An engine of a straddle-type vehicle includes first, second, and third cylinders arranged, in this order, from right to left in a front view of the vehicle; first, second, and third intake pipes in communication with the first, second, and third cylinders, respectively; and first, second, and third exhaust pipes in communication with the first, second, and third cylinders, respectively. The first, second, and third exhaust pipes have different lengths and the first, second, and third intake pipes have different lengths.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to straddle-type vehicles.

The present application claims priority to Japanese Patent Application No. 2013-108645 filed in Japan on May 23, 2013, the entire contents of which are hereby incorporated by reference.

2. Description of the Related Art

A straddle-type vehicle including an engine in which three cylinders are arranged in alignment with each other in a lateral direction of the vehicle, i.e., a “parallel three cylinder engine”, is conventionally known. JP 2007-83849 A discloses a motorcycle including a parallel three cylinder engine.

The parallel three cylinder engine disclosed in JP 2007-83849 A includes three exhaust pipes in communication with three cylinders. The exhaust pipes are first extended forward and then bent leftward and downward in a front view of the motorcycle so as to be connected to a bundle portion into which the exhaust pipes are collected. A muffler is connected to the bundle portion.

In a parallel three cylinder engine, when an attempt is made to equalize lengths of three exhaust pipes, flexibility of locating the three exhaust pipes is disadvantageously reduced. Besides, the resulting exhaust pipes might unfavorably be complicated in shape. A conceivable solution to these problems is to allow the three exhaust pipes to have different lengths.

However, merely allowing three exhaust pipes to have different lengths causes combustion variations between cylinders, thus making it impossible for a parallel three cylinder engine to deliver its original performance. Another conceivable solution is to devise an engine control method so as to reduce combustion variations, but devising such a method results in complicated control.

SUMMARY OF THE INVENTION

Accordingly, preferred embodiments of the present invention provide a straddle-type vehicle that includes a parallel three cylinder engine that delivers its original performance without equalizing lengths of the exhaust pipes.

A straddle-type vehicle according to a preferred embodiment of the present invention includes an internal combustion engine that includes a first cylinder, a second cylinder disposed leftward of the first cylinder in a front view of the vehicle, and a third cylinder disposed leftward of the second cylinder in the front view of the vehicle; a first intake pipe in communication with the first cylinder, a second intake pipe in communication with the second cylinder, and a third intake pipe in communication with the third cylinder; and a first exhaust pipe in communication with the first cylinder, a second exhaust pipe in communication with the second cylinder, and a third exhaust pipe in communication with the third cylinder. The first, second, and third exhaust pipes have different lengths. The first, second, and third intake pipes have different lengths.

In the above-described straddle-type vehicle, there is no need to equalize the lengths of the first, second, and third exhaust pipes, thus making it possible to increase the flexibility of locating the first, second, and third exhaust pipes. Besides, the first, second, and third exhaust pipes are easily prevented from being complicated in shape. Unfortunately, when the lengths of the first, second, and third exhaust pipes are different from each other, it is likely that there will occur combustion variations between the cylinders of the internal combustion engine. However, in the above-described straddle-type vehicle, the lengths of the first, second, and third intake pipes are also different from each other. Therefore, it is unnecessary to equalize the lengths of the first, second, and third intake pipes, thus making it possible to set the length of each intake pipe so as to reduce combustion variations between the cylinders without being restricted to the lengths of the other intake pipes. As a result, the parallel three cylinder engine is allowed to deliver its original performance without equalizing the lengths of the first, second, and third exhaust pipes.

According to a preferred embodiment of the present invention, the shortest of the first, second, and third intake pipes is preferably in communication with the cylinder with which the longest of the first, second, and third exhaust pipes is in communication. The longest of the first, second, and third intake pipes is preferably in communication with the cylinder with which the shortest of the first, second, and third exhaust pipes is in communication.

According to the above-described preferred embodiment, it is possible to reduce combustion variations between the cylinders more favorably without performing complicated control.

According to another preferred embodiment of the present invention, the longest of the first, second, and third exhaust pipes preferably is the second exhaust pipe.

According to the above-described preferred embodiment, each of the first, second, and third exhaust pipes is capable of being disposed at a suitable position.

According to still another preferred embodiment of the present invention, the straddle-type vehicle preferably further includes an air cleaner connected to the first, second, and third intake pipes.

According to the above-described preferred embodiment, the first, second, and third intake pipes have different lengths, but are connected to the same air cleaner.

According to yet another preferred embodiment of the present invention, the air cleaner preferably includes a first insertion opening into which the first intake pipe is inserted, a second insertion opening into which the second intake pipe is inserted, and a third insertion opening into which the third intake pipe is inserted. The first intake pipe preferably includes a first opening end disposed inside the air cleaner, the second intake pipe preferably includes a second opening end disposed inside the air cleaner, and the third intake pipe preferably includes a third opening end disposed inside the air cleaner. A length of the first intake pipe from the first insertion opening to the first opening end, a length of the second intake pipe from the second insertion opening to the second opening end, and a length of the third intake pipe from the third insertion opening to the third opening end are preferably different from each other.

According to the above-described preferred embodiment, lengths of portions of the first, second, and third intake pipes which are located outside of the air cleaner do not necessarily have to be different from each other. Consequently, flexibility of locating the first, second, and third intake pipes is increased.

