Title of Invention	LOW-FLOOR TYPE VEHICLE
Abstract	The present invention relates to a low-floor type vehicle which can suppress a lateral deviation between an advancing direction of a rear wheel and a ground contact portion of a front wheel attributed to the twisting of a vehicle body at the time of turning traveling or the like. [Means for Resolution] Amain frame 12 extends to a position above a swing arm pivotally supporting portion l8a from a position above a front portion of an engine 15 in the vicinity of a low floor portion 2, a rearmost engine mount portion C2 is mounted on a rear portion of the main frame 12, a frontmost engine mount portion C1 is mounted on a down frame 11, and the frontmost engine mount portion Cl is positioned on a straight line Lwhich connects the rearmost engine mount portionC2 and a ground contact portion FT of a front wheel 3 as viewed in a side view of a vehicle.

Title of Invention

LOW-FLOOR TYPE VEHICLE

Abstract

The present invention relates to a low-floor type vehicle which can suppress a lateral deviation between an advancing direction of a rear wheel and a ground contact portion of a front wheel attributed to the twisting of a vehicle body at the time of turning traveling or the like. [Means for Resolution] Amain frame 12 extends to a position above a swing arm pivotally supporting portion l8a from a position above a front portion of an engine 15 in the vicinity of a low floor portion 2, a rearmost engine mount portion C2 is mounted on a rear portion of the main frame 12, a frontmost engine mount portion C1 is mounted on a down frame 11, and the frontmost engine mount portion Cl is positioned on a straight line Lwhich connects the rearmost engine mount portionC2 and a ground contact portion FT of a front wheel 3 as viewed in a side view of a vehicle.

