Motorcycle

A motorcycle including a body frame 1 and an engine 20 mounted to the body frame 1, wherein the body frame 1 includes: left and right frame members (tank rails) 3 and 3 provided on one and the other sides in the vehicle width direction; a cross member 50 for connecting the left and right frame members with each other; and a bracket 53 provided into one body with the cross member 50, wherein a cylinder part (a cylinder head) 24 of the engine 20 is directly mounted to the bracket 53.

RELATED APPLICATIONS

This application is a U.S. national phase application of PCT/JP2006/322950, filed on Nov. 17, 2006, and claims the benefit of priority under 35 USC 119 of Japanese patent application no. 2005-332348, filed on Nov. 17, 2005, which applications are hereby incorporated by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a motorcycle comprising a body frame and an engine mounted to the body frame.

2. Description of Related Art

In a motorcycle, to improve the engine supporting rigidity of a body frame, an engine may be mounted in a space enclosed by left and right tank rails and left and right down tubes, and may be fixed to the left and right tank rails and down tubes through a separate bracket (refer to Japanese Patent No. 2,903,231, for example).

In a conventional motorcycle, the left and right tank rails and down tubes are used for supporting an engine. This causes a problem in that the number of components and the weight of the vehicle body increase, although supporting rigidity can be secured.

In order to solve such a problem, removal of the down tubes may be considered. When the down tubes are removed in a conventional structure in which left and right tank rails support the engine through a separate bracket, however, the rigidity in supporting the engine is likely to be deteriorated.

SUMMARY OF THE INVENTION

In view of the above, the invention provides a motorcycle with a reduced number of components and vehicle body weight, while achieving the necessary rigidity in supporting an engine.

The invention is a motorcycle including a body frame and an engine mounted to the body frame. The body frame comprises left and right frame members in the vehicle width direction; a cross member connecting the left and right frame members; and a bracket provided into one body with the cross member. A cylinder part of the engine is directly mounted to the bracket.

In the invention, the cylinder part is a collective term for a cylinder block, a cylinder head and a head cover. Further, integrating a bracket with a cross member means forming a bracket into one body with a cross member by welding, casting, pressing, forging or the like.

In accordance with the motorcycle according to the invention, a bracket is integrated with a cross member for connecting left and right frame members and a cylinder part of an engine is directly mounted to the bracket, so that a body frame directly supports an upper part of the engine and necessary rigidity in supporting the engine is secured. This allows the down tubes to be removed, and thereby, the number of components and the weight of the vehicle body is reduced.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention will be described hereinafter on the basis of the attached drawings.

FIGS. 1 to 7illustrate a motorcycle in accordance with an embodiment of the invention. Front, rear, left and right in this description are directions from the perspective of a person sitting on a seat. Upper and lower parts in this description are upper and lower parts relative to a direction vertical to a road surface.

In the drawings,1denotes a body frame of a motorcycle. The body frame1comprises a head pipe2, left and right tank rails (frame members)3extending obliquely downward from the head pipe2toward the rear of the vehicle, rear arm brackets4extending downward from rear ends of the tank rails3, left and right seat rails5extending obliquely upward from the tank rails3toward the rear of the vehicle and left and right seat stays6bridged between rear parts of the seat rails5and the rear arm brackets4.

The head pipe2holds a front fork7so that the front fork7can be steered left and right. A front wheel8is rotatably held at the lower end of the front fork7. A steering handle9is mounted on the upper end. A headlight15is provided on the front side of the head pipe2. A meter device16such as a speedometer is provided at the upper part of the headlight15.

The left and right rear arm brackets4hold the front end part of a rear arm10so that the rear arm10can vertically swing. The rear end part of the rear arm10rotatably holds the rear wheel11.

A fuel tank12is mounted on the left and right tank rails3. A double seat13is mounted on the left and right seat rails5.

A water-cooling type engine20is mounted under the left and right tank rails3. The engine20comprises a cylinder block23, a cylinder head24and head cover25piled on the upper mating surface of a crank case22in which a crank shaft21is housed, and a bolt is fastened in the piled components for connection.

A transmission case22afor having a change gear (not shown) built in is formed into one body with the crank case22at the rear part of the crank case22. The rear wheel11is driven for rotation through a chain26aby a drive shaft26provided on the rear part of the transmission case22a.

A front wall part of the cylinder head24is connected to an exhaust pipe27. The exhaust pipe27extends downward from the front wall part to pass under the engine20toward the rear part of the vehicle. The exhaust pipe27is connected to a muffler28provided on the right side of the rear wheel11.

A rear wall part of the cylinder head24is connected to an intake pipe29. The intake pipe29extends rearward under the fuel tank12to be connected to an air cleaner (not shown).