According to still yet another preferred embodiment of the present invention, the internal combustion engine preferably includes a crankcase; a cylinder body that contains the first, second, and third cylinders and is connected to the crankcase; and a cylinder head to which the first, second, and third intake pipes and the first, second, and third exhaust pipes are connected, the cylinder head being connected to the cylinder body. The straddle-type vehicle preferably includes an exhaust manifold which is disposed below the crankcase and to which the first, second, and third exhaust pipes are connected.

According to the above-described preferred embodiment, the exhaust manifold is disposed below the crankcase and, therefore, an overall lateral length of the internal combustion engine and the exhaust manifold are shorter than when the exhaust manifold is disposed rightward or leftward of the crankcase.

According to another preferred embodiment of the present invention, the first cylinder is preferably disposed rightward of a vehicle center line in the front view of the vehicle, and the third cylinder is preferably disposed leftward of the vehicle center line in the front view of the vehicle. The exhaust manifold is preferably disposed rightward or leftward of the vehicle center line in the front view of the vehicle.

According to the above-described preferred embodiment, the exhaust manifold is disposed so as to be deviated to the right or left from the vehicle center line. In such a case, if an attempt is made to equalize the lengths of the first, second, and third exhaust pipes, locations of the exhaust pipes are severely restricted, and shapes of the exhaust pipes are likely to be complicated. Hence, an advantageous effect of the present preferred embodiment of the present invention which reduces combustion variations without equalizing the lengths of the first, second, and third exhaust pipes is particularly pronounced.

According to still another preferred embodiment of the present invention, when one of a rightward end and a leftward end in the front view of the vehicle is defined as a first end and the other end is defined as a second end, the exhaust manifold is preferably disposed closer to the first end than the vehicle center line. The first exhaust pipe preferably includes a portion located closer to the second end than an axis of the first cylinder, the second exhaust pipe preferably includes a portion located closer to the second end than an axis of the second cylinder, and the third exhaust pipe preferably includes a portion located closer to the second end than an axis of the third cylinder.

In order to allow the parallel three cylinder engine to deliver its original performance, it is important to sufficiently ensure the lengths of the first, second, and third exhaust pipes. According to the above-described preferred embodiment, each exhaust pipe has such a shape so as to extend rightward and then extend leftward in the front view of the vehicle, or has such a shape so as to extend leftward and then extend rightward in the front view of the vehicle. Therefore, the length of each exhaust pipe is sufficiently ensured within a small space around the crankcase, the cylinder body, and the cylinder head. As a result, the first, second, and third exhaust pipes are compactly disposed while the original performance of the parallel three cylinder engine is maintained.

According to yet another preferred embodiment of the present invention, each of the first, second, and third exhaust pipes preferably includes a connection that is connected to the exhaust manifold. The connection of the longest of the first, second, and third exhaust pipes is preferably disposed below the connections of the other two exhaust pipes.

According to a preferred embodiment of the present invention, the first, second, and third exhaust pipes are not restricted to being equal in length, and therefore, the connections of the first, second, and third exhaust pipes are easily disposed at such positions. According to the above-described preferred embodiment, the lateral length of the exhaust manifold is shorter than when the connections of the first, second, and third exhaust pipes are arranged in alignment with each other in a lateral direction of the vehicle.

According to still yet another preferred embodiment of the present invention, in the front view of the vehicle, at least one of the first, second, and third exhaust pipes preferably includes a portion that overlaps with the axis of the cylinder with which the adjacent exhaust pipe is in communication.

According to the above-described preferred embodiment, it is possible to further ensure the lengths of the first, second, and third exhaust pipes. Consequently, the internal combustion engine is more likely to deliver its original performance.

According to another preferred embodiment of the present invention, the straddle-type vehicle preferably further includes a first connection pipe connected to the first exhaust pipe and the second exhaust pipe, and a second connection pipe connected to the second exhaust pipe and the third exhaust pipe.

According to the above-described preferred embodiment, the first exhaust pipe and the second exhaust pipe are in communication with each other through the first connection pipe, and the second exhaust pipe and the third exhaust pipe are in communication with each other through the second connection pipe. Thus, pressure fluctuations in the first, second, and third exhaust pipes are reduced, and therefore, fluctuations in the output torque of the internal combustion engine are reduced.

According to still another preferred embodiment of the present invention, the first connection pipe preferably includes a first connection connected to a portion of the first exhaust pipe which is located upstream of a midpoint position of the first exhaust pipe, and a second connection connected to a portion of the second exhaust pipe which is located upstream of a midpoint position of the second exhaust pipe. The second connection pipe preferably includes a first connection connected to a portion of the second exhaust pipe which is located upstream of the midpoint position of the second exhaust pipe, and a second connection connected to a portion of the third exhaust pipe which is located upstream of a midpoint position of the third exhaust pipe.

According to the above-described preferred embodiment, pressure fluctuations in the first, second, and third exhaust pipes are reduced in farther upstream regions thereof. As a result, fluctuations in the output torque of the internal combustion engine are more effectively reduced.

According to yet another preferred embodiment of the present invention, the straddle-type vehicle may be a motorcycle.

