Abstract:
An engine includes a housing having a single wall, where the wall has a rib and a flange, and the wall provides a primary structure and cooling for the engine. A closeout is attached to an outer surface of the wall, and the closeout and the wall form a cavity. The closeout provides a secondary structure for containing a coolant fluid flow within the cavity. The closeout may be corrugated, and the ribs may be exposed to the cavity.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present application relates to a rotary engine, and in particular to a rotary engine that includes a structurally efficient liquid cooled rotor housing. 
         [0003]    2. Background Information 
         [0004]    Engines typically compress air or other gaseous oxidizers prior to adding fuel and ignition to produce power. Many examples of engines with separable positive displacement compression systems exist. One example can be conceptualized from a Wankel engine. The Wankel engine, invented by German engineer Felix Wankel is a type of internal combustion engine which uses a rotary design. Its cycle takes place in a space between the inside of an oval-like epitrochoid-shaped housing and a rotor that is similar in shape to a Reuleaux triangle but with sides that are somewhat flatter. This design delivers smooth high-rpm power from a compact size. Since its introduction, the engine has been commonly referred to as the rotary engine. 
         [0005]    An improvement on the rotary engine uses a first rotor as a compressor to provide compressed air to a second rotor. The compressed air is then further compressed in the second rotor in advance of combustion. In some embodiments the exhaust of the second rotor is returned to the expanding section of the compressor rotor, thereby providing power recovery and increasing efficiency. This configuration has been referred to as a compound rotary engine. An example of such an engine is disclosed in U.S. Patent Publication 2010/0269782, assigned to the assignee of the present application. 
         [0006]    Rotary engine housings suffer from structural inefficiency and non-uniform cooling, resulting in increased weight and reduced engine life as well as relatively complex and expensive castings. Specifically, the traditional rotor housing is fabricated from a single piece casting with complex internal passages for cooling fluid to flow through to provide convective cooling of the housing. 
         [0007]    There is a need for a structurally efficient liquid cooled rotor housing for a rotary engine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic block diagram illustration of a compound rotary engine; 
           [0009]      FIG. 2  is a partial phantom view of the rotary engine of  FIG. 1 ; 
           [0010]      FIG. 3  is a partially assembled view of the rotary engine of  FIG. 1  illustrating the first rotor section; 
           [0011]      FIG. 4  is a partially assembled view of the rotary engine of  FIG. 1  illustrating the second rotor section; 
           [0012]      FIG. 5  is an exploded view of the rotary engine of  FIG. 1 ; 
           [0013]      FIG. 6  is a perspective view of a primary rotor housing detail of the second rotor housing; 
           [0014]      FIG. 7  is a cross-sectional illustration taken along the plane perpendicular to the axial midpoint of the primary rotor housing detail illustrated in  FIG. 6 ; and 
           [0015]      FIG. 8  is an exploded cross-sectional illustration of the inner surface of the primary rotor housing detail and a cooperating corrugated closeout which together form a coolant flow chamber. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  schematically illustrates a rotary engine  20  having a first rotor section  22  and a second rotor section  24 . The engine  20  is based on a rotary, e.g., Wankel-type engine. An intake port  26  communicates ambient air to the first rotor section  22  and an exhaust port  28  communicates exhaust products therefrom. A first transfer duct  30  and a second transfer duct  32  communicate between the first rotor section  22  and the second rotor section  24 . A fuel system  36  for use with a heavy fuel such as JP-8, JP-4, natural gas, hydrogen diesel and others communicate with the second rotor section  24  of the engine  20 . The engine  20  simultaneously offers high power density and low fuel consumption for various commercial, industrial, compact portable power generation, and aerospace applications. 
         [0017]    Referring to  FIG. 2 , the rotary engine  20  generally includes at least one shaft  38  which rotates about an axis of rotation A. The shaft  38  includes aligned eccentric cams  40 ,  42  ( FIGS. 3 and 4 ) which drive a respective first rotor  44  and second rotor  46  which are driven in coordinated manner by the shaft  38 . The first rotor  44  and second rotor  46  are respectively rotatable in volumes  48 ,  50  formed by a stationary first housing  52  and a stationary second housing  54  ( FIGS. 3 and 4 ). The housings may include trochoidal inner surfaces that define the volumes. The fuel system  36  may include one or more fuel injectors with two fuel injectors  36 A,  36 B shown in communication with the second rotor volume  50  generally opposite the side thereof where the transfer ducts  30 ,  32  are situated. It should be understood that other fuel injector arrangement, locations and numbers may alternatively or additionally be provided. The fuel system  36  supplies fuel into the second rotor volume  50 . The first rotor volume  48  in this embodiment provides a greater volume than the second rotor volume  50 . It should be understood that various housing configurations shapes and arrangements may alternatively or additionally be provided ( FIG. 5 ). 
         [0018]    The first rotor  44  and the second rotor  46  have peripheral surfaces which include three circumferentially spaced apexes  44 A,  46 A respectively. Each apex  44 A,  46 A includes an apex seal  44 B,  46 B, which are in a sliding sealing engagement with a peripheral surface  48 P,  50 P of the respective volumes  48 ,  50 . The surfaces of the volumes  48 ,  50  in planes normal to the axis of rotation A are substantially those of a two-lobed epitrochoid while the surfaces of the rotors  44 ,  46  in the same planes are substantially those of the three-lobed inner envelope of the two-lobed epitrochoid. 
