Motorcycle

A motorcycle including a radiator and having an engine offset, and in which increase in vehicle width is suppressed. A center of the engine is out of alignment with respect to a center of a head pipe toward one side in the vehicle width direction. The radiator is arranged in front of the engine. Cooling liquid flows in the radiator in the vehicle width direction. A first piping extends rearward from the other end portion of the radiator and a rear end portion of the first piping is connected to the engine. A second piping connects one end portion of the radiator in the vehicle width direction to the engine. The second piping extends from the one end portion of the radiator to the other side of the engine in the vehicle width direction, between the radiator and the engine, and extends rearward of the other side of the engine in the vehicle width direction.

RELATED APPLICATIONS

This application claims the benefit of priority under 35 USC 119 of Japanese patent application no. 2008-104246, filed on Apr. 14, 2008, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motorcycle, and particularly relates to a motorcycle including a radiator.

2. Description of Related Art

A motorcycle including a water-cooled engine is conventionally known.FIG. 9is a plan view of a cooling device of an engine disclosed by Japanese Patent Application Laid-Open No. 2007-077908. The cooling device ofFIG. 9includes a radiator101. Cooling liquid from the radiator101is supplied to the engine via a supply-side piping103. Cooling liquid from the engine is returned to the radiator101via a return-side piping104.

Piping connecting a radiator to an engine is preferably short in order to improve cooling efficiency of the engine or the like. Therefore, as shown inFIG. 9, the supply-side piping103and the return-side piping104are preferably arranged separately on both sides of the engine in a vehicle width direction.

Meanwhile, depending on the specifications of the straddle-type vehicle, a generator is often connected to one end portion of a crankshaft. In such a case, it is often desired to mount an engine such that its center is out of alignment with respect to a center of the vehicle in the vehicle width direction, in order to keep an angle of bank of the motorcycle great. That is, it is often desired to offset the engine from the body frame in the vehicle width direction.

However, if the engine is to be offset from the body frame toward one side in the vehicle width direction, and the supply-side piping and the return-side piping are arranged on both sides of the engine in the vehicle width direction, the vehicle width on one side is disadvantageously large.

SUMMARY OF THE INVENTION

The present invention addresses these issues and suppresses an increase in vehicle width of a motorcycle including a radiator and having an engine offset.

A motorcycle according to the present invention includes a body frame, an engine, a radiator, a first piping and a second piping. The body frame includes a head pipe. The engine is attached to the body frame so that a center of the engine is out of alignment with respect to a center of the head pipe toward one side in the vehicle width direction. The radiator is arranged in front of the engine. A cooling liquid flows in the radiator in the vehicle width direction. The first piping extends rearward from the other end portion of the radiator. A rear end portion of the first piping is connected to the engine. The second piping connects one end portion of the radiator in the vehicle width direction to the engine. The second piping, the engine, the radiator and the first piping form a circulating circuit through which the cooling liquid circulates. The second piping extends from the one end portion of the radiator to the other side of the engine in the vehicle width direction, between the radiator and the engine, and extends rearward of the other side of the engine in the vehicle width direction.

According to the present invention, an increase in vehicle width of a motorcycle including a radiator and having an engine offset is suppressed.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are now described in detail taking a motorcycle as shown inFIG. 1as an example. These embodiments are given only for illustrative purposes only and the present invention is not so limited.

The present invention is not limited to motorcycle1in a narrow sense, and may be another motorcycle, a scooter, a moped, an off-road vehicle or the like. In the present invention, a motorcycle also includes a vehicle having a front wheel and a rear wheel, at least one of which is constituted by a plurality of wheels, and that is tilted to change a traveling direction. In the following description, the front-back and left-right directions are from the perspective of a rider sitting upright on a seat9.

First Embodiment

(Schematic Configuration of Motorcycle1)

FIG. 1is a left side view of the motorcycle1according to a first embodiment of the present invention. As shown inFIG. 1, the motorcycle1includes a body frame10. The body frame10includes a head pipe11and a main frame12. The head pipe11is arranged in a front portion of motorcycle1. The main frame12extends from the head pipe11obliquely rearward and downward.

A steering shaft is rotatably inserted into the head pipe11. A handle13and a pair of front forks14are connected to the steering shaft. A front wheel15is rotatably attached to lower end portions of the paired front forks14. A pivot shaft16is attached to a rear portion of the main frame12. A rear arm17is pivotally attached to the pivot shaft16. A rear wheel18is rotatably attached to a rear end portion of the rear arm17.

