Patent Publication Number: US-8985085-B2

Title: Oil seal arrangement for rotary internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority on provisional U.S. application No. 61/512,463 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 an oil seal arrangement 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 eccentric rotary motion of the rotor is guided through a rotor phasing gear which is meshed with a stator phasing gear, and at least one oil seal is provided around the phasing gear to prevent oil from entering the combustion area. Double oil seal rings with radially spaced seals are typically provided in each end face of the rotor for improved sealing. However the rotor must be sufficiently large to accommodate this double oil seal while leaving sufficient room for the gas seals located radially outwardly thereof. 
     SUMMARY 
     In one aspect, there is provided a rotor of a rotary internal combustion engine, the rotor comprising a body having two axially spaced apart end faces and a peripheral face extending between the end faces, the peripheral face defining three circumferentially spaced apex portions, the body having a central bore for receiving an eccentric portion of a shaft therein, each of the end faces having an annular oil seal groove defined therein around the central bore, and an annular oil seal assembly snugly received within each oil seal groove, each oil seal assembly including a seal ring retaining first and second axially spaced apart annular sealing elements in substantial radial alignment with one another, the seal ring radially pressing each of the sealing elements in sealing engagement with a respective surface in the groove in opposite directions from one another, and a spring member biasing the seal ring axially away from the end face. 
     In another aspect, there is provided a rotary internal combustion engine comprising a stator body having an internal cavity defined by two axially spaced apart end walls and a peripheral wall extending between the end walls, the cavity having an epitrochoid shape defining 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 three circumferentially spaced apex portions, the rotor body being engaged to an eccentric shaft to rotate within the cavity with each of the apex portions remaining adjacent the peripheral wall, each of the end faces having an annular oil seal groove defined therein around the eccentric shaft, and an annular oil seal assembly snugly received within each oil seal groove, each oil seal assembly including a seal ring retaining first and second axially spaced apart annular sealing elements in substantial radial alignment with one another, the seal ring radially pressing each of the sealing elements in sealing engagement with a respective surface in the groove in opposite directions from one another, and a spring member biasing the seal ring axially away from the end face. 
     In a further aspect, there is provided a method of limiting radially outwardly directed oil leaks between an end face of a rotor of a Wankel engine and an adjacent end wall of a stator of the engine, the method comprising providing an annular groove within each end face of the rotor around a shaft of the rotor, sealingly engaging a seal ring with a first axial surface within the groove at a first location and with second axial surface within the groove at a second location, the first and second locations being axially spaced apart from one another, and biasing the seal ring against the end wall. 
    
    
     
       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 in accordance with a particular embodiment; 
         FIG. 2  is a schematic cross-sectional view taken along line  2 - 2  of  FIG. 1 ; and 
         FIG. 3  is a schematic enlarged view of an oil seal assembly shown in  FIG. 2 . 
     
    
    