Thus, the motorcycle that achieves the above-described effects can be obtained.

Various preferred embodiments of the present invention provide a straddle-type vehicle that includes a parallel three cylinder engine capable of delivering its original performance without equalizing lengths of exhaust pipes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a left side view of a motorcycle (straddle-type vehicle)1according to a preferred embodiment of the present invention, andFIG. 2is a right side view of the motorcycle1. In the following description, unless otherwise specified, “front”, “rear”, “right”, “left”, “up” and “down” indicate front, rear, right, left, up and down with respect to a rider sitting on a seat11of the motorcycle1, respectively. “Up” and “down” correspond to a vertically upward direction and a vertically downward direction when the motorcycle1is brought to a stop on a horizontal plane, respectively. Reference signs “F”, “Re”, “R”, “L”, “Up” and “Dn” in the drawings represent front, rear, right, left, up and down, respectively. It is to be noted that directions defined as viewed from the front of the vehicle may also be used in the following description. When the directions defined as viewed from the front of the vehicle and the directions defined with respect to the rider sitting on the seat11are compared to each other, right and left are reversed. Specifically, left and right defined as viewed from the front of the vehicle correspond to right and left defined with respect to the rider sitting on the seat11, respectively. Reference signs “R′” and “L′” indicate right and left defined as viewed from the front of the vehicle.

As illustrated inFIG. 1, the motorcycle1preferably includes a head pipe2. A handlebar3is supported by the head pipe2so that the handlebar3can be turned to the right and left. A front fork4is connected to a lower end portion of the handlebar3. A front wheel5is rotatably supported by a lower end portion of the front fork4. A body frame6is fixed to the head pipe2. The body frame6preferably includes a main frame7that extends obliquely downward and rearward from the head pipe2in a side view of the vehicle, a seat frame8that extends obliquely upward and rearward from the main frame7in the side view of the vehicle, and a back stay9connected to the main frame7and the seat frame8. A fuel tank10is disposed rearward of the head pipe2, and the seat11is disposed rearward of the fuel tank10. The fuel tank10and the seat11are supported by the body frame6. A rear arm13is rotatably supported by the main frame7. A front end portion of the rear arm13is connected to the main frame7via a pivot shaft12. A rear wheel14is rotatably supported by a rear end portion of the rear arm13.

An internal combustion engine20is supported by the body frame6. The internal combustion engine20is preferably a “parallel three cylinder engine” as will be described below, for example. Hereinafter, the internal combustion engine20will simply be referred to as the “engine20”. The engine20preferably includes a crankcase22, a cylinder body24that extends obliquely upward and forward from the crankcase22, a cylinder head26that extends obliquely upward and forward from the cylinder body24, and a head cover28connected to a front end portion of the cylinder head26. In the present preferred embodiment, the cylinder body24preferably is integral with the crankcase22. Alternatively, the cylinder body24and the crankcase22may be separate components. The engine20preferably includes a drive shaft46that outputs a driving force. The drive shaft46is connected to the rear wheel14via a chain15.

As illustrated inFIG. 3, a first cylinder31, a second cylinder32, and a third cylinder33are provided inside the cylinder body24. The first, second, and third cylinders31,32and33are disposed, in this order, from left to right. When the directions defined with respect to the rider sitting on the seat11and the directions defined as viewed from the front of the vehicle are compared to each other, right and left are reversed. Therefore, the first, second, and third cylinders31,32, and33are disposed in this order from right to left in the front view of the vehicle. The first, second, and third cylinders31,32, and33are arranged in alignment with each other in a lateral direction of the motorcycle1. A piston34is contained in each of the first, second, and third cylinders31,32, and33. Each piston34is connected to a crankshaft36via a connecting rod35. The crankshaft36is contained in the crankcase22.

Concaves27are provided in portions of the cylinder head26which are located above the first, second, and third cylinders31,32, and33. The cylinders31to33, the pistons34, and the concaves27define combustion chambers43. The cylinder head26is provided with intake ports95(seeFIG. 5) and exhaust ports96(seeFIGS. 5 and 6) which are in communication with the combustion chambers43.

A generator37is attached to a left end portion of the crankshaft36. A sprocket39is attached to a right end portion of the crankshaft36. A cam chain41is wound around the sprocket39. A gear42is fixed to a portion of the crankshaft36which is located leftward of the sprocket39.

As illustrated inFIG. 4, the engine20preferably includes a clutch38. The clutch38preferably includes a clutch housing38aand a clutch boss38b. The clutch housing38ais connected to the gear42. A torque of the crankshaft36is transmitted to the clutch housing38avia the gear42. The clutch housing38arotates together with the crankshaft36. A main shaft44is fixed to the clutch boss38b.

The engine20preferably includes a transmission40. The transmission40preferably includes a plurality of gears45provided at the main shaft44, a plurality of gears47provided at the drive shaft46, a shift drum48, and a shift fork49. Upon rotation of the shift drum48, the shift fork49causes the gears45and/or the gears47to move axially, thus changing a combination of the gears45and47which intermesh with each other. As a result, a transmission gear ratio is changed.

