Patent Publication Number: US-7717206-B2

Title: Air intake system for off-road vehicle

Description:
PRIORITY INFORMATION 
   The present application is based on and claims the benefit of U.S. application Ser. No. 10/790,932, filed on Mar. 2, 2004; U.S. Provisional Application No. 60/460,068, filed on Apr. 2, 2003; and U.S. Provisional Application No. 60/459,958, filed on Apr. 2, 2003, pursuant to 35 U.S.C. §119(e). 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an air intake system for an off-road vehicle, and more particularly to an improved air intake system for an off-road vehicle that has at least two seat assemblies. 
   2. Description of Related Art 
   Off-road vehicles are designed to be operated over rugged terrain. These vehicles are often operated off-road over terrain such as, for example, steep inclines and declines, rough roads, and areas covered in mud and water. 
   Off-road vehicles typically include a frame that is supported by wheels. In one common arrangement, the vehicle has four wheels, i.e., a pair of front wheels and a pair of rear wheels. An internal combustion engine is employed to power at least the rear or front wheels, and most commonly, all of the wheels. Typically, the engine is combined with a transmission to form an engine unit. The transmission transfers power to an output shaft from a crankshaft of the engine. The output shaft drives the wheels. For example, Japanese Utility Model Publication JP-Y2-H6-34213 discloses such an arrangement. 
   SUMMARY OF THE INVENTION 
   The engine has an air intake port communicating with a combustion chamber. An air intake system can be connected to the intake port to deliver air to the combustion chamber. The intake system can include components such as, for example, a throttle body and an air intake duct. Those components need sufficient protection. 
   Due to the typical environment in which off-road vehicles operate, the intake systems of the off-road vehicles are likely to be hit by rocks, wooden blocks or the like or to ingest water. The intake systems of the off-road vehicles, thus, require more protection than other types of vehicles. 
   A need therefore exists for an improved off-road vehicle that can substantially protect an air intake system of the vehicle. 
   One aspect of an embodiment of the present invention involves an off-road vehicle comprising a frame. A plurality of wheels supports the frame. At least two seat assemblies are disposed side by side on the frame. The seat assemblies are spaced apart from each other to define a space therebetween. An internal combustion engine powers the wheels. The engine comprises an air intake port. The air intake port is in direct communication with a combustion chamber. An air intake system delivers air to the intake port. At least a portion of the air intake system extends through the space. 
   In accordance with another aspect of an embodiment of the present invention, an off-road vehicle comprises a frame. A plurality of wheels supports the frame. At least two seat assemblies are disposed side by side on the frame. The seat assemblies are spaced apart from each other to define a space therebetween. An internal combustion engine powers at least one of the plurality of wheels. The engine comprises an air intake port and a combustion chamber. The air intake port communicates with a combustion chamber. The engine has a surface disposed within the space and the air intake port is at least partially positioned on the surface. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features, aspects and advantages of the present invention are described in detail below with reference to the drawings of a preferred embodiment, which is intended to illustrate and not to limit the invention. The drawings comprise six figures in which: 
       FIG. 1  is a side elevational view of an off-road vehicle configured in accordance with a preferred embodiment of the present invention; 
       FIG. 2  is a top plan view of the off-road vehicle of  FIG. 1 ; 
       FIG. 3  is a side elevational view of an engine unit of the off-road vehicle; 
       FIG. 4  is a side elevational view of a front differential and a portion of a steering mechanism of the off-road vehicle; 
       FIG. 5  is a partial sectional view taken along the line  5 - 5  of  FIG. 2 ; and 
       FIG. 6  is a partial sectional view taken along the line  6 - 6  of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference to  FIGS. 1-7 , an off-road vehicle, and particularly an air intake system for the off-road vehicle is described. While the intake system is described in connection with this particular type of vehicle, those of skill in the art will appreciate that certain features, aspects, and advantages of the present invention may have utility in a wide range of applications for other vehicles. For instance, certain features, aspects and advantages of the present invention can be used with snow vehicles, tractors, utility vehicles, and the like. 
   With reference to  FIGS. 1 ,  2  and  5 , the off-road vehicle  30  preferably has an open tubular-type frame  32 . The illustrated frame  32  comprises a main frame section  34 , a front frame section  36 , a rear frame section  38  and a compartment frame section (or pillar frame section)  40 . 
   The main frame section  34  includes a pair of side frame units  42  spaced apart side by side with each other. Each side frame unit  42  comprises a front tubular member  42   a  and a rear tubular member  42   b . Each tubular member  42   a ,  42   b  preferably is rectangular in section but other configurations can be used. In one variation, the front and rear members  42   a ,  42   b  can have a circular shape in section. Moreover, the members  42   a ,  42   b  can have an incomplete tubular shape such as, for example, a U-shape. A rear end of the front tubular member  42   a  is bent outwardly and is coupled with a mid portion of the rear tubular member  42   b . A forward end of the rear tubular member  42   b  is bent inwardly and is coupled with a mid portion of the front tubular member  42   a . Thus, in the illustrated arrangement, both of the front and rear tubular members  42   a ,  42   b  are nested together. The side frame units  42  preferably are connected by front, center and rear cross members  44  ( FIG. 2 ) that transversely extend between the tubular members  42   a ,  42   b.    
   The front frame section  36  extends generally upward from a front portion of the main frame section  34 . The rear frame section  38  also extends generally upward from a rear portion of the main frame section  34 . The rear frame section  38  preferably includes a pair of rear frame members  46 . Several struts connect the rear frame members  46  to the side members  42  of the main frame section  34  and support the rear frame members  46  above the side members  42 . 
   The compartment frame section  40  is disposed generally between the front and rear frame sections  36 ,  38  in a side view as shown in  FIG. 1 . The compartment frame section  40  includes a pair of compartment members  48  extending compartment members  48  are spaced apart from each other on both sides of the off-road vehicle  30  to be placed more outward than the main frame section  34  in the illustrated embodiment. 