Full Text	[Designation of Document] Specification [Title of the Invention] LOW-FLOOR TYPE VEHICLE [Technical Field] [0001] The present invention relates to a low-floor type vehicle such as a scooter-type motorcycle or the like. [Background Art] [0002] Conventionally, with respect to the above-mentioned low-floor type vehicle, there has been known a low-floor type vehicle in which a low floor portion which constitutes a foot rest portion for a rider is provided between a front-wheel steering handle and a rider seat, a vehicle driving engine is supported on a vehicle body frame in the vicinity of the low floor portion and a swing arm which pivotally supports a rear wheel is supported in a rocking manner on a rear portion of the engine (see patent document 1, for example). [Patent Document 1] JP-A-11-301559 [Disclosure of the Invention] [Problems that the Invention is to Solve] [0003] Recently, with respect to a low-floor type vehicle, there has been observed a tendency that a displacement of the above-mentioned engine is increased and this tendency leads to large-sizing and the increase of weight of the engine and a vehicle body frame. To cope with such a tendency, there has been a demand for a low-floor type vehicle which exhibits high vehicle-body rigidity. On the other hand, along with the increase of an engine driving force, it is necessary to sufficiently take the twisting of the whole vehicle body into consideration. That is, there has been a demand for the constitution which can obtain feeling of integrity of the vehicle body in the longitudinal direction by suppressing a lateral deviation between an advancing direction of the rear wheel and a ground contact portion of a front wheel attributed to the twisting of the vehicle body while ensuring a favorable turning performance by properly imparting the twisting to the vehicle body-Further, to satisfy such a demand, the adjustment of the vehicle body rigidity and the twisting is often performed by focusing on a shape of the vehicle body frame or a rubber mount of the engine in general. However, such a constitution may make the above-mentioned adjustment difficult and, at the same time, may increase a weight and a manufacturing const of the low-floor type vehicle. The present invention has been made under the above-mentioned circumstances and it is an object of the present invention to provide a low-floor type vehicle which can suppress a lateral deviation between an advancing direction of a rear wheel and a ground contact portion of a front wheel attributed to the twisting of a vehicle body and, at the same time, can suppress an increase of a vehicle body weight and a manufacturing cost. [Means for Solving the Problem] [0004] As the means for solving the above-mentioned problem, the invention described in claim 1 is characterized in that in a low-floor type vehicle (for example, a motorcycle 1, 101 of an embodiment) in which an engine (for example, an engine 15, 115 of the embodiment) which is supported on a vehicle body frame (for example, a vehicle body frame 6 of the embodiment) is arranged in the vicinity of a low-floor portion (for example, a low-floor portion 2 of the embodiment) which constitutes a foot rest portion, a swing arm (for example, a swing arm 25 of the embodiment) which pivotally supports a rear wheel (for example, a rear wheel 9 of the embodiment) is supported in a rocking manner on a rear portion of the engine, and the vehicle body frame includes a down frame (for example, a down frame 11 of the embodiment) which extends obliquely in the downward and rearward direction from a head pipe (for example, a head pipe 7 of the embodiment), a main frame (for example, a main frame 12 of the embodiment) which extends rearwardly above the engine from a lower portion of the down frame, and a seat frame (for example, a seat frame 13 of the embodiment) which extends obliquely in the upward and rearward direction from a rear portion of the main frame, the main frame extends to a position above at least a swing arm pivotally supporting portion (for example, a swing arm pivotally supporting portion 18a of the embodiment) from a position above a front portion of the engine, a rearmost engine mount portion (for example, a rearmost engine mount portion C2 of the embodiment) is mounted on a rear portion of the main frame, a frontmost engine mount portion (for example, a frontmost engine mount portion Cl of the embodiment) is mounted on the down frame, and the frontmost engine mount portion is positioned on a straight line (for example, a straight line L of the embodiment) which connects the rearmost engine mount portion and a ground contact portion (for example, a front wheel ground contact portion FT) of a front wheel (for example, a front wheel 3 of the embodiment) as viewed in a side view of a vehicle. [0005] The invention described in claim 2 is characterized in that a crankshaft portion (for example, a crankshaft portion CJ of the embodiment) of the engine is positioned on the line as viewed in a side view of the vehicle. [0006] The invention described in claim 3 is characterized in that a support portion (for example, an exhaust muffler support portion C4 of the embodiment) of the exhaust muffler (for example, an exhaust muffler 44A of the embodiment) of the engine is positioned on the line and above a ground contact portion (for example, a rear wheel ground contact portion RT of the embodiment) of the rear wheel as viewed in a side view of the vehicle. [0007] The invention described in claim 4 is characterized in that the down frame is arranged to be substantially orthogonal to the line as viewed in a side view of the vehicle. [0008] The invention described in claim 5 is characterized in that a third engine mount portion (for example, a third engine mount portion C3 of the embodiment) which supports an upper portion of the engine is provided above or below the line as viewed in a side view of the vehicle. [0009] The invention described in claim 6 is characterized in that the down frame includes an upper frame member (for example, an upper down pipe 58 of the embodiment) and a lower frame member (for example, a lower down pipe 59 of the embodiment) which extend in parallel vertically, and the third engine mount portion is provided in the vicinity of a joint portion of the upper frame member and the main frame. [0010] The invention described in claim 7 is characterized in that the engine (for example, an engine 115 of the embodiment) is a V-type engine which includes front and rear cylinders (for example, front and rear cylinders 117f, 117r of the embodiment) , and the third engine mount portion is arranged between the front and rear cylinders. [0011] The invention described in claim 8 is characterized in that the vehicle body frame is not provided with a frame member which extends to a position below the engine from the down frame and, at the same time, is not provided with a frame member which extends downwardly from the main frame on the engine rear side. [Advantage of the Invention] [0012] According to the invention described in claim 1, when the twisting is generated between the vehicle-body rear portion which includes the engine and the rear wheel which is suspended by way of a swing arm and the vehicle-body front portion which includes the vehicle body frame and a front-wheel steering system at the time of performing the turning traveling of the vehicle, by extending the main frame to a position above the swing arm pivotally supporting portion from a position above a front portion of the engine so as to ensure the rigidity of the main frame, it is possible to allow the twisting to be generated on a line which connects the frontmost engine mount portion and the rearmost engine mount portion and ensures a long distance between the engine mount portions, while by positioning the ground contact portion of the front wheel on the line, it is possible to suppress the deviation of the rear wheel in the advancing direction with respect to the ground contact portion. That is, by suppressing the deviation of the ground contact portion of the front wheel from the advancing direction of the rear wheel attributed to the twisting of the vehicle body while enhancing the turning performance of the vehicle by properly imparting the twisting to the vehicle body at the time of turning traveling, the feeling of integrity of the vehicle body in the longitudinal direction can be enhanced whereby a rider can feel the rigidity of the vehicle body and, at the same time, it is possible to freely set a response which the rider feels when the vehicle performs a quick motion. [0013] According to the invention described in claim 2, by approximating a twisting line of the vehicle body and the rotary center of the crankshaft having a large gyroscopic precession to each other, it is possible to obtain the targeted twisting characteristic more effectively. [0014] According to the invention described in claim 3, it is possible to easily generate the twisting of the vehicle body about the line which supports the engine including an exhaust system thereof and hence, it is possible to further effectively suppress the deviation between the ground contact portion of the front wheel and the advancing direction of the rear wheel. [0015] According to the invention described in claim 4, by restricting a length of the down frame, a deflection quantity of the down frame can be decreased whereby the deviation between the ground contact portion of the front wheel and the advancing direction of the rear wheel can be further suppressed. [0016] According to the invention described in claim 5, the low-floor-type vehicle can ensure the relatively high vehicle body rigidity and hence, the engine is supported even at the position remote from the line, whereby even when the weight of the engine is increased along with the increase of the displacement, an amount of twisting about the line can be easily adjusted. [0017] According to the invention described in claim 6, the rigidity of the down frame per se is increased and, at the same time, the engine is joined to a lower portion of the down frame and hence, it is possible to efficiently increase the rigidity of a front portion of the vehicle body. [0018] According to the invention described in claim 7, it is possible to efficiently ensure the engine supporting rigidity of the vehicle body frame when a high-performance and narrow-width V-type engine is mounted on the vehicle body frame. [0019] According to the invention described in claim 8, since the frame member is not provided below the engine, it is possible to arrange the engine at a low position and hence, it is possible to set a position of center of gravity of the vehicle at a lower position. Further, by eliminating respective frame members which extend downwardly from a down frame and the main frame, it is possible to reduce the weight and a cost of the low-floor type vehicle. [Best Mode for Carrying out the Invention] [0020] Hereinafter, an embodiment of the present invention is explained in conjunction with drawings. Here, the directions of front, rear, left, right and the like in the explanation made hereinafter are, unless otherwise specified, assumed to be equal to the corresponding directions of the vehicle. Further, in the drawings, an arrow FR indicates the frontward direction of the vehicle, an arrow LH indicates the leftward direction of the vehicle, and an arrow UP indicates upward direction of the vehicle, respectively. [Embodiment 1] [0021] A motorcycle 1 shown in Fig. 1 is a scooter-type vehicle (a low-floor type vehicle) which includes a low floor portion 2 which constitutes a footrest portion for a rider, wherein a front wheel 3 is pivotally supported on left and right front forks 4, the respective front forks 4 are pivotally supported on a head pipe 7 of a front end upper portion of a vehicle body frame 6 in a steerable manner by way of a handle stem 5, and a steering handle 8 is mounted on an upper portion of the handle stem 5. Here, a ground contact portion of the front wheel 3 (a front-wheel ground contact portion) is indicated by symbol FT shown in the drawing. [0022] The vehicle body frame 6 is formed by integrally joining plural kinds of steel members by welding or the like. Here, the vehicle body frame 6 is mainly constituted of a down frame 11 which extends obliquely in the downward and rearward direction from the head pipe 7, a main frame 12 which extends in the rearward direction from a lower portion of the down frame 11 and passes above an engine 15 which is arranged inside the low floor portion 2, and a seat frame 13 which extends obliquely in the upward and rearward directions from a rear portion of the main frame 12. [0023] The engine 15 which constitutes a prime motor of the motorcycle 1 is, for example, a water-cooled four-stroke single-cylinder engine and is configured such that a crankshaft is arranged in parallel in the lateral direction and a cylinder 17 is approximately frontwardly mounted on a front end portion of a crankcase 16 in an erected manner. Here, a crankshaft portion (the center of rotation of the crankshaft) as viewed in a side view of the vehicle is indicated by symbol CJ in the drawing. A transmission case 18 is contiguously mounted on a rear portion of the crankcase 16, and a front end portion of a swing arm 25 which pivotally supports a rear wheel 9 is pivotally supported on a rear end portion of the transmission case 18 in a vertically rocking manner by way of a pivot shaft 26 which extends in the lateral direction. [0024] The swing arm 25 has inner sides of front portions of left and right arm members 27, 27 connected with each other by a cross member 29, while the rear wheel 9 is pivotally supported on a rear end portion of the swing arm 25. Here, a ground contact portion of the rear wheel 9 (a rear-wheel ground contact portion) is indicated by symbol RT in the drawing A cushion connecting portion 29a is mounted on an upper portion of the cross member 29 in an erected manner, and between the cushion connecting portion 29a and a longitudinal intermediate portion of the main frame 12, a cushion unit 30 which is integrally formed of a buffer coil spring and a dumper is arranged in a state that the longitudinal direction (stroke direction) of the cushion unit 30 extends substantially in the longitudinal direction of the vehicle. [0025] In the inside of the transmission case 18, a continuously variable transmission 20 which is mainly constituted of a drive pulley 21 which is arranged coaxially with the crankshaft, a driven pulley 22 which is arranged coaxially with a power transmission shaft arranged behind the crankshaft, and an endless drive belt 23 which is extended between and wound around both pulleys is housed. A rotational power of the crankshaft has a speed thereof continuously changed by way of the continuously variable transmission 20 and, at the same time, is outputted to the left side drive sprocket wheel 34 which is mounted on a rear end portion of the transmission case 18 by way of a centrifugal clutch and a final reduction gear mechanism (neither one shown in the drawings). [0026] An endless drive chain 36 is extended and wound around the drive sprocket wheel 34 and a driven sprocket wheel 35 arranged on a left side of a rear wheel 9, and the power transmission is performed between the engine 15 and the rear wheel 9 by way of the drive chain 36. Here, the drive sprocket wheel 34 is arranged coaxially with the pivot shaft 26 of the swing arm 25. [0027] A radiator 39 is arranged in front of the cylinder head 17a, an air cleaner case 40 is arranged above the radiator 39, and an intake pipe 42 which extends obliquely in the downward and rearward direction from a throttle body 41 which is connected to a rear portion of the air cleaner case 40 is connected to an intake port formed in an upper portion of the cylinder head 17a. Further, an exhaust pipe 43 is connected to an exhaust port formed in a lower portion of the cylinder head 17a, while the exhaust pipe 43 is curved below the cylinder head 17a, passes below the crankcase 16 in the rearward direction and, thereafter, is raised obliquely in the upward and rearward direction behind the engine 15, and is connected to a silencer 44 which is arranged on a right side of a rear portion of the vehicle body. Hereinafter, there may be a case that the exhaust pipe 43 and the silencer 44 may be referred to as an exhaust muffler 44A in a collective manner. [0028] The vehicle body frame 6 and the engine 15 are covered with a synthetic resin-made vehicle body cover 46. The vehicle body cover 46 includes a front cowl 47 which covers a range which extends from a front portion of the head pipe 7 to both sides of the head pipe 7, an inner cover 4 8 which covers a rear portion of the head pipe 7, and an under cowl 49 which is contiguously formed with a lower portion of the front cowl 47 and covers both sides of a lower portion of the engine 15, a floor cover 50 which is contiguously formed with a lower portion of the inner cover 48 and covers an upper portion of the engine 15, and a rear side cover 51 which is formed on both sides of a lower portion of a seat 53 and covers both sides of the rear portion of the vehicle body. [0029] On the seat frame 13 and the rear side cover 51, a seat 53 which is integrally formed of a front seat portion for a rider and a rear seat portion for a rear pillion passenger is supported. The seat 53 is vertically rotatable about a hinge shaft 54 mounted on a front end portion thereof and hence, the rider can open or close an article accommodating box 55 arranged below the front seat portion and, at the same time, can get access to a fuel tank 56 arranged below the rear seat portion. The article accommodating box 55 has a front portion thereof positioned above a rear portion of the crankcase 16 and a rear portion thereof positioned above a front portion of the swing arm 25. Further, the article accommodating box 55 has a bottom portion thereof bifurcated such that the bottom portion strides over the cushion unit 30 and, at the same time, has a rear side of the bottom portion thereof inclined in the rearward and upward direction so as to ensure a gap which is used at the time of rocking the swing arm 25. [0030] The down frame 11 of the vehicle body frame 6 is mainly constituted of an upper down pipe (an upper frame member) 58 which is bifurcated to left and right sides from an upper portion of the head pipe 7 and extends obliquely in the downward and rearward direction, and a lower down pipe (a lower frame member) 59 which is bifurcated to a left and right sides from a lower portion of the head pipe 7 and extends obliquely in the downward and rearward direction more steeply than the upper down pipe 58. [0031] Between the lower portion of the head pipe 7 and the upper intermediate portion of the upper down pipe 58, a gusset pipe 60 which is arranged substantially horizontally is extended, wherein an upper end portion of the lower down pipe 59 is joined to a lower portion of the head pipe 7 by way of the gusset pipe 60. Here, in the drawing, symbol 61 indicates a gusset plate which strides over an upper portion of the lower down pipe 59, a front portion of the gusset pipe 60 and a lower portion of the head pipe 7. [0032] On a lower portion of the lower down pipe 59, a front engine hanger bracket 62 which extends obliquely in the downward and rearward direction in the same manner is contiguously formed, a front lower engine hanger 63 is fastened to a lower end portion of the engine hanger bracket 62, and a rear end portion of the front lower engine hanger 63 is fastened to a lower side of a front portion of the crankcase 16 of the engine 15 thus supporting the engine 15. Here, an axis center of a bolt along the vehicle width direction which fastens the front lower engine hanger 63 and the engine 15 (a frontmost engine mount portion) is indicated by symbol Cl in the drawing. [0033] The main frame 12 is mainly constituted of a pair of left and right main pipes 65 which correspond to left and right upper down pipes 58 and lower down pipes 59. The main pipes 65 are arranged substantially horizontally at a center portion of the vehicle body and have intermediate portions thereof slightly curved to project upwardly as viewed in a side view of the vehicle. Front end portions of the main pipes 65 are joined to lower portions of the lower down pipes 59 from behind and, at the same time, lower end portions of the upper down pipes 58 are j oined to front portions of the main pipes 65 from above. [0034] The main pipes 65 (main frames 12) extend from a position above the cylinder head 17a of the engine 15 to a position above the swing arm pivotally supporting portion 18a formed on a rear end portion of the transmission case 18, while to rear end portions of the main pipes 65, rear engine hanger brackets 66 which extend rearwardly are mounted contiguously. Further, on lower portions of the engine hanger brackets 66, rear upper engine hangers 67 which project downwardly are mounted, and lower end portions of the rear upper engine hangers 67 are connected to an upper side of a rear portion of the transmission case 18 thus supporting the transmission case 18. Here, an axis center of a bolt along the vehicle width direction which fastens the rear upper engine hangers 67 and the engine 15 (a rearmost engine mount portion) is indicated by symbol C2 in the drawing. [0035] Further, to the front portions of the main pipes 65 which constitute a joining portion with the upper down pipes 58, the front upper engine hangers 68 are fastened, and lower end portions of the front upper engine hangers 68 are fastened to an upper side of a front portion of the crankcase 16 of the engine 15 thus supporting the engine 15. Here, an axis center of a bolt along the vehicle width direction which fastens the front upper engine hangers 68 and the engine 15 (a third engine mount portion) is indicated by symbol C3 in the drawing. The engine 15 is suspended on the vehicle body frame 6 using these three portions consisting of the third engine mount portion C3, the frontmost engine mount portion Cl and the rearmost engine mount portion C2. [0036] The seat frame 13 is mainly constituted of left and right seat pipes 70 which extend obliquely in the upward and rearward direction from the vicinity of the curved portions of the left and right main pipes 65, and left and right rear pipes 71 which extend obliquely in the upward and rearward direction from rear end portions of the left and right main pipes 65. The seat pipes 70 have intermediate portions thereof bent such that the intermediate portions project obliquely in the front and upward direction as viewed in a side view of the vehicle and have rear end portions thereof connected to each other thus integrally forming laterally. Rear portions of the seat pipes 70 and rear portions of the rear pipes 71 are joined by way of rear side plates 72. Further, to bent portions of the seat pipes 70, upper end portions of rear gusset pipes 7 3 which extend obliquely in the upward and rearward direction with a steep inclination from rear end portions of the main pipes 65 are joined from below. [0037] Here, in this embodiment, the vehicle body frame 6 is formed of a so-called diamond-type frame which eliminates a frame member below the engine 15, wherein the engine 15 also functions as a reinforcing member of the vehicle body frame 6. Due to such a constitution, it is possible to lower the position of the engine 15 thus realizing the lowering of the center of gravity of the vehicle body frame 6. Further, due to the elimination of the frame member, it is possible to reduce a weight and a cost of the vehicle body frame 6. Further, the vehicle body frame 6 eliminates a frame member which extends downwardly from the main frame 12 at a rear side of the engine 15 (a so-called pivot plate) thus further reducing the weight and the cost of the vehicle body frame 6. [0038] A silencer 44 arranged on a right side of the rear portion of the vehicle body exhibits a cylindrical appearance which extends along a rearward and upward axis, for example, and is arranged at a position below the rear pipes 71 of the seat frame 13 as viewed in a side view of the vehicle. A support bracket 44b which projects upwardly is mounted on a longitudinally intermediate portion of the silencer 44 and the support bracket 44b is fastened to a muffler hanger 74 which is mounted on rear portions of the rear pipes 71 in a downwardly projecting manner thus allowing the seat frame 13 to support the silencer 44 (a rear portion of the exhaust muffler 44A) . Here, an axis center of a bolt along the vehicle width direction which fastens the seat frame 13 and the exhaust muffler 44A (a support portion of the exhaust muffler 44A) is indicated by symbol C4 in the drawing. The support portion (the exhaust muffler support portion) C4 is substantially positioned on a vertical line which passes the rear wheel ground contact portion RT. [0039] Here, as viewed in a side view of the vehicle of the motorcycle 1, the front wheel ground contact portion FT, the frontmost engine mount portion Cl at the front lower engine hangers 63, and the rearmost engine mount portion C2 at a rear upper engine hangers 67 are arranged to be positioned on a straight line L which extends rearwardly and upwardly. [0040] Further, the exhaust muffler support portion C4 at the muffler hangers 74 and the crankshaft portion CJ at the engine 15 are also substantially positioned on an extension of the straight line L as viewed in a side view of the vehicle. The lower down pipes 59 of the down frames 11 are arranged to be substantially orthogonal to the straight line L as viewed in a side view of the vehicle. [0041] Fig. 2 is a view which schematically shows a state in which the rear wheel ground contact portion RT is displaced laterally with respect to the front wheel ground contact portion FT due to the twisting of the vehicle body which is generated at the time of performing the turning traveling of the motorcycle 1. As shown in this drawing, when the motorcycle 1 is turned or a twisting force is applied between the front portion of the vehicle body and the rear portion of the vehicle body due to a disturbance, for example, the twisting is generated about the straight line L and hence, the front wheel gro.und contact portion FT is always positioned on the advancing direction of the rear wheel 9 (indicated by an arrow S in Fig. 2) . Cl, C2, that is, the straight line L. [0044] Here, by adjusting the rigidity of the third engine mount portion C3 which is spaced apart by a predetermined quantity 5 above the straight line L as viewed in a side view of the vehicle, it is possible to relatively easily adjust the twisting quantity of the vehicle body. Further, since the lower down pipes 59 which are contiguously formed with the third engine mount portion C3 are arranged substantially orthogonal to the 10 straight line L, a length of the lower down pipe 59 can be suppressed thus reducing a deflection quantity of the lower down pipes 59 whereby the twisting of the vehicle bodies is liable to be easily generated about the straight line L. [0045] 15 As a result, since the advancing direction of the rear wheel 9 is rocked about the straight line L which passes through the front wheel ground contact portion FT, even when the vehicle body is twisted about the straight line L and the rear wheel ground contact portion RT is deviated laterally, the advancing 20 direction of the rear wheel 9 is directed toward the front wheel ground contact portion FT. That is, by adopting the constitution of the present invention, even when the vehicle body is twisted, it is possible to easily adjust the rigidity of the vehicle body such that the front wheel ground contact 25 portion FT is not deviated from the advancing direction of the rear wheel 9 whereby a feeling of integrity in the longitudinal direction of the vehicle body at the time of turning can be enhanced. [0046] As has been explained above, the motorcycle 1 according to the embodiment is the low-floor type vehicle in which the engine 15 which is supported on the vehicle body frame 6 is arranged in the vicinity of the low-floor portion 2 which constitutes the foot rest portion, the swing arm 25 which pivotally supports the rear wheel 9 is supported in a rocking manner on the rear portion of the engine 15, and the vehicle body frame 6 includes the down frame 11 which extends obliquely in the downward