The engine20preferably includes a balancer90. The balancer90preferably includes a balancer shaft91, and a balancer weight92provided at the balancer shaft91. A gear93that intermeshes with the gear42is fixed to a right portion of the balancer shaft91. The balancer shaft91is connected to the crankshaft36via the gear42and the gear93. The balancer shaft91is driven by the crankshaft36, and is rotated together with the crankshaft36. A gear94is fixed to a left end portion of the balancer shaft91.

The gear42is preferably press-fitted to the crankshaft36. As mentioned above, the gear42intermeshes with both of the clutch housing38aof the clutch38and the gear93of the balancer90. The gear42preferably includes a press-fitted gear, thus making it possible to reduce an outer diameter of the gear42. A reduction in the outer diameter of the gear42reduces a distance between the crankshaft36and the main shaft44and a distance between the crankshaft36and the balancer shaft91. Note that the crankshaft36, the main shaft44, the drive shaft46and the balancer shaft91extend laterally (i.e., extend in a right-left direction), and are disposed parallel, or substantially parallel, to each other.

The engine20is preferably a water-cooled internal combustion engine, in which at least a portion of which is cooled by cooling water, for example. The engine20preferably includes a water pump52(seeFIG. 6) that conveys cooling water, a radiator54(seeFIG. 7) that cools the cooling water, a thermostat58(seeFIGS. 6 and 7), and an oil cooler56(seeFIGS. 6 and 7). As illustrated inFIG. 4, the water pump52preferably includes, a pump shaft62, and an impeller61fixed to the pump shaft62. A gear63that intermeshes with the gear94is fixed to the pump shaft62. The water pump52is arranged so as to be driven by the balancer shaft91.

As illustrated inFIG. 5, each intake port95preferably includes an inner end portion95aand an outer end portion95b. The inner end portion95afaces the combustion chamber43. An intake valve65is disposed in the intake port95. The intake valve65is arranged to open and close the inner end portion95aof the intake port95. A fuel injection valve67is disposed between the inner end portion95aand the outer end portion95bof the intake port95. The fuel injection valve67injects fuel into the intake port95. It is to be noted that a fuel supply device of the engine20is not limited to the fuel injection valve67that injects fuel into the intake port95, but may alternatively be a fuel injection valve that injects fuel into the combustion chamber43. The fuel supply device is not limited to a fuel injection valve, but may alternatively be a carburetor.

A throttle body53that contains a throttle valve29is connected to the outer end portion95bof the intake port95. The throttle valve29is provided for each of the cylinders31to33. The engine20includes the three cylinders31to33and therefore includes three throttle valves29. The throttle bodies53that contain the throttle valves29may be separate components or may be integral with each other. In the present preferred embodiment, the throttle bodies53preferably are separate components, and the three throttle bodies53in total are disposed from right to left, for example.

As illustrated inFIGS. 5 and 6, a first intake pipe121, a second intake pipe122, and a third intake pipe123are connected to the right, center, and left throttle bodies53in the front view of the vehicle, respectively. The first, second, and third intake pipes121,122, and123are in communication with the first, second, and third cylinders31,32, and33, respectively. As illustrated inFIG. 6, the first, second, and third intake pipes121,122, and123are disposed in this order from right to left and extend upward in the front view of the vehicle. As illustrated inFIG. 5, the intake pipes121to123extend obliquely upward and rearward from the throttle bodies53and then bend obliquely upward and forward in the side view of the vehicle. An end portion of each of the intake pipes121to123has a funnel-like shape. In other words, the end portion of each of the intake pipes121to123has an increased diameter toward its extremity.

An air cleaner59is disposed above the cylinder head26and the head cover28. The air cleaner59preferably includes a lower case59A, an upper case59B fixed to the lower case59A, and an element59C disposed inside the lower case59A and the upper case59B. The lower case59A and the upper case59B define an air cleaner case59D. It is to be noted that the air cleaner case59D is not limited to any particular constituent component (s). Three insertion openings59dare provided in a rear portion of the air cleaner case59D. In this preferred embodiment, the insertion openings59dare provided in the lower case59A. Alternatively, the insertion openings59dmay be provided in the upper case59B. As illustrated inFIG. 6, the three insertion openings59dare arranged from right to left in the front view of the vehicle. In the front view of the vehicle, the first intake pipe121is inserted into the right insertion opening59d, the second intake pipe122is inserted into the center insertion opening59d, and the third intake pipe123is inserted into the left insertion opening59d. In the following description, the terms “right”, “center” and “left” used for the insertion openings59drefer to right, center and left in the front view of the vehicle, respectively.

An opening end121aof the first intake pipe121, an opening end122aof the second intake pipe122, and an opening end123aof the third intake pipe123are opened inside the air cleaner case59D. As illustrated inFIG. 5, lengths of the three intake pipes121to123from the insertion openings59dto the opening ends121ato123aare different from each other. More specifically, a length L2between the opening end122aof the second intake pipe122and the center insertion opening59dis shorter than a length L1between the opening end121aof the first intake pipe121and the right insertion opening59d. A length L3between the opening end123aof the third intake pipe123and the left insertion opening59dis longer than the length L1between the opening end121aof the first intake pipe121and the right insertion opening59d.