   A floorboard or floor panel  50  extends in an area generally defined by the compartment members  48  in the top plan view ( FIG. 2 ) and is affixed at least to the main frame  34 . The floorboard  50  defines a passenger compartment together with the compartment frame section  40 . As best shown in  FIG. 5 , the illustrated floorboard  50  generally is a flat panel with a portion that projects upward. That is, the floorboard  50  comprises a horizontal section  51  defining a generally flat area and a projection  52  defining a tunnel extending along a longitudinal center plane LC ( FIG. 2 ) of the frame  32  that extends vertically and fore to aft. The horizontal section  51  can support feet of a driver and a passenger and also can be used as a step when the driver or the passenger enters or leaves the passenger area of the off-road vehicle  30 . The illustrated projection  52  is configured as a trapezoid in section and thus has slanted side surfaces  53  and a top surface  54 . Other configurations also can be used. 
   The main, front, rear and compartment frame sections  34 ,  36 ,  38 ,  40  preferably are welded to each other. The illustrated structure and arrangement of the frame  32 , and the combination of the frame  32  and the floorboard  50  are merely one example. Various structures, arrangements and combinations other than those are practicable. For instance, the respective frame sections  34 ,  36 ,  38 ,  40  can be provided with struts or reinforcement members that are not described above. 
   With reference to  FIGS. 1 and 2 , the off-road vehicle  30  preferably has a pair of front wheels  56  and a pair of rear wheels  58  both supporting the frame  32 . Each wheel  56 ,  58  preferably has a tire that is sized and configured to advantageously proceed over rough roads and in mud and water. Relative to most similar conventional off-road vehicles, the tire can have a higher internal pressure and/or can be equipped with an inner tube, if desired. In some embodiments, a tubeless tire, which is relatively wide and which has a relatively low air pressure, can be used. In one arrangement, the selected tires are sized as follows: 25×8-12 at the front end and 25×10-12 at the rear end. 
   The front and rear wheels  56 ,  58  preferably are coupled with the frame  32  through a front suspension mechanism  60  and a rear suspension mechanism  62 , respectively. The front suspension mechanism  60  swingably (up and down) and independently suspends both the front wheels  56 . The rear suspension mechanism  62  also swingably (up and down) and independently suspends both the rear wheels  58 . Thus, the illustrated off-road vehicle  30  preferably features four wheel independent suspension. 
   With reference to  FIGS. 1-3 , the off-road vehicle  30  preferably has a seat unit  66 . The illustrated seat unit  66  comprises a pair of seats or seat sections  68  such that the driver and the passenger can sit side by side. In some arrangements, the seat unit  66  can comprise a bench style, or split bench style, seat. In such arrangements, two or more seating positions are positioned laterally across the vehicle. 
   In the illustrated arrangements, a pair of separate seat sections  68  are provided. The rear frame section  38 , at least in part, forms a pair of seat pedestals (not shown). Each seat  68  and each seat pedestal together form a seat assembly. The illustrated off-road vehicle  30  thus has two sets of seat assemblies. The seat assemblies are spaced apart from each other to form a space  70  ( FIG. 2 ) therebetween. 
   A preferable construction or structure of an off-road vehicle similar to the off-road vehicle  30  is disclosed in, for example, a co-pending U.S. application Ser. No. 10/119,439 titled “ENGINE ARRANGEMENT FOR OFF-ROAD VEHICLE,” having a co-pending U.S. application Ser. No. 10/791,111, titled “OFF-ROAD VEHICLE WITH TRANSMISSION,” having U.S. application Ser. No. 12/116,118, titled “FLOOR ARRANGEMENT FOR OFF-ROAD VEHICLE,” having a co-pending U.S. application Ser. No. 10/790,932, titled “STEERING SYSTEM FOR OFF-ROAD VEHICLE,” having a co-pending U.S. application Ser. No. 10/791,164, titled “OFF-ROAD VEHICLE WITH AIR INTAKE SYSTEM,” having a co-pending U.S. application Ser. No. 11/775,772, titled “OFF-ROAD VEHICLE WITH WHEEL SUSPENSION,” having a co-pending U.S. application Ser. No. 10/792,463, titled “FRAME ARRANGEMENT FOR OFF-ROAD VEHICLE,” having and a co-pending U.S. application Ser. No. 12/116,118, titled “TRANSMISSION FOR OFF-ROAD VEHICLE,” having the entire contents of which are hereby expressly incorporated by reference. 
   In this description, the terms “front” and “forward” mean the direction in which the driver or passenger looks straight when seated on the seats  68 . Also, the terms “rear,” “rearward” and “backward” mean the direction opposite to the front direction. 
   Each seat  68  preferably comprises a seat cushion  72  and a seat back  74 . The seat cushion  72  extends generally horizontally over the seat pedestal and is detachably or removably affixed to the seat pedestal. The seat back  74  extends generally vertically and upward from a rear portion of the seat cushion  72 . In the illustrated arrangement, the seat cushion  72  and the seat back  74  are formed unitarily. In one variation, the seat cushion  72  and the seat back  74  can be separately formed and assembled together. 
   With reference to  FIG. 3 , the illustrated seat unit  66  has a forward end  78 , a rear end  80  and a top end  82 . In this arrangement, the forward end  78  of the seat unit  66  is defined by forward ends of the seat cushions  72 . If, however, the seat pedestals extend forward of the seat cushions  72 , forward ends of the seat pedestals can define the forward end of the seat unit  66 . An imaginary forward, generally vertical plane  84  can be defined through the forward end of the seat unit  68 . 
   The rear end  80  and the top end  82  preferably are defined by rear ends of the seat backs  74  and top ends of the seat backs  74 , respectively. An imaginary rearward, generally vertical plane  86  can be defined through the rear ends of the seat backs  74 . Also, an imaginary, generally horizontal plane  88  can be defined through the top ends  82  of the seat backs  74 . The seat  68 , however, can be shaped in various configurations. The seat back may be omitted under some circumstances. If the seat back  74  is omitted, the imaginary rear, generally vertical plane  86  can be defined more forwardly as indicated by the reference numeral  86 A. Furthermore, the rear, generally vertical plane  86  may be defined more forwardly as indicated by the reference numeral  86 B if the thickness of the seat back  74  is reduced. Also, the generally horizontal plane  88  may be shifted downward to a top surface  82 A of each of the seat cushions  72  as indicated by the reference numeral  88 A. 
