For many years, there has been interest in developing and using alternative fuels for vehicles, and particularly, overland vehicles, for example, automobiles, buses, trucks, etc. Over that period of time, many such vehicles have been retrofitted to operate using natural gas. More recently, with increasingly stringent air pollution standards, fleets of vehicles that have been retrofitted to operate with natural gas are more common.
In currently retrofitted vehicles, the natural gas is often stored in a cylindrically shaped pressurized metal vessel, such as, a steel or aluminum tank, designed specifically for storing gases such as natural gas, propane, nitrogen, etc. under high pressure. The cylindrical shape of the tank provides a circular cross section about an axis which eliminates bending stresses and helps reduce the weight of the tank. Since the cylindrical steel natural gas storage tank is not suitable for and cannot be readily retrofitted in place of the vehicle's liquid fuel storage tank, the natural gas storage tank is often housed in the storage area or trunk of the vehicle, thereby eliminating or severely limiting the use of the trunk for other storage. Therefore, there is a need for a natural gas storage tank that can take the place of the vehicle's liquid fuel storage tank. Other gas storage tank designs and structures are known in the art.
For example, the Pechstein U.S. Pat. No. 2,156,400 is directed to a spherical container for storing fluids such as gases and liquids. The spherical container has a foundation with at least three reinforcing supports adapted to transmit the forces exerted by the dead weight and the weight of the contents of the container upon the foundation. The container further includes lower struts connected at their ends to points on the inner wall of the container where the container rests on the supports to form at least one lower polygonal frame. The container further has upper struts connected at both ends to the inner wall of the container at points lying in its horizontal middle portion to form at least one upper polygonal frame. Inclined struts connect the corner points of the upper and lower polygonal frames to provide a self supporting framework which is adapted to transfer the loads due to the dead weight and the weight of the contents of the container directly upon the supports without substantially stressing the walls of the container.
The Albrecht U.S. Pat. No. 2, 296,414 is directed to heavily reinforced storage tanks for liquids and gases that are present in high volume and have angular sides made of flat or curved plates. The storage tank has flat side, top and bottom walls of metal plates. A plurality of vertically spaced tiers of braces are set at angles to adjacent vertical walls. Each tier has a plurality of parallel, horizontal, equally spaced braces lying in a common plane. Each of the braces forms a triangular truss with adjacent vertical walls to cause the stresses in the bracing members and the wall plates to be compensating stresses.
The Pflederer U.S. Pat. No. 3,368,708 is directed to a filament wound storage vessel capable of withstanding high internal pressures. The cylindrical wall of the tank is formed of helically wound, fibrous material impregnated with thermal setting resin serving to bond fibers together as an integral structure.
While all of the above known tanks are effective to confine a gas under high pressure, the designs of the tanks are directed to their particular application. For example, the design of the currently used steel cylindrical tank is directed to a tank that is intended to be portable and not permanently affixed to any particular structure. Therefore, the tank has specifications relating to its size, shape and weight that facilitate portability.
In contrast, the Pechstein '400 and Albrecht '414 patents are designed to store large volumes of pressurized gas and are not designed for portability. The Pflederer '708 patent is designed to have a removable head portion at one end which presents different design considerations and a different structure. None of the above tanks provide a tank structure that may be constructed in any desired shape as may be required for installation in a vehicle. Further, Applicants are not aware of any of those pressurized tank structures serving any purpose other than holding a pressurized liquid or gas.