Abstract:
A corner seal assembly for a rotor of a rotary engine, the assembly comprising a pair of corner seal elements, each seal element of the pair being arranged to provide a seal between the rotor and a respective one of a pair of opposed end faces of the rotary engine, the seals being arranged to be resiliently coupled to one another whereby the seals exert substantially the same force on each one of the pair of opposed end faces.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to combustion seals for internal combustion engines. In particular but not exclusively the invention relates to combustion seals for Wankel rotary engines. 
       BACKGROUND 
       [0002]    Rotary engines can provide a number of advantages over reciprocating piston engines including reduced complexity and increased power for a given engine weight. 
         [0003]    An example of a known rotary engine  100  of Wankel type is shown in  FIG. 1 . The engine  100  has a housing  110  and an eccentric shaft  120  that provides a drive output. The eccentric shaft  120  has a shaft portion  120 ′ having a longitudinal axis and an eccentric portion projecting in a substantially radial direction from a longitudinal axis of the shaft portion  120 ′. The shaft portion  120 ′ is arranged to be generally coaxial with a stationary gear  122  that is provided in a fixed orientation with respect to the housing  110 . The stationary gear  122  is arranged to engage a rotor phasing gear  132  of a rotor  130 , the rotor  130  being rotatably coupled to the eccentric portion of the eccentric shaft  120 . 
         [0004]    In use the rotor  130  describes a rotation-translation motion within a cavity  112  formed in the housing  110 , the cavity  112  having a trochoidal shape. 
         [0005]    In the example of  FIG. 1  the rotor phasing gear  132  is an internal gear whilst the stationary gear  122  is an external gear, the eccentric shaft  120  being arranged to rotate three times for each rotation of the rotor  130 . 
         [0006]      FIG. 2  shows a cross-section of a portion of the rotor  130  showing corner seal elements  150  provided in cut-out portions  131  of the rotor  130 . The cut-out portions  131  are provided in each of three corners of each side face  130 A of the rotor. Coil spring elements are provided between the corner seal elements and an internal face of the cut-out portion  131 , the spring elements being arranged to urge the corner seal elements against a respective end plate (or ‘sidewall’ or ‘end face’)  112  of the housing  110 . The corner seal elements  150  are arranged to be slidable within the cut-out portions  131 . 
         [0007]    A tip seal  160  is provided along a side of the rotor at each of three corners  130 B of the rotor  130 . Each tip seal  160  is provided in a recess  161  formed in the rotor  130 . A leaf spring element  162  is arranged to urge the tip seal  160  against the sidewall  112  of the housing  110 . 
       STATEMENT OF THE INVENTION 
       [0008]    In a first aspect of the invention there is provided a corner seal assembly for a rotor of a rotary engine, the assembly comprising a pair of corner seal elements, each seal element of the pair being arranged to provide a seal between the rotor and a respective one of a pair of opposed end faces of the rotary engine, the seals being arranged to be resiliently coupled to one another whereby the seals exert substantially the same force on each one of the pair of opposed end faces. 
         [0009]    Embodiments of the invention have the advantage that loads exerted on a side of the rotor by the action of the corner seal elements against respective end faces may be arranged to be substantially equal on opposed sides of the rotor. This has the effect that a rate of wear of an engine may be reduced. Furthermore, a smoothness of operation of the engine may be increased due to equalisation of the loads on respective end faces. 
         [0010]    Some embodiments of the invention have the advantage that a rotor arranged to receive a corner seal module according to some embodiments of the invention may be formed in a more convenient manner. In some embodiments the rotor may be formed using a more cost effective forming process. In some embodiments the rotor may be formed with improved precision. 
         [0011]    Preferably the assembly has a body portion arranged to be provided between the pair of seal elements. 
         [0012]    Preferably the body portion is movable along a direction having a component normal to a plane parallel to the end faces of the engine. 
         [0013]    In general, the end faces of the engine are substantially parallel to a plane of opposed sides of the rotor. Typically, the rotor is arranged to rotate in a plane parallel to the end faces of the engine. 
         [0014]    The body portion may be slidably movable along said direction. 
         [0015]    The seal elements may be resiliently coupled to one another by means of the body portion. 
         [0016]    Preferably the seal elements are each resiliently coupled to a respective opposed end of the body portion. 
         [0017]    Alternatively the seal elements may be directly coupled to one another by means of a seal coupling. 
         [0018]    The seal coupling may be arranged to pass through the body portion. 
         [0019]    Alternatively or in addition the seal coupling member may be arranged to pass through a portion of the rotor. 
         [0020]    The seal coupling may comprise a resilient member, preferably a spring member. 
         [0021]    The seal coupling may comprise one or more resilient members. 