   Thus, the forward, rear and top ends  78 ,  86 ,  82 , the imaginary forward and rear generally vertical planes  84 ,  86  and the imaginary generally horizontal plane  88  are normally determined depending on a configuration of the seat assembly, which includes the seat  68  and the seat pedestal in the illustrated arrangement. More practically, the rear end  86  should be substantially on the imaginary, generally vertical forward plane  86 A or the imaginary, generally vertical rear plane  86 B. Also, the top end  82  should be substantially the top surface  82 A of the seat cushions  72  and should be on the imaginary, generally horizontal plane  88 A. 
   Because the seats  68  are positioned on the seat pedestals, which have a certain height, a relatively large space is formed below the imaginary horizontal plane  88 A. Additionally, the seat unit  66  can have any number of seats, such as, for example, three seats in some alternative arrangements. 
   With reference to  FIGS. 1 ,  2  and  6 , the off-road vehicle  30  preferably has a carrier or cargo box  92  behind the seat unit  66 . The illustrated carrier  92  extends over a rear portion of the rear frame section  38  and is suitably affixed at least to the rear frame members  46 . In one arrangement, the carrier  92  can be tipped rearward to allow its contents to be dumped. The carrier  92  preferably is formed generally in the shape of a rectangular parallelepiped and has a bottom, a front, a rear and a pair of lateral sides. That is, the carrier  92  is generally configured as an open-topped box. 
   As best shown in  FIG. 6 , the bottom of the carrier  92  preferably comprises steps  96  on both sides such that side portions  98  of the bottom are positioned higher than a central portion  100  of the bottom. The steps  96  advantageously reduce the likelihood that the rear wheels  58  would contact carrier  92  when the rear wheels  58  are in an upper most position of suspension travel. It should be noted that the described movement of the rear wheels  58  is the relative movement thereof in relation to the carrier  92 . The center bottom portion  100  thus increases the capacity of the carrier  92 . Each step  96  preferably extends fore to aft as shown in  FIG. 2 . Longitudinally shortened steps (similar to wheel wells) also can be used. 
   The center bottom portion  100  helps lower the center of gravity of the carrier  92 . The illustrated off-road vehicle  30  thus features enhanced stability. The steps  96  also reduce lateral movement of loads. Manufacture of the carrier  92  is simple and cost effective because the steps  96  only extend fore to aft. In addition, the steps  96  may increase the stiffness of the carrier  92 . 
   With reference to  FIGS. 1 ,  2  and  4 , the off-road vehicle  30  comprises a steering mechanism  104 . The steering mechanism  104  in the illustrated arrangement includes a steering wheel  106 . The steering wheel  106  is affixed to the frame  32  for steering movement in front of the seat  68  for the driver, which is located on the left-handed side of the illustrated off-road vehicle  30 . 
   The illustrated steering mechanism  104  preferably comprises a steering shaft unit  110  coupled with the steering wheel  106 , a tie-rod (not shown) coupled with the front wheels  56 , and a rack-and-pinion assembly  112  ( FIG. 4 ) that connects the steering shaft unit  110  to the tie-rod. The rack-and-pinion assembly  112  converts the pivotal movement of the steering wheel  106  to an axial movement of the tie-rod. The rack-and pinion assembly  112  preferably is housed in a gear case  114 . 
   The steering wheel  106  can be rotated clockwise and counterclockwise to effect turning movement of the steerable wheels. In some arrangements, a control stick can be used in place of a steering wheel  106 . Other suitable directional control devices also can be used, such as, without limitation, handlebars, push-buttons, foot pedals and the like. 
   As best shown in  FIG. 2 , the illustrated steering shaft unit  110  comprises an upper steering shaft  116  and a lower steering shaft  118  both pivotally affixed to the frame  32 . The upper shaft  116  extends upward and rearward toward the driver&#39;s area and the steering wheel  106  is affixed to the top end of the upper shaft  116 . The upper shaft  116  preferably extends generally parallel to the longitudinal center plane LC. The lower shaft  118  extends toward the longitudinal center plane LC (i.e., toward a laterally central area of the vehicle) from a lower end of the upper shaft  116  through a universal joint (not shown) and is coupled with the rack-and-pinion assembly  112 , which is mounted within the case  114 . 
   The tie rods preferably are connected to rod sections that extend outward from the rack and pinion assembly  112 . In some arrangements, an inner ball joint couples the rod sections to the respective tie rods. Also, an outer ball joint preferably couples each tie rod to a knuckle arm (not shown) that is associated with each front wheel  56 . Each knuckle arm is coupled with a king pin (not shown) that extends from an axle of the front wheel  56 . The tie-rods move axially along with the rod sections when the steering shaft  110  is rotated. 
   As described above, the vehicle  30  preferably includes four wheel independent suspension. In such arrangements, as discussed above, the outer ball joints can move around on an imaginary sphere that is defined about the inner ball joint. In other words, the outer ball joint can move transversely as well as around the surface of the imaginary sphere. The knuckle are is only capable of moving along an arc defined by the suspension link connecting the wheel to the frame. The knuckle arm, thus, rotates about the king pin and causes bump steering unless the curve defined by the suspension link is consistent with the sphere defined about the inner ball joint. In addition, bump steering causes changes in the toe angle of the front wheels. 
