Abstract:
A rotary machine including a rotor having apexes provided with apex seals achieves better efficiency through the use of apex split seals which minimize leakage across the apex seals to thereby allow operation at relatively high pressure values.

Description:
CROSS REFERENCE  
       [0001]     This application claims the benefit of U.S. provisional patent application, application No. 60/544,683 filed Feb. 17, 2004 by the applicant hereof. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to rotary machines of the trochoidal type, and more particularly, to apex seals for the rotors of such machines.  
       BACKGROUND OF THE INVENTION  
       [0003]     Trochoidal machines (the term “trochoidal” as used herein is also intended to encompass epitrochoidal machines as well as true trochoidal ones) have long been known. Perhaps the most well known example is the Wankel engine. Such machines have, however, been used for other purposes, including, for example, the compression of gas. As is well known, such rotary machines include a rotor that is nominally triangular in shape and which generally has the appearance of an equilateral triangle whose three sides are convex. The rotor is mounted on an eccentric on the machine shaft and typically is tied to a housing by means of a spur gear configuration on one side of the rotor meshed with a ring gear formation on the corresponding side of the machine housing.  
         [0004]     The rotor is contained in a chamber that is trochoidal in shape. Seals are carried at each apex of the rotor to sealingly engage the chamber periphery. Side seals are also carried by the rotor near its periphery for sealingly engaging the sides of the chamber and typically, so-called corner seals are located at the interface of the ends of the apex seals and the ends of the side seals on both sides of the rotor. Intake and exhaust porting is provided in the chamber periphery with one port being located on one side of the so-called “waist” of the chamber and the exhaust port on the other.  
         [0005]     Oppositely of the porting, other components may be located, depending upon the use to which the machine is being put. In the case of an engine, ignition devices are located of one or both sides of the waist oppositely of the ports. Alternatively, fuel injection devices may be located in generally the same place as the ignition devices if the engine is to operate on the diesel cycle.  
         [0006]     While engines of this sort have been commercially produced, particularly for powering vehicles, they have not achieved the acceptance of conventional reciprocating engines for a variety of reasons.  
         [0007]     Specifically, a known type of a rotary engine that has been commercially sold as a power plant for a vehicle has a theoretical compression ratio of 10:1 but only produces a maximum internal pressure in the range of 85 to 100 psi. during the compression part of the rotary cycle at cranking speed. On the other hand, a reciprocating engine having the same compression ratio would, at cranking speed, produce an internal pressure in the range of 170 to 200 psi., and if the seals of either engine were perfect, the internal pressure would be significantly higher. The difference between the theoretical and actual pressures is the result of seal leakage. Seal leakage is more critical in a rotary engine than in a reciprocating engine because at 6000 rpm, a reciprocating engine&#39;s compression phase takes approximately 0.005 seconds, whereas that of the rotary engine takes approximately 0.0075 seconds. The seals of the rotary engine are therefore subject to leakage for a 50% longer period of time than those of reciprocating engines at the same rpm.  
         [0008]     Because rotary engines can and do operate at significantly higher rpms, the problem is somewhat lessened. However, due to the lesser compression attainable in rotary engines, the same are currently inferior to reciprocating engines in terms of power produced per unit of fuel, which translates into a reduction in gas milage, and increased hydrocarbon admissions. Thus, rotary engine performance is far inferior to its potential.  