A radiator30is provided on the upper-front part of the engine20. Left and right upper wall parts of the radiator30are fixed to radiator brackets32mounted to the lower surface of the left and right tank rails3by fastening a bolt. A lower end part on the left side is fixed to the cylinder head24through the arm bracket31by fastening a bolt.

The left and right seat rails5and the seat stays6are covered with left and right side covers38made of resin. The side covers38are substantially in the shape of a reverse triangle in which a front edge38aextends along the upper surface of the tank rail3, an upper edge38bextends along the lower edge parts of the fuel tank12and the seat13and a lower edge38cextends along the seat stay6in a side view of the vehicle.

Front covers40made of resin are provided on the outer sides of the left and right tank rails3. Front covers40function as an air scoop for introducing running wind into the radiator30.

Tank rails3are formed from welded plural metal plates and have a cross section in the shape of a rectangle whose dimension in the vertical direction is larger than in the width direction. Tank rails3gradually become larger in dimension in the vertical direction from the rear side to the front side. The height of the front end parts3aof tank rails3in the vertical direction is substantially equal to the height of the head pipe2in the axial direction. This allows the strength in connection between tank rails3and the head pipe2and the rigidity to be improved, so that endurance against a large bending moment operating on the connecting part between the head pipe2and tank rails3can be achieved.

Tank rails3include inside inclined parts3bhaving an interval therebetween that widens in the vehicle width direction from the head pipe2toward the rear part of the vehicle in a plan view, and straight line parts3cextending substantially straight from rear ends of the inside inclined parts3bto the rear part of the vehicle. The front end parts3aof inside inclined parts3band3bare welded to the head pipe2for bonding. An interior angle of inside inclined parts3band3bis set at around 60 degrees.

Upper and lower gussets33and34, which are in the shape of a triangle in plan view, are welded for bonding on the upper and lower sides of the left and right inside inclined parts3band3b. The gussets function as a reinforcing member. The upper gusset33is a flat plate. The lower gusset34includes a flat bottom wall34aand a vertical wall34brising upward from a rear edge of the bottom wall34a. A resonator chamber for secondary air (not shown) is provided in a space enclosed by the head pipe2and the upper and lower gussets33and34.

A lateral gusset35functioning as a reinforcing member is provided on inner wall surfaces of the left and right tank rails3. The lateral gusset35is in the shape of a bar having a U-shaped horizontal cross-section. The lateral gusset35extends from the rear part of the inside inclined parts3bof tank rails3to the vicinity of the front end part of the straight part3cin an axial direction of tank rails3and in a direction away from the head pipe2. Opening edges of the U-shaped lateral gusset35are welded on the inner wall surfaces of the tank rails3. The front end part35ais welded to the vertical wall34bof the lower gusset34for bonding.

A reservoir tank36for supplying the radiator30with cooling water is provided on a front side part of a middle cross member51, which is provided between the left and right tank rails3and is mentioned later. The reservoir tank36is offset to the left with respect to a center line of the vehicle body C so as to be provided along the inside of the left tank rail3(refer toFIG. 7). Removing a maintenance cover39detachably mounted to the side cover38allows the reservoir tank36to be supplied with cooling water (refer toFIG. 1).

The engine20is directly mounted to pairs of left and right front, middle and lower brackets53,54and55, which are provided into one body with cylindrical front, middle and lower cross members50,51and52connecting the left and right tank rails3and the left and right rear arm brackets4and which are made of sheet metal. A detailed structure of the engine20is as follows.

The front cross member50is provided between the inner walls of the front end parts of the straight parts3cof tank rails3. Flange parts50aformed on the left and right end parts of the front cross member50are welded to the inner walls for bonding. The flange parts50aare located over the rear end part35bof the lateral gusset35. That is, the front cross member50and the lateral gusset35are provided within a dimension in the height direction of tank rails3so as to be different in location in the height direction.

A pair of left and right front brackets53is welded to the front cross member50into one body for bonding with predetermined intervals in the vehicle width direction. The front brackets53are located within planes of shadows of tank rails3in a side view of the vehicle so as not to be in sight from the outside.

The front brackets53include belt-shaped supporting parts53bextending downward from the cross member50so as to be a little bit inclined rearward and front and rear flange parts53cformed by bending outside in the vehicle width direction from the top end of the supporting part53b. The flange parts53care welded to the front cross member50. A bolt hole53ais formed at the lower end part of the supporting part53b. The flange part53ccan be extended to the lower end part of the supporting part53b, of course. Contrary to the above, it is also possible to adopt a structure of providing only the supporting part53bwithout providing the flange parts53c.