and rearward direction from the head pipe 1, the main frame 12 which extends rearwardly above the engine 15 from the lower portion of the down frame 11, and the seat frame 13 which extends obliquely in the upward and rearward direction from the rear portion of the main frame 12, wherein the main frame 12 extends to the position above the swing arm pivotally supporting portion 18a from the position above the front portion of the engine 15, the rearmost engine mount portion C2 is mounted on the rear portion of the main frame 12, the frontmost engine mount portion Cl is mounted on the down frame 11, and the frontmost engine mount portion Cl is positioned on the straight line L which connects the rearmost engine mount portion C2 and the ground contact portion FT of the front wheel 3 as viewed in a side view of a vehicle. [0047] According to this constitution, at the time of performing the turning traveling of the motorcycle 1, when the twisting is generated between the vehicle-body rear portion which includes the engine 15 and the rear wheel 9 which is suspended by way of the swing arm 25 and the vehicle-body front portion which includes the vehicle body frame 6 and the front-wheel steering system, by extending the main frame 12 to the position above the swing arm pivotally supporting portion 18a from the position above the front portion of the engine 15 so as to ensure the rigidity of the main frame 12, it is possible to allow the twisting to be generated about the straight line L which connects the f rontmost engine mount portion Cl and the rearmost engine mount portion C2 thus ensuring the long distance between the engine mount portions, while by positioning the ground contact portion FT of the front wheel 3 on the straight line L , it is possible to suppress the deviation of the rear wheel 9 in the advancing direction with respect to the ground contact portion FT . That is, by suppressing the deviation of the ground contact portion FT of the front wheel 3 from the advancing direction of the rear wheel 9 attributed to the twisting of the vehicle body while enhancing the turning performance of the vehicle by properly imparting the twisting to the vehicle body at the time of performing turning traveling, the feeling of integrity of the vehicle body in the longitudinal direction can be enhanced whereby the rider can feel the rigidity of the vehicle body and, at the same time, it is possible to freely set a response which a rider feels when the vehicle performs a quick motion. [0048] Further, in the above-mentioned motorcycle 1, by positioning the crankshaft portion CJ of the engine 15 on the straight line L as viewed in a side view of the vehicle, the twisting line of the vehicle body and the rotary center of the crankshaft having the large gyroscopic precession are approximated to each other and hence, it is possible to obtain the targeted twisting characteristic more effectively. [0049] Further, in the above-mentioned motorcycle 1, by positioning the support portion C4 of the exhaust muffler 44A of the engine 15 on the straight line L as viewed in a side view of the vehicle and above a ground contact portion RT of the rear wheel 9, it is possible to easily generate the twisting of the vehicle body about the straight line L which supports the engine 15 including the exhaust system thereof and hence, it is possible to further effectively suppress the deviation Detween the ground contact portion FT of the front wheel and Lhe advancing direction of the rear wheel. [0050] Still further, in the above-mentioned motorcycle 1, by arranging the down frame 11 to be substantially orthogonal to the straight line L as viewed in a side view of the vehicle, the length of the down frame 11 is restricted and hence, the deflection quantity of the down frame 11 can be decreased whereby the deviation between the ground contact portion FT of the front wheel and the advancing direction of the rear wheel can be further suppressed. [0051] Further, in the above-mentioned motorcycle 1, by arranging the third engine mount portion C3 which supports the upper portion of the engine 15 above the straight line L as viewed in a side view of the vehicle, the inotorcycle 1 can ensure the relatively high vehicle body rigidity and hence, the engine 15 is supported even at the position which is remote from the straight line L, whereby even when the weight of the engine is increased along with the increase of the displacement, an amount of twisting on the straight line L can be easily adjusted. [0052] Here, in the above-mentioned motorcycle 1, the down frame 11 includes the upper down pipes 58 and the lower down pipes 59 which extend in parallel in the vertical direction and the third engine mount portion C3 is provided in the vicinity of the joining portion between the upper down pipes 59 and the main frame 12. Accordingly, the rigidity of the down frame 11 per se is enhanced and, at the same time, the lower portion of the down frame 11 is joined to the engine 15 and hence, it is possible to efficiently increase the rigidity of the front portion of the vehicle body. [0053] rhich extends downwardly from the main frame 12 on the 3 ide of the engine 15 and hence, it is possible to arrange Further, in the above-mentioned motorcycle 1, the vehicle body frame 6 is not provided with a frame member which extends to a position below the engine 15 from the down frame 11 and, at the same time, is not provided with a frame member which extends downwardly from the main frame 12 on the rear the engine 15 at a low position whereby it is possible to set a position of center of gravity of the vehicle at a lower position Further, by eliminating respective frame members which extend downwardly from the down frame 11 and the main frame 12, it is possible to reduce a weight and a cost of the low-floor type vehicle. [Embodiment 2] [0054] Next, a second embodiment of the present invention is explained. The second embodiment differs from the first embodiment only with respect to the engine type and hence, parts identical with the parts of the first embodiment are given same symbols and their explanation is omitted. [0055] As shown in Fig. 3, an engine 115 which constitutes a prime mover of a motorcycle 101 is, for example, a water-cooled four-stroke V-type two-cylinder engine and is configured such that a crankshaft is arranged in parallel in the lateral direction, the front cylinders 117f are approximately frontwardly mounted on a front end portion of a crankcase 116 in an erected manner, and the rear cylinders 117r are approximately upwardly mounted on an upper portion of the crankcase 116 in an erected manner. The above-mentioned transmission case 18 is contiguously mounted on a rear portion of the crankcase 116, [0056] A radiator 39 is arranged in front of a front cylinder head 117fa, an air cleaner case 40 is arranged above the radiator 39, and respective intake pipes 142 which are bifurcated and extend from a throttle body 41 which is connected to a rear portion of the air cleaner 4 0 are respectively connected to intake ports formed in an upper portion of the front cylinder head 117fa and a front portion of a rear cylinder head 117ra . Further, to exhaust ports formed in a lower portion of the front cylinder head 117fa and a rear portion of the rear cylinder head 117ra, exhaust pipes 143 are respectively connected. These exhaust pipes 143 are converged into one pipe behind the engine 115 and the converged exhaust pipe is raised obliquely in the upward and rearward direction and is connected to a silencer 44. [0057] Front lower engine hangers 63 mounted on lower portions of lower down pipes 59 are fastened to a lower side of a front portion of the crankcase 116 of the engine 115 at a frontmost engine mount portion Cl and support the engine 115. Further, rear upper engine hangers 67 mounted on rear end portions of main pipes 65 are connected to an upper side of a rear portion of a transmission case 18 of the engine 115 at a rearmost engine mount portion C2 and support the engine 115. Further, front upper engine hangers 68 mounted on front portions of the main pipes 65 are fastened to an upper side of a front portion of the crankcase 116 of the engine 115 at a third engine mount portion C3 and support the engine 115. Here, the front upper engine hangers 68 and the third engine mount portion C3 are positioned between the front and rear cylinders 117f, 117r as viewed in a side view of the vehicle. [0058] Then, as viewed in a side view of the vehicle, a ground contact portion FT of a front wheel 3 of the motorcycle 101, the frontmost engine mount portion Cl at the front lower engine hangers 63, and the rearmost engine mount portion C2 at a rear upper engine hangers 67 are substantially arranged to be positioned on a straight line L which extends rearwardly and upwardly. Further, an exhaust muffler support portion C4 at the muffler hangers 74 and a crankshaft portion CJ at the engine 15 are also substantially positioned on an extension of the straight line L as viewed in a side view of the vehicle. Still further, the third engine mount portion C3 at the front upper engine hangers 68 is arranged in a spaced-apart manner above the straight line L by a predetermined amount. [0059] As has been explained above, in the motorcycle 101 of the second embodiment, the engine 115 which is supported on the vehicle body frame 6 is the V-type engine having the front and rear cylinders 117f, 117r and the third engine mount portion C3 is arranged between the front and rear cylinders 117f, 117r and hence, it is possible to efficiently ensure the engine support rigidity when the high-performance and narrow-width V-type engine is mounted on the vehicle body frame 6. [0060] Here, the present invention is not limited to the above-mentioned respective embodiments and, for example, the third engine mount portion C3 may be arranged below the straight line L. Further, the main frame 12 maybe extended to a position behind a swing arm pivot of the main frame 12 thus constituting a portion of the seat frame 13. Further, it is needless to say that the constitutions of the above-mentioned embodiments are examples of the present invention and the detailed constitutions of the engine type and the vehicle body frame 6 are not limited to the above-mentioned respective embodiments and various modifications are conceivable without departing from the gist of the present invention. [Brief Description of the Drawings] [0061] [Fig. 1] A side view of a motorcycle according to a first embodiment of the present invention. [Fig. 2] An operation explanatory view of the above-mentioned motorcycle. [Fig. 3] A side view of a motorcycle according to a second embodiment of the present invention. [Description of Reference Numerals and Signs] [0062] I, 101: motorcycle (low-floor type vehicle) 2: low-floor portion 3: front wheel 6: vehicle body frame 7: head pipe 9: rear wheel 11: down frame 12: main frame 13: seat frame 15, 115: engine 18a: swing arm pivotally supporting portion 25: swing arm 44A: exhaust muffler 58: upper down pipe (upper frame member) 59: lower down pipe (lower frame member) Cl: frontmost engine mount portion C2: rearmost engine mount portion C3: third engine mount portion C4: exhaust muffler support portion FT: front wheel ground contact portion RT: rear wheel ground contact portion CJ: crankshaft portion L: straight line [Designation of Document] Claims [Claim 1] A low-floor type vehicle in which an engine which is supported on a vehicle body frame is arranged in the vicinity of a low-floor portion which constitutes a foot rest portion, a swing arm which pivotally supports a rear wheel is supported in a rocking manner on a rear portion of the engine, and the vehicle body frame includes a down frame which extends obliquely in the downward and rearward direction from a head pipe, a main frame which extends rearwardly above the engine from a lower portion of the down frame, and a seat frame which extends obliquely in the upward and rearward direction from a rear portion of the main frame, wherein the main frame extends to a position above at least a swing arm pivotally supporting portion from a position above a front portion of the engine, a rearmost engine mount portion is mounted on a rear portion of the main frame, a frontmost engine mount portion is mounted on the down frame, and the frontmost engine mount portion is positioned on a straight line which connects the rearmost engine mount portion and a ground contact portion of a front wheel as viewed in a side view of a vehicle. [Claim 2] A low-floor type vehicle according to claim 1, wherein a crankshaft portion of the engine is positioned on the line as viewed in a side view of the vehicle. [Claim 3] A low-floor type vehicle according to claim 1 or claim 2, wherein a support portion of an exhaust muffler of the engine is positioned on the line and above a ground contact portion of the rear wheel as viewed in a side view of the vehicle. [Claim 4] A low-floor type vehicle according to any one of claims 1 to claim 3, wherein the down frame is arranged to be substantially orthogonal to the line as viewed in a side view of the vehicle. [Claim 5] A low-floor type vehicle according to any one of claims 1 to claim 4, wherein a third engine mount portion which supports an upper portion of the engine is provided above or below the line as viewed in a side view of the vehicle. [Claim 6] A low-floor type vehicle according to claim 5, wherein the down frame includes an upper frame member and a lower frame member which extend in parallel vertically, and the third engine mount portion is provided in the vicinity of a joint portion of the upper frame member and the main frame. [Claim 7] A low-floor type vehicle according to claim 5 or claim 6, wherein the engine is a V-type engine which includes front and rear cylinders, and the third engine mount portion is arranged between the front and rear cylinders. [Claim 8] A low-floor type vehicle according to any one of claims 1 to claim 6, wherein the vehicle body frame is not provided with a frame member which extends to a position below the engine from the down frame and, at the same time, is not provided with a frame member which extends downwardly from the main frame on the engine rear side.