As illustrated inFIG. 6, each of the first, second, and third intake pipes121,122, and123preferably includes a portion located inside of the air cleaner case59D and a portion located outside of the air cleaner case59D. Hereinafter, inside of the air cleaner case59D and outside of the air cleaner case59D will simply be referred to as “inside of the air cleaner59” and “outside of the air cleaner59”, respectively. A portion121A of the first intake pipe121located outside of the air cleaner59, a portion122A of the second intake pipe122located outside of the air cleaner59, and a portion123A of the third intake pipe123located outside of the air cleaner59are equal in length. A portion121B of the first intake pipe121located inside of the air cleaner59, a portion122B of the second intake pipe122located inside of the air cleaner59, and a portion123B of the third intake pipe123located inside of the air cleaner59have different lengths. Therefore, the first, second, and third intake pipes121,122, and123have different lengths. The second intake pipe122is shorter than the first intake pipe121, and the third intake pipe123is longer than the first intake pipe121. Of the three intake pipes121to123, the third intake pipe123is the longest, and the second intake pipe122is the shortest.

As illustrated inFIG. 5, the first, second, and third intake pipes121,122, and123are equal in diameter. The first, second, and third intake pipes121,122, and123are disposed so that axes thereof correspond to each other in the side view of the vehicle. It is to be noted that dimensions and locations of the first, second, and third intake pipes121,122, and123may be changed as appropriate.

As illustrated inFIG. 5, each exhaust port96preferably includes an inner end portion96aand an outer end portion96b. The inner end portion96afaces the combustion chamber43. An exhaust valve66is disposed in the exhaust port96. The exhaust valve66is arranged to open and close the inner end portion96aof the exhaust port96. An exhaust pipe connection port97is provided at the outer end portion96bof the exhaust port96.

As illustrated inFIG. 6, the engine20preferably includes a first exhaust pipe101, a second exhaust pipe102, and a third exhaust pipe103each connected to the associated exhaust pipe connection port97. The first, second, and third exhaust pipes101,102and103are in communication with the first, second, and third cylinders31,32, and33, respectively. The exhaust pipe connection ports97are provided at a front portion of the cylinder head26, and therefore, upstream end portions of the first, second, and third exhaust pipes101,102, and103are connected to the front portion of the cylinder head26. The first, second, and third exhaust pipes101,102, and103have different lengths. More specifically, the second exhaust pipe102is longer than the first exhaust pipe101, and the third exhaust pipe103is shorter than the first exhaust pipe101.

As illustrated inFIG. 8, in the side view of the vehicle, the first exhaust pipe101preferably includes an upper portion101A that extends obliquely downward and forward from the cylinder head26, first and second intermediate portions101B and101C that extend obliquely downward and rearward from the upper portion101A, and a lower portion101D that extends rearward from the second intermediate portion101C. As illustrated inFIGS. 7 and 8, in the side view of the vehicle, the second exhaust pipe102preferably includes an upper portion102A that extends obliquely downward and forward from the cylinder head26, first and second intermediate portions102B and102C that extend obliquely downward and rearward from the upper portion102A, and a lower portion102D that extends rearward from the second intermediate portion102C. As illustrated inFIG. 7, in the side view of the vehicle, the third exhaust pipe103preferably includes an upper portion103A that extends obliquely downward and forward from the cylinder head26, first and second intermediate portions103B and103C that extend obliquely downward and rearward from the upper portion103A, and a lower portion103D that extends rearward from the second intermediate portion103C. As illustrated inFIG. 6, in the front view of the vehicle, the first intermediate portions101B,102B, and103B extend obliquely downward and rightward, and the second intermediate portions101C,102C, and103C extend obliquely downward and leftward.

As illustrated inFIG. 6, the first intermediate portion101B and the second intermediate portion101C of the first exhaust pipe101are at least partially located rightward of an axis31cof the first cylinder31in the front view of the vehicle. The first intermediate portion102B and the second intermediate portion102C of the second exhaust pipe102are at least partially located rightward of an axis32cof the second cylinder32in the front view of the vehicle. The first intermediate portion103B and the second intermediate portion103C of the third exhaust pipe103are at least partially located rightward of an axis33cof the third cylinder33in the front view of the vehicle. In this manner, in the front view of the vehicle, the first exhaust pipe101preferably includes a portion located rightward of the axis31cof the cylinder31with which the exhaust pipe101is in communication, the second exhaust pipe102preferably includes a portion located rightward of the axis32cof the cylinder32with which the exhaust pipe102is in communication, and the third exhaust pipe103preferably includes a portion located rightward of the axis33cof the cylinder33with which the exhaust pipe103is in communication.

The first intermediate portion102B and the second intermediate portion102C of the second exhaust pipe102partially overlap with the axis31cof the first cylinder31in the front view of the vehicle. The first intermediate portion103B and the second intermediate portion103C of the third exhaust pipe103partially overlap with the axis32cof the second cylinder32in the front view of the vehicle.