An engine20serving as a power source is suspended on the main frame12. A cross-flow-type radiator40is arranged in front of the engine20. A “cross-flow-type radiator” means a radiator in which cooling liquid flows in the vehicle width direction. “Flowing in the vehicle width direction” means flowing from one side to the other side in the vehicle width direction in a plan view, and includes flowing obliquely upward or obliquely downward from one side to the other side in the vehicle width direction. It is to be noted, however, that a so-called turn-flow-type radiator in which cooling liquid flows from one side to the other side in the vehicle width direction and then flows back to the other side in the vehicle width direction is not a “cross-flow-type radiator”.

As shown inFIGS. 2 and 3, a radiator fan41is arranged on a rear surface of the radiator40in order to improve the cooling liquid cooling efficiency of the radiator40when, for example, the motorcycle1halts or has a low speed.

While water is used as the cooling liquid in this embodiment, the cooling liquid is not limited to water. The cooling liquid may be, for example, a mixture of water and a liquid other than water, such as a mixture of water and antifreeze. Furthermore, the cooling liquid may be a liquid in which one or a plurality of solutes is dissolved in one or a plurality of solvents.

In the present embodiment, the engine20is a water-cooled transverse four-cylinder engine. However, the engine is not limited to a specific type as long as it is cooled using cooling liquid. The engine may be, for example, a transverse two-cylinder engine, a transverse three-cylinder engine or a transverse five or more-cylinder engine. Furthermore, the engine may be a single-cylinder engine, an in-line multiple-cylinder engine, a horizontally-opposed multiple-cylinder engine or a V-type multiple-cylinder engine.

An exhaust pipe27is connected to the engine20. An exhaust muffler28is connected to a distal end portion of the exhaust pipe27. Exhaust gas purifying catalyst29is arranged within the exhaust pipe27. Exhaust gas from the engine20is emitted into the external air via the exhaust pipe27and the exhaust muffler28. The exhaust gas is purified by the exhaust gas purifying catalyst29arranged within the exhaust pipe27. Specifically, concentrations of carbon monoxide and NOx in the exhaust gas are reduced.

The exhaust gas purifying catalyst29is not limited to a specific type and may be a conventionally and normally used catalyst. Generally, an exhaust gas purifying catalyst exhibits low catalytic activity at a normal temperature. Therefore, when the motorcycle1starts, the exhaust gas purifying catalyst29exhibits low catalytic activity. In a state in which the engine20is warmed up and the temperature of the exhaust gas purifying catalyst29rises, the exhaust gas purifying catalyst29exhibits high catalytic activity.

(Schematic Structure of Engine20)

Referring mainly toFIGS. 2 and 3, the engine20will be described in detail. As shown inFIG. 3, the engine20includes a crankshaft21that extends in the vehicle width direction and is accommodated in a crankcase22. As shown inFIG. 2, a cylinder member39is attached to a first half part of the crankcase22and extends obliquely upward from the crankcase22toward a front direction. The cylinder member39extends in a direction proximate to the radiator40such that a distance between the radiator40and the cylinder member39narrows in an upward direction.

The cylinder member39includes a body cylinder23attached to the first half part of the crankcase22, and a head cylinder24attached to an upper portion of the body cylinder23. The head cylinder24is located behind the radiator40. An upper end portion of the head cylinder24is located behind radiator fan41attached to a rear surface of the radiator40. Four cylinders are formed in parallel in the body cylinder23. A piston is slidably and displaceably arranged in each of the cylinders. Each piston is connected to the crankshaft21.

As shown inFIG. 3, a generator25is arranged in a left end portion of the crankshaft21. Rotation of the crankshaft21is transmitted to the generator25to drive the generator25. As shown inFIG. 2, a water pump26is arranged in the crankcase22obliquely downward of the generator25.

As shown inFIG. 3, a center axis C1of the engine20is rightward of a center axis C2of the motorcycle1in the vehicle width direction. That is, in the present embodiment, the engine20is offset rightward in the vehicle width direction.