         [0009]     Apex seals are perhaps the greatest cause of lack of compression due to leakage in a rotary engine of the type having a rotor provided with apexes. Specifically, internal combustion engines of all types typically rely on so-called “gas energization” of seals to produce the desired sealing effect during compression and combustion phases of their cycle of operation. Seals that are gas-energized are typically found somewhat loosely in grooves in which they may move slightly from side to side and in and out of the groove. Conventionally, a light biasing spring will be placed between the bottom of the groove and the innermost end of the seal to bias the opposite end of the seal into light sealing contact with the operating chamber wall. When subject to pressure, as during compression or combustion phases of the operating cycle, the pressure acts against the high pressure side of the seal to force the opposite side to seal tightly against the side of the groove. The gas under pressure also enters the groove to act against the radially inner end of the seal and bias the same outwardly into good sealing engagement with the wall of the operating chamber. This is true whether the seal is a piston ring, an apex seal, or a side seal. There is, however, a major difference in the operation of apex seals. During the compression phase of an engine, the apex seal must seal against the trailing wall of the seal receiving groove to achieve compression. When the compression phase is completed, and the combustion phase is entered, the higher pressure now exists on the opposite side of the apex seal, requiring it to shift within its groove so that its leading side seals against the leading side of the seal receiving groove. This shifting of the apex seal leads to the momentary creation of a leakage path around the seal between the sides of the groove as the seal transitions from sealing engagement against one groove wall to sealing engagement against the other groove wall. Moreover, when the pressure acting against the leading face and inward end of the seal, acts against the outermost end of the seal and the trailing face may reach a value so that there is a net positive pressure acting on the seal in the radially inward direction. It can be sufficient to exceed the combined force of the biasing spring and centrifugal force generated by the mass of the apex seal. Consequently, a small gap may occur at the interface of the outermost tip of the seal and the wall of the operating chamber, allowing leakage through this gap as well. All of this creates a loss of efficiency.  
         [0010]     A second point of failure of apex seals can occur when the pressure from combustion increases very rapidly. In order to maintain a tight seal between the outer sealing edge of the apex seal and the operating chamber wall, the pressure at the inner part of the apex seal must also increase substantially equally as rapidly. However, since the gas to create the pressure must travel through a narrow gap between the apex seal and the side of the groove in which the seal resides, the outward biasing pressure cannot increase as rapidly and an inwardly movement of the seal results in a loss of sealing contact, especially at high rpm.  
         [0011]     A third cause of leakage can occur as an apex seal passes 300° past bottom dead center (bdc) to the time it reaches the exhaust port, typically located at about 60° past bdc. During this time, pressure in the trailing chamber is required to hold the apex seal tight against the leading face of the groove in which it resides. However, frictional forces at the tip of the apex seal act counter to the pressure forces and at some point in time between 300° and 60° past bdc, a gap will occur on both sides of the apex seal resulting in undesirable leakage around the apex seal.  
         [0012]     Still another cause of loss of pressure occurs as the apex seal passes recesses in the operating chamber wall employed in ignition and/or fuel injection systems.  
         [0013]     A further cause may result from seal warpage. Extreme heat encountered in the operating cycle of the engine may cause a conventional apex seal to warp out to in or from side to side resulting in the creation of more leakage paths at the tip of the seal.  
         [0014]     Still another cause of leakage may result if the seal resonates at its natural frequency along its length. Because the slot in which the seals are received are larger than the seal, i.e., the slot width is greater than the width of the seal, the seal may resonate, creating gaps which allow leakage.  
         [0015]     The present invention is directed to overcoming one or more of the above problems.  
       SUMMARY OF THE INVENTION  
       [0016]     It is the principal object of the invention to provide a new and improved rotary machine. More specifically, it is an object of the invention to provide a new and improved apex seal construction for use in rotary machines, which considerably reduces the leakage associated with conventional apex seal operation in rotary machines.  
         [0017]     An exemplary embodiment achieves the foregoing objects in a rotary machine that includes a housing defining an operating chamber having a wall with a shaft journalled in the housing and having an eccentric within the chamber. A rotor is located within the chamber and is journalled on the eccentric and has a plurality of equally angularly spaced apexes and is timed to the housing to rotate and translate within the chamber so that all of the apexes are in close proximity to the wall for all positions of the rotor within the chamber. Intake and exhaust ports to the interior of the chamber are provided and apex seal receiving groove means are provided at each of the apexes and opened towards the wall. Two apex seals are located at each of the apexes and mounted for sliding movement in the groove means thereat while essentially preventing leakage through the groove means. Each such apex seal includes an inner mounting section received in the groove means at the apex at which the seal is located and an outwardly directed toe located outwardly of the groove means. The toes of the two apex seals at each groove means are directed oppositely away from one another and sealingly engage the wall at spaced locations.  