   To reduce bump steering, as shown in  FIG. 4 , the gear case  114  preferably is mounted on a front differential housing  122 . The front differential housing  122  advantageously is positioned on the longitudinal center plane LC of the frame  32 . The front differential housing  122  also preferably is disposed between the front tubular members  42   a  at a location just rearward of a forwardmost cross member  44  in the illustrated arrangement. In one arrangement, the gear case  114  can be unitarily formed with the differential housing  122 . The front differential housing  122  incorporates a front differential gear unit  124  and is relatively stiff. The gear case  114  preferably has a bracket  126  extending downward and the differential housing  122  comprises a mount surface  128 . The bracket  126  is affixed to the mount surface  128  by bolts  130  or other suitable mounting techniques. 
   Preferably, the mount surface  128  is a top surface of the housing  122 . That is, a bottom surface of the illustrated gear case  114  can be secured to the top surface of the housing  122 . Accordingly, sufficient clearance can be provided adjacent another surface of the gear case  114  to enable the lower steering shaft  118  to be coupled to the rack-and-pinion assembly  112 . The illustrated arrangement also advantageously enables the steering shaft  110  to be shortened, which decreases its weight, because the surface adjacent to the coupling region is closer to the top surface  128  of the housing  122 . Moreover, the tie-rods are positioned in the illustrated arrangement in a manner that reduces the likelihood that they will interfere with the shafts of the front differential  124 , which are described in greater detail below. 
   Because the front differential housing  122  and the gear case  114  are secured together at a location along the longitudinal center plane LC, the tie-rods can be elongated relative to a construction in which the gear case  114  is mounted off-center with respect to the longitudinal center plane LC. Further, the tie-rods can have substantially equal lengths to each other while also being elongated in the illustrated arrangement. The elongation of the tie rods results in an increased diameter or circumference of the imaginary spherical surface. The enlarged imaginary spherical surface greatly increases the available suspension designs with which bump steering can be reduced. Moreover, the illustrated arrangement greatly decreases the toe angle changes of the right and left front wheels  56  caused by movements controlled by the suspension system. Accordingly, greater design freedom is provided while simultaneously reducing bump steering. Furthermore, no special brackets or stays are used to mount the rack and pinion arrangement (e.g., the gear case  114 ) and the gear case  114  can be securely mounted to the frame  32  through the front differential housing  122 . During assembly of the vehicle, the gear case  114  can be affixed to the front differential housing  122  before the housing  122  is affixed to the frame  32  which eases assembly because the connection of the front differential housing  122  and the gear case  144  can occur outside of the cramped space within the vehicle. 
   Also, the mounting arrangement only requires the mount surface  128  to be formed on the differential housing  122 , because the gear case  114  can have the bracket  126  regardless whether the gear case  114  is affixed to the differential housing  122  or not. 
   With reference to  FIGS. 1 and 2 , a hood or bonnet  134  surrounds at least a front portion of the main frame section  34 , the front frame section  36 , the front wheels  56  and a major portion of the steering mechanism  104 . A dashboard  136  preferably depends from a rear portion of the hood  134 . The dashboard  136  faces toward the passenger compartment and a meter unit  138  preferably is disposed in a central portion of the dashboard  136 . The meter unit  138  preferably incorporates meters and/or gauges such as, for example, a speedometer, a fuel level meter, and the like. Because of this meter unit arrangement, the driver can easily view the individual meters at a glance. 
   With reference to  FIGS. 1-5 , the off-road vehicle  30  has a prime mover that powers the off-road vehicle  30  and particularly the front and rear wheels  56 ,  58 . The prime mover preferably is an internal combustion engine  142 . Alternatively, an electric motor can replace the engine  142 . Engine power is transferred to the front and rear wheels  56 ,  58  through a suitable transmission  144  and a suitable drive mechanism  146 . In the illustrated arrangement, the engine  142  and the transmission  144  are coupled together to form an engine unit  148 . The illustrated transmission  144  advantageously includes an endless V-belt transmission mechanism and a switchover mechanism. The illustrated drive mechanism  146  comprises a forward driveshaft  150  extending forward from the engine unit  148 , a rear driveshaft  152  extending rearward from the engine unit  148 , the front differential  124  is coupled with the front axles (not shown) of the front wheels  56 , and a rear differential  154  is coupled with the rear axles (not shown) of the rear wheels  58 . In some arrangements, a single axle can replace the half axles. 
   As shown in  FIGS. 1-3 , the engine unit  148  preferably is positioned generally lower than the imaginary, generally horizontal plane  88  and generally in the space  70  defined between the seat assemblies. The illustrated engine  142  operates on a four-stroke combustion principle, however, other engine operating principles also can be used. The engine  142  preferably has a single cylinder block  158  that extends generally upward and rearward from a lower section of the engine unit  148 . That is, the cylinder block  158  has a cylinder axis CA that inclines relative to vertical at a certain angle. The illustrated cylinder axis CA inclines from vertical at approximately 45 degrees. 
   In the illustrated arrangement, the engine  142  is an internal combustion engine. As such, the cylinder block  158  preferably defines a cylinder bore (not shown) therein. A piston (not shown) is reciprocally disposed within the cylinder bore (not shown). A cylinder head  160  preferably closes an upper end of the cylinder bore to define, together with the cylinder bore and the piston, a combustion chamber  163 . 
   The cylinder head  160  also defines a pair of intake ports  162  and a pair of exhaust ports  166  that communicate with the combustion chamber  163 . An intake valve can be provided at each intake port  162  to selectively open the combustion chamber  163  to an air intake system  164 . In the illustrated arrangement, the air intake system  164  is coupled with the intake ports  162  at a front surface  165  of the cylinder head  160 . The front surface  165  of the cylinder head  160  preferably is disposed substantially within the space  70  and preferably faces generally forward and upward. With reference to  FIG. 2 , the front surface  165  desirably is disposed generally between the seats  68 . 
   The air intake system  164  introduces air into the combustion chamber  163  through the intake ports  162  when the intake valves (not shown) open the passage into the combustion chamber  163 . An exhaust valve (not shown) also is provided at each exhaust port  166  to selectively open the combustion chamber  163  to an exhaust system  168 . In the illustrated arrangement, the exhaust system  168  is coupled with the exhaust ports  166  at a rear surface  169  of the cylinder head  160 . The rear surface  169  of the cylinder head  160  is positioned substantially opposite to the front surface  165  and generally faces rearward and downward. The exhaust system  168  routes exhaust gases from the combustion chamber  163  to an outside location. 