     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. 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. 
     For efficient engine operation the working chambers  32  are sealed by apex seals, face seals and end seals. 
     Each rotor apex portion  30  has a groove defined therein and extending radially inwardly into the rotor body  24 , from one end face  26  to the other. An apex seal  52  is received within each groove, and protrudes radially from the peripheral face  28 . In a particular embodiment, each apex seal  52  extends axially beyond both end faces  26 , and has an axial dimension which is as close as possible to a distance between the two end walls  14  of the cavity  20 , taking into consideration 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. In the embodiment shown in  FIG. 2 , each apex seal  52  is monolithic, i.e. is formed of a single seal member. Alternately, each apex seal  52  may be formed of two or more cooperating seal members. More than one apex seal  52  may also be provided on each apex portion  30 . Each apex seal  52  is biased radially outwardly against the peripheral wall  18  through a respective spring (not shown). 
     An end seal  54  is received within a respective cylindrical recess (not shown) defined at each end of the groove. Each end seal  54  has a radial slot defined therein, which receives the respective end of the apex seal  52 . Each end seal  54  is biased against the respective end wall  14  through a suitable spring (not shown). 
     Each end face  26  of the rotor  24  has at least one groove  58  (see  FIG. 2 ) defined therein running from each apex portion  30  to each adjacent apex portion  30 , with a face seal  60  being received within each groove  58 . In a particular embodiment, each face seal  60  is monolithic. Each face seal groove  58  and corresponding face seal  60  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  60  urges it axially outwardly so that the face seal  60  projects axially away from the adjacent rotor end face  26  into sealing engagement with the adjacent end wall  14  of the cavity. Each face seal  60  is in sealing engagement with the end seal  54  adjacent each end thereof, for example by being received in a corresponding groove (not shown) defined in the end seal  54 , or through abutment therewith. The end seals  54 , face seals  60  and apex seals  52  thus cooperate to form a seal against the respective end wall  14 . 
     Referring to  FIG. 2 , the rotor  24  includes a phasing gear  62  which is received in a complementary annular phasing gear groove  64  defined in one of the end faces  26 . The phasing gear groove  64  is defined around and in proximity of the rotor&#39;s central bore  56  (see  FIG. 1 ) which receives the eccentric portion  36  of the shaft  38 . The rotor phasing gear  62  is secured in the gear groove  64  co-axially with the rotor axis  34 , or in other words, with the central bore  56 . The rotor phasing gear  62  is meshed with a fixed stator phasing gear  66  secured to the outer body  12  co-axially with the shaft  38 , in order to maintain the relative motion of the inner rotor  24  relative to the stationary outer body  12 . 
     The rotor phasing gear  62  includes an annular meshing section  68  coaxial with the rotor axis  34 , which includes a plurality of radially inwardly oriented teeth  70  regularly distributed about a circumference thereof. The axially outer surface of the teeth  70  is in alignment or substantially in alignment with the portion of the end face  26  located radially outwardly of the phasing gear  62 . 
     The rotor phasing gear  62  also includes an annular attachment section  72  which is connected to the meshing section  68  and coaxial therewith. The attachment section  72  is axially inwardly offset from the teeth  70  such as to leave sufficient room for the stator phasing gear  66  to mesh with the teeth  70 . 
     The attachment section  72  includes a radial portion  74  extending radially inwardly from an axially inner end  76  of the meshing section  68  and an axial portion  78  extending axially inwardly from the radial portion  74 , creating a substantially Z-shaped cross-section for the phasing gear  62 . The axial portion  78  includes a plurality of axially extending and circumferentially spaced apart fastener bores  80  defined therethrough (only one of which is shown). Each bore  80  receives a fastener  82  therein, with the fasteners extending axially inwardly beyond the phasing gear  62  and into the body of the rotor  24  to a depth sufficient to adequately connect the phasing gear  62  to the rotor body  24 . 
     The axial portion  78  is defined such that the bores  80  and as such the fasteners  82  received therein are located radially inwardly of the teeth  70 . The teeth  70  and fasteners  82  are thus aligned with two different annular sections of the rotor body  24 , with the section aligned with the fasteners  82  being defined radially inwardly of the section aligned with the teeth  70 . In the embodiment shown, the entire axial portion  78  is located radially inwardly of the teeth  70 . 
     In the embodiment shown, the fasteners  82  are split rivets which include an inner pin  84  press-fitted into the central bore of a hollow outer pin  86  to press-fit the rivet into the fastener bore  80 . Alternately, other adequate type of fasteners can be used, such as for example bolts, blind rivets, solid and hollow rivets, etc. 