Where the number of cylinders arranged in the vehicle width direction is 2n (n is a natural number), the “center axis of the engine in the vehicle width direction” passes a center between a center axis of an nthcylinder and a center axis of an (n+1)thcylinder from one side in the vehicle width direction, and extends in the front-back direction. For example, in the present embodiment, as the engine20is a transverse four-cylinder engine, the center axis C1passes a center between a center axis of the second cylinder from the right and the third cylinder from the right in the vehicle width direction, and extends in the front-back direction. Further, where the number of cylinders arranged in the vehicle width direction is 2m+1 (m is an integer equal to or greater than 0), the “center axis of the engine in the vehicle width direction” passes a center axis of an (m+1)thcylinder from the right in the vehicle width direction, and extends in the front-back direction. Specifically, in the case of a single-cylinder engine, the center axis of the engine in the vehicle width direction passes a center axis of a cylinder and extends in the front-back direction. In the case of a three-cylinder engine, the center axis of the engine in the vehicle width direction passes a center axis of a cylinder located at a center, and extends in the front-back direction.

Moreover, the “center axis of the straddle-type vehicle in the vehicle width direction” passes a center axis of the head pipe and extends in the front-back direction in a plan view. The center axis C2in the present embodiment passes a center axis of the head pipe11(FIG. 1) and extends in the front-back direction.

As shown inFIG. 3, because the generator25is arranged in the left end portion of the crankshaft21, a distance W2from the center axis C1of the engine20to a left end portion of the engine20is longer than a distance W1from the center axis C1of the engine20to a right end portion of the engine20.

As shown inFIG. 3, a center axis of the radiator40is substantially identical in position to the center axis C1of the motorcycle1in the vehicle width direction. That is, the radiator40is substantially not offset in the vehicle width direction.

A right end of the engine20is substantially flush with a right end of the radiator40in the vehicle width direction, and a left end of the engine20is substantially flush with a left end of the radiator40. More specifically, both ends of the radiator40are located slightly inward of those of the engine20in the vehicle width direction.

As shown inFIGS. 2,3and6, the engine20is connected to the radiator40by a first piping31and a second piping32. The first piping31is connected to the left end portion of the radiator slightly below a central portion of the radiator40in a height direction. As shown inFIG. 2, the first piping31is connected to a lower portion of a second half part of the crankcase22.

As shown inFIG. 3, the second piping32is connected to the right, upper end portion of the radiator40. As shown inFIGS. 2 and 6, the second piping32is connected to the head cylinder24via a thermostat35.

As shown inFIG. 6, cooling water cooled in the radiator40is transferred to the engine20via the first piping31and circulates in the engine20. Cooling water circulating in the engine20is transferred to the radiator40via the second piping32. In this way, the first piping31, the second piping32, the radiator40and the engine20form a circulating circuit30through which cooling liquid circulates.

The first piping31and the second piping32may be directly connected, respectively, to the engine20and the radiator40. Alternatively, the first piping31and the second piping32may be connected to the engine20and the radiator40by joints, for example. Specifically, in the present embodiment, as shown inFIGS. 2 and 6, the first piping31is connected to the radiator40by a joint33and to the crankcase22by a joint34. As shown inFIGS. 3 and 6, the second piping32is connected to the radiator40by a joint36and to the head cylinder24by a joint37, the thermostat35and a joint38. Thermostat35is not shown inFIG. 3for convenience of description.

In the present embodiment, at least one of the first piping31and the second piping32is substantially constituted by resin piping. Specifically, a longer of the first piping31and the second piping32, that is, at least the second piping32is substantially constituted by resin piping. More specifically, in the present embodiment, both the first piping31and the second piping32are constituted by resin piping formed integrally.

The first piping31and the second piping32may be formed integrally or by connecting a plurality of pipings. For example, the first piping31and the second piping32may be formed by connecting a plurality of resin pipings by resin, rubber or metal joints. In the present embodiment, the “piping is substantially constituted by the resin piping” encompasses the piping that is formed by a plurality of resin pipings connected by non-resin joints.

As shown inFIG. 2, the first piping31extends obliquely rearward from the left end portion of the radiator40and downward toward the left of the engine20. The first piping31is connected to the lower portion of the second half part of the crankcase22via below the generator25.

As shown inFIG. 3, the second piping32extends from the right end portion of the radiator40substantially horizontally toward the left of the engine20, between the radiator40and the engine20, in the front-back direction. The second piping32is bent rearward at the diagonally forward left of the engine20. As shown inFIGS. 2 and 3, the second piping32extends rearward at the left of the engine20.

As shown inFIG. 2, the second piping32includes a first piping section32a, a second piping section32band a third piping section32c. The first piping section32aand the second piping section32bconstitute a radiator-side piping section42. The third piping section32cconstitutes an engine-side piping section43.