Full Text

[Designation of Document] Specification
[Title of the Invention] LOW-FLOOR TYPE VEHICLE
[Technical Field]
[0001]
The present invention relates to a low-floor type vehicle such as a scooter-type motorcycle or the like. [Background Art] [0002]
Conventionally, with respect to the above-mentioned low-floor type vehicle, there has been known a low-floor type vehicle in which a low floor portion which constitutes a foot rest portion for a rider is provided between a front-wheel steering handle and a rider seat, a vehicle driving engine is supported on a vehicle body frame in the vicinity of the low floor portion and a swing arm which pivotally supports a rear wheel is supported in a rocking manner on a rear portion of the engine (see patent document 1, for example). [Patent Document 1] JP-A-11-301559 [Disclosure of the Invention] [Problems that the Invention is to Solve] [0003]
Recently, with respect to a low-floor type vehicle, there has been observed a tendency that a displacement of the above-mentioned engine is increased and this tendency leads to large-sizing and the increase of weight of the engine and

a vehicle body frame. To cope with such a tendency, there has been a demand for a low-floor type vehicle which exhibits high vehicle-body rigidity. On the other hand, along with the increase of an engine driving force, it is necessary to sufficiently take the twisting of the whole vehicle body into consideration. That is, there has been a demand for the constitution which can obtain feeling of integrity of the vehicle body in the longitudinal direction by suppressing a lateral deviation between an advancing direction of the rear wheel and a ground contact portion of a front wheel attributed to the twisting of the vehicle body while ensuring a favorable turning performance by properly imparting the twisting to the vehicle body-Further, to satisfy such a demand, the adjustment of the vehicle body rigidity and the twisting is often performed by focusing on a shape of the vehicle body frame or a rubber mount of the engine in general. However, such a constitution may make the above-mentioned adjustment difficult and, at the same time, may increase a weight and a manufacturing const of the low-floor type vehicle.
The present invention has been made under the above-mentioned circumstances and it is an object of the present invention to provide a low-floor type vehicle which can suppress a lateral deviation between an advancing direction of a rear wheel and a ground contact portion of a front wheel

attributed to the twisting of a vehicle body and, at the same
time, can suppress an increase of a vehicle body weight and
a manufacturing cost.
[Means for Solving the Problem]
[0004]
As the means for solving the above-mentioned problem, the invention described in claim 1 is characterized in that in a low-floor type vehicle (for example, a motorcycle 1, 101 of an embodiment) in which an engine (for example, an engine 15, 115 of the embodiment) which is supported on a vehicle body frame (for example, a vehicle body frame 6 of the embodiment) is arranged in the vicinity of a low-floor portion (for example, a low-floor portion 2 of the embodiment) which constitutes a foot rest portion, a swing arm (for example, a swing arm 25 of the embodiment) which pivotally supports a rear wheel (for example, a rear wheel 9 of the embodiment) is supported in a rocking manner on a rear portion of the engine, and the vehicle body frame includes a down frame (for example, a down frame 11 of the embodiment) which extends obliquely in the downward and rearward direction from a head pipe (for example, a head pipe 7 of the embodiment), a main frame (for example, a main frame 12 of the embodiment) which extends rearwardly above the engine from a lower portion of the down frame, and a seat frame (for example, a seat frame 13 of the embodiment) which extends obliquely in the upward and rearward direction from a rear

portion of the main frame, the main frame extends to a position above at least a swing arm pivotally supporting portion (for example, a swing arm pivotally supporting portion 18a of the embodiment) from a position above a front portion of the engine, a rearmost engine mount portion (for example, a rearmost engine mount portion C2 of the embodiment) is mounted on a rear portion of the main frame, a frontmost engine mount portion (for example, a frontmost engine mount portion Cl of the embodiment) is mounted on the down frame, and the frontmost engine mount portion is positioned on a straight line (for example, a straight line L of the embodiment) which connects the rearmost engine mount portion and a ground contact portion (for example, a front wheel ground contact portion FT) of a front wheel (for example, a front wheel 3 of the embodiment) as viewed in a side view of a vehicle. [0005]
The invention described in claim 2 is characterized in that a crankshaft portion (for example, a crankshaft portion CJ of the embodiment) of the engine is positioned on the line as viewed in a side view of the vehicle. [0006]
The invention described in claim 3 is characterized in that a support portion (for example, an exhaust muffler support portion C4 of the embodiment) of the exhaust muffler (for example, an exhaust muffler 44A of the embodiment) of the engine

is positioned on the line and above a ground contact portion (for example, a rear wheel ground contact portion RT of the embodiment) of the rear wheel as viewed in a side view of the vehicle. [0007]
The invention described in claim 4 is characterized in that the down frame is arranged to be substantially orthogonal to the line as viewed in a side view of the vehicle. [0008]
The invention described in claim 5 is characterized in that a third engine mount portion (for example, a third engine mount portion C3 of the embodiment) which supports an upper portion of the engine is provided above or below the line as viewed in a side view of the vehicle. [0009]
The invention described in claim 6 is characterized in that the down frame includes an upper frame member (for example, an upper down pipe 58 of the embodiment) and a lower frame member (for example, a lower down pipe 59 of the embodiment) which extend in parallel vertically, and the third engine mount portion is provided in the vicinity of a joint portion of the upper frame member and the main frame. [0010]
The invention described in claim 7 is characterized in that the engine (for example, an engine 115 of the embodiment)

is a V-type engine which includes front and rear cylinders (for example, front and rear cylinders 117f, 117r of the embodiment) , and the third engine mount portion is arranged between the front and rear cylinders. [0011]
The invention described in claim 8 is characterized in that the vehicle body frame is not provided with a frame member which extends to a position below the engine from the down frame and, at the same time, is not provided with a frame member which extends downwardly from the main frame on the engine rear side. [Advantage of the Invention] [0012]
According to the invention described in claim 1, when the twisting is generated between the vehicle-body rear portion which includes the engine and the rear wheel which is suspended by way of a swing arm and the vehicle-body front portion which includes the vehicle body frame and a front-wheel steering system at the time of performing the turning traveling of the vehicle, by extending the main frame to a position above the swing arm pivotally supporting portion from a position above a front portion of the engine so as to ensure the rigidity of the main frame, it is possible to allow the twisting to be generated on a line which connects the frontmost engine mount portion and the rearmost engine mount portion and ensures a long distance between the engine mount portions, while by

positioning the ground contact portion of the front wheel on the line, it is possible to suppress the deviation of the rear wheel in the advancing direction with respect to the ground contact portion. That is, by suppressing the deviation of the ground contact portion of the front wheel from the advancing direction of the rear wheel attributed to the twisting of the vehicle body while enhancing the turning performance of the vehicle by properly imparting the twisting to the vehicle body at the time of turning traveling, the feeling of integrity of the vehicle body in the longitudinal direction can be enhanced whereby a rider can feel the rigidity of the vehicle body and, at the same time, it is possible to freely set a response which the rider feels when the vehicle performs a quick motion. [0013]
According to the invention described in claim 2, by approximating a twisting line of the vehicle body and the rotary center of the crankshaft having a large gyroscopic precession to each other, it is possible to obtain the targeted twisting characteristic more effectively. [0014]
According to the invention described in claim 3, it is possible to easily generate the twisting of the vehicle body about the line which supports the engine including an exhaust system thereof and hence, it is possible to further effectively suppress the deviation between the ground contact portion of

the front wheel and the advancing direction of the rear wheel. [0015]
According to the invention described in claim 4, by restricting a length of the down frame, a deflection quantity of the down frame can be decreased whereby the deviation between the ground contact portion of the front wheel and the advancing direction of the rear wheel can be further suppressed. [0016]
According to the invention described in claim 5, the low-floor-type vehicle can ensure the relatively high vehicle body rigidity and hence, the engine is supported even at the position remote from the line, whereby even when the weight of the engine is increased along with the increase of the displacement, an amount of twisting about the line can be easily adjusted. [0017]
According to the invention described in claim 6, the rigidity of the down frame per se is increased and, at the same time, the engine is joined to a lower portion of the down frame and hence, it is possible to efficiently increase the rigidity of a front portion of the vehicle body. [0018]
According to the invention described in claim 7, it is possible to efficiently ensure the engine supporting rigidity of the vehicle body frame when a high-performance and

narrow-width V-type engine is mounted on the vehicle body
frame.
[0019]
According to the invention described in claim 8, since the frame member is not provided below the engine, it is possible to arrange the engine at a low position and hence, it is possible to set a position of center of gravity of the vehicle at a lower position. Further, by eliminating respective frame members which extend downwardly from a down frame and the main frame, it is possible to reduce the weight and a cost of the low-floor type vehicle. [Best Mode for Carrying out the Invention] [0020]
Hereinafter, an embodiment of the present invention is explained in conjunction with drawings. Here, the directions of front, rear, left, right and the like in the explanation made hereinafter are, unless otherwise specified, assumed to be equal to the corresponding directions of the vehicle. Further, in the drawings, an arrow FR indicates the frontward direction of the vehicle, an arrow LH indicates the leftward direction of the vehicle, and an arrow UP indicates upward direction of the vehicle, respectively. [Embodiment 1] [0021]
A motorcycle 1 shown in Fig. 1 is a scooter-type vehicle

