Patent Publication Number: US-6910546-B2

Title: Motorcycle induction system

Description:
PRIORITY INFORMATION 
     This application is based on and claims priority to Japanese Patent Application No. 2001-174491 filed Jun. 8, 2001, the entire contents of which is hereby expressly incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an induction system for motorcycle. More specifically, the present invention relates to an air silencer and filter arrangement for a motorcycle engine. 
     2. Description of the Related Art 
     In a motorcycle having a V-type engine, the engine is generally mounted on the frame with the crankshaft oriented transversely with respect to the longitudinal direction of the motorcycle. A space is therefore defined between the fore and aft cylinders and one or more carburetors are disposed in this space. The cylinders are formed with intake ports at the sides facing toward the space so as to be connected with the carburetor or carburetors in the space. 
     In this type of motorcycle, an air filter is typically disposed behind the engine so that intake passages extend from the air filter, around the aft cylinder, and to the space between the cylinders. Such an intake system is difficult to manufacture because the intake passages are relatively long. 
     Other induction system designs have included an air chamber and filter disposed above the engine. However, because the fuel tank is typically disposed directly above the engine of a motorcycle, there is little space between the top of the engine and the fuel tank for an air chamber and air filter assembly. 
     Japanese Patent No. 2857926 discloses a motorcycle having an induction system comprising an air box disposed rearward from the engine in which two air filters are disposed. Each air filter is fed with a different intake pipe. The intake pipes open through an upper surface of the air box. One filter is disposed adjacent an upper surface of the air box and a smaller is disposed below the first filter. This design, however, is difficult to use with a V-type engine having the throttle bodies disposed in the space between the cylinders. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, motorcycle includes a frame, an engine supported by the frame, a wheel supporting the frame, and a transmission connecting the engine with the wheel. The motorcycle also includes an induction system configured to guide air to the engine. The induction system includes first intake air chamber having a first inlet, a first outlet, and a first filter. Additionally, the intake system includes a secondary air chamber having a second filter and a second outlet portion, the first outlet being connected to the second intake air chamber. 
     By providing the motorcycle with an induction system having two intake air chambers, each having its own filter, the induction system can be arranged to take advantage of different places on the motorcycle where space is available for induction system components. For example, one of the air chambers can be disposed on top of the engine, and another air chamber can be disposed on the side of the engine. Additionally, by connecting the first intake air chamber to the second intake air chamber, a plurality of intake passages of the engine can be connected to the second intake air chamber, thereby providing a common volume of air from which induction air is drawn to the engine. Thus, noise emanating from the intake passages of the engine are attenuated to substantially the same degree. Additionally, other characteristics of the air flow into each induction passage is uniform because all of the induction air enters a common passage before being diverted to the intake passages. For example, the temperature and pressure of the induction air in the second chamber can be detected and used for engine control routines. 
     In accordance with another aspect of the invention, an induction system for an internal combustion engine includes the first intake air chamber having a first inlet, a first air filter, and a first outlet. The induction system also includes a second intake air chamber including a second inlet, a second air filter, and a second outlet connected to an induction passage of the engine. The first intake air chamber is connected to the second air intake chamber downstream of the second air filter. 
     In accordance with another aspect to the present invention, a motorcycle includes a frame, an engine supported by the frame, a wheel supporting the frame, and a transmission connecting the engine with the wheel. The motorcycle also includes an induction system configured to guide air to the engine. The induction system includes a first intake air chamber connected to a second intake air chamber. The first intake air chamber is disposed on the side of the engine and the second intake air chamber is disposed above the top of the engine. 
     By providing an induction system which has one intake air chamber on the side of the engine and another intake chamber above the top of the engine, the motorcycle takes advantage of two different spaces adjacent the engine which are available for culminating induction system components. For example, in a motorcycle having a V-type engine, the present induction system provides a large effective volume, without interfering with the space between the cylinders which can be used to accommodate throttle bodies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects and advantages of the present invention will now be described with reference to the drawings of a preferred embodiment, which embodiment is intended to illustrate and not to limit the invention, and in which figures: 
         FIG. 1  is a right side elevational view of a motorcycle constructed in accordance with certain features, aspects, and advantages of the present invention; 
         FIG. 2  is a left side elevational view of the motorcycle shown in  FIG. 1 ; 
         FIG. 3  is a top plan view of the motorcycle shown in  FIG. 1 ; 
         FIG. 4  is an enlarged right side elevational view of the engine from the motorcycle shown in  FIG. 1 , throttle bodies being disposed between the cylinders, the exhaust system being removed, and the induction system shown in phantom; 
         FIG. 5  is a sectional view of one of the throttle bodies shown in FIG.  4  and showing the fuel injector in solid line; 
         FIG. 6  is a top plan view of the throttle bodies removed from the engine of FIG.  4  and connected to an idle speed controller system; 
         FIG. 7  is a perspective view of the throttle bodies of  FIG. 6  illustrating fuel line connections thereto; 
         FIG. 8  is a top plan view of a forward portion of the exhaust system of the motorcycle shown in FIG.  1 . 
