Patent Publication Number: US-9850758-B2

Title: Apex and face seals with rotary internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 13/273,824 filed Oct. 14, 2011, which claims priority on provisional U.S. application No. 61/512,457 filed Jul. 28, 2011, the entire contents of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The application relates generally to an internal combustion engine using a rotary design to convert pressure into a rotating motion, more particularly, to sealing arrangements for such an engine. 
     BACKGROUND OF THE ART 
     Rotary engines such as the ones known as Wankel engines use the eccentric rotation of a piston to convert pressure into a rotating motion, instead of using reciprocating pistons. In these engines, the rotor includes a number of apex portions which remain in contact with a peripheral wall of the rotor cavity of the engine throughout the rotational motion of the rotor. 
     The space around the rotor within the rotor cavity defines a number of working chambers which must be sealed from one another in order for the engine to work efficiently. Prior art sealing arrangements typically have gaps between some of the adjacent seal members, which may be due to manufacturing tolerances and/or differential thermal expansions of the seal elements and rotor. 
     SUMMARY 
     In one aspect, there is provided a rotor for a rotary internal combustion engine comprising: a body having first and second axially spaced apart end faces, and a peripheral face extending between the end faces and defining at least three circumferentially spaced apex portions, the first and second end faces each having a groove defined therein between each of the apex portions and each adjacent one of the apex portions, the grooves of the first and second end faces being disposed adjacent to and radially inwardly of the peripheral surface of the rotor; at each of the apex portions: an apex seal protruding radially from the peripheral face of the body and being biased radially away therefrom, and first and second end seals received in a corresponding recess defined in the first and second end face, respectively, the first end seal protruding axially from the first end face and being biased axially outwardly away therefrom, and the second end seal protruding axially from the second end face and being biased axially outwardly away therefrom, the apex seal being engaged with the first and second end seals; a first face seal located in each groove of the first end face and extending between adjacent ones of the apex portions, each first face seal being biased axially outwardly away from the first end face, each first face seal having opposed curled ends each abutting the first end seal of a respective one of the adjacent apex portions; and a second face seal located in each groove of the second end face and extending between adjacent ones of the apex portions, each second face seal being biased axially outwardly away from the second end face, each second face seal having opposed curled ends each abutting the second end seal of a respective one of the adjacent apex portions. 
     In another aspect, there is provided a rotary internal combustion engine comprising: a stator body having an internal cavity defined by axially spaced apart end walls and an inner surface extending between the end walls, the cavity having an epitrochoid shape defining at least two lobes; a rotor body having two axially spaced apart end faces each extending in proximity of a respective one of the end walls of the stator body, and a peripheral face extending between the end faces and defining a number of circumferentially spaced apex portions which is one more than a number of the lobes of the cavity, the rotor body being engaged to an eccentric shaft to rotate within the cavity with each of the apex portions remaining in proximity of the inner surface of the cavity; at each of the apex portions: an apex seal protruding radially from the peripheral face of the body and being radially biased against the inner surface of the cavity, and first and second end seals received in a corresponding recess defined in the first and second end face, respectively, the first end seal being axially biased against the first end wall, and the second end seal being axially biased against the second end wall, the apex seal being engaged with the first and second end seals; a first face seal extending from each of the apex portions to each adjacent one of the apex portions, each first face seal extending from the first end face adjacent to and radially inwardly of the peripheral surface of the rotor and being axially biased against the first end wall, each first face seal having opposed curled ends each abutting the first end seal of a respective one of the apex portions; and a second face seal extending from each of the apex portions to each adjacent one of the apex portions, each second face seal extending from the second end face adjacent to and radially inwardly of the peripheral surface of the rotor and being axially biased against the second end wall, each second face seal having opposed curled ends each abutting the second end seal of a respective one of the apex portions. 
