Patent Publication Number: US-2002002902-A1

Title: Piston-to-cylinder seal for a pneumatic engine

Description:
REFERENCE TO RELATED APPLICATION  
     [0001] This application is a continuation of Application Ser. No. 09/613,569, filed Jul. 10, 2000, entitled Piston-To-Cylinder Seal for a Pneumatic Engine, which is incorporated herein by reference, and which is a continuation of Application Ser. No. 09/363,023, filed Jul. 29, 1999, entitled Piston-To-Cylinder Seal for a Pneumatic Engine, now U.S. Pat. No. 6,085,631, which is a continuation-in-part of Application Ser. No. 09/178,595, entitled Pneumatic Engine, filed Oct. 26, 1998 now U.S. Pat. No. 6,006,517. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] In the design of pneumatic engines, there has existed an historic problem of releasing “back pressure” caused by a return stroke of the engine piston after a firing or compression stroke has occurred. This problem has caused engine designers to employ complicated exhaust valves or to leave a clearance between the piston diameter and the cylinder diameter, so pressurized air could escape during the return stroke.  
       [0003] The mechanics of the pneumatic engine are very simple. When the piston is moving from the intake valve, it is in the compression stroke. When the piston is furthest away from the intake valve it exhausts any pressure left from the compression cycle. When the moving towards the intake valve, it is in the return cycle. This return cycle is where the piston&#39;s movement back to the firing position is critical; no pressure buildup should occur. In all designs only the inertia of the rotating components force the piston down during this cycle.  
       [0004] In the prior art, there exist pneumatic engines without a seal on the piston. These designs do not create back-pressure but are very inefficient during the compression stroke because of air loss between the piston and the cylinder wall. If an O-ring type seal, or any seal that seals in both direction, is used between the piston diameter and the cylinder diameter, the compression stroke becomes very inefficient since any compressed air would then exhaust at the top of the stroke. However, when the piston is returning to its firing position it can create up to 5 five atmospheres of back-pressure before the firing sequence begins again. This effect slows down the rotational speed of the rotating components. Thus more inertia and heavier parts such as flywheels are needed to compensate. These effects in other engines that create back-pressure requires an exhaust valve to vent this pressure. If no exhaust valve is used, such seals significantly lower the performance of the engine, and in some cases cause the engine not to function.  
       [0005] The present invention is therefore directed to an engine seal adapted to seal against the piston wall only during the compression stroke, but not during the return stroke, thereby obviating the need for either an exhaust valve or higher mass engine components.  
       SUMMARY OF THE INVENTION  
       [0006] Within a piston cylinder of a pneumatic engine, the inventive system comprises a piston proportioned for complemental travel within said piston cylinder, said piston having a radial compression surface thereof and means for effecting the axial reciprocation of said piston within said piston housing. The system further includes a piston seal including means for securement to said compression surface of said piston and an integrally dependent resilient annular skirt normally biased inwardly toward a longitudinal system axis, said skirt, in combination with said securement means, defining a radius of less than that from said system axis to interior walls of said cylinder during low pressure (return stroke) phases of a work cycle of the pneumatic engine and, during high pressure (compression stroke) phases thereof, defining a radius greater than that from the system axis to said inner wall of said cylinder. Therein, said inward bias of said skirt is overcome thereby causing axial and radial lifting of the skirt against inner walls of the cylinder, to effect a piston seal of a high integrity during high pressure phases of the engine work cycle. During low pressure phases, no seal is effected since the skirt has not yet expanded.  
       [0007] The piston seal more particularly includes a hollow cylindrical segment having an interior diameter complemental with an outside diameter of the piston to be sealed oppositely to the compression region of the engine cylinder. An upper base of the hollow cylindrical segment defines, in part, a surface which is complemental to lower annular surfaces of said piston which are radially inward from the inside diameter of the cylinder. The inventive includes, radially outwardly from said upper base of said cylindrical segment, an integrally dependent resilient annular umbrella-like skirt having a radial extent, when measured from the system axis, which is normally less than the radius from said axis to the outside diameter of the piston. Therein, the annular skirt in normally biased inwardly toward the system axis and radially away from the cylinder wall in which interface. Therefore sealing of said skirt against the cylindrical wall will occur only in the presence of elevated fluid pressure beneath the skirt which causes an axial lifting, and thereby radial expansion, of said skirt bringing the periphery thereof into fluid tight deformable contact with said wall of said cylinder during high pressure phases of the work cycle of the pneumatic engine.  
       [0008] It is accordingly an object of the present invention to provide an improved compression seal for a cylinder of a pneumatic engine.  
       [0009] It is another object to provide an improved piston-cylinder system, inclusive of a pneumatic piston seal, which will provide improved fluid integrity at the piston-cylinder interface during compression strokes of the engine.  
       [0010] It is a further object of the invention to provide a method of unsealing of a piston of a pneumatic engine during return strokes thereof.  
       [0011] It is a still further object to provide a piston seal for a pneumatic engine of a type particularly adapted for use with toy vehicles.  
       [0012] It is a further object to provide a piston seal of the above type which does not require manufacture thereof integrally with the manufacture of the piston of such an engine and does not require use of a return valve or high mass engine components.  
       [0013] The above and yet other objects and advantages of the present invention will become apparent from the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention, and claims appended herewith.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 is a perspective view of the inventive piston seal.  
     [0015]FIG. 2 is a top view thereof.  
     [0016]FIG. 3 is an operational view of the piston seal showing the same at the beginning of a low pressure phase (return stroke) of a pneumatic engine work cycle.  