         [0019]    In operation, air enters the engine  20  through the intake port  26  ( FIG. 1 ). The first rotor  44  provides a first phase of compression and the first transfer duct  30  communicates the compressed air from the first rotor volume  48  to the second rotor volume  50  ( FIGS. 2 and 3 ). The second rotor  46  provides a second phase of compression, combustion and a first phase of expansion, then the second transfer duct  32  communicates the exhaust gases from the second rotor volume  50  to the first rotor volume  48  ( FIGS. 2 and 4 ). The first rotor  44  provides a second phase of expansion to the exhaust gases, and the expanded exhaust gases are expelled though the exhaust port  28  ( FIGS. 1 and 2 ). The shaft  38  completes one revolution for every cycle, so there are three (3) crank revolutions for each complete rotor revolution. As each rotor face completes a cycle every revolution and there are two rotors with a total of six faces, the engine produces significant power within a relatively small displacement. 
         [0020]    The shaft  38  may include axially separable sections which, may be separable between the cams  40 ,  42  to facilitate assembly. Alternatively or additionally, the first rotor cam  40  and the second rotor cam  42  may also be separable sections. The separable sections of the shaft  38  may be assembled through a tie rod or other fastener arrangement to facilitate assembly such as assembly of the rotationally stationary gears  60 ,  62 . 
         [0021]    The shaft  38  may also support bearings, bushings or other low-friction devices about enlarged shaft portions. The enlarged shaft portions permit relatively large diameter bearings, bushings or other low-friction devices to provide a robust and reliable interface which increase structural rigidity and reduce lubrication requirements. 
         [0022]      FIG. 6  is a perspective view of a primary rotor housing detail of the second housing  54 , where the detail includes a cooling surface  80 . The detail may be for example machined or cast from aluminum, titanium or steel. The surface  80  is sub-divided into a plurality of sections by a plurality of axial fins, for example  82 - 84 . The fins  82 - 84  provide increased rigidity and improved cooling to the hot surface  80 . Liquid coolant flows through holes, for example  85 - 88 , and the coolant flow is primarily axial. Side housings  89 ,  90  ( FIG. 5 ) may be connected to the second housing  54  via through holes in flanges  92 ,  94 . 
         [0023]      FIG. 7  is a cross-sectional illustration taken along the plane perpendicular to the axial midpoint of the primary rotor housing detail illustrated in  FIG. 6 . Area  96  in the vicinity of the fuel injector through hole is typically exposed to the highest local heat fluxes in the engine combustion zone, requiring increased local cooling to reduce life limiting thermal strains. This region also experiences the highest pressures within the engine cycle. Therefore, it is contemplated that additional ribs may be located in the vicinity of the fuel injector through holes to provide additional cooling surfaces and to provide structural integrity while maintaining thin walls between the coolant and the combustion zone. These structural support fins also provide increased cooling effectiveness by functioning as cooling fins, protruding into the coolant flow and enhancing convective heat transfer. Cooler areas of the inner surface  80 , such as for example area  98  of the intake port, may require less ribs to transfer heat from the coolant to the surface  80  in that vicinity. These regions also see reduced internal operating pressures, allowing for simultaneous optimization of cooling and structure with the envisioned approach. In the case of spark ignition engines the additional ribs may be located in the vicinity of the spark plug(s). 
         [0024]      FIG. 8  is an exploded cross-sectional illustration of the inner surface  80  and a cooperating corrugated metallic closeout  100 . The closeout  100  may be fabricated from sheet metal and welded to ribs  102 ,  104  to form a first axial flow chamber  106  in cooperation with the inner surface  80 . The closeout for an adjacent second axial flow chamber  108  is removed to illustrate coolant holes  110 - 113  for the adjacent chamber in a first side surface  114 . Each chamber may include one or more coolant holes in the axial sidewall. Other materials and attachment mechanisms are also viable in this application, including attachment by adhesives, mechanical fasteners or brazing, as well as bonded non-metallic closeouts. 
         [0025]    In contrast to the prior art which used a single piece casting to create internal axial coolant flow passages in the rotor housing, the rotor housing  54  includes a primary rotor housing detail and a secondary closeout sheet which together form axial flow passages. The primary housing detail reacts engine loads and provides cooling of the combustion chamber wall to maintain temperatures within engine operating constraints, while the closeout sheet forms the passages with an inner surface of the rotor housing. The corrugated structure of the closeout performs two functions. It provides structural stiffness to the closeout while keeping weight to a minimum. Since the primary housing detail carries the engine internal loads (e.g., pressure, thermal, torque and bearing loads) as well as the engine external loads (e.g., thrust, torque, vibration, mounting and other interface loads), the closeout only has to accommodate coolant pressure loads and is significantly free of engine loads. The closeout also serves to locally control the cross sectional flow area for the coolant. The corrugation geometry (spacing and profile) are varied to change the local cross sectional flow area between the primary housing detail and the closeout. This capability provides another parameter for local optimization of coolant convective heat transfer by allowing increased coolant velocities without requiring higher coolant flow rates. While there may be some small but measurable amount of engine load transferred to the closeout from the primary housing detail, the amount of load is significantly smaller that the engine load on the primary housing detail, and therefore the closeout is considered to be significantly “free” of carrying engine loads. 
         [0026]    The improved rotor housing may of course also be employed in a rotary engine that uses single rotor. Although the embodiment(s) presented herein illustrate axial coolant flow, one of ordinary skill will of course recognize that a primary housing detail and one or more closeout sheets may also be combined for example, to form circumferential flow passages, or a combination of axial, radial and/or circumferential flow passages. 
         [0027]    It will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claims.