Abstract:
An EGR gas passageway member is removably attached to a motorcycle cylinder assembly between the cylinder head and the cylinder of said motorcycle cylinder assembly in manner such that presence of the EGR gas passageway member is partially concealed. The EGR gas passageway member allows motorcycles to be provided with EGR systems without significantly impacting the aesthetic appearance of the engines of such motorcycles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to motorcycles. More particularly, the invention pertains to an exhaust gas recirculation (EGR) system for a motorcycle engine. 
     2. General Background 
     A typical motorcycle comprises an exposed engine and, in many cases, the engine is the primary visual focal point of a motorcycle. As such, aesthetics is typically a primary concern in design of a motorcycle engine. For that reason, almost every part of a motorcycle engine, from the intake manifold to the exhaust system, is configured to be visually appealing. Nonetheless, motorcycle engines necessarily must comprise key components to operate, which in some cases negatively impact the aesthetics of the motorcycle engines. For this reason, motorcycle designers and owners often avoid adding beneficial, but unnecessary, components and systems to motorcycle engines. 
     An example of a beneficial, but non-critical, engine component is an EGR system. EGR systems reduce nitrogen oxide emissions by recirculating a portion of the exhaust gases into the intake system. The recirculated exhaust gases increase the specific heat capacity of the gases flowing into combustion chambers and thereby reduce combustion temperature. Reduced combustion temperature reduces nitrogen oxide production. Most modern EGR systems comprise an EGR valve, which controls the amount and timing of exhaust gas recirculation such that the impact of EGR systems on engine performance is virtually negligible. 
     Despite the benefits of EGR systems in reducing harmful emissions, most motorcycle engines lack such systems due to the negative impact such systems can have on the overall aesthetics of motorcycle engines. This is because EGR systems typically comprise tubing that is external to the cylinder heads for channeling exhaust gases from the exhaust system and to the intake system. Such tubing is often seen as being aesthetically unpleasing. 
     Despite the aesthetically unpleasing nature of EGR systems, increasing emission standards makes such systems more desirable. This is particularly true for carbureted engines, which tend to have worse emissions as compared to fuel injected engines. 
     SUMMARY OF THE INVENTION 
     The present invention provides a means for incorporating EGR systems into motorcycle engines without significantly impacting the aesthetic appearance of such engines. 
     In a first aspect of the invention, a motorcycle cylinder head comprises a plurality of aluminum alloy air cooling fins and an EGR gas passageway. The EGR gas passageway is substantially surrounded by an alloy having higher heat resistance than said aluminum alloy and the EGR gas passageway is at least substantially concealed such that the presence of the EGR gas passageway is not readily apparent. 
     Another aspect of the invention pertains to an EGR gas passageway member. The EGR gas passageway member comprises at least one air cooling fin and an EGR gas passageway. The EGR gas passageway member is configured and adapted to be removably fixed to a motorcycle cylinder assembly comprising a cylinder and a cylinder head. The air cooling fin of the EGR gas passageway member is configured and adapted to at least partially conceal the presence of the EGR gas passageway member. 
     In yet another aspect of the invention, a motorcycle cylinder assembly comprises a cylinder head, a cylinder, and an EGR gas passageway member. The cylinder head is removably attached to the cylinder and the EGR gas passageway member is removably attached to the motorcycle cylinder assembly between the cylinder head and the cylinder. 
     Further features and advantages of the present invention, as well as the operation of the invention, are described in detail below with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an assembly view of an embodiment of a cylinder assembly comprising the invention as viewed in perspective from above the cylinder assembly. 
         FIG. 2  is another assembly view of the embodiment of a cylinder assembly of  FIG. 1  as viewed in perspective from beneath the cylinder assembly. 
         FIG. 3  is a perspective view of the cylinder assembly shown in  FIGS. 1 and 2  in its assembled configuration. 
         FIG. 4  is a top view of the cylinder head of the cylinder assembly shown in  FIGS. 1-3 , without the EGR gas passageway member. 
         FIG. 5  is a cross-sectional view of the cylinder head shown in  FIG. 4 , taken about the line  5 - 5  shown in  FIG. 4 . 
         FIG. 6  is a side view of the EGR gas passageway member shown in  FIGS. 1-3 . 
         FIG. 7  is a cross-sectional view of the EGR gas passageway, taken about the line- 7 - 7  shown in  FIG. 6 . 
     
    
    
     Reference numerals in the written specification and in the drawing figures indicate corresponding items. 
     DETAILED DESCRIPTION 
     A preferred embodiment of motorcycle cylinder assembly  20  is shown in  FIGS. 1-3 . The cylinder assembly  20  preferably comprises a cylinder head  22 , a cylinder  24 , and an EGR gas passageway member  26 . The EGR gas passageway member  26  preferably constitutes a portion of the cylinder head  22 , but is preferably removable therefrom. In a similar manner, the EGR gas passageway member  26  could also constitute a portion of the cylinder  24  and be removable therefrom. 
     In view of the foregoing, the cylinder head  22  comprises a main body  28  that is configured to removably receive the EGR gas passageway member  26 . More specifically, the main body  28  of the cylinder head  22  comprises a recess  30  which is configured to mate with the EGR gas passageway member  26  in a manner such that the bottom surfaces of the cylinder head and the EGR gas passageway member are coplanar. The main body  28  of the cylinder head  22  also comprises an exhaust chamber  32  that has primary  34  and secondary  36  output ports. The primary output port  34  is configured to connect to an exhaust assembly in a conventional manner. The secondary output port  36  is configured to operatively attach the exhaust chamber  32  to the EGR gas passageway member  26 . The main body  28  of the cylinder head  22  further comprises an intake chamber  38  that has an intake port  40  and that is operatively connected to an EGR valve mount  42  via a gas passageway  44 . Still further, the main body  28  of the cylinder head  22  comprises air cooling fins  46  to dissipate heat from the cylinder head and is preferably formed of an aluminum alloy for that same reason. 
     The cylinder  24  of the motorcycle cylinder assembly  20  is preferably a conventional cylinder comprising a cylinder bore  48  and plurality of air cooling fins  50 . Like the main body  28  of the cylinder head  22 , preferably at least the air cooling fins  50  of the cylinder  24  are formed of an aluminum alloy. 
     The EGR gas passageway member  26  comprises a main body  52  that is preferably formed out of a material, such as stainless steel, which has greater heat resistance than the aluminum alloy of the main body  28  of the cylinder head  22 . As shown in  FIG. 7 , the main body  52  of the EGR gas passageway member  26  comprises an EGR gas passageway  54  that operatively connects an upward facing inlet port  56  of the main body  52  to a downward facing outlet port  58  of the main body. The EGR gas passageway member  26  preferably also comprises at least one air cooling fin  60 . Preferably, the at least air cooling fin  60  is integrally formed with the main body  52  of the EGR gas passageway member  26 . 
     The EGR gas passageway member  26  is preferably attached to the main body  28  of the cylinder head  22  via one or more bolts (not shown) or other removable fasteners. Optionally, a gasket can be provided between the upper surface of the EGR gas passageway member  26  and downward facing surface of the recess  30  of the main body  28  of the cylinder head  22 . When attached to the main body  28  of the cylinder head  22 , the inlet port  56  of the EGR gas passageway member  26  is aligned with the secondary outlet port  36  of the main body of the cylinder head and is thereby operatively connected thereto. The opposite end of the EGR gas passageway member  26  is preferably configured to protrude slightly from main body  28  of the cylinder head  22  to thereby allow an external connection to the outlet port  58  of the EGR gas passageway member to be made. Preferably, the outlet port  58  of the EGR gas passageway member  26  is operatively connected to the intake chamber  38  of the main body  28  of the cylinder head  22  through an EGR valve (not shown) such that the flow of exhaust gases through the EGR gas passageway  54  of the EGR gas passageway member can be more precisely controlled. The EGR valve mount  42  of the main body  28  of the cylinder head  22  is configured to at least partially support such an EGR valve. 
     With the EGR gas passageway member  26  and main body  28  of the cylinder head  22  attached to each other, the cylinder head is then attached to the cylinder  24  in a conventional manner via bolts. Once assembled as shown in  FIG. 3 , the EGR gas passageway member  26  cylinder assembly  20  becomes substantially concealed between the main body  28  of the cylinder head  22  and the cylinder  24 . As shown, the air cooling fin  60  of the EGR gas passageway member  26  has an outer contour that is configured to match the outer contour of the adjacent air cooling fins of the main body  28  of the cylinder head  22  and the cylinder  24 . Additionally, although not shown, the air cooling fin  60  of the EGR gas passageway member  26  may be capped via a material that conceals any discoloration of the EGR gas passageway member  26  resulting from exhaust gases passing therethrough. 
     In view of the foregoing, it should be appreciated that the invention provides for an aesthetically pleasing system for incorporating an EGR system into a motorcycle engine and is advantageous over the prior art. 
     As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents. For example, although the EGR gas passageway member  26  preferably forms part of the cylinder head  22 , it could alternatively be formed as part of the cylinder  24 . 
     It should also be understood that when introducing elements of the present invention in the claims or in the above description of exemplary embodiments of the invention, the terms “comprising,” “including,” and “having” are intended to be open-ended and mean that there may be additional elements other than the listed elements. Additionally, the term “portion” should be construed as meaning some or all of the item or element that it qualifies. Moreover, use of identifiers such as first, second, and third should not be construed in a manner imposing any relative position or time sequence between limitations. Still further, the order in which the steps of any method claim that follows are presented should not be construed in a manner limiting the order in which such steps must be performed, unless such an order is inherent.