     The configuration of the rotor phasing gear  62  may advantageously allow for the radial size of the gear  62  to be minimized for a given diameter of the teeth  70 , by eliminating the annular outer portion which would otherwise be required for an attachment along the outer diameter. As such, the same phasing gear  62  may be used with rotors having a smaller rotor face profile. The smaller phasing gear  62  may also allow for larger oil seals to be used with smaller rotors. The smaller phasing gear  62  may also leave more room for the combustion area for a given rotor, when compared to the same rotor using a phasing gear attached along its outer diameter, since the location of the fasteners usually define an inner limit for the combustion area 
     Referring to  FIGS. 2-3 , each end face  26  includes an annular oil seal groove  88  defined therein around the central bore and located radially inwardly of the face seal grooves  58 . An annular oil seal assembly  90  is snugly received within each oil seal groove  88 . Each oil seal assembly  90  prevents leakage flow of the lubricating oil radially outwardly thereof between the respective rotor end face  26  and outer body end wall  14 . 
     As can be seen more clearly in  FIG. 3 , each oil seal assembly  90  includes an inner seal ring  92  protruding axially from the end face  26  and biased away from the end face by a spring member  104  which is received in the oil seal groove  88  axially inwardly of the seal ring  92 . The seal ring  92  has axially spaced apart first and second circumferential slots  94 ,  96  defined therein. The first slot  94  opens in the radially outer surface  98  of the inner seal ring  92  while the second slot  96  opens in the radially inner surface  100  of the seal ring  92 , thus defining a substantially S-shaped cross-section for the seal ring  92 . In the embodiment shown, the first slot  94  is located axially outwardly of the second slot  96 , and the slots  94 ,  96  have a rectangular cross-section. The inner seal ring  92  extends in contact with the radially inner surface  108  of the oil seal groove  88 , which in the embodiment shown in defined by the radially outer surface of the meshing section  68  of the rotor phasing gear  62 . 
     Each of the slots  94 ,  96  includes an annular sealing element  102 , for example an o-ring, compressed therein. In a particular embodiment, the seal ring  92  is made of an adequate metal, for example steel, cast iron or an adequate type of super alloy, and the o-rings are made of a more flexible material, for example rubber or any adequate type of polymer such as a perfluoroelastomer (e.g. Kalrez™). The two sealing elements  102  are thus axially spaced apart and substantially radially aligned. For example, as can be seen in  FIG. 3 , the two axially spaced sealing elements  102  are positioned such as to overlap at least partially along the radial direction. 
     Each oil seal assembly  90  also includes an outer seal ring  106  protruding axially from the end face  26  and biased away from the end face by a spring member  110  received in the oil seal groove  88  axially inwardly of the outer seal ring  106 . The outer seal ring  106  extends in contact with the radially outer surface  98  of the inner seal ring  92  and with the radially outer surface  112  of the oil seal groove  88 . The outer seal ring  106  has an axially extending rectangular cross-section. In a particular embodiment, the inner and outer seal rings  92 ,  106  are made of a same material. 
     As such, the sealing element  102  contained in the first slot  94  is compressed between the inner and outer seal rings  92 ,  106  and forms a seal therebetween, while the sealing element  102  contained in the second slot  96  is compressed between the inner seal ring  92  and the radially inner surface  108  of the oil seal groove  88  and forms a seal therebetween. 
     In the embodiment shown, the outer seal ring  106  extends axially inwardly further than the inner seal ring  92 . The oil seal groove  88  thus includes an outer section  114  and an inner section  116  separated by a shoulder  118 , with the outer section  114  being defined axially deeper than the inner section  116 . The outer section  114  is sized to snugly receive the outer seal ring  106  and corresponding spring member  110  therein with the outer seal ring  106  abutting the shoulder  118 , and the inner section  116  is sized to snugly receive the inner seal ring  92  and corresponding spring member  104  therein. 
     In an alternate embodiment which is not shown, the outer seal ring  106  and corresponding spring member  110  are omitted, and the oil seal groove  88  includes a single section with the S-shaped inner seal ring  92  being received in contact with the radially inner and outer surfaces  108 ,  112  of the groove  88 . 
     The two sealing elements  102  which are substantially radially aligned allows for a reduction of the radial envelope of the oil seal assembly  90  when compared to prior radially offset double seals. In a particular embodiment, the radial dimension R of the oil seal assembly  90  may be approximately 55% of the radial dimension of a typical combination of two radially spaced apart oil seals. Reduced radial dimension for the oil seals may allow for the use of a larger phasing gear or, as used with a reduced size phasing gear as shown, for a smaller rotor size for a given combustion area. This configuration may allow for double seals to be used on smaller rotors, when compared to prior radially spaced apart double seals. Although two oil seals are described, it may be desirable in some instances to provide more seals as described, and/or other oil sealing as well. 
     The phasing gear  62  and/or oil seal assembly  90 , whether used separately or together, may also allow for the Wankel engine to have a more compact configuration and/or lower weight. 
     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, any suitable phasing gear arrangement may be employed. 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.