As shown inFIG. 4, the first piping section32ais connected to the joint36. A left end portion of the first piping section32ais connected to the second piping section32b. As shown inFIG. 2, the first piping section32aextends substantially horizontally to the vehicle width direction between the radiator40and the engine20. Specifically, the first piping section32ais arranged between the head cylinder24and the radiator40and at a position lower than the radiator fan41. Further, as shown inFIG. 3, at least a part of the first piping section32aoverlaps with the cylinder member39in a plan view. Specifically, at least a part of the first piping section32aoverlaps with the head cylinder24in a plan view.

As shown inFIG. 2, the second piping section32bextends from a connection section, in which the second piping section32bis connected to the first piping section32a, substantially linearly obliquely upward and rearward at the left of the engine20. The radiator-side piping section42thereby becomes higher from the radiator40side to the engine20side.

A rear end portion of the second piping section32bis connected to the third piping section32cserving as the engine-side piping section43. A rear end portion of the third piping section32cis connected to a joint37. The third piping section32cextends obliquely downward to rearward at the left of the engine20. A connection section32d, in which the third piping section32cis connected to the second piping section32b, is thereby located at the highest position of the second piping32.

In this way, connection section32din which the second piping section32bis connected to the third piping section32cis located at the highest position of the second piping32. A bleeder piping45is connected to connection section32dvia a joint44and thus is connected to the highest portion of the second piping32. As shown inFIGS. 2 and 3, a front end portion of the bleeder piping45is connected to the left end portion of the upper end portion of the radiator40.

Referring mainly toFIG. 6, a configuration of the circulating circuit30through which cooling water circulates is described in more detail. A main circuit of the circulating circuit30includes the water pump26, a circulation path50, the head cylinder24, the second piping32, the radiator40and the first piping31, all of which are arranged in the engine20.

The circulation path50connects the water pump26to the head cylinder24. Cooling water pressured by the water pump26is transferred to a water jacket formed in the head cylinder24via circulation path50and cools the head cylinder24. The circulation path50may be formed either within the engine20or by piping arranged outside of the engine20.

Cooling water from the head cylinder24is transferred to the radiator40via the thermostat35and the second piping32. The cooling water is cooled in the radiator40and is returned to the water pump26via the first piping31.

The water pump26and the radiator40are also connected to each other by a circulation path51. An oil cooler52is arranged on the circulation path51and is supplied with cooling water. Therefore, the oil cooler52cools lubricating oil supplied to a slide section or the like of the engine20.

Circulating circuit30includes a circulation path53connecting the head cylinder24to the joint44and a circulation path54connecting the head cylinder24to the water pump26. If the thermostat35is closed, cooling water from the head cylinder24flows into the second piping32through the joint44via circulation path53.

The joint44and the radiator40are connected to the radiator40by the bleeder piping45. Air in the second piping32is emitted from the second piping32via bleeder piping45.

In considering the cooling efficiency of the engine20, the first piping31and the second piping32are preferably as short as possible. Therefore, if the engine is offset toward one side in the vehicle width direction as described in the present embodiment, a turn-flow-type radiator is normally used so that the first piping and the second piping are arranged on the other side of the engine in the vehicle width direction.

However, the inventors have found that a turn-flow-type radiator is lower in cooling efficiency than a cross-flow-type radiator. Therefore, even if a turn-flow-type radiator is used and lengths of the first and second pipings are made small by arranging the first and second pipings on the other side of the engine in the vehicle width direction, the cooling liquid cooling efficiency cannot be improved due to deterioration in cooling capability of the radiator itself. As a result, the inventors reached a configuration, as shown in the present embodiment, in which the radiator40is a cross-flow-type radiator and in which both the first piping31and the second piping32are arranged on one side of the engine20in the vehicle width direction. With this configuration, high cooling liquid cooling efficiency is realized and the vehicle width of the motorcycle1is suppressed.

In a transverse multiple-cylinder engine as shown in the present embodiment, in particular, a width of the engine tends to be large. Therefore, the configuration of the present embodiment is particularly effective for such an engine.

It is noted, however, that if the second piping32is led from one side to the other side in the vehicle width direction as shown in the present embodiment, the length of the second piping32becomes large. Therefore, if the second piping section is arranged to be monotonically higher or monotonically lower from, for example, a radiator40side to an engine20side, a tilt angle of the second piping section is small. Consequently, a problem occurs in that air tends to be accumulated in the second piping section.

To solve the problem, in the present embodiment, the second piping32is formed so that the connection section32din which the radiator-side piping section42is connected to the engine-side piping section43is the highest. The bleeder piping45is connected to the connection section32d. Air in the second piping32is thereby gathered in the connection section32dand efficiently emitted from the bleeder piping45. According to the present embodiment, therefore, accumulation of air in the second piping32is suppressed.