(a low-floor type vehicle) which includes a low floor portion 2 which constitutes a footrest portion for a rider, wherein a front wheel 3 is pivotally supported on left and right front forks 4, the respective front forks 4 are pivotally supported on a head pipe 7 of a front end upper portion of a vehicle body frame 6 in a steerable manner by way of a handle stem 5, and a steering handle 8 is mounted on an upper portion of the handle stem 5. Here, a ground contact portion of the front wheel 3 (a front-wheel ground contact portion) is indicated by symbol FT shown in the drawing. [0022]
The vehicle body frame 6 is formed by integrally joining plural kinds of steel members by welding or the like. Here, the vehicle body frame 6 is mainly constituted of a down frame 11 which extends obliquely in the downward and rearward direction from the head pipe 7, a main frame 12 which extends in the rearward direction from a lower portion of the down frame 11 and passes above an engine 15 which is arranged inside the low floor portion 2, and a seat frame 13 which extends obliquely in the upward and rearward directions from a rear portion of the main frame 12. [0023]
The engine 15 which constitutes a prime motor of the motorcycle 1 is, for example, a water-cooled four-stroke single-cylinder engine and is configured such that a crankshaft

is arranged in parallel in the lateral direction and a cylinder 17 is approximately frontwardly mounted on a front end portion of a crankcase 16 in an erected manner. Here, a crankshaft portion (the center of rotation of the crankshaft) as viewed in a side view of the vehicle is indicated by symbol CJ in the drawing. A transmission case 18 is contiguously mounted on a rear portion of the crankcase 16, and a front end portion of a swing arm 25 which pivotally supports a rear wheel 9 is pivotally supported on a rear end portion of the transmission case 18 in a vertically rocking manner by way of a pivot shaft 26 which extends in the lateral direction. [0024]
The swing arm 25 has inner sides of front portions of left and right arm members 27, 27 connected with each other by a cross member 29, while the rear wheel 9 is pivotally supported on a rear end portion of the swing arm 25. Here, a ground contact portion of the rear wheel 9 (a rear-wheel ground contact portion) is indicated by symbol RT in the drawing A cushion connecting portion 29a is mounted on an upper portion of the cross member 29 in an erected manner, and between the cushion connecting portion 29a and a longitudinal intermediate portion of the main frame 12, a cushion unit 30 which is integrally formed of a buffer coil spring and a dumper is arranged in a state that the longitudinal direction (stroke direction) of the cushion unit 30 extends substantially in the

longitudinal direction of the vehicle. [0025]
In the inside of the transmission case 18, a continuously variable transmission 20 which is mainly constituted of a drive pulley 21 which is arranged coaxially with the crankshaft, a driven pulley 22 which is arranged coaxially with a power transmission shaft arranged behind the crankshaft, and an endless drive belt 23 which is extended between and wound around both pulleys is housed. A rotational power of the crankshaft has a speed thereof continuously changed by way of the continuously variable transmission 20 and, at the same time, is outputted to the left side drive sprocket wheel 34 which is mounted on a rear end portion of the transmission case 18 by way of a centrifugal clutch and a final reduction gear mechanism (neither one shown in the drawings). [0026]
An endless drive chain 36 is extended and wound around the drive sprocket wheel 34 and a driven sprocket wheel 35 arranged on a left side of a rear wheel 9, and the power transmission is performed between the engine 15 and the rear wheel 9 by way of the drive chain 36. Here, the drive sprocket wheel 34 is arranged coaxially with the pivot shaft 26 of the swing arm 25. [0027]
A radiator 39 is arranged in front of the cylinder head

17a, an air cleaner case 40 is arranged above the radiator 39, and an intake pipe 42 which extends obliquely in the downward and rearward direction from a throttle body 41 which is connected to a rear portion of the air cleaner case 40 is connected to an intake port formed in an upper portion of the cylinder head 17a. Further, an exhaust pipe 43 is connected to an exhaust port formed in a lower portion of the cylinder head 17a, while the exhaust pipe 43 is curved below the cylinder head 17a, passes below the crankcase 16 in the rearward direction and, thereafter, is raised obliquely in the upward and rearward direction behind the engine 15, and is connected to a silencer 44 which is arranged on a right side of a rear portion of the vehicle body. Hereinafter, there may be a case that the exhaust pipe 43 and the silencer 44 may be referred to as an exhaust muffler 44A in a collective manner. [0028]
The vehicle body frame 6 and the engine 15 are covered with a synthetic resin-made vehicle body cover 46. The vehicle body cover 46 includes a front cowl 47 which covers a range which extends from a front portion of the head pipe 7 to both sides of the head pipe 7, an inner cover 4 8 which covers a rear portion of the head pipe 7, and an under cowl 49 which is contiguously formed with a lower portion of the front cowl 47 and covers both sides of a lower portion of the engine 15, a floor cover 50 which is contiguously formed with a lower portion

of the inner cover 48 and covers an upper portion of the engine 15, and a rear side cover 51 which is formed on both sides of a lower portion of a seat 53 and covers both sides of the rear portion of the vehicle body. [0029]
On the seat frame 13 and the rear side cover 51, a seat 53 which is integrally formed of a front seat portion for a rider and a rear seat portion for a rear pillion passenger is supported. The seat 53 is vertically rotatable about a hinge shaft 54 mounted on a front end portion thereof and hence, the rider can open or close an article accommodating box 55 arranged below the front seat portion and, at the same time, can get access to a fuel tank 56 arranged below the rear seat portion. The article accommodating box 55 has a front portion thereof positioned above a rear portion of the crankcase 16 and a rear portion thereof positioned above a front portion of the swing arm 25. Further, the article accommodating box 55 has a bottom portion thereof bifurcated such that the bottom portion strides over the cushion unit 30 and, at the same time, has a rear side of the bottom portion thereof inclined in the rearward and upward direction so as to ensure a gap which is used at the time of rocking the swing arm 25. [0030]
The down frame 11 of the vehicle body frame 6 is mainly constituted of an upper down pipe (an upper frame member) 58

which is bifurcated to left and right sides from an upper portion of the head pipe 7 and extends obliquely in the downward and rearward direction, and a lower down pipe (a lower frame member) 59 which is bifurcated to a left and right sides from a lower portion of the head pipe 7 and extends obliquely in the downward and rearward direction more steeply than the upper down pipe 58. [0031]
Between the lower portion of the head pipe 7 and the upper intermediate portion of the upper down pipe 58, a gusset pipe 60 which is arranged substantially horizontally is extended, wherein an upper end portion of the lower down pipe 59 is joined to a lower portion of the head pipe 7 by way of the gusset pipe 60. Here, in the drawing, symbol 61 indicates a gusset plate which strides over an upper portion of the lower down pipe 59, a front portion of the gusset pipe 60 and a lower portion of the head pipe 7. [0032]
On a lower portion of the lower down pipe 59, a front engine hanger bracket 62 which extends obliquely in the downward and rearward direction in the same manner is contiguously formed, a front lower engine hanger 63 is fastened to a lower end portion of the engine hanger bracket 62, and a rear end portion of the front lower engine hanger 63 is fastened to a lower side of a front portion of the crankcase

16 of the engine 15 thus supporting the engine 15. Here, an axis center of a bolt along the vehicle width direction which fastens the front lower engine hanger 63 and the engine 15 (a frontmost engine mount portion) is indicated by symbol Cl in the drawing. [0033]
The main frame 12 is mainly constituted of a pair of left and right main pipes 65 which correspond to left and right upper down pipes 58 and lower down pipes 59. The main pipes 65 are arranged substantially horizontally at a center portion of the vehicle body and have intermediate portions thereof slightly curved to project upwardly as viewed in a side view of the vehicle. Front end portions of the main pipes 65 are joined to lower portions of the lower down pipes 59 from behind and, at the same time, lower end portions of the upper down pipes 58 are j oined to front portions of the main pipes 65 from above. [0034]
The main pipes 65 (main frames 12) extend from a position above the cylinder head 17a of the engine 15 to a position above the swing arm pivotally supporting portion 18a formed on a rear end portion of the transmission case 18, while to rear end portions of the main pipes 65, rear engine hanger brackets 66 which extend rearwardly are mounted contiguously. Further, on lower portions of the engine hanger brackets 66, rear upper engine hangers 67 which project downwardly are mounted, and

lower end portions of the rear upper engine hangers 67 are connected to an upper side of a rear portion of the transmission case 18 thus supporting the transmission case 18. Here, an axis center of a bolt along the vehicle width direction which fastens the rear upper engine hangers 67 and the engine 15 (a rearmost engine mount portion) is indicated by symbol C2 in the drawing. [0035]
Further, to the front portions of the main pipes 65 which constitute a joining portion with the upper down pipes 58, the front upper engine hangers 68 are fastened, and lower end portions of the front upper engine hangers 68 are fastened to an upper side of a front portion of the crankcase 16 of the engine 15 thus supporting the engine 15. Here, an axis center of a bolt along the vehicle width direction which fastens the front upper engine hangers 68 and the engine 15 (a third engine mount portion) is indicated by symbol C3 in the drawing. The engine 15 is suspended on the vehicle body frame 6 using these three portions consisting of the third engine mount portion C3, the frontmost engine mount portion Cl and the rearmost engine mount portion C2. [0036]
The seat frame 13 is mainly constituted of left and right seat pipes 70 which extend obliquely in the upward and rearward direction from the vicinity of the curved portions of the left