         FIG. 9  is a right side elevational view of the exhaust system shown in  FIG. 8 ; 
         FIG. 10  is a right side elevational view of a transmission and lubricant reservoir from the motorcycle shown in  FIG. 1 ; 
         FIG. 11  is a partial sectional view of the lubricant reservoir shown in  FIG. 10 ; 
         FIG. 12  is a right side elevational view of the oil reservoir of  FIG. 10 , with an outer cover removed; 
         FIG. 13  is a top perspective view of the reservoir of  FIG. 11 , as viewed along arrow  12  shown in  FIG. 11 ; 
         FIG. 14  is a map illustrating the relationship between idle speed controller valve opening V plotted on the vertical axis and oil temperature L on the horizontal axis; 
         FIG. 15  is a graph illustrating the relationship between idle speed controller valve opening V plotted on the vertical axis and time T plotted on the horizontal axis; 
         FIG. 16  is an enlarged right side elevational view of the induction system included in the motorcycle in  FIG. 1 ; 
         FIG. 17  is a sectional view of the first intake air chamber illustrated in  FIG. 16  take along Line  17 — 17 ; and 
         FIG. 18  is a top plan and partial cut-away view of the second air intake chamber illustrated in FIG.  16 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to  FIG. 1 , a motorcycle is illustrated in side elevation view and is identified generally by the reference numeral  10 . The motorcycle  10  is powered by an internal combustion engine  12  having an induction system  14  which is constructed in accordance with certain features, aspects and advantages of the present invention. The motorcycle  10  is shown as a typical embodiment in which the present invention can be used. 
     As is known to those of ordinary skilled in the art, the motorcycle  10  is generally comprised of a frame assembly  16 . Preferably, the frame assembly  16  is of a double cradle type frame. The frame assembly  16  also supports a front fork assembly  18 , also known as a “hand stand-type telescopic” fork assembly. The fork assembly  18  includes an outer tube  20  and an inner tube  22 . 
     A bracket assembly includes a lower bracket  24  and an upper bracket  26  connecting the outer tubes  20  of the two front forks. Additionally, the bracket assembly is pivotally supported by a head tube  28  defined at a forward portion of the frame assembly  16 . 
     A handlebar  30  is mounted to the bracket assembly. In particular, the handlebar  30  is mounted to the upper bracket  26  with a handlebar clamp  31 , adjacent the upper bracket  26 . 
     The handlebar  30  can carry a variety of controls. For example, the handlebar  30  can include a twist-grip-type throttle normally positioned on the right end of the handlebar  30 , a front brake level disposed adjacent to the throttle grip, a clutch lever, typically disposed adjacent the left end of the handlebar, as well as a variety of other controls such as an engine kill switch, headlight switch, as well as other controls. 
     The bracket assembly also supports a headlight  32 . The bracket assembly can also support additional gauges, such as, for example, but without limitation, a tachometer  34  and a speedometer  36 . 
     A wheel  38  is journalled for rotation at a lower end of the fork assembly  18 . Additionally, a front brake is also mounted to the wheel and partially supported by the lower end of the fork assembly  18 . In the illustrated embodiment, the brake includes one disk for each side of the front wheel  38  and one caliper for each disk. Additionally, a fender  40  is supported above the front wheel  38 . 
     A rider&#39;s seat  42  is disposed rearwardly from the handlebar  30  and is supported by a seat rail  43 . A leg protector  47  is mounted on each side of the motorcycle  10  on the seat  43  rail to protect the rider&#39;s legs. Thus, a rider can steer the motorcycle  10  when seating on the seat  42  by rotating the handlebar  30 , holding each end of the handlebar  30  with one hand. 
     A fuel tank  44  is supported by a tank rail  45  of the frame  16  and is disposed forwardly from the seat  42 , between the seat  42  and the handlebar  30 . However, a decorative cover similar in shape to the fuel tank  44  could be installed in this position in lieu of the gas tank  44 , with the gas tank located in another position. 
     The rear wheel  46  is journaled by the frame assembly  16  in any suitable manner. The rear wheel preferably is attached to the frame assembly  16  with a rear arm  48 . The illustrated rear arm  48  is supported by a rear arm bracket  49  ( FIG. 2 ) to pivot relative to frame assembly  16  above the pivot shaft (not shown). Preferably, a rear fender  50  is suspended above at least a portion of the rear wheel  46  by a fender bracket  51  in a manner well known to those of the ordinary skilled in the art. Additionally, a taillight unit  52  is supported by the rear fender  50 . The taillight unit  52  preferably includes a set of turn signals, a support for a license plate, and a license plate light (not shown). 
     The illustrated rear wheel  46  is driven by a transmission  54  (FIG.  2 ). A portion of the transmission  54  is contained at least partially within a crankcase transmission assembly of the engine  14 . The transmission  54  drives the rear wheel  46  through a final drive assembly  56 . 
     The final drive assembly  56  includes a drive sprocket  58  which is driven by a crankshaft (not shown) of the engine  14  through plurality of gear sets defining a speed change transmission. The final drive  56  also includes a driven sprocket  60  mounted to the rear wheel  46 . A flexible transmitter  62  such as a tube rubber belt is wound around the drive sprocket  58  and a driven sprocket  60 . 
     Transmission  54  also includes a gear shifter  64  for shifting the transmission  54  between different gear ratios defined by the gears disposed therein. The gear shifter  64  is disposed adjacent to a left foot rest  66  which is supported by foot rest bracket  68 . Thus, operators can shift the transmission  54  using their left foot. Similar to the foot rest  66 , a right side foot rest  70  is supported on the right side of the motorcycle  10  by a foot rest bracket  72 . A rear brake pedal  73  is pivotally mounted near the foot rest  70  such that an operator can operate the rear brake pedal  73  with the operator&#39;s right foot. Thus, as operators straddle the seat  42 , they can rest their feet on the foot rests  66 ,  70 . 
     With reference to  FIG. 4 , the engine  14  is a V-twin type engine operating on a four-cycle principle. To this end, the engine  14  includes an engine body  80  which cooperates with a number of systems in order to provide power output. These systems include an induction system  82  ( FIGS. 4 ,  5 , and  16 - 18 ), a fuel system  84  (partially illustrated in FIGS.  6  and  7 ), an exhaust system  86  (partially illustrated in FIGS.  8  and  9 ), a lubrication system  88  (partially illustrated in FIGS.  10 - 13 ), an ignition system (not shown), and a feedback control system. 