As shown inFIG. 4, an interval w1between the left tank rail3and the front-left bracket53is set to be larger than an interval w2between the right tank rail3and the supporting part53bof the front-right bracket53. In other words, the left and right front brackets53are offset to the right in the vehicle width direction with respect to the center line of the vehicle body C. This allows efficiency in operation of mounting the engine20to the vehicle to be improved as described later.

The middle cross member51is provided between the inner walls of the top end parts of the left and right rear arm brackets4. The flange parts51aformed on the left and right end parts of the middle cross member51are bonded to the inner walls by welding.

The pair of left and right middle brackets54are bonded by welding into one body with the middle cross member51with a predetermined intervals in the vehicle width direction so as to be symmetrical with respect to the center line of the vehicle body C. The left and right middle brackets54include belt-shaped supporting parts54bextending downward from the middle cross member51so as to be a little bit inclined frontward and flange parts54cformed by bending outside in the vehicle width direction from the supporting parts. The top ends of the flange parts54care welded to the middle cross member51. A bolt hole54ais formed at the lower end part of the supporting part54b. The bolt hole54ais located at a forward part of a front edge part of the rear arm bracket4in a side view of the vehicle.

A lower cross member52is arranged between the inner walls of the lower end parts of the left and right rear arm brackets4. A side stand bracket56is provided at the left end part of the lower cross member52. A flange part52ais formed on the right end bracket. The flange part52aand the side stand bracket56are inserted at the lower end parts of rear arm brackets4to be welded for fixing. A pair of left and right lower brackets55is welded for bonding into one body with the lower cross member52with a predetermined interval in the vehicle width direction.

The lower brackets55include suspension parts55aprojecting forward from the lower ends of the rear arm brackets4and center stand supporting parts55bprojecting downward. The left and right suspension parts55aare provided with bolt holes55c. The lower brackets55are symmetrical with respect to the center line of the vehicle body C.

An upper boss part24aprojecting rearward is formed into one body on the upper end part of a rear wall of the cylinder head24, which is a component of the cylinder part of the engine20. The upper boss part24aand the rear end part of the head cover25are overlapped with the left and right tank rails3in a side view of the vehicle. The upper boss part24ais provided with a bolt inserting hole24bso that the bolt inserting hole24bwould be coaxial with the bolt holes53aof the left and right front brackets53.

The upper boss part24ais provided between the left and right front brackets53. Inserting a fastening bolt58into the bolt hole53a, the bolt inserting hole24band the bolt hole53afrom the left side of the vehicle and fastening a nut58aallow the upper boss part24ato be directly fixed to front brackets53. A wide operating space, which is formed according to widening of the interval w1between the left tank rail3and the front-left bracket53, is used for inserting the fastening bolt58into the bolt hole53a. This prevents difficulty in efficiency in operation of mounting the engine20from occurring while the front brackets53are overlapped with tank rails3.

As described above, the left and right front brackets53and the upper boss part24aare shifted to one side from the center line of the vehicle body C (the right side in the embodiment) while the engine20is mounted so that a cylinder axis C′ thereof would be shifted by an amount of “d” to the right side from the center line of the vehicle body C. This is likely to deteriorate the balance in weight in the vehicle width direction (to make the right side heavier than the left side). Accordingly, in the embodiment, components of an engine and components mounted to the vehicle are shifted to the other side (the left side in the embodiment) from the center line of the vehicle C so as to improve the balance in weight in the vehicle width direction, as shown inFIGS. 5 and 8to10.

Concretely, a cam shaft driving mechanism21′ and a cooling water pump61, which are used as components of an engine, and an ignition coil62and a reservoir tank36, which are used as components mounted to the vehicle, are provided so as to be shifted to the left side from the center line of the vehicle C.

The cam shaft driving mechanism21′ comprises a crank sprocket21aformed at a left side part of the crank shaft21, a cam sprocket60amounted to a left side part of the cam shaft60and a timing chain21bwound around the both sprockets60aand21a. The cam shaft driving mechanism21′ passes through chain rooms24cand23aformed at left side parts of the cylinder head24and the cylinder block23.

The cooling water pump61comprises a pump case61amounted to a left side wall of the cylinder head24, a pump cover61bmounted to a left end opening of the case and an impeller61cprovided in the pump case61aand the pump cover61b. The impeller61cis mounted at a left end of the cam shaft60coaxially with the cam sprocket60a.

Cooling water for an engine is sucked from the radiator30into the cooling water pump61through an intake61dto be supplied to a cooling jacket in the cylinder head24, and then, further sent to the radiator30through a cooling water hose61eto be sucked again into the cooling water pump61.

The ignition coil62is detachably mounted to a bracket53dfixed on the front side of the cross member.