     In a further aspect, there is provided a method of sealing chambers of a Wankel engine defined between a rotor cavity and a rotor thereof, the cavity having axially spaced apart first and second end walls and a peripheral wall extending between the end walls, and the rotor having two axially spaced apart first and second end faces and a peripheral face extending between the end faces and defining circumferentially spaced apex portions, the method comprising: at each one of the apex portions, radially pushing at least a portion of an apex seal against the peripheral wall; between each adjacent ones of the apex portions, axially pushing a first face seal extending from the first end face against the first end wall; between each adjacent ones of the apex portions, axially pushing a second face seal extending from the second end face against the second end wall; at each one of the apex portions, axially pushing a first end seal engaged with the apex seal and extending from the first end face against the first end wall, abutting a curled end of an adjacent one of the first face seals with the first end seal, and abutting a curled end of another adjacent one of the first face seals with the first end seal; and at each one of the apex portions, axially pushing a second end seal engaged with the apex seal and extending from the second end face against the second end wall, abutting a curled end of an adjacent one of the second face seals with the end seal, and abutting a curled end of another adjacent one of the second face seals with the second end seal. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic cross-sectional view of a rotary internal combustion engine having a rotor in accordance with one embodiment; 
         FIG. 2  is a schematic tridimensional view of part of an apex portion of the rotor of the engine of  FIG. 1 ; 
         FIG. 3  is a schematic top view of the apex portion of  FIG. 2 ; 
         FIG. 4  is a schematic front view of the apex portion of  FIG. 2 ; 
         FIG. 5  is a schematic tridimensional view of a spring energizing one of the apex seals of the apex portion of  FIG. 2 ; 
         FIG. 6  is a schematic front view of an apex portion in accordance with an alternate embodiment; and 
         FIG. 7  is a schematic front view of an apex portion in accordance with another alternate embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a rotary internal combustion engine  10  known as a Wankel engine is schematically shown. The engine  10  comprises an outer body  12  having axially-spaced end walls  14  with a peripheral wall  18  extending therebetween to form a rotor cavity  20 . The inner surface of the peripheral wall  18  of the cavity  20  has a profile defining two lobes, which is preferably an epitrochoid. 
     An inner body or rotor  24  is received within the cavity  20 . The rotor  24  has axially spaced end faces  26  adjacent to the outer body end walls  14 , and a peripheral face  28  extending therebetween. The peripheral face  28  defines three circumferentially-spaced apex portions  30 , and a generally triangular profile with outwardly arched sides. As will be detailed further below, the apex portions  30  are in sealing engagement with the inner surface of peripheral wall  18  to form three working chambers  32  between the inner rotor  24  and outer body  12 . The geometrical axis  34  of the rotor  24  is offset from and parallel to the axis  22  of the outer body  12 . 
     In the embodiment shown, the outer body  12  is stationary while the rotor  24  is journaled on an eccentric portion  36  of a shaft  38 , the shaft  38  being co-axial with the geometrical axis  22  of the cavity  20 . Upon rotation of the rotor  24  relative to the outer body  12  the working chambers  32  vary in volume. An intake port  40  is provided through one of the end walls  14  for admitting air, or air and fuel, into one of the working chambers  32 . Passages  42  for a spark plug or other ignition mechanism, as well as for one or more fuel injectors (not shown) are provided through the peripheral wall  18 . An exhaust port  44  is also provided through the peripheral wall  18  for discharge of the exhaust gases from the working chambers  32 . Alternately, the exhaust port  44  and/or the passages  42  may be provided through the end wall  14 , and/or the intake port  40  may be provided through the peripheral wall  18 . 
     During engine operation the working chambers  32  have a cycle of operation including the four phases of intake, compression, expansion and exhaust, these phases being similar to the strokes in a reciprocating-type internal combustion engine having a four-stroke cycle. 
     At least one oil seal ring  46  is disposed in a circular groove in each end face  26  of the rotor between the bearing  48  for the rotor  24  on the shaft eccentric  36  and the face seals. Each oil seal  46  impedes leakage flow of lubricating oil radially outwardly thereof between the respective rotor end face  26  and outer body end wall  14 . Suitable springs (not shown) are provided for urging each oil seal  46  axially into contact with the adjacent end wall  14  of the outer body  12 . 