The first exhaust pipe101and the second exhaust pipe102are connected to each other through a first connection pipe105and are in communication with each other via the first connection pipe105. The second exhaust pipe102and the third exhaust pipe103are connected to each other through a second connection pipe106and are in communication with each other via the second connection pipe106. The first connection pipe105preferably includes a first connection105aconnected to a portion of the first exhaust pipe101which is located upstream of a midpoint position of the first exhaust pipe101, and a second connection105bconnected to a portion of the second exhaust pipe102which is located upstream of a midpoint position of the second exhaust pipe102. The second connection pipe106preferably includes a first connection106aconnected to a portion of the second exhaust pipe102which is located upstream of the midpoint position of the second exhaust pipe102, and a second connection106bconnected to a portion of the third exhaust pipe103which is located upstream of a midpoint position of the third exhaust pipe103. Note that the “midpoint positions of the first, second, and third exhaust pipes101,102, and103” refer to midpoint positions of the first, second, and third exhaust pipes101,102, and103in longitudinal directions thereof. The midpoint positions of the first, second, and third exhaust pipes101,102, and103correspond to midpoints between upstream ends of the first, second, and third exhaust pipes101,102, and103which are connected to the exhaust pipe connection ports97, and connections101E,102E, and103E which define downstream ends of the first, second, and third exhaust pipes101,102, and103and will be described below. It is to be noted that the connections of the first connection pipe105and the second connection pipe106are not limited to any particular positions. Either or both of the first connection pipe105and the second connection pipe106may be omitted.

An exhaust manifold68is disposed below the crankcase22. The exhaust manifold68is disposed leftward of a vehicle center line CL in the front view of the vehicle. Note that the term “vehicle center line CL” refers to a line that passes through a lateral center of the motorcycle1and coincides with a center line of the front wheel5and a center line of the rear wheel14. The connections101E,102E, and103E of the first, second, and third exhaust pipes101,102, and103are connected to the exhaust manifold68. As illustrated inFIG. 2, a muffler110is connected to a rear end portion of the exhaust manifold68.

The connection101E of the first exhaust pipe101is located rightward of the connection103E of the third exhaust pipe103in the front view of the vehicle. The connection102E of the second exhaust pipe102is disposed below the connection101E of the first exhaust pipe101and the connection103E of the third exhaust pipe103. The connection102E of the second exhaust pipe102is disposed obliquely downward and leftward of the connection101E of the first exhaust pipe101, and obliquely downward and rightward of the connection103E of the third exhaust pipe103in the front view of the vehicle.

As illustrated inFIG. 8, the radiator54is disposed forward of the engine20. The radiator54is disposed forward of the cylinder body24, the cylinder head26, and the head cover28. The radiator54is inclined forward. An upper end portion of the radiator54is located forward of a lower end portion of the radiator54. A fan55is disposed rearward of the radiator54.

As illustrated inFIG. 7, a front end102fof the second exhaust pipe102is located forward of a rear end54bof the radiator54in the side view of the vehicle. As used herein, the terms “front end” and “rear end” refer to a foremost portion and a rearmost portion, respectively. A front end103fof the third exhaust pipe103is located rearward of the rear end54bof the radiator54. As illustrated inFIG. 8, a front end101fof the first exhaust pipe101is located rearward of the rear end54bof the radiator54in the side view of the vehicle. Of the first to third exhaust pipes101to103, the second exhaust pipe102which is the longest extends farthest forward. Furthermore, of the first to third exhaust pipes101to103, the second exhaust pipe102which is the longest extends farthest downward.

As illustrated inFIG. 6, the thermostat58is disposed rightward of the vehicle center line CL in the front view of the vehicle. The thermostat58is disposed forward of the engine20. The thermostat58is disposed forward of the crankcase22and the cylinder body24. The oil cooler56is attached to the crankcase22. The oil cooler56is disposed forward of the crankcase22.

A portion of the third exhaust pipe103is disposed forward of the oil cooler56. A portion of the second exhaust pipe102is disposed forward of the thermostat58. Another portion of the second exhaust pipe102is disposed forward of an oil filter57.

A cooling water passage (not illustrated) through which cooling water flows is provided inside the engine20. An outlet80oof the cooling water passage is provided at a front portion of the cylinder body24. The engine20preferably includes water piping72A connected to the outlet80oand an inlet54i(seeFIG. 7) of the radiator54, water piping73A connected to an outlet54o(seeFIG. 8) of the radiator54and the thermostat58, water piping73B connected to the thermostat58and a suction port52i(seeFIG. 8) of the water pump52, water piping74A connected to the outlet80oof the cooling water passage and the oil cooler56, and water piping74B connected to the oil cooler56and the thermostat58.

As illustrated inFIG. 7, a portion of the water piping72A is disposed rearward of a portion of the third exhaust pipe103and forward of the cylinder body24. As illustrated inFIG. 8, a portion of the water piping73B is disposed rearward of the first exhaust pipe101and forward of the cylinder body24. As illustrated inFIG. 6, a portion of the water piping74A is disposed rearward of a portion of the third exhaust pipe103and forward of the crankcase22and the cylinder body24. A portion of the water piping74B is disposed rearward of a portion of the second exhaust pipe102and a portion of the third exhaust pipe103and forward of the crankcase22and the cylinder body24.

As described above, the motorcycle1according to the present preferred embodiment preferably includes the parallel three cylinder engine20, for example. In the parallel three cylinder engine20, if an attempt is made to equalize the lengths of the three exhaust pipes101to103, flexibility of locating the exhaust pipes101to103might be reduced, and/or the exhaust pipes101to103might be complicated in shape. However, in the present preferred embodiment, the three exhaust pipes101to103have different lengths. According to the present preferred embodiment, it is unnecessary to equalize the lengths of the three exhaust pipes101to103, thus making it possible to increase the flexibility of locating the exhaust pipes101to103and to prevent the exhaust pipes101to103from being complicated in shape.