   A cylinder head cover  170  is attached to the cylinder head  160  to enclose one or more camshafts (not shown). The camshafts (not shown) preferably are journaled on the cylinder head  160 . The camshafts (not shown) actuate the intake and exhaust valves at speeds that are generally in proportion to the engine speed. Other suitable methods of actuating the valves also can be used. 
   An upper section of the illustrated engine unit  148  includes the cylinder block  158 , the cylinder head  160  and the cylinder head cover  170 . The upper section at least in part extends rearwardly beyond the imaginary rear, generally vertical plane  86  (and  86 A or  86 B). 
   A lower section of the engine unit  148 , which is the balance of the engine unit  148 , comprises a crankcase  174 , which closes a lower end of the cylinder bore (not shown). A crankshaft  176  preferably is journaled within the crankcase  174  and is coupled with the piston (not shown) in any suitable manner. In the illustrated arrangement, the crankshaft  176  extends generally transverse to a direction of travel of the vehicle but other orientations also can be used. The reciprocal movement of the piston results in rotation of the crankshaft  176 . The crankshaft  176  preferably drives the camshafts via a camshaft drive mechanism. 
   The crankcase  174  also houses an input shaft for a shiftable portion of the transmission  144 . The input shaft is positioned forward of the crankshaft  176 . The lower section of the engine unit  148  also comprises a V-belt housing  178 , which is positioned next to the crankcase  174  in the illustrated arrangement. Moreover, in the illustrated arrangement, the V-belt housing  178  is defined on the left-hand side of the crankcase  174 . The V-belt housing  178  houses the V-belt transmission mechanism (e.g., continuously variable transmission). Thus, the lower section of the engine unit  148  (which comprises at least the crankcase  174  and the V-belt housing  178 ) also defines, at least in part, a transmission housing  180 . The transmission  144  will be described in greater detail below. 
   With reference to  FIGS. 1-3  and  5 , the illustrated air intake system  164  extends forward to a location under the hood  134  from the intake ports  162  of the engine  142 . The intake system  164  preferably comprises a throttle body or carburetor  182 , an accumulator or plenum chamber  184 , an air intake duct  186  and an air cleaner unit  188 . 
   With reference to  FIG. 3 , the throttle body  182  is connected to the intake ports  162  through an air intake conduit  192 . The throttle body  182  comprises a throttle valve  194  that regulates a rate of airflow amount delivered to the combustion chamber  163 . The throttle valve  194  preferably is a butterfly valve and generally is journaled for pivotal movement. The level of airflow depends on an angular position of the throttle valve  194 —when the throttle valve is closed or substantially closed, minimal air flow results, while when the throttle valve is opened or substantially opened, maximum air flow results. 
   An accelerator pedal or control member  196  ( FIG. 5 ) preferably is disposed at a front end of the floorboard  50  for pivotal movement to control the position of the throttle valve  194 . A throttle cable connects the accelerator pedal  196  to the throttle valve  194 . The driver thus can control the throttle valve  194  by adjusting an angular position of the accelerator pedal  196  with a foot  198 . Normally, the greater the throttle valve  194  opens, the higher the rate of airflow amount and the higher the engine speed. Other suitable mechanisms and/or electrical connections also can be used to transmit operator demand to the throttle valve or engine. 
   With reference to  FIG. 5 , the heel (i.e., lower portion of the foot  198 ) of the driver can lean against the slanted side surface  53  on the left-hand side of the projection  52  when the foot  198  is in position to operate the accelerator pedal  196  because the slanted side surface  53  is located generally adjacent to the accelerator pedal  196 . In other words, the slanted portion  53  functions as a foot brace and reduces the likelihood that the operator&#39;s foot  198  will slide off of the accelerator pedal  196  when the off-road vehicle  30  is operated over rough terrain or when the off-road vehicle  30  turns a sharp corner at a relatively high speed, which increases the centrifugal forces transmitted to the foot  198 . Thus, the illustrated construction can provide the driver with better body control and improved driving body position. Similarly, the slanted side surface  53  on the right-hand side also can function as the foot brace. Thus, the passenger, or driver in some configurations, can also have a foot brace for use during operation of the vehicle. 
   With reference again to  FIG. 3 , the throttle body (e.g., the carburetor)  182 , which functions as a charge former, preferably also has a fuel measurement mechanism that measures an amount of fuel mixed with the air in accordance with the rate of airflow. Because of this fuel measurement mechanism, the air/fuel ratio supplied to the engine can be controlled and/or optimized depending upon engine operating conditions. The fuel is delivered to the throttle body  182  from a fuel tank (not shown) that can be suitably mounted and suitably positioned on the frame  32 . 
   Other charge formers such as, for example, a fuel injection system can be used. The fuel injection system has a fuel injector that is configured to spray fuel directly into the combustion chamber  163  or into a portion of the air intake system downstream of the throttle valve. An engine control unit (ECU) can control the amount of fuel injected, for example, in accordance with the airflow rate. 
   With reference to  FIGS. 1 and 2 , the accumulator  184  can be coupled with an inlet of the throttle body  182 . The accumulator  184  generally forms a portion of the intake duct  186  in the broad sense of the term but provides a larger volume or cross-sectional area as compared to the balance of the intake duct  186 . Such a construction allows air to accumulate prior to delivery to the throttle body  182 . As best shown in  FIG. 1 , the accumulator  184  is generally shaped as an arcuate configuration. Such a construction advantageously smoothens the delivery of air to the engine. Furthermore, because the accumulator  184  has a relatively large volume and is disposed next to the throttle body  182 , the intake efficiency of the induction system is greatly improved. That is, sufficient air can be quickly supplied to the engine  142  even when the engine is being operated at a relatively high engine speed. This is advantageous due to the longer length of the intake duct  186 . 