     The working chambers  32  are sealed by an apex seal assembly and face or gas seals. Referring particularly to  FIGS. 2 and 4 , each rotor apex portion  30  has two circumferentially spaced apart grooves  50  defined therein and extending radially inwardly into the rotor body  24 , one on each side of the apex, from one end face  26  to the other. The apex seal assembly includes an apex seal  52  received within each one of the grooves  50 , and protruding radially from the peripheral face  28 . Each apex seal  52  in the embodiment shown extends axially beyond both end faces  26 , and has an axial dimension which is close to a distance between the two end walls  14  of the cavity  20 , taking into consideration such things as the difference in thermal expansion between the material(s) of the outer body  12  and the material of the apex seal  52 , which in a particular embodiment is made of a suitable type of ceramic. Although each apex seal  52  is shown has monolithic and including a single seal member, alternately each apex seal may be composed of two or more cooperating seal members. 
     As shown, each apex seal  52  has a substantially rectangular shape, with a first end  54  having an indentation defined therein from an inner surface thereof. The indentation thus defines a radially extending surface  56  spaced from the first end  54 , and the first end defines a finger  58  protruding from that surface  56 . The fingers  58  of the two apex seals  52  of the same apex seal assembly are located axially opposite one another. 
     At each apex portion  30 , each end face  26  includes a recess  60  in communication with both grooves  50 , and an end plate  62  is received therein and extends radially therefrom. As such, each apex portion  30  includes two axially spaced apart end plates  62 . As can be best seen in  FIG. 2 , each end plate  62  includes a thicker base  64  and a plate member  66  extending radially outwardly from the base  64 , with the base  64  and plate member  66  forming a continuous outer surface extending continuously with the corresponding rotor end face  26 . Each end plate  62  includes two radial slots  68  defined through the plate member  66  and part of the base  64 , each slot  68  being in alignment with a respective one of the grooves  50  (see  FIG. 4 ). Each apex seal  52  has its finger  58  received in the aligned slot  68  of one of the end plates  62 , and the opposed second end  70  received in the respective slot  68  of the other end plate  62 , such that each of the plates  62  receives one finger  58  and one second end  70 . Alternately, the end plates  62  can be replaced by an integral part of the rotor body defining the plate members  66  and slots  68 . 
     Referring to  FIG. 2 , each groove  50  receives a first biasing member  72 , located between the inner surface  74  of the corresponding apex seal  52  and the rotor body  24 . The first biasing member  72  pushes the apex seal  52  radially outwardly away from the peripheral face  28  of the rotor  24  and against the peripheral wall  18  of the cavity  20 . 
     Each groove  50  also receives a second biasing member  76  located at the first end  54  of the respective apex seal  52 , between the plate member  66  of the adjacent end plate  62  and the radially extending surface  56  defined under the finger  58 , pushing the apex seal  52  axially away from that adjacent end plate  62  and thus axially outwardly away from the opposite end face  26  of the rotor  24 . The two second biasing members  76  of the same apex seal assembly are in contact with different ones of the end plates  62 , and the two apex seals  52  are biased in axially opposite directions, each one against a respective one of the end walls  14 . At each apex portion  30 , each end wall  14  therefore has one of the apex seals  52  in contact therewith, and the other of the apex seals  52  in close proximity therewith, such as to create a tortuous potential leakage path  78  shown in  FIG. 3  which necessitate the escaping flow to travel axially between the two apex seals  52  along the entire apex portion, and as such may help limit fluid communication at the junction between the peripheral wall  18  and each of the end walls  14 . 
     In the embodiment shown, the first and second biasing members  72 ,  76  for each apex seal  52  correspond to, respectively, a radial action portion and an axial action portion of a same spring  80 , the two portions  72 ,  76  being distinct from one another. Each apex seal  52  is biased independently from the other through its own spring  80 . 