     With reference to  FIG. 4 , the engine body  80  includes a crankcase  90 , a pair of cylinder blocks  92 ,  94 , a pair of cylinder heads  96 ,  98 , and cylinder head covers  100 ,  102 . 
     The crankcase  90  rotatably supports and journals a crankshaft (not shown) for rotation therein. The cylinder blocks  92 ,  94  are mounted to the crankcase  90  at an angle relative to one another. The cylinder blocks  92 ,  94  each define a cylinder bore (not shown) therein. A piston (not shown) reciprocates within each cylinder bore. 
     The pistons are connected to the crankshaft with piston rods. As such, the pistons reciprocate within their respective cylinder bores thereby driving the crankshaft in a rotating direction. 
     Each of the cylinder heads  96 ,  98  includes recesses on their respective lower surfaces (not shown). The recesses are in line with the cylinder bores defined within the cylinder blocks  92 ,  94 . Together, the cylinder bores, the recesses, and the heads of the piston define combustion chambers (not shown). 
     Within each of the cylinder heads  96 ,  98 , inner intake passages are defined which extend to the recesses defined on the lower surface of the cylinder heads  96 ,  98 . The intersections of the inner intake passages with the recesses define inner intake ports. The terminal ends of the inner intake passages on the outer surfaces of the heads  96 ,  98  define outer intake ports  104 ,  106 , respectively. In the illustrated embodiment, the outer intake ports  104 ,  106  are disposed on the sides of the cylinder heads  96 ,  98  which face inwardly toward each other. 
     Intake valves (not shown) are disposed at the inner intake ports of each cylinder heads  96 ,  98 . The engine  14  is a pushrod-type engine. Thus, at least one camshaft is rotatably journaled within the crankcase  90 . The camshaft is driven by the crankshaft through a gear reduction (not shown). An arrangement of pushrods operates the intake valves to open and close the inner intake ports at a desirable timing. Alternatively, the engine  14  can be configured as an overhead cam engine. In such an arrangement, the camshafts are jounaled in each of the cylinder heads  96 ,  98  so as to drive the intake valves 
     The cylinder heads  96 ,  98  also define inner exhaust passages (not shown). The inner ends of the exhaust passages terminate in the recesses in the lower surfaces of the cylinder heads  96 ,  98 . The intersection of the inner exhaust passages with the recesses define inner exhaust ports (not shown). The outer ends of the inner exhaust passages terminate on the right side of the cylinder heads  96 ,  98 . The intersection of the inner exhaust ports and the outer surface of the cylinder heads  96 ,  98 , define outer exhaust ports  108 ,  110 . Similar to the intake valves, exhaust valves (not shown) are disposed in the cylinder heads  96 ,  98  and are operated by the pushrods. 
     Mounting flanges  112 ,  114  are mounted to the periphery of the exhaust ports  108 ,  110 , respectively. The mounting flanges  112 ,  114  provide mounting surfaces for connections to exhaust pipes, described in greater detail below. 
     The induction system  82  is configured to guide air into the combustion chambers of the engine  14 . In the illustrated embodiment, the induction system  82  includes a first intake air chamber  116 , a conduit  118 , a second intake air chamber  120 , and two throttle body assemblies  122 ,  124 . Together, the first intake air chamber  116 , the conduit  118  and the second intake air chamber  120  define an induction silencing and filter arrangement disclosed in greater detail below with reference to  FIGS. 16-18 . 
     The throttle body assemblies  122 ,  124  include inlet ends  126 ,  128  which are open to the interior of the second intake air chamber  120 . Additionally, the throttle body assemblies  122 ,  124  include outlet ends  130 ,  132 , respectively, connected to the outer intake ports  104 ,  106 , respectively. 
     With reference to  FIG. 7 , each of the throttle assemblies  122 ,  124 , as schematically represented in  FIG. 7 , include an inlet sleeve  134  which defines the inlets  126 ,  128 . A lower end of the sleeves  134  extend downwardly from the second intake air chamber  120  and mate with a throttle passage  136 . Preferably, the sleeves  134  are made of a flexible material. The throttle valve passage  136  preferably is made from a more rigid material. 
     With reference to  FIG. 5 , the throttle valve portion  136  rotatably journals a throttle valve  138 . The throttle valve  138  is configured to meter a flow of air therethrough. In the illustrated embodiment, the throttle valve  138  is a butterfly-type valve which, when in a closed position, prevents substantially all air flow through the throttle valve passage  136 . A downstream end of the throttle valve passage  136  is connected to an upper end of a throttle joint assembly  140 . The lower end of the throttle joint assembly  140  defines the outlet ends  130 ,  132  of the throttle bodies  122 ,  124 . 
     As noted above, the throttle valve  138  is rotatably journaled within the throttle valve passage  136 . The throttle valve  138  is connected to the throttle grip disposed on the handlebar  30  in a known manner. In the illustrated embodiment, the throttle valves  138  are connected to a common shaft. A pulley  139  ( FIG. 6 ) is mounted to one end of the shaft. A cable (not shown) extends between the throttle grip and the pulley and thereby controls the movement of the throttle valves  138 . As such, the greater the opening of the throttle valve  138 , the more air A flows into the combustion chambers, and thus the greater the power output of the engine  14 . 
     With reference to  FIG. 6 , the induction system  82  also includes an idle speed control system  150 . The idle speed control system  150  is configured to guide air into the induction system, downstream from the throttle valve  138 . In the illustrated embodiment, the idle speed control system  150  includes an air supply  152 , an idle speed air flow controller  154 , and an idle speed air output  156 . 