and right main pipes 65, and left and right rear pipes 71 which extend obliquely in the upward and rearward direction from rear end portions of the left and right main pipes 65. The seat pipes 70 have intermediate portions thereof bent such that the intermediate portions project obliquely in the front and upward direction as viewed in a side view of the vehicle and have rear end portions thereof connected to each other thus integrally forming laterally. Rear portions of the seat pipes 70 and rear portions of the rear pipes 71 are joined by way of rear side plates 72. Further, to bent portions of the seat pipes 70, upper end portions of rear gusset pipes 7 3 which extend obliquely in the upward and rearward direction with a steep inclination from rear end portions of the main pipes 65 are joined from below. [0037]
Here, in this embodiment, the vehicle body frame 6 is formed of a so-called diamond-type frame which eliminates a frame member below the engine 15, wherein the engine 15 also functions as a reinforcing member of the vehicle body frame 6. Due to such a constitution, it is possible to lower the position of the engine 15 thus realizing the lowering of the center of gravity of the vehicle body frame 6. Further, due to the elimination of the frame member, it is possible to reduce a weight and a cost of the vehicle body frame 6. Further, the vehicle body frame 6 eliminates a frame member which extends

downwardly from the main frame 12 at a rear side of the engine 15 (a so-called pivot plate) thus further reducing the weight and the cost of the vehicle body frame 6. [0038]
A silencer 44 arranged on a right side of the rear portion of the vehicle body exhibits a cylindrical appearance which extends along a rearward and upward axis, for example, and is arranged at a position below the rear pipes 71 of the seat frame 13 as viewed in a side view of the vehicle. A support bracket 44b which projects upwardly is mounted on a longitudinally intermediate portion of the silencer 44 and the support bracket 44b is fastened to a muffler hanger 74 which is mounted on rear portions of the rear pipes 71 in a downwardly projecting manner thus allowing the seat frame 13 to support the silencer 44 (a rear portion of the exhaust muffler 44A) . Here, an axis center of a bolt along the vehicle width direction which fastens the seat frame 13 and the exhaust muffler 44A (a support portion of the exhaust muffler 44A) is indicated by symbol C4 in the drawing. The support portion (the exhaust muffler support portion) C4 is substantially positioned on a vertical line which passes the rear wheel ground contact portion RT. [0039]
Here, as viewed in a side view of the vehicle of the motorcycle 1, the front wheel ground contact portion FT, the frontmost engine mount portion Cl at the front lower engine

hangers 63, and the rearmost engine mount portion C2 at a rear upper engine hangers 67 are arranged to be positioned on a straight line L which extends rearwardly and upwardly. [0040]
Further, the exhaust muffler support portion C4 at the muffler hangers 74 and the crankshaft portion CJ at the engine 15 are also substantially positioned on an extension of the straight line L as viewed in a side view of the vehicle. The lower down pipes 59 of the down frames 11 are arranged to be substantially orthogonal to the straight line L as viewed in a side view of the vehicle. [0041]
Fig. 2 is a view which schematically shows a state in which the rear wheel ground contact portion RT is displaced laterally with respect to the front wheel ground contact portion FT due to the twisting of the vehicle body which is generated at the time of performing the turning traveling of the motorcycle 1. As shown in this drawing, when the motorcycle 1 is turned or a twisting force is applied between the front portion of the vehicle body and the rear portion of the vehicle body due to a disturbance, for example, the twisting is generated about the straight line L and hence, the front wheel gro.und contact portion FT is always positioned on the advancing direction of the rear wheel 9 (indicated by an arrow S in Fig. 2) .

Cl, C2, that is, the straight line L. [0044]
Here, by adjusting the rigidity of the third engine mount portion C3 which is spaced apart by a predetermined quantity 5 above the straight line L as viewed in a side view of the vehicle, it is possible to relatively easily adjust the twisting quantity of the vehicle body. Further, since the lower down pipes 59 which are contiguously formed with the third engine mount portion C3 are arranged substantially orthogonal to the
10 straight line L, a length of the lower down pipe 59 can be suppressed thus reducing a deflection quantity of the lower down pipes 59 whereby the twisting of the vehicle bodies is liable to be easily generated about the straight line L. [0045]
15 As a result, since the advancing direction of the rear wheel 9 is rocked about the straight line L which passes through the front wheel ground contact portion FT, even when the vehicle body is twisted about the straight line L and the rear wheel ground contact portion RT is deviated laterally, the advancing
20 direction of the rear wheel 9 is directed toward the front wheel ground contact portion FT. That is, by adopting the constitution of the present invention, even when the vehicle body is twisted, it is possible to easily adjust the rigidity of the vehicle body such that the front wheel ground contact
25 portion FT is not deviated from the advancing direction of the

rear wheel 9 whereby a feeling of integrity in the longitudinal direction of the vehicle body at the time of turning can be enhanced. [0046]
As has been explained above, the motorcycle 1 according to the embodiment is the low-floor type vehicle in which the engine 15 which is supported on the vehicle body frame 6 is arranged in the vicinity of the low-floor portion 2 which constitutes the foot rest portion, the swing arm 25 which pivotally supports the rear wheel 9 is supported in a rocking manner on the rear portion of the engine 15, and the vehicle body frame 6 includes the down frame 11 which extends obliquely in the downward and rearward direction from the head pipe 1, the main frame 12 which extends rearwardly above the engine 15 from the lower portion of the down frame 11, and the seat frame 13 which extends obliquely in the upward and rearward direction from the rear portion of the main frame 12, wherein the main frame 12 extends to the position above the swing arm pivotally supporting portion 18a from the position above the front portion of the engine 15, the rearmost engine mount portion C2 is mounted on the rear portion of the main frame 12, the frontmost engine mount portion Cl is mounted on the down frame 11, and the frontmost engine mount portion Cl is positioned on the straight line L which connects the rearmost engine mount portion C2 and the ground contact portion FT of

the front wheel 3 as viewed in a side view of a vehicle. [0047]
According to this constitution, at the time of performing the turning traveling of the motorcycle 1, when the twisting is generated between the vehicle-body rear portion which includes the engine 15 and the rear wheel 9 which is suspended by way of the swing arm 25 and the vehicle-body front portion which includes the vehicle body frame 6 and the front-wheel steering system, by extending the main frame 12 to the position above the swing arm pivotally supporting portion 18a from the position above the front portion of the engine 15 so as to ensure the rigidity of the main frame 12, it is possible to allow the twisting to be generated about the straight line L which connects the f rontmost engine mount portion Cl and the rearmost engine mount portion C2 thus ensuring the long distance between the engine mount portions, while by positioning the ground contact portion FT of the front wheel 3 on the straight line L , it is possible to suppress the deviation of the rear wheel 9 in the advancing direction with respect to the ground contact portion FT . That is, by suppressing the deviation of the ground contact portion FT of the front wheel 3 from the advancing direction of the rear wheel 9 attributed to the twisting of the vehicle body while enhancing the turning performance of the vehicle by properly imparting the twisting to the vehicle body at the time of performing turning traveling, the feeling

of integrity of the vehicle body in the longitudinal direction can be enhanced whereby the rider can feel the rigidity of the vehicle body and, at the same time, it is possible to freely set a response which a rider feels when the vehicle performs a quick motion. [0048]
Further, in the above-mentioned motorcycle 1, by positioning the crankshaft portion CJ of the engine 15 on the straight line L as viewed in a side view of the vehicle, the twisting line of the vehicle body and the rotary center of the crankshaft having the large gyroscopic precession are approximated to each other and hence, it is possible to obtain the targeted twisting characteristic more effectively. [0049]
Further, in the above-mentioned motorcycle 1, by positioning the support portion C4 of the exhaust muffler 44A of the engine 15 on the straight line L as viewed in a side view of the vehicle and above a ground contact portion RT of the rear wheel 9, it is possible to easily generate the twisting of the vehicle body about the straight line L which supports the engine 15 including the exhaust system thereof and hence, it is possible to further effectively suppress the deviation Detween the ground contact portion FT of the front wheel and Lhe advancing direction of the rear wheel. [0050]

Still further, in the above-mentioned motorcycle 1, by arranging the down frame 11 to be substantially orthogonal to the straight line L as viewed in a side view of the vehicle, the length of the down frame 11 is restricted and hence, the deflection quantity of the down frame 11 can be decreased whereby the deviation between the ground contact portion FT of the front wheel and the advancing direction of the rear wheel can be further suppressed. [0051]
Further, in the above-mentioned motorcycle 1, by arranging the third engine mount portion C3 which supports the upper portion of the engine 15 above the straight line L as viewed in a side view of the vehicle, the inotorcycle 1 can ensure the relatively high vehicle body rigidity and hence, the engine 15 is supported even at the position which is remote from the straight line L, whereby even when the weight of the engine is increased along with the increase of the displacement, an amount of twisting on the straight line L can be easily adjusted. [0052]
Here, in the above-mentioned motorcycle 1, the down frame 11 includes the upper down pipes 58 and the lower down pipes 59 which extend in parallel in the vertical direction and the third engine mount portion C3 is provided in the vicinity of the joining portion between the upper down pipes 59 and the