Unfortunately, merely allowing the exhaust pipes101to103to have different lengths is likely to cause combustion variations between the cylinders31to33, thus making it difficult for the parallel three cylinder engine20to deliver its original performance. However, in the present preferred embodiment, the three intake pipes121to123have different lengths. According to the present preferred embodiment, it is unnecessary to equalize the lengths of the three intake pipes121to123, thus making it possible to set the length of each of the intake pipes121to123without being restricted by the lengths of the other intake pipes.

According to the present preferred embodiment, the second intake pipe122that is the shortest of the three intake pipes121to123is in communication with the second cylinder32with which the second exhaust pipe102that is the longest of the three exhaust pipes101to103is in communication. The third intake pipe123that is the longest of the three intake pipes121to123is in communication with the third cylinder33with which the third exhaust pipe103that is the shortest of the three exhaust pipes101to103is in communication. Consequently, it is possible to suitably reduce combustion variations between the cylinders31to33without performing complicated control.

The second exhaust pipe102, which is the longest of the three exhaust pipes101to103, is in communication with the second cylinder32, i.e., the center one of the three cylinders31to33. The second exhaust pipe102, which is the longest of the three exhaust pipes101to103, is centrally disposed, thus making it easy to suitably dispose the exhaust pipes101to103so that interference therebetween is prevented.

The first, second, and third intake pipes121,122and123have different lengths but are connected to the same air cleaner59. The first, second, and third intake pipes121,122, and123are inserted into the air cleaner59through the insertion openings59d. The opening end121aof the first intake pipe121, the opening end122aof the second intake pipe122, and the opening end123aof the third intake pipe123are disposed inside the air cleaner59. As illustrated inFIG. 5, the length L1between the opening end121aand the insertion opening59d, the length L2between the opening end122aand the insertion opening59d, and the length L3between the opening end123aand the insertion opening59dare different from each other. Thus, the portions of the intake pipes121to123which are disposed inside of the air cleaner59have different lengths, and therefore, the portions of the intake pipes121to123which are located outside of the air cleaner59do not need to have different lengths. As a result, the flexibility of locating the intake pipes121to123is increased.

The length L2between the opening end122aand the insertion opening59dis shorter than the length L1between the opening end121aand the insertion opening59dand is also shorter than the length L3between the opening end123aand the insertion opening59d. As illustrated inFIG. 6, the portion122B of the centrally-disposed second intake pipe122located inside of the air cleaner59is shorter than the portion121B of the first intake pipe121located inside of the air cleaner59and is also shorter than the portion123B of the third intake pipe123located inside of the air cleaner59. Therefore, as illustrated inFIG. 9, a concave59Dm may be provided in the center of the air cleaner case59D. During traveling, the rider of the motorcycle1may lean forward in order to reduce air resistance received by his or her body. When the air cleaner59is disposed forward of the seat11, the rider is allowed to lean forward easily by providing the concave59Dm in the air cleaner case59D.

As illustrated inFIG. 6, the engine20preferably includes the exhaust manifold68to which the three exhaust pipes101to103are connected. The exhaust manifold68is disposed below the crankcase22, and therefore, an overall lateral length of the engine20and the exhaust manifold68is shorter than when the exhaust manifold68is disposed rightward or leftward of the crankcase22. As a result, slimming of the motorcycle1including the parallel three cylinder engine20is facilitated.

As mentioned above, the left and right inFIG. 3correspond to the right and left in the front view of the vehicle. As illustrated inFIG. 3, the first cylinder31is disposed rightward of the vehicle center line CL in the front view of the vehicle, and the third cylinder33is disposed leftward of the vehicle center line CL in the front view of the vehicle. As illustrated inFIG. 6, the exhaust manifold68is disposed leftward of the vehicle center line CL in the front view of the vehicle. When the exhaust manifold68is disposed so as to be deviated to the left in this manner, a distance between the left exhaust pipe connection port97and the exhaust manifold68and a distance between the right exhaust pipe connection port97and the exhaust manifold68are different from each other. Hence, if an attempt is made to equalize the lengths of the three exhaust pipes101to103, the locations of the exhaust pipes101to103are severely restricted, and the exhaust pipes101to103are likely to be complicated in shape. However, according to the present preferred embodiment, it is possible to reduce combustion variations between the cylinders31to33without equalizing the lengths of the exhaust pipes101to103as mentioned above. Consequently, in the parallel three cylinder engine20, the exhaust manifold68is easily disposed so as to be deviated to the left. By the same token, the exhaust manifold68may be disposed rightward of the vehicle center line CL in the front view of the vehicle.

As illustrated inFIG. 6, in the front view of the vehicle, the exhaust manifold68is disposed leftward of the vehicle center line CL, and the three exhaust pipes101to103preferably include portions located rightward of the axes31cto33cof the cylinders31to33with which the exhaust pipes101to103are in communication, respectively. In order to allow the engine20to deliver its original performance, it is important to sufficiently ensure the lengths of the exhaust pipes101to103. The exhaust pipes101to103each have such a shape so as to extend rightward and then extend leftward in the front view of the vehicle. Therefore, the lengths of the exhaust pipes101to103are sufficiently ensured within a small space around the crankcase22, the cylinder body24, and the cylinder head26. As a result, the exhaust pipes101to103are compactly disposed while the original performance of the engine20is maintained.