   In the illustrated arrangement, the air intake conduit  192 , the throttle body  182  and the accumulator  184  together extend forwardly of the engine within a region defined between the seats  68 . Upper portions of the throttle body  182  and the accumulator  184  preferably are positioned slightly higher than the top ends  82 A of the seat cushions  72 . A forward-most portion of the accumulator  184  turns downward at or just forward of the forward end of the seat assemblies. 
   Because of this arrangement, the throttle body  182  and at least a portion of the accumulator  184  are interposed between the seat assemblies and are positioned within, or just adjacent to, the space  70 . Thus, the throttle body  182  and the accumulator  184  are positioned within a protective region of the vehicle that is located higher than a lowermost surface of the frame assembly or the floorboard  50 . Such positioning reduces the likelihood that dirt and other road debris that may be kicked up underneath the vehicle will damage the throttle body  182  or the accumulator  184 . Such placement also facilitates servicing of these components and protects these components from water damage while fording a stream, a mud bog or the like. 
   The illustrated accumulator  184 , which is positioned within the most downstream portion of the illustrated intake duct  186 , ends above a lowermost surface defined by the rear frame section  38 . The balance of the air intake duct  186 , which has a smaller volume or cross-sectional area than the accumulator  184 , preferably comprises a downstream section  200 , a middle section  202  and an upstream section  204 , which are provide a contiguous air flow path in the illustrated embodiment. The downstream section  200  extends downwardly from the accumulator  184  to a lowermost portion of the rear frame section  38 . The middle section  202  extends forwardly in a generally horizontal direction from a lower end of the downstream section  200 . 
   With reference to  FIG. 5 , in the illustrated arrangement, the middle section  202  extends through a tunnel defined by the projection  52  of the floorboard  50 . Because of this arrangement, the middle section  202  advantageously is positioned higher than the horizontal section  51  of the floorboard  50 , which greatly reduces the likelihood of damage from rocks, sticks, road debris or the like. Furthermore, the driver and/or the passenger are able to maintain a good riding body position because the horizontal section  51  is positioned generally vertically lower than the middle section  202 . Moreover, the illustrated arrangement contributes to a lower center of gravity for the off-road vehicle  30  because the height of the seats  68  does not need to be increased to accommodate the middle section  202  or another portion of the air induction system. 
   The middle section  202  preferably ends at a location close to the front frame section  36 . The upstream section  204  extends generally vertically upward from the middle section  202 . In addition, the upstream section  204  preferably is positioned within a space defined below the hood  134 . To increase the protection from ingestion of water, the forwardmost portion of the upstream section  204  extends forward and slightly downward along a lower surface of the hood  134 . 
   The air cleaner unit  188  preferably is attached at an upstream end of the intake duct  186  and extends generally along the lower surface of the hood  134 . The illustrated air cleaner unit  188  has a relatively large volume and has a cleaner element therein. The air cleaner unit  188  also has an air inlet port. Ambient air is drawn into the air cleaner unit  188  through the air inlet port and passes through the filtration element such that foreign substances such as, for example, dust, mud or water can be substantially removed from the air that is being introduced into the engine. 
   The air, which has been cleaned in the cleaner unit  188 , flows to the accumulator  184  through the intake duct  186 . The airflow amount is regulated by the throttle valve  194  in the throttle body  182 . Simultaneously, an amount of fuel is measured by the fuel amount measurement mechanism in the throttle body  182  in response to the air amount. An air/fuel charge that has a proper air/fuel ratio is formed and is delivered to the combustion chamber  163  when the intake valves open the intake ports  162 . The air/fuel charge is ignited by an ignition system (not shown) and burns within the combustion chamber  163 . The burning of the charge causes expansion of the gases and increased pressure that results in movement of the piston. The crankshaft  176  is rotated within the crankcase  174  by the movement of the piston. 
   With reference to  FIGS. 1-3 , the burnt charge, i.e., exhaust gases, are discharged through the exhaust system  168 . The illustrated exhaust system  168  preferably comprises a pair of exhaust conduits  208  and a muffler  210 . The exhaust conduits  208  are coupled with the respective exhaust ports  166  and extend generally rearward. The exhaust conduits  208  extend generally parallel to each other. Preferably, the exhaust conduits  208  have a wavy shape that serpentines up and down, as shown in  FIGS. 1 and 2 . Rearward ends of the exhaust conduits  208  preferably extend beyond a rear end of the rear frame section  38 . The muffler  210  is coupled with the rear ends of the exhaust conduits  208 . 
   The muffler  210  preferably has a cylindrical shape. A center axis of the muffler  210  preferably extends in a generally transverse direction relative to the longitudinal center plane LC of the frame  32 . The muffler  210  has a relatively large volume to reduce exhaust energy and noise. An outlet port  212  can be formed at a side surface, which is on a left-hand side in the illustrated embodiment. Other arrangements also can be used. The exhaust gases flow through the exhaust conduits  208  and are discharged through the outlet port  212  of the muffler  210 . 
   The engine  142  can have systems, devices, components and members other than those described above. For example, the illustrated engine  142  can employ a liquid cooling system that uses coolant (e.g., water), which is circulated through a heat exchanger, to cool the engine  142 . 
   With reference to  FIGS. 1-3 , the change speed mechanism and the V-belt transmission mechanism together have a common output shaft  216 . The output shaft  216  extends generally parallel to the crankshaft  176  at a location in front of the crankshaft  176 . The output shaft  216  preferably extends through the crankcase  174  and the V-belt housing  178  and is journaled for rotation relative to these components. Because of this arrangement, the output shaft  216  is positioned at a location generally between the front wheels  56  and the crankshaft  176 . In other words, the crankshaft  176  is positioned between the output shaft  216  and the rear wheels  58 . 
   The crankshaft  176  extends into the V-belt housing  178  and carries a drive pulley  218  ( FIG. 3 ). The output shaft  216  carries a driven pulley  220 . The drive and driven pulleys  218 ,  220  both comprise an axially fixed pulley member and an axially movable pulley member that is movable along the respective axis of the crankshaft  176  or the output shaft  216 . Together, the pulley members form a V-shaped valley that expands and contracts with changes in engine speed. 