     Referring to  FIG. 5 , the spring  80  according to a particular embodiment is shown in isolation. The axial action portion  76  includes a first end  82  of the spring  80  and at least two band sections  84  with adjacent band sections  84  being interconnected by a fold  86 . In the embodiment shown, the axial action portion  76  includes three band sections  84 . The band sections  84  extend radially and are axially spaced apart from one another. One of the band sections  84  contacts the radially extending surface  56  (see  FIG. 2 ) of the apex seal  52  and another of the band sections  84  contacts a radially extending element of the rotor body, which in the embodiment shown is plate member  66  (see  FIG. 2 ). In a particular embodiment, the axial action portion  76  defines about 5% to 10% of the length of the spring. 
     The spring  80  is a monolithic band which also includes a longitudinal portion  88  extending axially between the axial action portion  76  and the radial action portion  72 . The longitudinal portion  88  is thus connected to the adjacent band section  84  through a fold  86 . 
     The radial action portion  72  forms a major part of the length of the spring  80 . The radial action portion  72  contacts the axially extending inner surface  74  of the apex seal  52  (see  FIG. 2 ) in two spaced apart locations, and contacts the bottom surface of the groove  50  between these two locations. In the embodiment shown, the spring includes five successive sections. The first section  90  extends from the longitudinal portion  88  and contacts a first plane  92  defined perpendicularly to the radial direction  94 , this first plane  92  corresponding to the inner surface  74  of the apex seal  52 . The second section  96  extends from the first section  90  and contacts a second plane  98  parallel to the first plane  92  and radially offset therefrom, which corresponds to the bottom surface of the groove  50 . The third section  100  extends axially from the second section  96 , and is located between the two planes  92 ,  98 . At least when the spring  80  is in a relaxed state, and in a particular embodiment also when the spring  80  is in a compressed state, the third section  100  extends without contacting the planes  92 ,  98 , i.e. without contacting the apex seal  52  and bottom surface of the groove  50 . The fourth section  102  extends from the third section  100  and contacts the second plane  98  or bottom surface of the groove  50 . The fifth section  104  extends from the fourth section  102  and contacts the first plane  92  or inner surface  74  of the apex seal  52 , and includes the second end  106  of the spring  80 . 
     A distance between the two spaced apart points of contact of the spring  80  with the bottom surface of the groove  50 , or between the mid-points of the contact zones if the contact is done along an elongated portion of the surface, defines the wheel base W of the spring. In a particular embodiment, the wheel base W extends along between 55% and 75% of a total length of the radial action portion  72 . 
     In a particular embodiment, the second end  106  of the spring  80  is curved, so that the portions of the spring  80  contacting the apex seal  52  are round to minimize sharp edge contact with the apex seal  52  and as such reduce the risk of damage to the apex seal  52 , particularly in cases where the apex seal  52  is made of ceramic. In a particular embodiment, the spring  80  is made of a suitable metal, for example low alloy steel, stainless steel, Ti alloys, and if necessary of a suitable type of super alloy such as, for example, A-286 or Inconell 750. 
     It can be seen that the axial action portion  76  intersects the first plane  92 , in order to extend into the indentation forming the radially extending surface  56  of the apex seal  52 . 
     Referring back to  FIG. 4 , each end face  26  of the rotor  24  has a plurality of grooves  108  defined therein running from each apex portion  30  to each adjacent apex portion  30 , with a face seal  110  being received within each groove  108 . In a particular embodiment, each face seal  110  is monolithic. Each end face groove  108  and corresponding face seal  110  are arc-shaped and disposed adjacent to but inwardly of the rotor periphery throughout their length. A spring (not shown) located behind each face seal  110  urges it axially outwardly so that the face seal  110  projects axially away from the adjacent rotor end face  26  into sealing engagement with the adjacent end wall  14  of the cavity. 