         [0018]     In a preferred embodiment, the chamber wall is a peripheral wall and the groove means open radially outwardly with the apex seals at each of the apexes mounted for radial sliding movement in the associated groove means.  
         [0019]     In one embodiment, each of the groove means consists of a single groove and both of the apex seals at each apex are received in the single groove at the apex at which they are located.  
         [0020]     In a preferred embodiment, each of the groove means, at a radially inner location, is vented.  
         [0021]     In one embodiment, there is further provided a vent passage between the two seals at each apex.  
         [0022]     A preferred embodiment contemplates the use of biasing means in each of the single grooves for substantially independently biasing each of the two seals at the apex in an outwardly direction.  
         [0023]     In a highly preferred embodiment, the biasing means includes an elongated leaf spring having a concave side opening outwardly within the groove and two opposed ends, with each spring end being bifurcated to prove two spring fingers thereat, one for each of the seals in the single groove.  
         [0024]     In a highly preferred embodiment, the rotary machine is a rotary engine and even more preferably, the rotary engine is a trochoidal or epitrochoidal engine.  
         [0025]     A preferred embodiment contemplates that the apex seals be bar-like and have outer, rounded sealing surfaces to make sealing contact with the wall generally along a line such that for all angular positions of the rotor within the chamber, the area on the radially outer sealing surface from the line of contact to the toe rounded end is less than the area of a pressure-responsive surface on an inner part of the toe.  
         [0026]     Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0027]      FIG. 1  is a sectional view of a rotary machine, specifically, a trochoidal engine, having a nominally triangular rotor with apex seals at each apex;  
         [0028]      FIG. 1   a  is an enlarged view of one apex in  FIG. 1 ;  
         [0029]      FIG. 1   b  is an enlarged view of another apex in  FIG. 1 ;  
         [0030]      FIG. 1   c  is an enlarged view of still another apex in  FIG. 1 ;  
         [0031]      FIG. 2  is a side elevation of an apex seal employed in the invention;  
         [0032]      FIG. 3  is an end view of the apex seal;  
         [0033]      FIG. 4  is a view similar to  FIG. 2 , but of a modified embodiment of the apex seal;  
         [0034]      FIG. 5  is a plan view of a biasing spring used with the seal;  
         [0035]      FIG. 6  is an enlarged, fragmentary view of the mounting of an apex seal within an apex groove;  
         [0036]      FIG. 7  is a view similar to  FIG. 1   c , but enlarged and showing certain dimensions of seal components believed to be optimal; and  
         [0037]      FIG. 8  is a view of an exemplary embodiment of an apex seal made according to the invention passing over an opening or recess in the operating chamber wall. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]     An exemplary embodiment of the invention hereof will be described in the context of a trochoidal or so-called Wankel engine. However, it is to be understood that the seal construction of the present invention may be utilized in rotary machines other than engines as, for example, a compressor or expander, or a compressor/expander. It will also be appreciated by those skilled in the art that the invention is not limited to trochoidal machines (here, trochoidal is being used in the strict sense), but epitrochoidal machines and slant axis rotary machines as well. Consequently, no limitation to a particular type of rotary machine or to a particular use, such as use as an engine, is intended except insofar as expressly stated in the appended claims.  
         [0039]     With the foregoing in mind, the invention will now be described.  
         [0040]     Referring to  FIG. 1 , a rotary machine in the form of a trochoidal or Wankel engine is illustrated and is seen to include a housing  10  defining a trochoidal operating chamber  12  having a peripheral wall  14 . As is well known, the peripheral wall  14  includes a waist area  16  where the wall narrows slightly. At one point on the periphery of the wall  14 , an inlet port  18  is located while on the opposite side of the waist  16  in that same area of the port  18 , an outlet port  20  is provided.  
         [0041]     A shaft  22  is journalled in the housing  10  and within the chamber  12  mounts an eccentric  24  on which a rotor  26  is journalled. The rotor  26  may be described as being nominally triangular and is formed as an equilateral triangle having three equally angularly spaced apexes  28  and bulging or convex sides  30  extending between adjacent apexes.  