Moreover, in the present embodiment, the connection section32dis arranged laterally to the engine20. The bleeder piping45can thereby be arranged laterally to the engine20, such that positional interference among the bleeder piping45, the radiator40and the cylinder member39is suppressed. As compared with, for example, an instance in which the connection section32dand the bleeder piping45are arranged between the engine20and the radiator40, the engine20and the radiator40can be made small in size as a whole.

Iron piping is conventionally and mainly used to connect the engine to the radiator. In a state in which the engine is sufficiently warmed up, the temperature of the cooling liquid is relatively high. Generally, this is considered to efficiently cool high-temperature cooling liquid by a small radiator, by improving the cooling efficiency of the entire cooling liquid circulating circuit including the radiator. The piping connecting the engine to the radiator is thus normally metal piping having high heat conductivity.

If the piping connecting the engine to the radiator is resin piping, for example, a radiation amount from the cooling liquid in the piping is small and the cooling efficiency for cooling the cooling liquid tends to be deteriorated. Considering the cooling efficiency for cooling the cooling liquid, therefore, it is not always preferable to use resin piping to connect the engine to the radiator.

Nevertheless, if iron piping is used to connect the engine to the radiator, cooling liquid warmed by the engine is cooled by the piping connecting the engine to the radiator during warming up of the engine. The time required to warm up the engine therefore tends to be long. As stated above, the exhaust gas purifying catalyst29exhibits low catalytic activity in the low temperature state. Thus, the catalytic activity of the exhaust gas purifying catalyst29is relatively low during warming up of the engine, and it is difficult to reduce emission of exhaust gas that is lower in degree of purification than exhaust gas emitted when the engine is warmed up. Accordingly, it tends to be difficult to comply with recent stricter emission controls.

In this embodiment, by contrast, at least one of the first piping31and the second piping32is constituted by resin piping. During warming up of the engine20, reduction in temperature of cooling liquid in the first piping31and the second piping32is thereby suppressed, and engine20can be warmed up relatively quickly. Accordingly, emission of exhaust gas before the engine20is warmed up that is lower in degree of purification than exhaust gas emitted when the engine20is warmed up is effectively reduced, thereby facilitating compliance with recent stricter emission controls.

In the present embodiment, at least the longer of the first piping31and the second piping32is constituted by resin piping. Reduction in the temperature of cooling liquid in the first piping31and the second piping32is thereby effectively suppressed.

In the present embodiment, both the first piping31and the second piping32may be constituted by resin piping. Reduction in the temperature of cooling liquid in the first piping31and the second piping32is thereby particularly effectively suppressed.

Moreover, in the present embodiment, the radiator40is a cross-flow-type radiator. Cooling efficiency for cooling the cooling liquid is thus high in the radiator40, and high cooling efficiency for cooling the cooling liquid after the engine20is sufficiently warmed up is thereby attained.

In the present embodiment, the first piping section32aoverlaps with the cylinder member39in a plan view. A front-back length of the engine20can thus be reduced. Furthermore, the first piping section32ais arranged at a position lower than the radiator fan41, such that positional interference between the radiator fan41and the first piping section32ais suppressed. As a result, the radiator40and the engine20can be arranged proximately in the front-back direction, and the engine20and the radiator40can therefore be made small in size as a whole.

(Method of Manufacturing Resin Piping)

In the present embodiment, the method of manufacturing the resin piping is not limited to a specific method. The resin piping can be manufactured by, for example, a so-called RFM (RP TOPLA Floating core Molding) formation method such as that disclosed in Japanese Patent No. 3771295 or the like.

If the resin piping is to be manufactured by the RFM formation method, as shown inFIG. 7, a forming die81in which a formation space80substantially identical in external shape to the resin piping to be manufactured is prepared. While the forming die81is kept at a predetermined temperature, molten resin82is filled up in the formation space80. As shown inFIG. 8, by applying gas pressure from a proximal end side of the formation space80, a floating core83substantially identical in inside diameter to the resin piping to be manufactured is moved from the proximal end side to a distal end side of the formation space80, whereby resin piping substantially uniform in thickness is manufactured.

MODIFICATION EXAMPLE

An embodiment has been described in which both the first piping31and the second piping32are constituted by resin piping. However, the first piping31and the second piping32may not necessarily be resin piping. For example, a part of or a front portion of the relatively short first piping31may be made of metal. In addition, both the first piping31and the second piping32may be made of metal.