the storage vessel. Storage vessels may be constructed of any size desired to allow sufficient ground clearance when mounted under a vehicle.

BACKGROUND OF THE INVENTION 
The present invention relates generally to cryogenic storage vessels and 
more particularly to vehicle-mounted tanks capable of being manufactured 
in a variety of sizes. 
The typical cryogenic storage vessel consists of a cylindrically-shaped 
inner storage vessel for holding liquid natural gas ("LNG") or other 
cryogen under pressure ranging from about 50 psig to about 300 psig. A 
relatively thin outer shell of the same general shape and slightly larger 
dimension surrounds the inner storage vessel, forming an insulation 
chamber therebetween. The outer shell has a port to allow evacuation of 
air from the insulation chamber. 
Prior to evacuation, thermal insulating material is disposed in the 
insulation chamber to prevent radiant and conductive heat transfer between 
the external environment and the internal storage vessel. Cryogenic 
storage vessels of this type are generally described in U.S. Pat. No. 
4,548,335 to Remes. 
One particular use for cryogenic vessels is to store LNG, which may be used 
to fuel specially equipped vehicles. The LNG is stored in on-board vessels 
analogous to the gas tank on conventional automobiles. On these vehicles, 
space is limited, so the size and shape of the LNG storage vessel must be 
optimized. A vessel having a horizontal dimension greater than its 
vertical dimension allows greater storage capacity while maintaining 
ground clearance. However, different types of vehicles have different 
space limitations. Ellipsoidal storage vessels can be specially 
fabricated, but providing matched pairs of pressure heads is difficult and 
time consuming. A unique forming die must be made for each desired size of 
storage vessel. A cryogenic storage vessel that may be easily and cheaply 
fabricated for assembly in a wide range of sizes to fit various vehicle 
designs is desirable. 
Accordingly, it is a general object of the invention to provide a 
vehicle-mounted cryogenic storage vessel. 
It is a further object of the invention to provide such a vessel that may 
be assembled in a variety of sizes. 
It is another object of the invention to provide such a vessel that is of 
durable, low-cost construction. 
These and other objects of the invention will become apparent when the 
following detailed description of the invention is read in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawings, FIG. 1A shows a cryogenic storage vessel 
constructed in accordance with well-known methods. A metal sheet 10 is 
formed into a cylinder by welding two opposite edges together. A pair of 
hemispherical pressure heads 12, 14 are then secured to the metal sheet 
10. It should be noted that both the inner storage vessel and the outer 
shell of a double-walled cryogenic storage vessel are constructed using 
the same methods. The pressure heads 12, 14 are fabricated in a wide range 
of sizes and specifications; however, cryogenic storage vessels 
constructed with these pressure heads must be generally cylindrical in 
shape. Special shapes are difficult to produce and very expensive. 
As previously noted, an efficient method of constructing desirable. Often, 
cylindrical vessels do not allow enough ground clearance for this purpose. 
FIG. 1B shows a cryogenic storage vessel constructed according to the 
teachings of the present invention. A vessel body 16 is constructed from a 
pair of semi-circular wall portions 18, 20. A pair of flat wall extensions 
22, 24 of any desired length are welded to the semi-circular wall portions 
18, 20 to form a wall of elliptical cross section. Alternatively, the body 
16 may be formed of one sheet of metal. To do so the sheet is roll formed 
into the desired ellipsoidal shape, and its ends are welded. 
A cylindrical pressure head of the type previously described is cut along 
its diameter to form two halves 26, 28. A curved insert 30 is secured as 
by welding between the end halves 26, 28. The assembly consisting of the 
two halves 26, 28 and the insert 30 is secured to one end of the vessel 
body 16. 
Similarly, a second pressure head is formed and welded to the other end of 
the body 16. As will be apparent to one of ordinary skill in the art, the 
construction techniques described are equally applicable to both the inner 
storage vessel and the outer shell. The outer shell is of the same general 
shape as the inner storage vessel, but of slightly larger dimension. In 
some applications, an outer shell is not required. In that case, a single 
shell made according to the invention would be employed. 
Various methods of insulating cryogenic storage vessels are well known in 
the art and are described, for example, in U.S. Pat. No. 4,579,249 issued 
to Patterson et al. and U.S. Pat. No. 4,461,398 issued to Argy. If 
fiberglass sheets or super insulation are used as insulating material, 
they are wrapped around the outer surface of the inner vessel before the 
outer shell is placed thereover. The inner vessel and outer shell are 
spaced from each other by support members. The outer shell typically 
includes a valve 37 (FIG. 2) to facilitate evacuation of the insulation 
chamber formed therebetween after construction of the storage vessel has 
been completed. 
FIG. 2 is useful in explaining the benefits of the present invention in 
terms of the variability of dimensions allowed thereby. The inner storage 
vessel 39 is enclosed within the outer shell 40. Each has a pressure head 
secured thereto. Each pressure head has a radius as defined hereafter 
based upon its diameter before it was cut. These radii determine the 
required dimensions of the walls 39 and 40. Specifically, the pressure 
head for the inner shell 39 has a radius r.sub.1 about a point 42. The 
outer pressure head halves have a radius r.sub.2 about the same point 42. 
The length 1 of both the shells 39 and 40 may vary depending on the 
capacity of the vessel desired. It will be apparent to one of ordinary 
skill in the art that an insulated cryogenic storage vessel of any size 
desired may be constructed by varying r.sub.1, r.sub.2 and 1. The only 
limitation being the availability of pressure heads having the desired 
radius. Thus, cryogenic storage vessels may be constructed to fit in a 
wide range of vehicles. 
The present invention has been described with respect to certain 
embodiments and conditions, which are not meant to limit the invention. 
Those skilled in the art will understand that variations from the 
embodiments and conditions described herein may be made without departing 
from the invention as set forth in the appended claims.