     The air supply  152 , in the illustrated embodiment, is comprised of an air hose  158 . The air hose  158  has an inlet end connected to the induction system  82 . Preferably, the inlet of the air hose  158  is connected to the second intake air chamber  120  so as to communicate with an interior volume defined within the second intake air chamber  120 . The outlet end of the hose  158  is connected to an inlet  160  of the idle speed air flow controller  154 . 
     The idle speed air flow controller  154  includes a linear control valve  162 . The linear control valve  162  is mounted to the frame  16  with a bracket  163  and includes a valve member (not shown) driven by a stepper motor (not shown). The stepper motor controls the movement of the valve so as to open and close internal passages which connect the inlet  160  with an outlet of the control valve  162 . In the illustrated embodiment, the control valve  162  includes a first outlet  164  and a second outlet  166 . 
     Preferably, the control valve  162  is configured to provide proportional control over the internal passages connecting the inlet  160  with the outlets  164 ,  166 . It is to be noted that the stepper solenoid could also be used in place of the stepper motor to control the movement of the valve within the control valve  162 . 
     The outlets  164 ,  166  are connected to delivery hoses  168 ,  170 . The outlet ends, the air hoses  168 ,  170  are connected to the throttle bodies  126 ,  128 , respectively, downstream from the throttle valves disposed therein. In particular, with reference to  FIG. 5 , the throttle bodies  126 ,  124  each include an idle speed air inlet  172 ,  174 , respectively. The hoses  168 ,  170  are connected to the inlet  172 ,  174 , respectively. 
     In operation, air is supplied to the idle speed control system  150  to the air supply  152 . Under control of the stepper motor within the idle speed air flow controller  154 , the linear valve proportionally opens and closes the internal openings between the inlet  160  and the outlet  164 ,  166 . The movement of the stepper motor is controlled preferably by an electronic control unit (ECU) (not shown) which is part of a feedback control system for controlling the operation of the engine  14 , described in greater detail below. 
     By allowing air to flow from the inlet  160  to the outlets  164 ,  166 , the idle speed air flow controller  154  allows air to flow into the induction system  82  downstream from the throttle valves  138 . Thus, when the throttle valves  138  are closed, or substantially closed, the air A flows into the combustion chambers. Additionally, movement of the stepper motor provides a proportional change in the openings between the inlet  160  and the outlets  164 ,  166 , thereby providing controlled air flow flowing into the induction system through the inlets  172 ,  174  (FIG.  5 ). Thus, the controller  154  can change the speed of the engine  14  without a corresponding movement of the throttle valves  138 . 
     With reference to  FIG. 7 , the fuel supply system is configured to direct fuel into the air flowing through the induction system  82  and the internal passages defined within the cylinder heads  96 ,  98 . In the illustrated embodiment, the fuel supply system  84  operates under a port fuel injection principle. However, other types of fuel delivery systems can be used. For example, the fuel supply system  84  could incorporate carburetors or direct fuel injection. 
     The fuel supply system  84  includes the fuel tank  44  (FIG.  1 ), a fuel pump arrangement (not shown) and fuel injectors  180 ,  182 . Preferably, the fuel pump arrangement includes at least one fuel pump mounted either in the fuel tank  44  or sub-fuel tank (not shown) defined within the fuel tank  44  or separately therefrom. Additionally, the fuel pump preferably is configured to pressurize the fuel to a pressure appropriate for fuel injection. An inlet of the fuel injector  180  is connected to the fuel pump by a fuel line  184 . Preferably, the fuel line  184  is metallic, and in particular, stainless steel. 
     The outlet of the fuel injector  180  is connected to a fuel line  186 . An inlet of the fuel injector  182  is connected with a fuel line  188 . Another fuel line  190  is connected to the fuel lines  186 ,  188  through fuel line joints  192 ,  194 , respectively. 
     Preferably, the fuel lines  186 ,  188  are metallic, and in particular, stainless steel. Additionally, the fuel line  190  and the joints  192 ,  194  preferably are made of a rubber material. 
     An outlet of the fuel injector  182  is connected to a fuel return line  196 . Preferably, the fuel line  196  is made of a metallic material, and in particular, stainless steel. Additionally, the fuel line  196  is connected to the fuel tank  44  through a pressure regulator (not shown). 
     With reference to  FIG. 5 , the fuel injectors  180 ,  182  are mounted to the boot portions  140 ,  141  of the throttle bodies  122 ,  124 , respectively. Each fuel injector  180 ,  182  includes an injection nozzle  200  mounted in an injection aperture  202  defined in the boot portions  140 ,  141 . The injection nozzles  200  are arranged so as to inject fuel into the induction passage defined by the throttle bodies  122 ,  124  and the inner induction passages defined in the cylinder heads  96 ,  98 . 
     Each of the fuel injectors  180 ,  182  include an actuator therein for opening and closing a fuel valve within the fuel injectors  180 ,  182 . For example, the fuel injectors  180 ,  182  can include a solenoid for opening and closing the valve which controls a flow of fuel through the discharge nozzles  200 . The solenoids are powered, and thus controlled, via fuel injection control lines  204 ,  206 , respectively. The fuel injection control lines  204 ,  206  are connected to the ECU. The ECU controls the timing and duration of fuel injection in accordance with a feedback control scenario, discussed below in greater detail. 