     Each end plate  62  has two openings  112  defined therethrough in continuity with adjacent ones of the grooves  108  of the corresponding end face  26 , and each opening  112  receives therein the end of one of the face seals  110 . The two ends  114  of each face seal  110  are curled radially outwardly and abut a respective one of the apex seals  52 , more particularly the apex seal  52  of each apex seal assembly which is biased against the same one of the end walls  14  as the face seal  110 . The ends  114  are curled such as to be able to contact the apex seal  52  without the pointed extremity  114   a  of the face seal  110  contacting the apex seal  52 . The curled ends  114  may reduce the risk of damage to the apex seal  52 , particularly in cases where the apex seal  52  is made of ceramic and the face seal  110  is made of metal. 
     As such, in each apex portion  30 , the second end  70  of the apex seal  52  which is biased against a first one of the end walls  14  extends between and is in contact with the curled ends  114  of the two adjacent face seals  110  which are biased against that first end wall  14 , and the second end  70  of the apex seal  52  which is biased against the second end wall  14  extends between and is in contact with the curled ends  114  of the two adjacent face seals  110  which are biased against that second end wall  14 . 
     The apex seals  52  limit fluid communication along the peripheral wall  18 , and the face seals  110  and apex seals  52  directly cooperate to provide a continuous contact area in sealing engagement with each end wall  14  of the cavity  20 . This seal contact area encircles the rotor axis and provides a seal adjacent to the rotor periphery against inward flow of combustion gases between the rotor end faces  26  and the end walls  14 . The apex seals  52  and face seals  110  directly cooperate to limit fluid communication along the end walls  14  and near the junction between each end wall  14  and the peripheral wall  18 , without the need for an intermediary seal. The elimination of the intermediary seal, seal plug and associated spring may advantageously reduce the number of elements necessary to obtain the desired seal. 
     Referring to  FIG. 6 , an apex seal assembly according to another embodiment is shown. Here the apex seal assembly includes a single apex seal provided at each of the apex portions  230 . The single apex seal includes at least two portions or seal elements  252  which are biased away from one another such as to contact the opposite end walls  14  of the cavity. Similarly to the previously described embodiment, the curved end  114  of the two face seals  110  extending into each apex portion  230  abut the corresponding sealing element or portion of the apex seal  252  on opposites sides thereof, such as to cooperate to limit fluid communication along the end walls  14  and near the junction between each end wall  14  and the peripheral wall  18 . 
     In another embodiment with is not shown, each apex seal assembly includes more than two circumferentially spaced apart apex seals, with at least one being biased against each of the end walls  14 . 
     Referring to  FIG. 7 , an apex seal assembly according to a further embodiment is shown. The apex seal assembly at each of the apex portions  330  includes a single apex seal  352  protruding radially from the peripheral face  28 , and first and second end seals  116  (only one of which is shown) respectively engaged to the first and second end of the apex seal  352 , and biased against the respective end wall  14  through a suitable spring (not shown). The apex seal  352  can be monolithic or made of two or more cooperating portions or seal elements. Each end seal  116  is located in a cylindrical recess defined in the respective end face at the end of the apex seal groove, and has a radial slot  118  defined therein which receives the respective end of the apex seal  352 . The curved end  114  of the two face seals  110  extending into each apex portion  330  abut the end seal  116  on opposites sides thereof such as to cooperate to limit fluid communication along the end walls  14  and near the junction between each end wall  14  and the peripheral wall  18 . By contrast with the engagement of a straight end of a face seal in a corresponding slot of an end seal, the configuration shown may reduce twisting moment on the end seals, which may help in reducing the risk of damaging the apex seals, particularly for ceramic apex seals. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the biasing members need not be springs, per se, but rather any suitable apparatus having the functions described. The configuration of the springs shown are but one example of many possible configurations having the function(s) described. The multiple apex seals at each apex and/or seal elements forming part of the apex seal assembly need not be identically configured, but may have any suitable individual configuration. Therefore, modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.