A middle boss part22bprojecting upward is formed into one body on a rear wall of the transmission case22aof the crank case22. The middle boss part22bis provided between the left and right middle brackets54. The middle boss part22bis provided with a bolt inserting hole22dthat is substantially coaxial with the bolt hole54a. The middle boss part22bis directly fixed to middle brackets54by fastening bolt59inserted from the outside in the vehicle width direction.

A lower boss part22cprojecting rearward is formed into one body at a lower end part of a rear wall of the transmission case22a. The lower boss part22cis provided between the suspension parts55aof lower brackets55. The lower boss part22cis provided with a bolt inserting hole22ethat is substantially coaxial with the bolt hole55a. The lower boss part22cis directly fixed to suspension parts55aby a fastening bolt60inserted from the outside in the vehicle width direction.

The middle bracket54and the suspension part55aof the lower bracket55are exposed outside from the rear arm bracket4in a side view of the vehicle. Accordingly, an operation of inserting the fastening bolts59and60can be easily performed.

As described above, in the engine20, the upper end part, the middle part and the lower end part of the rear side wall of the engine20are directly fixed to the body frame1, respectively.

In accordance with the invention, the front brackets53are welded into one body with the front cross member50connecting the left and right tank rails3to each other and the cylinder head24forming a cylinder part of the engine20is directly mounted to the front brackets53. This allows the supporting rigidity necessary for the engine20to be secured.

In the embodiment, the upper part and the lower part of the crank case22of the engine20are directly mounted to the pair of left and right middle and lower brackets54and55provided into one body with the middle and lower cross members51and52connecting the left and right rear arm brackets4to each other. Accordingly, the supporting rigidity of a whole engine20can be secured. This allows a down tube to be omitted, and thereby, the number of components and the weight of the vehicle body to be reduced.

In the embodiment, the upper end part of the cylinder head24forming the cylinder part is directly mounted to the body frame1, so that the distance from a case suspension part can be large. This allows the supporting rigidity to be further improved.

The upper boss part24a, which is to be mounted to the front bracket53, is formed into one body with the cylinder head24to be overlapped with the left and right tank rails3in a side view of the vehicle. This allows the front bracket53to be short, so that the bending moment operating on the bracket can be smaller than the case that the front bracket is long. Further, the upper boss part24acan be covered up by means of the tank rail3, and thereby, a clear-cut appearance can be achieved.

In the embodiment, the interval w1between the left tank rail3and the front-left bracket53is set to be larger than the interval w2between the right tank rail3and the front-right bracket53. This allows a space for operation in inserting the fastening bolt58into the upper boss part24aoverlapped with the tank rail3in the width direction to be secured.

Further, the balance in weight in the vehicle width direction is likely to be deteriorated (the right side is likely to be heavier) since the left and right front brackets53are shifted to the right side in the vehicle width direction from the center line of the vehicle body C in the embodiment. The balance in weight, however, can be improved by means of the cam shaft driving mechanism21′ and the cooling water pump61, which are used as components of an engine, provided so as to be shifted to the left side in the vehicle width direction from the center line of the vehicle body C. In this case, the cooling water pump61is provided at the left end part of the cam shaft60and outside the cam sprocket60a. Accordingly, the cooling water pump61is shifted largely to the left side, so that it greatly contributes to improvement in balance in weight.

Moreover, an ignition coil62and the reservoir tank36are shifted to the left side from the center line of the vehicle body C. This also allows the balance in weight to be improved.

Moreover, the lateral gusset35is fixed to the inner wall surfaces of the left and right tank rails3and parts of the tank rails3, which have the rigidity improved by means of the lateral gusset35, are connected to each other by the front cross member50. In view of this point, the supporting rigidity of the engine can be also improved.

In addition, the lateral gusset35and the front cross member50are arranged within a dimension of the height of the tank rail3so as to be different in location in vertical direction. Accordingly, providing the lateral gusset35does not cause a complicated connecting structure of the front cross member50.

In the embodiment, a case is described in which the cylinder head24, which forms a component of the cylinder part, is directly mounted to the body frame1. In the invention, however, the cylinder block23or the head cover25, which is another component of the cylinder part, may be directly mounted to the body frame1. Further, the side wall of the cylinder part may be directly mounted to the body frame although the rear wall of the cylinder part is mounted to the body frame in the embodiment. Moreover, the boss part may be provided outside one or two brackets, of course, although the upper boss part24ais provided between the left and right brackets53.

In the embodiment, a case is described in which the cooling water pump is provided coaxially at the other side end of the cam shaft. The cooling water pump in the invention, however, may be provided in a place other than the above, in a crank case, for example, of course.