     [0017]FIG. 4 is an operational view of the piston seal showing the same at the beginning of a high pressure (compression stroke) phase of the engine work cycle.  
     [0018] FIGS.  5  is a view, similar to the view of FIG. 4, however showing the entire piston, piston seal, cylinder and air inlet assembly.  
     [0019]FIG. 6 is a view, similar to the view of FIG. 5, however showing the piston in its comparison stroke, however advanced twenty degrees within the engine cycle from the position of FIG. 5.  
     [0020]FIG. 7 is a system view, similar to the views of FIGS. 5 and 6, however showing the piston and associated seal in a low pressure phase of the engine cycle corresponding to that of FIG. 3.  
     [0021]FIG. 8 is a system view similar to that of FIGS. 5 through 7, however, showing a near-completed down or return stroke of the system, in which a high pressure phase had not yet been reached.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0022] With reference to the perspective view of FIG. 1, an inventive piston seal  10  may be seen to include a substantially cylindrical sleeve  12  including, integrally dependent from a radial base  14 , an annular skirt  16 . As may be noted, said cylindrical sleeve  12  and annular skirt  16  are polarly symmetric about a longitudinal axis  18  thereof, also referred to herein as a system axis. The transverse width of skirt  16  is about one-half the width or thickness of the sleeve  12 .  
     [0023] A top view of the seal is shown in FIG. 2.  
     [0024] With reference to the enlarged view of FIG. 3, there may be seen further elements which comprise the instant inventive piston compression/description system for use in a pneumatic engine. More particularly, FIG. 3 includes a cross-sectional view of a piston cylinder  20  of a pneumatic engine and a piston  22  which is proportioned for complemental travel therewith. As may be noted, the system also includes a piston rod  24  which comprises means for effecting the axial reciprocation of the piston  22  within the piston cylinder  20 . It is to be understood that the illustrated piston constitutes but one of numerous geometries to which the present invention is applicable.  
     [0025]FIG. 3 further shows a radial compression surface  26  of said piston  22 . Against substantially all of this surface, with the exception of outer annular region  28 , said piston seal  10  is complementally or, otherwise as by bonding means, secured. Thereby, the interior diameter of cylindrical sleeve  12  of the seal  10  as well as radial base  14  thereof will be secured, this leaving only resilient annular skirt  16  without direct securement to compression surface  26  of the piston  22 . It is to be noted that skirt  16  of seal  10  is normally biased inwardly toward system. axis  18  such that, during a low pressure phase or return stroke of the work cycle (which is shown in FIG. 3) of the pneumatic engine, skirt  16  will exhibit the geometry shown therein. That is, skirt  16  will not touch interior wall  30  of the piston cylinder  20 . In the view of FIG. 3, this geometry is shown permits the escape of air  32  through cylinder aperture  34 .  
     [0026] During a high pressure phase or compression stroke of the work cycle of the pneumatic engine, the piston and piston seal are lower within piston cylinder  20  and are moving upward relative to bottom surface  36  of the piston cylinder. See FIG. 4. Therein high pressure air bursts  38  and  38   a  create a high pressure region  40  within cylinder  20  thereby applying sufficient axial and radial pressure against the underside of skirt  16  to overcome said inward bias. When this occurs, the upper surface of skirt  16  will deformably urge against wall  30  of the cylinder thereby creating a high pressure, high integrity annular seal within region  42 , between said surface  30  of cylinder  20 , said skirt  16  of seal  10  and an annular interface region  44  of the piston  22 . Therein, it is noted that while the radius of skirt  16  relative to system axis  18  is normally less than the radius of cylinder wall  30  therefrom, during high pressure phases of the engine work cycle, such as that shown in FIG. 4, the radius of skirt  16  will be forcibly increased, by the effect of air burst  38   a,  to one which is greater than the radius of wall  30 , thereby, in combination with the deformable property of said seal  10 , creating the above-referenced high pressure high intensity seal within annular region  42  of the system.  
     [0027] With reference to the relationship of the views of FIGS. 3 and 4 to an entire work cycle of a pneumatic engine of a type to which the present invention is applicable, there is shown in FIG. 5 a view of an entire piston, cylinder and associated air inlet  45  assembly for a pneumatic engine to which the present invention is applicable. Therein, FIG. 5 (which corresponds to that of FIG. 4) show a high compression phase of the engine work cycle, that is, the part of the work cycle during which piston  22  is moving upward but has not yet reached cylinder apertures  34  through which air is released. In FIG. 6, inlet ball  46  is closed relative to cylinder inlet  48 . Also spring  50 , which rests on rod  52 , is shown in the process of pushing off of ball  46  to impart kinetic energy to piston  22 .  
     [0028] The view of FIG. 7 corresponds to that of FIG. 3. This phase of the work cycle corresponds to the point of lowest internal compression within the cylinder  20 , i.e., the return stroke.  
     [0029] In FIG. 8 is shown the downward motion of piston  22 , however, before sufficient pressure has been reached within region  40  to overcome the inward bias of piston seal skirt  16  toward axis  18  of the system. Accordingly, during the phases of the work cycle shown in FIGS. 7 and 8, the skirt  16  maintains its normally closed inward biased (also shown in FIG. 1), thereby permitting escape of air within region  40  in order to release back pressure that would otherwise develop therein. Thereby, maximum engine efficiency is obtained.  
     [0030] While there has been shown and described the preferred embodiment of the instant invention it is to be appreciated that the invention may be embodied otherwise than is herein specifically shown and described and that, within said embodiment, certain changes may be made in the form and arrangement of the parts without departing from the underlying ideas or principles of this invention as set forth in the claims appended herewith.