         [0042]     The rotor  26  includes, on one side thereof, an internal ring gear  32  which revolves with the rotor  26  about the eccentric  24 . A fixed gear  34  which is stationary and mounted to the housing  10  is meshed with the ring gear  32 , the gear  34  being generally in the form of a spur gear.  
         [0043]     Oppositely of the ports  18  and  20 , the peripheral wall  14  includes two openings  36  on opposite sides of the waist  16  in that area. The openings  36  establish fluid communication between the interior of the chamber  12  and ignition devices or fuel injection devices, or both.  
         [0044]     Each side of the rotor  26  includes conventional side seals  40  extending between the apexes  28 .  
         [0045]     As seen in various figures, at each of the apexes  28 , a radially inwardly directed groove  42  is located. The groove  42  includes a bottom wall  44 , a leading sidewall  46 , and a trailing sidewall  48 . A radially outwardly facing open end  50  is provided for each groove  42 .  
         [0046]     Within each groove  42  is a biasing structure, generally designated  52 , to be described in greater detail hereinafter, and an apex seal construction, generally designated  54 , which includes a leading edge seal  56  and a trailing edge seal  58 .  
         [0047]     A preferred embodiment also includes a vent passage  60  in fluid communication with the bottom wall  44  of each groove  42  which extends to the eccentric  24  on the shaft  22  so that the radially inner end of each groove  42  is essentially vented to atmosphere for purposes to be seen.  
         [0048]     In some instances, grooves  62  may be cut in abutting sides of the leading seal  56  and a trailing seal  58  as shown in  FIGS. 4 and 6 . As seen in  FIG. 7 , for example, the grooves  62  together with the vent passages  60  provide a means of venting a space  64  defined by the peripheral wall  14  and radially outer parts of the leading seal  56  and the trailing seal  58 , again, for purposes to be seen.  
         [0049]      FIGS. 1   b  and  1   c  contain essentially the same illustration as  FIG. 1   a , except that the position of the leading and trailing seals  56  and  58  has shifted. In  FIG. 1   a , the leading edge seal  56  is extended a greater distance out of the groove  42  than has the trailing edge seal  58 . This configuration is assumed by the seals at approximately 102 degrees past bdc, bdc being shown at a point  65  in  FIG. 1 .  
         [0050]     In contrast, in  FIG. 1   b , the situation has reversed with the trailing edge seal  58  extending further out of the groove  42  than the leading edge  56  as would occur at about 222 degrees past bdc.  FIG. 1   c  shows again a reversal of the condition where the leading edge seal  56  is again further out of the groove  42  than the trailing edge seal  58 . This would be the configuration at approximately 342 degrees past bdc.  
         [0051]     Referring now to  FIG. 6 , it can be seen that the cross section leading edge seal  56  is a mirror image of the trailing edge seal  58  and J or L shaped. Each seal terminates in a radially outwardly and circumferentially directed toe  70 . Each toe, in turn, is rounded about a radius “R”  72 . In a preferred embodiment, the toes  70  are angled at 60 degrees to the centerline of a groove  42  or to the abutting, flat side surfaces  74  and  76  of the seals  56  and  58 . The seals  56  and  58  are generally in the form of elongated bars and, consequently, the seal  56  has a flat surface  78  opposite its flat surface  74  and parallel thereto while the seal  58  has an opposite flat surface  80  opposite the flat surface  76  and parallel thereto.  
         [0052]     In an exemplary seal construction, the spacing between the surfaces  74  and  78  of the leading edge seal  56  and between the surfaces  76  and  80  of the trailing seal  58  is twice the radius “R”  72 . It will also be observed that taken in a direction 90 degrees to the abutting surfaces  74  and  76  of the seals  56  and  58 , the circumferential extent of each of the toes  70  is 1.5 “R.” 
         [0053]     For example, as shown in  FIG. 7 , the thickness of each seal  56  and  58  may be 1.5 mm, while the circumferential dimension of each toe  70 ,  72  and the radius of each toe  70 ,  72  may 0.750 mm.  
         [0054]     Other relative dimensions may be employed so long as certain criteria set forth hereinbelow are followed.  