   An endless belt  222  or chain, which belt has a V-configuration in section is wound around the drive pulley  218  and the driven pulley  220 . Normally, the movable pulley member of the drive pulley  218  is urged to stay apart from the fixed pulley member by the bias force of a bias member such as, for example, a spring. The movable pulley member of the driven pulley  220  is urged to stay close to the fixed pulley member by the bias force of a bias member such as, for example, a spring. 
   Each movable pulley member can move axially against the bias force by a clutch mechanism which is provided on either pulley  218 ,  220 . The clutch mechanism acts by centrifugal force created when the crankshaft or output shaft turns at a speed higher than a preset speed. The change in diameter of one pulley causes a corresponding change in the other pulley. Thus, both diameters of the drive pulley  218  and the driven pulley  220  vary to automatically change the transmission ratio between the drive pulley  218  and the driven pulley  220 , normally in response to the engine speed. 
   With reference to  FIGS. 1-3 , the V-belt housing  178  preferably has an air inlet port  226  at a rear end and an air outlet port  228  at a front end. An air inlet duct  230  ( FIGS. 1 and 2 ) preferably is coupled to the inlet port  226 , while an air outlet duct  232  preferably is coupled to the outlet port  228 . The inlet duct  230  extends generally rearward and upward and generally behind the seat back  74  on the left-hand side. The inlet duct  230  has an inlet opening  233  that opens forward and is positioned higher than top surfaces of the seat cushions  72 . The outlet duct  232  extends generally upward and rearward and generally along a bottom surface of the seat cushion  72  on the left-hand side. The outlet duct  232  has an outlet opening  234  that opens generally rearward. 
   Cooling air is introduced into the V-belt housing  178  through the inlet duct  230  and the air inlet port  226  when the crankshaft  176 , the output shaft  216  and the drive and driven pulleys  218 ,  220  rotate. In some arrangements, one or both of the pulleys can be provided with fan blades to help induce higher speed air flow as the engine speed increases. Other embodiments can provide a ram air type of air flow. Having circulated with the belt chamber of the transmission, the air then is discharged through the outlet port  228  and the outlet duct  232 . 
   With reference to  FIGS. 1-3 , the engine output that has been transferred to the output shaft  216  through the V-belt mechanism is transferred to the drive mechanism  146  through the change speed transmission mechanism. This mechanism preferably is configured to provide a parking state, a high speed forward state, a neutral state, a low speed forward state, and a reverse state. The mechanism preferably comprises a suitable gear train that allows an operator to select among at least the above-mentioned operating states. A bevel gear assembly  236  can be coupled with the mechanism. 
   The mechanism also comprises a shift lever unit  240  that extends from the crankcase  174 . The shift lever unit  240  preferably is connected to the rest of the switchover mechanism within the crankcase  174  through a suitable linkage (not shown). The shift lever unit  240  preferably is placed generally within the space defined between the seats  68 . The illustrated lever unit  240  is positioned generally at the forward-most portion of the space. Such placement facilitates ease of use. 
   The shift lever unit  240  preferably comprises a lever  244  and a lever cover  246 . The lever  244  preferably is affixed to the frame  32  directly or indirectly for pivotal movement around a fulcrum. In one variation, the shift lever unit  240  can comprise a lever that moves axially. The driver thus can control the change speed mechanism in the crankcase  174  and vary the transmission operating state among at least the parking state, the high speed forward state, the neutral state, the low speed forward state and the reverse state by operating the lever  244 . 
   Because of the advantageous configuration of the drive train relative to the shift lever unit  240 , the shift lever unit  240  is positioned close proximity to the change speed mechanism of the transmission  144 . The linkage thus can be short enough to make the switchover mechanism compact and also to improve the feeling that the driver might have when operating the shift lever unit  240 . 
   With reference to  FIGS. 1-4 , the output of the switchover mechanism is transferred to the drive mechanism  146  through the bevel gear  236 . In the illustrated arrangement, the bevel gear  236  is coupled with a forward intermediate shaft  248 . The forward drive shaft  150  is pivotally coupled to the forward intermediate shaft  248  through a universal joint  250 . That is, the universal joint  250  comprises a first yoke  252 , a second yoke  254  and a cross pin  256  pivotally coupling the first and second yokes  252 ,  254 . 
   The forward driveshaft  150  is coupled with a front differential input shaft  262  ( FIG. 4 ) of the front differential  124 . The front differential housing  122  preferably encloses at least a portion of the input shaft. The front differential input shaft is coupled with a mechanism of the front differential  124 , such as a pinion or differential gear. A pair of output shafts  262  extends from the mechanism of the front differential  124 . Each output shaft  262  is connected to a respective one of the front wheels  56 . 
   Preferably, the gear case  114  of the rack-and-pinion assembly  112  is positioned behind the output shafts  262 . This arrangement advantageously locates the tie-rods and the knuckle arms of the steering system  104  in a space located behind linkages that connect the respective output shafts  263  with the associated front wheels  56 . Thus, the knuckle arms can have a sufficient length and bump steering can be reduced. Further, such a placement provides some degree of protection to these components. 
   With reference to  FIG. 5 , the forward driveshaft  150  extends forwardly within the tunnel defined by the projection  52  of the floorboard  50  and generally adjacent to the middle section  202  of the intake duct  186 . The forward driveshaft  150  thus is positioned higher than the horizontal section  51  of the floorboard  50 . Accordingly, the forward driveshaft  150  is generally protected from significant impacts from rocks, sticks, road debris and the like. In some arrangements, at least a length of a lower opening of the tunnel can be closed with a protective plate or the like to further protect both the driveshaft  150  and the middle section  202  of the intake duct  186 . 