     In operation, fuel from the fuel tank  44  is pressurized by the fuel pump and delivered to the fuel line  184  under a pressurize appropriate for fuel injection. The pressurized fuel first reaches the fuel injector  180 . Fuel that is not injected by the fuel injector  180  then flows to the fuel injector  182  through the fuel lines  186 ,  190 ,  188 , in that order. The fuel flowing through these fuel lines which is not injected by the fuel injector  182 , returns to the fuel tank through the fuel line  196  and the pressure regulator valve. 
     The circulation of excess fuel through the fuel injectors  180 ,  182  and the fuel lines  184 ,  186 ,  190 ,  188 ,  196 , helps to cool the fuel injectors. Additionally, by providing a positive flow of excess fuel through these fuel lines and fuel injectors, there is less opportunity for the fuel to be heated through contact with the metallic fuel lines  184 ,  186 ,  188 ,  196 , which pass in close proximity to the cylinder blocks  92 ,  94  and the cylinder heads  96 ,  98  of the engine  14 . When fuel is heated, aspiration of gases trapped within the fuel is accelerated. Thus, maintaining the fuel at a lower temperature helps in preventing gases from aspirating out of the fuel. 
     Additionally, by using a rubber fuel line for the portion of the fuel passages that extend below the throttle bodies  122 ,  124 , the fuel is further insulated from heat. For example, as shown in  FIG. 7 , the fuel line  190  extends beneath the throttle bodies  122 ,  124 . With reference to  FIG. 4 , the fuel line  190 , thus, is disposed in close proximity to both the cylinder blocks  92  and  94 . As such, this portion of the fuel delivery system  84  is particularly susceptible to heating through the convection of hot air circulating around the cylinder blocks  92 ,  94  as well as radiation of heat from those components. By using a rubber fuel line  190  in this area, the fuel is further protected from heating. 
     Further, the repeated opening and closing of the valve within the fuel injector  180  causes fuel pressure waves to travel through the fuel line  186  toward the fuel injector  182 . Additionally, the repeated opening and closing of the valve within the fuel injector  182  causes fuel pressure waves to travel through the fuel line  188  toward the fuel injector  180 . Such pressure waves in the fuel delivery system  84  causes undesirable variations in the fuel injection flow discharged through the nozzles  200 . Thus, by using a rubber fuel line  190  between the fuel injectors  180 ,  182 , these pressure waves can be attenuated, thereby reducing the effect of the fuel pressure waves on the fuel injection rates. It is to be noted that other resilient materials can be used to form the fuel line  190 . 
     Yet another advantage of using a flexible and/or resilient material for the fuel line  190 , is that during insulation, the throttle body assemblies  122 ,  124  can be twisted relative to each other about the throttle valve shaft axis. Such manipulation makes it easier to align the flanges  130 ,  132  with the intake ports  104 ,  106 . 
     It is also to be noted that by extending the fuel lines  186 ,  190 ,  188  through the space between the cylinder blocks  92 ,  94  and beneath the throttle bodies  122 ,  124 , more space around and above the throttle bodies  122 ,  124  can be used for other components of the induction system  82 , such as the second intake air chamber  120 . Thus, this arrangement of fuel lines  186 ,  190 ,  188  effectively utilizes an area that is typically unused in a motorcycle. 
     With reference to  FIG. 1 , the exhaust system  86  includes individual exhaust header pipes  210 ,  212 , a merging chamber  214 , and a muffler  216 . With reference to  FIGS. 8 and 9 , the header pipe  210  is connected to the exhaust port  110  of ( FIG. 4 ) of the rear cylinder head  98  through the cooperation of the exhaust flange  114  and the exhaust pipe flange  218 . 
     The flanges  114 ,  218  are connected with the plurality of bolts (not shown). As such, the internal exhaust passage defined within the cylinder head  98  is connected to the internal exhaust passage defined within the exhaust header pipe  210 . The exhaust header pipe  212  is connected to the exhaust port  108  in the same manner using the exhaust flange  112 . 
     As shown in  FIG. 1 , the exhaust header pipe  210  extends forwardly from the exhaust port  110  and then curves rearwardly toward the merging portion  214 . The header pipe  212  extends from the exhaust port  108  with a larger radius curvature than that of the header pipe  210 , and also connects to the merging portion  214 . 
     The merging portion  214  preferably is shaped to provide some silencing. The outlet of the merging portion  214  is connected to the muffler  216  through an exhaust pipe  220 . 
     In operation, as fuel and air charges delivered to the combustion chambers from the fuel and induction systems  84 ,  82 , respectively, are combusted, the exhaust gases generated therefrom are discharged from the exhaust ports  108 ,  110  into the header pipes  212 ,  210 , respectively. The exhaust gases travel through the header pipes  210 ,  212 , and through the merging portion  214 , in which the exhaust gases expand and are combined, thereby attenuating some of the acoustical energy travelling therewith. The exhaust gases exit the merging portion  214  through the exhaust pipe  220  and are further silenced in the muffler  216 . 
     With continued reference to  FIGS. 1 ,  8 , and  9 , the exhaust system  86  includes an arrangement of heat shields. As shown in  FIG. 8 , flange shield  224  has a shape that is generally complimentary to the flange  218  and extends over the flange  218  as well as the flange  114 . The flange cover  224  includes a notched portion  226  which receives the upstream end of the header pipe  210 . Another flange cover (not shown) extends over the flange connecting the header pipe  212  to the exhaust port  108 . 0   
     The exhaust system  86  also includes a main heat shield body  228  which extends from a position proximate to the flange cover  224 , over the merging portion  214 , to a point adjacent the muffler  216 . With reference to  FIG. 8 , a gap a preferably is defined between the main heat shield body  228  and the flange cover  224 . Similarly, a gap preferably is defined between the main heat shield body  228  and the flange cover covering the flange  112 . 