         [0055]     In all events, it is important that the width of each groove  42  be substantially the size as twice the thickness of one of the seals  56 ,  58 . Needless to say, the groove base  42  will be somewhat wider than that thickness so as to enable the seals  56 ,  58  to slidably move between the positions illustrated in  FIGS. 1   a ,  1   b , and  1   c  during rotation of the rotor  26 . However, no significant gap, as is customary in current gas-energized seals, should be present. In short, the width dimension of the groove should be such that the seals  56 ,  58  slide within the grooves  42  without side to side shifting substantially fill any leakage paths through the groove as can be found in customary and conventional apex seals. That is to say, the tightest fit that will allow sliding movement of the seals  56 ,  58  under operating conditions should be used.  
         [0056]     The rounded toes  70  of the seals provide that the toes make contact with the peripheral wall  14  of the operating chamber in essentially a line contact as shown at  82  and  84  in  FIG. 1   c . Biasing means are provided, as mentioned previously, to bias seals  56 ,  58  against the peripheral wall  14  and as seen in  FIGS. 2, 3 , and  4 , include an elongated, curved leaf spring  88 , whether or not the seal  56 ,  58  is provided with the vent groove  62 .  
         [0057]     As seen in  FIG. 5 , each leaf spring  88  includes bifurcated ends  90 . The bifurcated ends  90  define two spring fingers  92  at each end of the leaf spring  88 , one for each end of the seals  56  and  58 . As seen in  FIG. 6 , one pair of the spring fingers  92  provide an outward bias for the seal  56 , while the other spring fingers  92  provide an outward bias for the seal  58 . Because the bifurcation extends very nearly to the center of the leaf spring  88 , it will be appreciated that essentially an independent bias is provided to each of the seals  56  and  58  by a unitary structure, thereby minimizing assembly costs.  
         [0058]     Returning now to  FIG. 6 , it can be seen that each toe has a radially outer sealing surface  96  and an opposite pressure-responsive surface  98  that is located outside of the radially outer end of the groove  42 . The foregoing dimensions or relative dimensions of the constructions of the seals given in connection with the description of  FIGS. 6 and 7  are chosen such that the area of the pressure-responsive surface  98  will always be greater than the area of the sealing surface  96  exposed to high pressure during an operational cycle. That area, of course, will be the effective area between the line contact shown at  82  in  FIG. 1   c  and  FIG. 8  and the point on the toe  70  most remote from a plane defined by, for example, one of the side surfaces  74 ,  76 ,  78 ,  80 . The effective area subject to pressure tending to drive the seal  56  or  58  into the groove  42  will then always be less than the pressure acting on the pressure-responsive surface  98  which is exposed to the same pressure in any event. Consequently, good sealing contact will be made with the peripheral wall  14  through gas energization without the need for the gas to enter the groove  42  and create a leakage path.  
         [0059]     Additionally, the spark plug or fuel injection ports  36  may be dimensioned so as to be bridged by the two seals as shown in  FIG. 8  to minimize pressure loss on the high pressure side of one seal assembly  54  to the low pressure side thereof upon the seal assembly crossing such a port  36 .  
         [0060]     It can be shown that the total force acting outwardly on the leading and trailing seals  56  and  58  is reduced from that found in conventional apex seals because high pressure is acting only on the leading seal  56  or the trailing seal  58  if it is acting at all, and the spring force may be minimal as well. Thus, seal wear is reduced.  
         [0061]     From the foregoing description, it will be appreciated that various forms of leakage through grooves corresponding to the grooves  42  herein, but in conventional rotary machines, is considerably reduced using the invention, thus allowing higher pressures to be obtained within the machine. Furthermore, because the apex seals of the present invention do not shift from side to side within the grooves  42 , it is possible to extend the side seals  40  completely to the apex seals, and thus eliminate the corner seals used in conventional engines while retaining their function. Consequently, use of an apex seal assembly made according to the invention achieves all the benefits of gas energization of seals while eliminating various leakage paths about the seal and reducing the frictional force with which the seals engage the operating chamber wall  14  to thereby minimize wear.