   In the illustrated arrangement, a rear intermediate shaft  258  also is connected to the bevel gear  236  through a suitable connection. The rear driveshaft  152  is connected to the rear intermediate shaft  258  through a spline coupling  260 . Other couplings or a unitary shaft can also be used. The rear driveshaft  152  is coupled with a rear differential input shaft (not shown) of the rear differential  154 . The rear differential input shaft preferably is coupled with the rear wheels  58  through another differential mechanism formed within the rear differential  154 . 
   The off-road vehicle  30  preferably has other devices, components and members. For example, the differentials can be selectively lockable such that the differential function can be eliminated on demand. Moreover, a brake system can be provided to slow or stop rotation of the wheels  56 ,  58  or another driveline component (e.g., the driveshafts). A brake pedal  270  ( FIG. 5 ) can be disposed next to the accelerator pedal  196  and can be connected to brake units that are coupled with the wheels  56 ,  58 . In some arrangements, the brake units can comprise disk brake configurations. The driver thus can stop the off-road vehicle  30  by operating the brake pedal  270 . 
   Various ducts, conduits, cables and the like other than the forward driveshaft  150  and the air intake duct  186 , which are symbolically indicated by a reference numeral  274  of  FIG. 5 , also can extend through the tunnel defined by the projection  52  of the floorboard  50 . For example, a brake cable and a coolant hose can pass therethrough. The brake cable could form a portion of the brake system and connects the brake pedal and brake units disposed at the respective wheels  56 ,  58 . The coolant hose could extend between the engine  142  and a radiator (not shown) that might be disposed under the hood  134  or in another suitable location. Because of this duct and conduit arrangement, those ducts, conduits and cables also can be placed higher than the horizontal section  51  of the floorboard  50  and are well protected without impinging upon the driver and passenger seating areas and without substantially raising the center of gravity of the vehicle. 
   In one arrangement, the crankshaft  176  can be positioned beyond the imaginary rear vertical plane  86 ,  86 A,  86 B and the output shaft  216  can be positioned between the forward vertical plane  84  and the rear vertical plane  86 ,  86 A,  86 B. In the illustrated arrangement, both the output shaft  216  and the crankshaft  176  are disposed between the imaginary forward generally vertical plane  84  and the imaginary rear generally vertical plane  86 . This is also true in the illustrated arrangement even if the imaginary rear vertical plane is defined by the plane  86 B. A majority of the illustrated engine unit  148 , thus, can be located generally below the seat unit  66 . Such an arrangement allows the wheelbase of the off-road vehicle  30  to be shortened in comparison with an arrangement in which a majority of the engine unit  148  is located behind the seat unit  66 . Accordingly, the illustrated off-road vehicle  30  benefits from a substantially shortened wheel base which results in improved maneuverability. 
   In the illustrated arrangement, a majority of the engine unit  148  also is laterally positioned generally between the seats  68 . However, in some arrangement, it may be advantageous to place a majority of the engine unit  148  under one of the seats  68 . The illustrated engine unit  148  can be accommodated in such a position because the cylinder block  158 , the cylinder head  160  and the cylinder head cover  170  are inclined upward. Thus, they can be positioned behind the imaginary rear vertical plane  86 ,  86 A,  86 B by slightly shifting the position of the crankshaft  176 , or the positions of the crankshaft  176  and the output shaft  216 , rearward. In some arrangements, the engine  142  can be disposed generally on its side such that the engine body extends generally horizontally without having a significant portion extending upward. 
   In the illustrated arrangement, the engine  142  is located generally rearward of the change speed mechanism including the output shaft  216 . Moreover, the engine is positioned generally rearward of, and lower than, the seating area. Thus, heat generated by the engine  142  can be substantially isolated from the driver and/or the passenger, and particularly isolated from the feet of those persons both when seating and when mounting or dismounting from the vehicle. The seat backs  74  further insulate the driver and/or passenger from any heat that may radiate from the engine or exhaust system. In addition, the cylinder block  158 , the cylinder head  160  and the cylinder head cover  170  in this arrangement generally are directed rearward and are positioned generally rearward of the occupants. Thus, it is very unlikely that the engine heat will affect the occupants of the vehicle. 
   The exhaust system  168  carries a great deal of heat as well while the intake system  164  and the charge former, e.g., the throttle body  182 , generally do not generate or conduct much heat. The intake system  164  and the charge former are generally protected from heat carried by the exhaust system  168  because the exhaust system  168  is positioned opposite to the intake system  164  in the illustrated arrangement. Thus, the engine heat and the exhaust heat can be generally isolated from the intake system  164  during forward operation of the off-road vehicle  30 . The temperature of the intake air, therefore, is not greatly affected by the heat generated during operation of the off-road vehicle  30  and engine output efficiency can be kept in good condition. Along these lines, placement of a radiator preferably is generally below the air intake such that heat generated in the region of the radiator does not adversely affect engine performance through heating of the air inducted into the engine. 
   Furthermore, in the illustrated intake system  164 , the intake system  164  generally does not extend along a heat generating or conducting surface of the engine  142 . Thus, the engine heat is generally isolated from the intake system  164  in this arrangement. Also, the illustrated air cleaner  188  is greatly spaced from the engine  142 . As such, any air that is heated by the engine  142  and the exhaust system  168  will not be drawn into the air intake system  164 , which improves the engine output efficiency. Additionally, due to the elevated nature of the air inlet and air cleaner  188 , water also is very unlikely to be drawn into the intake system  164 . Furthermore, because the air cleaner  188  is positioned below the hood  134 , water is unlikely to splash its way into the air cleaner. 
   As illustrated, the exhaust conduits  208  extend along a relatively lower portion of the off-road vehicle  30  in the illustrated arrangement because the exhaust conduits  208  are directed generally downward and rearward instead a wrapping around from a forward or lateral surface of the engine. The exhaust conduits  208 , thus, are sufficiently spaced apart from the driver and/or the passenger. As a result, the seats  68  can be positioned closer to the engine  142 , which allows a narrower overall construction for the vehicle or a closer mounting of the split seats  68 . 
   Although the present invention has been described in terms of a certain preferred 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. The scope of the present invention is intended to be defined only by the claims that follow.