main frame 12. Accordingly, the rigidity of the down frame 11 per se is enhanced and, at the same time, the lower portion of the down frame 11 is joined to the engine 15 and hence, it is possible to efficiently increase the rigidity of the front portion of the vehicle body. [0053]
rhich extends downwardly from the main frame 12 on the 3 ide of the engine 15 and hence, it is possible to arrange
Further, in the above-mentioned motorcycle 1, the vehicle body frame 6 is not provided with a frame member which extends to a position below the engine 15 from the down frame 11 and, at the same time, is not provided with a frame member which extends downwardly from the main frame 12 on the rear
the
engine 15 at a low position whereby it is possible to set a position of center of gravity of the vehicle at a lower position Further, by eliminating respective frame members which extend downwardly from the down frame 11 and the main frame 12, it is possible to reduce a weight and a cost of the low-floor type vehicle. [Embodiment 2] [0054]
Next, a second embodiment of the present invention is explained.
The second embodiment differs from the first embodiment only with respect to the engine type and hence, parts identical with the parts of the first embodiment are given same symbols

and their explanation is omitted. [0055]
As shown in Fig. 3, an engine 115 which constitutes a prime mover of a motorcycle 101 is, for example, a water-cooled four-stroke V-type two-cylinder engine and is configured such that a crankshaft is arranged in parallel in the lateral direction, the front cylinders 117f are approximately frontwardly mounted on a front end portion of a crankcase 116 in an erected manner, and the rear cylinders 117r are approximately upwardly mounted on an upper portion of the crankcase 116 in an erected manner. The above-mentioned transmission case 18 is contiguously mounted on a rear portion of the crankcase 116, [0056]
A radiator 39 is arranged in front of a front cylinder head 117fa, an air cleaner case 40 is arranged above the radiator 39, and respective intake pipes 142 which are bifurcated and extend from a throttle body 41 which is connected to a rear portion of the air cleaner 4 0 are respectively connected to intake ports formed in an upper portion of the front cylinder head 117fa and a front portion of a rear cylinder head 117ra . Further, to exhaust ports formed in a lower portion of the front cylinder head 117fa and a rear portion of the rear cylinder head 117ra, exhaust pipes 143 are respectively connected. These exhaust pipes 143 are converged into one pipe

behind the engine 115 and the converged exhaust pipe is raised obliquely in the upward and rearward direction and is connected to a silencer 44. [0057]
Front lower engine hangers 63 mounted on lower portions of lower down pipes 59 are fastened to a lower side of a front portion of the crankcase 116 of the engine 115 at a frontmost engine mount portion Cl and support the engine 115. Further, rear upper engine hangers 67 mounted on rear end portions of main pipes 65 are connected to an upper side of a rear portion of a transmission case 18 of the engine 115 at a rearmost engine mount portion C2 and support the engine 115. Further, front upper engine hangers 68 mounted on front portions of the main pipes 65 are fastened to an upper side of a front portion of the crankcase 116 of the engine 115 at a third engine mount portion C3 and support the engine 115. Here, the front upper engine hangers 68 and the third engine mount portion C3 are positioned between the front and rear cylinders 117f, 117r as viewed in a side view of the vehicle. [0058]
Then, as viewed in a side view of the vehicle, a ground contact portion FT of a front wheel 3 of the motorcycle 101, the frontmost engine mount portion Cl at the front lower engine hangers 63, and the rearmost engine mount portion C2 at a rear upper engine hangers 67 are substantially arranged to be

positioned on a straight line L which extends rearwardly and upwardly. Further, an exhaust muffler support portion C4 at the muffler hangers 74 and a crankshaft portion CJ at the engine 15 are also substantially positioned on an extension of the straight line L as viewed in a side view of the vehicle. Still further, the third engine mount portion C3 at the front upper engine hangers 68 is arranged in a spaced-apart manner above the straight line L by a predetermined amount. [0059]
As has been explained above, in the motorcycle 101 of the second embodiment, the engine 115 which is supported on the vehicle body frame 6 is the V-type engine having the front and rear cylinders 117f, 117r and the third engine mount portion C3 is arranged between the front and rear cylinders 117f, 117r and hence, it is possible to efficiently ensure the engine support rigidity when the high-performance and narrow-width V-type engine is mounted on the vehicle body frame 6. [0060]
Here, the present invention is not limited to the above-mentioned respective embodiments and, for example, the third engine mount portion C3 may be arranged below the straight line L. Further, the main frame 12 maybe extended to a position behind a swing arm pivot of the main frame 12 thus constituting a portion of the seat frame 13.
Further, it is needless to say that the constitutions

of the above-mentioned embodiments are examples of the present
invention and the detailed constitutions of the engine type
and the vehicle body frame 6 are not limited to the
above-mentioned respective embodiments and various
modifications are conceivable without departing from the gist
of the present invention.
[Brief Description of the Drawings]
[0061]
[Fig. 1]
A side view of a motorcycle according to a first embodiment of the present invention. [Fig. 2]
An operation explanatory view of the above-mentioned motorcycle. [Fig. 3]
A side view of a motorcycle according to a second embodiment of the present invention. [Description of Reference Numerals and Signs] [0062]
I, 101: motorcycle (low-floor type vehicle) 2: low-floor portion 3: front wheel 6: vehicle body frame 7: head pipe 9: rear wheel

11: down frame
12: main frame
13: seat frame
15, 115: engine
18a: swing arm pivotally supporting portion
25: swing arm
44A: exhaust muffler
58: upper down pipe (upper frame member)
59: lower down pipe (lower frame member)
Cl: frontmost engine mount portion
C2: rearmost engine mount portion
C3: third engine mount portion
C4: exhaust muffler support portion
FT: front wheel ground contact portion
RT: rear wheel ground contact portion
CJ: crankshaft portion
L: straight line

[Designation of Document] Claims [Claim 1]
A low-floor type vehicle in which an engine which is supported on a vehicle body frame is arranged in the vicinity of a low-floor portion which constitutes a foot rest portion, a swing arm which pivotally supports a rear wheel is supported in a rocking manner on a rear portion of the engine, and the vehicle body frame includes a down frame which extends obliquely in the downward and rearward direction from a head pipe, a main frame which extends rearwardly above the engine from a lower portion of the down frame, and a seat frame which extends obliquely in the upward and rearward direction from a rear portion of the main frame, wherein
the main frame extends to a position above at least a swing arm pivotally supporting portion from a position above a front portion of the engine, a rearmost engine mount portion is mounted on a rear portion of the main frame, a frontmost engine mount portion is mounted on the down frame, and the frontmost engine mount portion is positioned on a straight line which connects the rearmost engine mount portion and a ground contact portion of a front wheel as viewed in a side view of a vehicle. [Claim 2]
A low-floor type vehicle according to claim 1, wherein a crankshaft portion of the engine is positioned on the line

as viewed in a side view of the vehicle. [Claim 3]
A low-floor type vehicle according to claim 1 or claim 2, wherein a support portion of an exhaust muffler of the engine is positioned on the line and above a ground contact portion of the rear wheel as viewed in a side view of the vehicle. [Claim 4]
A low-floor type vehicle according to any one of claims 1 to claim 3, wherein the down frame is arranged to be substantially orthogonal to the line as viewed in a side view of the vehicle. [Claim 5]
A low-floor type vehicle according to any one of claims 1 to claim 4, wherein a third engine mount portion which supports an upper portion of the engine is provided above or below the line as viewed in a side view of the vehicle. [Claim 6]
A low-floor type vehicle according to claim 5, wherein the down frame includes an upper frame member and a lower frame member which extend in parallel vertically, and the third engine mount portion is provided in the vicinity of a joint portion of the upper frame member and the main frame. [Claim 7]
A low-floor type vehicle according to claim 5 or claim 6, wherein the engine is a V-type engine which includes front

and rear cylinders, and the third engine mount portion is arranged between the front and rear cylinders. [Claim 8]
A low-floor type vehicle according to any one of claims 1 to claim 6, wherein the vehicle body frame is not provided with a frame member which extends to a position below the engine from the down frame and, at the same time, is not provided with a frame member which extends downwardly from the main frame on the engine rear side.

Documents:

1326-che-2006 abstract-duplicate.pdf

1326-che-2006 claims-duplicate.pdf

1326-CHE-2006 CORRESPONDENCE OTHERS.pdf

1326-CHE-2006 CORRESPONDENCE PO.pdf

1326-che-2006 description (complete)-duplicate.pdf

1326-che-2006 drawings-duplicate.pdf

1326-che-2006-abstract.pdf

1326-che-2006-claims.pdf

1326-che-2006-correspondnece-others.pdf

1326-che-2006-description(complete).pdf

1326-che-2006-drawings.pdf

1326-che-2006-form 1.pdf

1326-che-2006-form 18.pdf

1326-che-2006-form 26.pdf

1326-che-2006-form 3.pdf

1326-che-2006-form 5.pdf

1326-che-2006-priority-document.pdf

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Patent Number

232246

Indian Patent Application Number

1326/CHE/2006

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

16-Mar-2009

Date of Filing

27-Jul-2006

Name of Patentee

HONDA MOTOR CO., LTD

Applicant Address

1-1, MINAMIAOYAMA 2-CHOME, MINATO-KU, TOKYO,

Inventors:

#	Inventor's Name	Inventor's Address
1	HOSOYA, YUKIO	C/O HONDA R&D CO., LTD., 4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA 351-0193,
2	TAKENAKA, MASAHIKO	C/O HONDA R&D CO., LTD., 4-1, CHUO 1-CHOME, WAKO-SHI, SAITAMA 351-0193,

PCT International Classification Number

B62K11/02,B62M7/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2005-220897	2005-07-29	Japan