     The main heat shield body  228  is secured to various other portions of the exhaust system  86 . For example, clamps  230  secure the upstream portions of the main body  228  to the individual header pipes  210 ,  212 . Additionally, a portion of the main heat shield body  228  is mounted to the merging portion at a mount  232 . Finally, a bracket  234  is used to secure the main heat shield body  228  to the exhaust pipe  220 . 
     With reference to  FIGS. 8 and 9 , the flange cover  224  includes a mounting boss  236  extending outwardly from the flange  224  adjacent the notch  226 . Additionally, the main heat shield body  228  includes a mounting boss  238  extending from an upstream and thereof and generally parallel to the mounting boss  236  of the flange cover  224 . The mounting bosses  236 ,  238  are connected with a plurality of washers  240  and a bolt  242  as illustrated in FIG.  9 . Thus, the flange cover  224  is supported by the main heat shield member  228 . Preferably, the main heat shield member  228 , the flange cover  224 , and the flange cover covering the exhaust flange  112 , provided with a polished outer surface thereby enhancing the overall exterior appearance of the exhaust system  86 . 
     Additionally, forward and rearward heat shield members  246 ,  248  are mounted to an exterior of the main heat shield member  228 . The additional heat shield members  246 ,  248  provide additional protection to the legs and clothing of an operator of the motorcycle  10 . 
     With reference to  FIGS. 10-13 , the lubrication system  88  preferably is a dry-sump-type lubrication system. As such, the lubrication system  88  includes a reservoir  250  for storing lubricant therein and two lubricant pumps (not shown) for circulating lubricant through the lubrication system  88 . 
     With reference to  FIG. 11 , the lubricant reservoir  250  is formed with three major components. A central body portion  252  of the reservoir  250  is made integrally with a portion of the transmission  54 . In particular, the central body member  252  is made integrally with a transfer case  254  of the transmission  54 . A cover  255  is mounted to the transfer case  254 . As shown in  FIG. 11 , the central body portion  252  defines a large central aperture  256  extending from the right to the left side of the central body portion  252 . 
     The lubricant reservoir  250  also includes an outer casing member  258  attached to the right side of the central body portion  252 . The outer casing member  258  includes an inner face which sealingly engages with the right side of the aperture  256 . 
     Additionally, the lubricant reservoir  250  includes an inner case member  260 . A periphery of the inner case member  260  extends around the left side periphery of the aperture  256  and sealingly engages therewith. Thus, together the central body portion  252 , the outer case member  258 , and the inner case member  260  define an interior lubricant chamber  262 . 
     As shown in  FIGS. 10 and 11 , the outer case member  258  includes ridges or “beads”  264  which extends generally longitudinally along the outer case member  258 . The beads  264  provide additional surface area through which greater heat exchange can occur between lubricant within the lubricant reservoir  262  and the atmosphere. Above the beads  264 , an outer heat insulation member  266  is mounted to the outer casing member  258 . A bolt  268  secures the outer heat insulation member  266  to the outer casing member  258 . 
     With reference to  FIGS. 11-13 , the inner case member  260  defines a left sidewall of the reservoir  250 . An additional heat insulation member  270  extends over a portion of the top of the lubricant reservoir  250 , the left sidewall, and a portion of the rear wall. Preferably, the insulation member  270  is formed from a piece of sheet insulation material having a first portion  272  covering a portion of the upper wall of the lubricant reservoir  250 , a second portion  274  extending over a portion of the inner case member  260 , and a third portion  276  overlying a portion of the rear wall, of the lubricant reservoir  250 . 
     As shown in  FIG. 12 , the insulation member can be secured to the lubricant reservoir with a plurality of rivets  278 . Optionally, a portion of the third portion  276  can be folded forwardly so as to define a further inner portion  280  that can be overlapped by the second portion  274 . Preferably, in this configuration, some of the rivets  278  can be used to secure the second portion  274  to the further portion  280 . 
     With reference to  FIGS. 10 ,  12 , and  13 , the lubricant reservoir  250  includes a lubricant refill opening  282  positioned to allow an operator or repair person to add lubricant to the lubricant reservoir  250 . The upper end of the opening  282  is normally closed with a cap  284 . 
     With reference to  FIG. 10 , a ullage rod  286  is attached to the cap  284  and extends downwardly into the interior volume  262  of the reservoir  250 . As known in the art, by removing the cap  284  and the ullage rod  286 , an operator or repair person can monitor the level of lubricant in the reservoir  250 . 
     With reference to  FIG. 10 , a lubricant scavenge line  290  extends from a discharge port  292  of a scavenge pump of the lubrication system  88 . As shown in  FIG. 11 , the scavenge line  290  is connected to an inlet  292  of the reservoir  250 . preferably, the reservoir  250  includes a guide pipe  294  extending from the inlet  292  upwardly towards an upper portion of the interior volume  262 . 
     By providing the guide pipe as such, lubricant initially entering the interior volume  262  is kept separate from a pool of lubricant within the interior volume  262  until reaching the outlet of the guide tube  294 . This is advantageous because, firstly, gases trapped within lubricant flowing into the guide pipe  249  are prevented from mixing with lubricant pooled in the interior volume  262 . Thus, by guiding lubricant entering the reservoir  250  through the guide tube  294 , gases have the opportunity to a separate out of the liquid lubricant directly into an empty space above the level of lubricant within the interior volume  262 . Additionally, the outlet  296  ( FIG. 10 ) of the reservoir  250  is disposed adjacent to the inlet  292 . Thus, the guide tube  294  prevents lubricant entering the reservoir from the inlet  292  from immediately exiting the reservoir  250  through the outlet  296 . Thus, lubricant entering the reservoir  250  through the guide tube  294  circulates within the reservoir  250  before reaching the outlet  296 . 
