The present invention relates to elevators, and, more particularly, to pneumatically operated elevators relying upon air pressure to move the elevator cab.
In high rise structures, access elevators are limited in height they serve by the weight of the steel cables. Theses cables become so heavy that elevator load capacity is greatly reduced, generally limiting the height served to about 30 floors. To accommodate this condition, elevator systems are segmented into steps of vertical lift, to transfer floors where other elevators at offset locations commence another lift, the number of segments is determined by the structure height. This system, today's state of the art, is cumbersome, uses too much space and is costly.
There have been various proposals for using air pressure to move an elevator cab upwardly and downwardly, and in one instance, to move a transport vehicle horizontally in a tube.
Existing patents on pneumatic elevators rely on shafts containing an elevator cab which is moved by drawing in or expelling large volumes of air from the shaft directly to the outside. This process requires large volumes of filtered treatment of air for variations in weather and seasonal changes and tends to be impractical, awkward and costly.
Illustrative of such efforts in the prior art are Kilpatrick U.S. Pat. No. 3,318,418, Hopkins U.S. Pat. No. 3,949,953, Diggs U.S. Pat. No. 4,023,500, Sassak U.S. Pat. Nos. 4,487,410 and 4,997,060, and Sors U.S. Pat. Nos. 5,447,211 and 5,583,326. Some of these devices rely upon a fan or other means, to provide a large volume of air at substantial velocity acting on the bottom of the cab to move it upwardly and to then reduce the volume of air in a controlled manner to allow the car to move downwardly.
Sors U.S. Pat. Nos. 5,447,211 and 5,583,326 rely upon creating a negative pressure above the car to cause it to rise by reason of the vacuum.
Sassak U.S. Pat. No. 4,997,060 discloses the use of air to provide a cushion for a car in a free fall in a high-rise structure.
Diggs U.S. Pat. No. 4,023,500 is of interest in that he creates a differential in pressure to move a passenger carrying vehicle along a tunnel.
As will be readily appreciated, moving large volumes of air at high velocity into a shaft containing a cab to provide a lifting motion is relatively expensive if the air is drawn from outside the building and since it should be filtered or otherwise treated so as not to contaminate the remainder of the building into which the air will normally escape.
It is an object of the present invention to provide a novel pneumatic elevator assembly in which the cab moves upwardly and downwardly in an essentially closed system of shafts using the same circulated air to move the cab in both directions and requiring only replacement of the small amount of air which is lost by leakage.
It is also an object to provide such an pneumatic elevator assembly which may be fabricated relatively economically and which is relatively simple to operate and maintain.
Another object is to provide such an elevator assembly which is fail-safe and can be used effectively in high-rise buildings.
Still another object is to provide such an elevator assembly which circulates the same air at substantially ambient atmospheric pressure.