Alternatively, in the front view of the vehicle, the exhaust manifold68may be disposed rightward of the vehicle center line CL, and the three exhaust pipes101to103may include portions located leftward of the axes31cto33cof the cylinders31to33with which the exhaust pipes101to103are in communication, respectively. Also in that case, the exhaust pipes101to103are compactly disposed while the original performance of the engine20is maintained.

In the front view of the vehicle, the second exhaust pipe102preferably includes a portion that overlaps with the axis31cof the first cylinder31with which the adjacent first exhaust pipe101is in communication. In the front view of the vehicle, the third exhaust pipe103preferably includes a portion that overlaps with the axis32cof the second cylinder32with which the adjacent second exhaust pipe102is in communication. Such a structure makes it possible to sufficiently ensure the lengths of the second exhaust pipe102and the third exhaust pipe103.

The exhaust pipes101to103preferably include the connections101E to103E connected to the exhaust manifold68, respectively. The connection102E of the second exhaust pipe102that is the longest of the exhaust pipes101to103is disposed below the connection101E of the exhaust pipe101and the connection103E of the exhaust pipe103. According to the present preferred embodiment, the exhaust pipes101to103are not restricted to being equal in length, and therefore, the connections101E to103E of the exhaust pipes101to103can be easily disposed at such positions. The lateral length of the exhaust manifold68is shorter than when the connections101E to103E of the three exhaust pipes101to103are arranged in alignment with each other in the lateral direction of the motorcycle1.

As illustrated inFIG. 6, the first exhaust pipe101and the second exhaust pipe102are connected to each other through the first connection pipe105, and the second exhaust pipe102and the third exhaust pipe103are connected to each other through the second connection pipe106. Thus, pressure fluctuations in exhaust gas inside the first, second, and third exhaust pipes101,102, and103are reduced, and therefore, fluctuations in output torque of the engine20are reduced.

The connections of the first connection pipe105may be located at any appropriate positions. For example, in the present preferred embodiment, the first connection105aof the first connection pipe105is connected to the portion of the first exhaust pipe101which is located upstream of the midpoint position of the first exhaust pipe101, and the second connection105bof the first connection pipe105is connected to the portion of the second exhaust pipe102which is located upstream of the midpoint position of the second exhaust pipe102. The connections of the second connection pipe106may be located at any appropriate positions. For example, in the present preferred embodiment, the first connection106aof the second connection pipe106is connected to the portion of the second exhaust pipe102which is located upstream of the midpoint position of the second exhaust pipe102, and the second connection106bof the second connection pipe106is connected to the portion of the third exhaust pipe103which is located upstream of the midpoint position of the third exhaust pipe103. Thus, pressure fluctuations in the exhaust pipes101to103are reduced in farther upstream regions thereof. As a result, fluctuations in the output torque of the engine20are more effectively reduced.

In the present preferred embodiment, the term “intake pipes” refers to air passages between the throttle bodies53and the opening ends121ato123ainside the air cleaner59. In the present preferred embodiment, the intake pipes121to123are each preferably provided by a single pipe member, for example. Alternatively, one or two or more of the intake pipes121to123may be provided by a plurality of pipe members.

In the present preferred embodiment, the term “exhaust pipes” refers to exhaust gas passages between the exhaust pipe connection ports97of the cylinder head26and the exhaust manifold68. In the present preferred embodiment, the exhaust pipes101to103are each preferably provided by a single pipe member, for example. Alternatively, one or two or more of the exhaust pipes101to103may be provided by a plurality of pipe members.

As illustrated inFIG. 6, in the present preferred embodiment, the air cleaner case59D is provided with the three separate insertion openings59d, and thus the three insertion openings59dinto which the intake pipes121to123are inserted are independent of one another. Alternatively, the two or three insertion openings59dmay be provided continuously. For example, the three insertion openings59dinto which the intake pipes121to123are inserted may be continuous with each other, so that the air cleaner case59D is apparently provided with a single opening. In other words, the three insertion openings59dmay be combined into a single opening. Herein, irrespective of the apparent number of the openings, the three insertion openings59dexist so long as the three intake pipes121to123are inserted thereinto.

In the present preferred embodiment, the three insertion openings59dare preferably arranged in the lateral direction of the motorcycle1. However, the locations of the three insertion openings59dare not limited to any particular locations. For example, one of the insertion openings59dmay be located above or below the other insertion openings59d.

The straddle-type vehicle according to the present preferred embodiment is a “street” motorcycle1. Alternatively, the straddle-type vehicle may be any other type of motorcycle other than a street motorcycle. The term “straddle-type vehicle” refers to a vehicle that a rider straddles when getting on the vehicle. The straddle-type vehicle is not limited to the motorcycle1, but may be any other vehicle such as an ROV (Recreational Off-Highway Vehicle), for example.

The engine20is not limited to a water-cooled engine, but may be an air-cooled engine.