     Additionally, the reservoir  250  includes an internal wall  298  extending upwardly from the bottom of the reservoir  250  so as to form a partial partition within the interior volume  262 . The wall  298  can thus further enhance the circulation of lubricant throughout the reservoir  250  before reaching the outlet  296 . In the illustrated embodiment, the wall  298  is formed integrally with the main body portion  252  of the reservoir  250 . 
     With reference to  FIG. 10 , the outlet  296  of the reservoir  250  is connected to feed pipe  300 . The outlet of the feed pipe  300  is connected to an inlet  302  of the supply pump. The supply pump draws lubricant from the lubricant reservoir  250 , through the supply line  300 , then pressurizes and thus urges lubricant through numerous lubricant galleries defined within the engine  14  and the transmission  54 . After the lubricant is circulated through the engine  14  and the transmission  54 , the lubricant falls to a lower portion of the engine  14  and is again drawn back to the lubricant reservoir  250  by the scavenge pump. 
     With reference to  FIG. 10 , a lubricant temperature sensor  304  is mounted to the lubricant reservoir  250 . A portion of the sensor  304  is exposed to the interior volume  262  of the reservoir  250 . The sensor  304  is configured to detect a temperature of lubricant within the interior volume  262  and produce a signal indicative thereof. The sensor  304  is connected to the ECU through a lubricant temperature signal line (not shown). The ECU can be configured to use the signal from the sensor  304  in a feedback control system for controlling operation of the engine  14 , described in greater detail below. 
     The motorcycle  10  also includes an ignition system (not shown). The ignition system can be powered by known power sources typically used for motorcycles. For example, the motorcycle  10  can include an AC generator driven by the engine  14  and a battery. The ignition system, which includes ignition coils (not shown) can draw power from the battery and/or the AC generator to supply power to sparkplugs (not shown) for combusting the air-fuel charges within the combustion chambers. Preferably, the coils are controlled by the ECU in accordance with the feedback control system. 
     The feedback control system, which utilizes the ECU, can control numerous operating parameters of the engine  14 . For example, but without limitation, the feedback control system can include various maps, generally known in the art, for determining appropriate fuel injection and ignition data based on the output of various sensors. Such sensors can include, for example, but without limitation, the lubricant temperature sensor  304 , as well as numerous other sensors such as a throttle position sensor, air pressure sensor, air temperature sensor, throttle position sensor, (not shown), as well as others. 
     The ECU can be configured to detect the output of the sensors, correlate these outputs with data from the control maps, and output control signals to the fuel injectors  180 ,  182  and the sparkplugs for proper fuel injection and ignition control. Additionally, the ECU can use the output of the lubricant temperature sensor  304  to control the idle speed control system  150 . 
     For example,  FIG. 14  illustrates data from a control map plotted on a two-dimensional graph. The vertical axis represents the opening V of the linear valve  166 . The horizontal axis represents the temperature L of lubricant within the reservoir  250 . The solid line in the graph of  FIG. 14  illustrates an ideal movement of the valve  166  according to the temperature L of lubricant within the reservoir  250 . In particular, the solid line  320  indicates the target ISC valve opening V to keep the engine  14  running at 900 rpm. As shown in  FIG. 14 , the idle speed control valve  166  would start from an opening V T1  and gradually close as the temperature L of the lubricant increased. This movement of the ISC valve  166  would maintain the engine speed at 900 rpm. 
     The dashed line  322  on the graph  14  illustrates the compensated ISC valve opening V. For example, the line  322  represents a target ISC valve opening V, plus a predetermined amount  324 . Thus, at the lubricant temperature L 1  the compensated ISC valve opening V is V 1 . Similarly, at temperatures L 2  and L 3 , the compensated ISC valve openings are V 2  and V 3 , respectively. This data provides data points  326 ,  328 , and  330 . 
     With reference to  FIG. 15 , the feedback control system can use the data points  326 ,  328 , and  330  in order to control the ISC system  150  in accordance with the output from the lubricant temperature sensor  304 . For example, if the output from the lubricant temperature sensor  304  indicates a temperature less than or equal to temperature L 1 , the ISC valve  166  opens to V 1  in accordance with the data point  326 . Further, the ECU holds the ISC valve  166  at the opening V 1  for a time T 1 . After the time T 1 , elapses, the opening V is gradually reduced over time to a closed position. A schematic illustration of the movement of the ISC valve  166  is illustrated as line  332 . Similarly, the movement of the ISC valve  166  when the output signal of the lubricant temperature sensor  304  corresponds to the temperatures L 2  and L 3  is illustrated as lines  334  and  336 , respectively. 
     Thus, constructed as such, the ECU can sample the temperature of the lubricant within the reservoir  250  once when the ignition switch of the motorcycle  14  is turned on. At that time, the ECU can sample the output from the sensor  304  and determine the proper ISC valve opening V, then operate the ISC control valve  166  to open the ISC valve to the opening V. The ECU can then hold the ISC valve  166  at the opening V until the predetermined time T has expired. Thereafter, the ECU can allow the ISC control valve  166  to gradually return to a closed position. 
     In this manner, the ECU can control the ISC valve  166  with relatively few operations. In contrast, a more complicated approach would be to continually sample the output of the lubricant temperature sensor  304  and continually move the ISC valve  166  smoothly from an initial opening to a closed position as the lubricant temperature rises. Such a scenario requires additional processing capacity and thus would require more expensive ECU. 
     With reference to FIGS.  4  and  16 - 18 , the induction system  82  is described in greater detail. As shown in  FIG. 16 , the first induction air chamber  116  is generally triangular in shape in side elevational view. 