         [0022]    The seal coupling may further comprise one or more substantially incompressible and substantially inextensible members. 
         [0023]    Preferably the assembly is arranged to be coupled to a corner of the rotor. 
         [0024]    Preferably the assembly is arranged to be provided in a slot provided in the rotor. 
         [0025]    The slot may have a pair of opposed ends provided with openings formed in respective opposed sides of the rotor. 
         [0026]    The assembly may further comprise a tip seal assembly arranged to provide a seal between a tip of the rotor and a sidewall of the engine. 
         [0027]    In a second aspect of the invention there is provided a unitary module comprising an assembly according to the first aspect of the invention, the module being arranged to be removably attachable to the rotor. 
         [0028]    Preferably the module is arranged to be provided in the slot provided in the rotor. 
         [0029]    The module may comprise an outer tube member arranged to be inserted into the slot provided in the rotor. 
         [0030]    The outer tube member may be provided with an opening along at least a portion of a length thereof. 
         [0031]    The opening may be arranged to receive a portion of the tip seal therethrough. 
         [0032]    The tube member may be arranged to house at least a portion of the assembly therein. 
         [0033]    This has the advantage of simplifying assembly of the rotor. 
         [0034]    The tube member may have an opening provided along at least a portion of a length thereof. The opening may be arranged to receive a portion of the tip seal therethrough. 
         [0035]    In a third aspect of the invention there is provided a rotary engine having a corner seal assembly according to the first aspect of the invention. 
         [0036]    In a fourth aspect of the invention there is provided a rotary engine having a module according to the second aspect of the invention. 
         [0037]    In a fifth aspect of the invention there is provided a method of forming a corner seal assembly for a rotor of a rotary engine, comprising: providing a pair of corner seal elements, each corner seal element of the pair being arranged to provide a seal between the rotor and a respective one of a pair of opposed end faces of the rotary engine; resiliently coupling the corner seal elements to one another whereby the seal elements may be arranged to exert substantially the same force on each one of the pair of opposed end faces of the rotary engine. 
         [0038]    The method may further comprise the step of providing the rotor; and installing the corner seal assembly in the rotor. 
         [0039]    The step of installing the corner seal assembly may comprise the step of forming corner seal cavities at each of three opposed corners of the rotor, the corner seal cavities each being arranged to receive a corner seal element. 
         [0040]    The step of forming corner seal cavities may comprise the step of forming cavities arranged to pass from one side of the rotor to the other, the cavities being open at respective opposed sides of the rotor. 
         [0041]    Thus a requirement to drill separate holes in opposed sides of the rotor may be eliminated. Alignment of openings in opposed sides of the rotor may therefore be effected substantially automatically. 
         [0042]    Preferably the step of forming the cavities comprises the step of forming the cavities by means of a cutting operation. 
         [0043]    The cutting operation may comprise the steps of cutting the cavity by means of one selected from amongst a laser cutting operation, a wire cutting operation and a water jet cutting operation. 
         [0044]    The method may further comprise the step of providing the corner seal assembly in the form of a unitary module, the pair of corner seals of the corner seal assembly being resiliently coupled to one another. 
         [0045]    The step of installing the corner seal assembly in the rotor may comprise the step of inserting the module into one of the corner seal cavities. 
         [0046]    The step of providing the pair of corner seals in the form of a unitary module may comprise the step of applying a removable binding medium to the module to prevent separation of one or more components of the module. 
         [0047]    The binding medium may comprise one selected from amongst a wax and a plastics material. 
         [0048]    The step of inserting the module into one of the corner seal cavities may be followed by the step of removing the binding medium. 
         [0049]    Alternatively the step of inserting the module into one of the corner seal cavities may be preceded by the step of removing the binding medium. 
         [0050]    The step of removing the binding medium may comprise the step of performing at least one selected from amongst heating and chemical washing of the binding medium. 
         [0051]    Some embodiments of the invention have the advantage that the problem of misalignment of respective recesses formed in opposed sides of a rotor within which respective corner seals are arranged to move is substantially eliminated since a single recess may be formed within which both corner seals slide. This has the advantage that a longevity of a rotary engine may be increased due to a reduction in strain on components of the engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]    Embodiments of the invention will now be described with reference to the accompanying figures in which: 
           [0053]      FIG. 1  shows a perspective view of a portion of a prior art Wankel rotary engine; 
           [0054]      FIG. 2  shows a cross-sectional view of a portion of a rotor of a prior art rotary engine; 
           [0055]      FIG. 3  shows an exploded cross-sectional view of a portion of the rotor of  FIG. 2 ; 
           [0056]      FIG. 4  shows a perspective view of a portion of the rotor of  FIG. 2 ; 
           [0057]      FIG. 5  shows an exploded view of a portion of a rotor according to an embodiment of the invention; 
           [0058]      FIG. 6  shows a further exploded view of a portion of a rotor according to an embodiment of the invention; 
           [0059]      FIG. 7  shows an exploded view of a portion of a rotor according to an embodiment of the invention; 
           [0060]      FIG. 8  is a cut-away view of a portion of a rotor according to an embodiment of the invention showing a single recess formed through a corner portion of the rotor; and 
           [0061]      FIG. 9  is a perspective view of a portion of a rotor according to an embodiment of the invention showing a single recess formed through the corner portion of the rotor. 
       
    
    
     DETAILED DESCRIPTION 
       [0062]      FIG. 5  shows a portion of a rotor  230  formed according to an embodiment of the invention using a wire cutting operation in which a single wire is employed to cut a corner seal recess (or ‘slot’)  231  in each of three corners  230 B of the rotor  230 . The corner seal recess  231  may also be referred to as a corner seal cavity  231 . Other fabrication methods are also useful such as laser cutting, moulding, casting, milling or other machining or any other suitable method. 
         [0063]    The rotor  230  has a corner seal assembly installed therein, the corner seal assembly having a body portion  252  arranged to be provided in the recess  231 . In the embodiment of  FIG. 5  the body portion has an aperture  253  provided therethrough. Resilient elements  254  (see also  FIG. 6 ) having coil springs provided in cylindrical casings  254 C are provided within the aperture  253  and arranged whereby opposed corner seal elements  250  provided in the recess  231  at opposed ends of the recess and on opposite sides of the body portion  252  are resiliently coupled to one another. Thus in some embodiments the body portion  252  does not itself provide a medium through which forces between respective opposed corner seal elements  250  are transmitted. 
         [0064]    In some embodiments the resilient elements  254  shown in  FIG. 6  are provided by known cartridges for attaching watch straps to a watch body. 
         [0065]    In some embodiments each of the resilient elements  254  of  FIG. 6  are replaced by a conventional coil spring. 
         [0066]    In some embodiments in which the body portion has an aperture  253  formed therethrough a shuttle member  255  ( FIG. 6 ) may be provided within the aperture  253  between a pair of resilient elements  254 . The shuttle member  255  is arranged to provide a medium through which forces may be transmitted between respective opposed corner seal elements  250 . 
         [0067]    In some embodiments the body portion  252  is arranged to be slidable in the recess  231 . In some embodiments the corner seal elements  250  are coupled to the body portion  252  by means of resilient coupling elements whereby the body portion effects coupling between the corner seal elements  250 . It is to be understood that in such embodiments the body portion itself provides a medium through which forces between respective opposed corner seal elements are transmitted. 
         [0068]    In some embodiments of the invention the corner seal elements  250  and body portion  252  are provided with recessed portions  251 B,  251 C arranged to receive a tip seal  260  and corresponding leaf spring element  262  therein. The recessed portion  251 B of the body portion  252  and recessed portion  251 C of each of the corner seal elements  250  are arranged to be aligned with one another, providing an open channel facing away from the rotor  230 . The leaf spring element  262  is arranged to be provided between the body portion  252  and the tip seal  260 . 
         [0069]    In some embodiments the tip seal  260  is maintained in a required position within the recessed portions  251 B,  251 C by entrapment between the rotor and a sidewall of a housing of a rotary engine in which the rotor  230  is provided. 
         [0070]      FIG. 7  shows the rotor  230  of  FIG. 6  in which the corner seal elements  250  are substantially in the positions assumed when the rotor  230  is in normal use. 
         [0071]      FIGS. 8 and 9  show the rotor  230  of  FIG. 7  with the corner seal assembly removed. 
         [0072]    In some embodiments of the invention the corner seal assembly is provided in the form of a unitary module or cartridge arranged to be slotted into the corner seal recess  231 . In some embodiments the assembly may be provided in a substantially tubular member arranged to be slotted into the corner seal recess  231 . 
         [0073]    In some embodiments the corner seal assembly and tip seal assembly are provided in the form of a single module that is also arranged to be slotted into a corner seal recess  231 . The corner seal assembly may be provided in a substantially tubular member having a slot provided therealong through which at least a portion of a tip seal of the tip seal assembly may be arranged to pass. 
         [0074]    The assembly may be supplied in a form in which a binder medium is arranged to maintain components of the assembly in a substantially fixed configuration with respect on one another to aid assembly. The binder medium may be a wax, a plastics material or any other suitable medium that may be removed once the assembly has been delivered to a customer. In some embodiments the binder is arranged to be removed once the assembly has been installed in a rotor. 
         [0075]    Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps. 
         [0076]    Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. 
         [0077]    Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.