     The first intake air chamber  116  includes an inlet  350  disposed on an inner side thereof. Preferably, the inlet  350  leads to a first expansion chamber  352  defining an entrance to the first intake air chamber  116 . 
     The first intake air chamber  116  also includes an air filter  354  through which air from the expansion chamber  352  passes before it reaches an outlet  356  disposed at a top of the first intake air chamber  116 . 
     With reference to  FIG. 17 , the first intake air chamber  116  is formed of an inner main body portion  356  and an outer cover member  358 . An interior volume  360  is defined between the main body portion  356  and the outer cover  358 . Thus, induction air A flowing from the first expansion chamber  352  is further expanded upon entering the interior volume  360 . 
     The filter  354  is mounted to the main body portion  356  via a flange member  362 . The flange member  362  and the filter  354  define a partition within the first intake air chamber  116  and separates the interior volume  360  from a second interior volume  364 . The outlet  356  is disposed at an upper end of the second chamber  364 . As shown in  FIG. 17 , a drain hose  366  extends from a bottom portion of the chamber  364  to thereby allow liquids, such as fuel, to drain from the chamber  364 . 
     The duct  118  has an inlet end  368  connected to the outlet  356  of the first intake air chamber  116 . The duct  118  extends upwardly from the first intake air chamber  116  then curves horizontally to connect with an inlet  370  ( FIG. 16 ) of the second intake air chamber  120 . The duct  118  defines a cross-sectional flow area that is smaller than a cross-sectional flow area defined by the first intake air chamber  116 . 
     With reference to  FIGS. 16 and 18 , the second air intake chamber  120  is formed of a lower member  372  and an upper member  374 . The upper and lower members  374 ,  372  are joined together around a periphery  376  thereof. An interior volume  378  is defined therebetween. As shown in  FIG. 16 , the inlet  370  is defined in the lower member  372 . 
     The second intake air chamber  120  includes two inlets, i.e., the first inlet  370 , and a second inlet  380 . The inlet  380  is comprised of a lid member  382  which defines a rearwardly facing atmospheric opening  384 . The lid member  382  is mounted over an aperture  386  defined in the upper member  374 . 
     A second filter assembly  388  overlies the aperture  386 . Preferably, the filter assembly  388  includes an upper flange  390  which extends around the periphery of the aperture  386 . Preferably, the lid member  382  includes a peripheral flange  392  which extends over the flange  390 . A plurality of screws  394  secure the lid  382  to the upper member  374  with the flange  390  sandwiched between the upper member  374  and the flange  392 . The filter assembly  388  includes an outlet  394  on a lower surface thereof. 
     With continued reference to  FIG. 16 , the lower member  372  of the second intake air chamber  120  includes two outlets  396 ,  398  which receive the sleeves  134  of the throttle body assemblies  122 ,  124 , respectively. 
     The induction system  82  is also configured to receive gases from the crankcase of the engine  14  and to guide those gases back to the combustion chamber of the engine  114  for combustion therein. A breather pipe  400  includes an inlet end on the exterior of the second intake air chamber  120  and an outlet end  402  terminating within the second intake air chamber  120  downstream from the outlet  394  of the second folder assembly  388 . Preferably, another hose or a plurality of hoses and conduits (not shown) connects the inlet of the breather hose  400  with the crankcase  90  of the engine  14 . As such, blow-by gases and other gases which aspirate out of lubricant within the engine  14  can be guided to the breather hose  400 . 
     Preferably, an additional oil separator (not shown) is connected to the inlet of the breather hose  400  so as to prevent liquid oil from reaching the interior volume  378  of the second intake air chamber  120 . Because the outlet  402  of the breather pipe  400  terminates in the interior volume  378  downstream from the outlet  394  of the filter assembly  388 , such blow-by gases can be directly drawn through the throttle bodies  122 ,  124  into the combustion chambers for combustion therein. 
     With reference to  FIGS. 16 and 18 , the second intake air chamber  120  preferably includes an intake air temperature sensor  404 . The intake air pressure temperature sensor  404  is configured to detect a temperature of air within the interior volume  378  and generate a signal indicative thereof. The air temperature sensor  404  is connected to the ECU through an air temperature signal line  406 . Thus, the ECU can use the output of the intake air temperature sensor  404  in the feedback control system disclosed above. 
     With reference to  FIG. 16 , the second intake air chamber  120  also includes an idle speed controller air aperture  406 . In the illustrated embodiment, the aperture  406  is defined in the lower member  372 . The aperture  406  is connected to the inlet  152  ( FIG. 6 ) of the idle speed control system  150 . As such, the idle speed control system  150  can draw air A from the second intake air chamber  120  from a point downstream from the outlet  394  of the second filter assembly  388 . 
     As shown in  FIG. 4 , the first intake air chamber is disposed on the right side of the engine, overlying the space formed between the cylinders  92 ,  94 , in side elevational view. Additionally, the second intake air chamber  120  lies over the top of the engine body  80 . Because each of the intake air chambers  116 ,  120  include their own filters, and since the first intake air chamber  116  communicates with the second intake air chamber  120  at a point downstream from the outlet  394  of the second air filter  388 , the volumetric capacity of the induction system  82  is expanded. In particular, the interior volume  378  of the second intake air chamber  120  is fed with filtered air from both the filter  354  and the filter assembly  388 . Thus, the induction system  82  effectively utilizes the limited space available above the top of the engine body  80  as well as the an area on the side of the engine body  80 . 
     Although the present invention has been described in terms of a certain embodiment, other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. For instance, various components may be repositioned as desired. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow.