Title of Invention

INTAKE DEVICE FOR ENGINE IN TWO-OR THREE-WHEELED MOTOR VEHICLES

Abstract

In a two or three wheeled motor vechile,a strong swirl of an air-fuel mixture is to be produced in a combustion chamber to improve the fuel econoy even without the provision of any special swirler in an intake system. In a two or three wheeled motor vehicle wherein an engine E is disposed in such a manner that the axes of a cylinder bore 35a and a combustion chamber 36a contiguous thereto are substantially aligned with a vetical plane V including a centre line of a vehicle body frame 15,an intake system 47 including an intake port 38 which is open to the combustion chamber 36a and an intake pipe 45 which is contigous to an upstram side of the intake port 38,is disposed so as to extend in a tangential direction of a peripheral edge of the combustion chamber 36a and cross the vertical plane V.

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] PROVISIONAL/COMPLETE SPECIFICATION [See Section 10] "INTAKE DEVICE FOR ENGINE IN TWO-OR THREE-WHEELED MOTOR VEHICLES" HONDA GIKEN KOGYO KABUSHIKI KAISHA, a corporation of Japan, 1-1, Minamiaoyama 2-chome, Minato-ku, Tokyo, Japan The following specification particularly describes the nature of the invention and the manner in which it is to be performed :- [Detailed Description of the Invention] [0001]— [Technical Field to Which the Invention Pertains] The present invention relates to an intake device for an engine, in a two- or three-wheeled motor vehicle wherein the engine is disposed in such a manner that the axes of a cylinder bore and a combustion chamber contiguous thereto are substantially aligned with a vertical plane including a center line of a vehicle body frame. 40002] [Prior Art] A two-wheeled motor vehicle wherein an engine is disposed in such a manner that the axes of a cylinder bore and a combustion chamber contiguous thereto are substantially aligned with a vertical plane including a center line of a vehicle body frame, is already known as is disclosed, for example, in Japanese Utility Model Publication No. Sho 62-39993. [0003]— [Problem to be Solved by the Invention] Recently there has been a keen demand for the improvement of fuel economy in a two- or three-wheeled motor vehicle, and for meeting the demand it is necessary to increase the flowing velocity of intake air in an intake port for allowing an air-fuel mixture to be agitated in both combustion chamber and cylinder bore and create a swirl for making lean burn of the mixture possible. However, in the conventional two-wheeled motor vehicle of the type being considered, as is disclosed also in the above publication, an intake system in the engine is disposed on the foregoing vertical plane, so with the intake system alone it is impossible to increase the flowing velocity of the intake air to a sufficient extent or create a swirl of the mixture. For producing a swirl it is necessary that the intake port be provided with a swirler for swirling a stream of intake air which passes the intake port. But this is not desirable because the shape and structure of the intake port become complicated, the productivity is deteriorated and the cost increases. [0005] The present invention has been accomplished in view of such circumstances and it is an object of the invention to provide an intake device for an engine in a two- or three-wheeled motor vehicle which, even without the provision of any special swirler in the intake system, can produce a strong swirl of an air-fuel mixture in both combustion chamber and cylinder bore and can effect lean burn and improve the fuel economy. It is another object of the present invention to provide an intake device for an engine in a two- or three-wheeled motor vehicle capable of increasing the flowing velocity of intake air to a sufficient extent, allowing an air-fuel mixture to be agitated effectively in both combustion chamber and cylinder bore, permitting the fuel economy to be improved by lean burn, and having a rational layout to prevent interference of an intake system with a radiator in the case of a water-cooled type engine adopted for preventing the occurrence of knocking caused by lean burn, [0007] [Means for Solving the Problem] For achieving the above-mentioned object, in a two-or three-wheeled motor vehicle wherein an engine is disposed in such a manner that the axes of a cylinder bore and a combustion chamber contiguous thereto are substantially aligned with a vertical plane including a center line of a vehicle body frame, an intake device according to the present invention is firstly characterized in that an intake system including an intake port which is open to the combustion chamber and an intake pipe which is contiguous to an upstream side of the intake port, is disposed so as to extend in a tangential direction of a peripheral edge of the combustion chamber and cross the vertical plane. [0008] According to this first feature, the length of the intake system extending in a tangential direction of the peripheral edge of the combustion chamber can be ensured sufficiently without, being interfered by the body frame and vehicle body components attached thereto. Consequently, by utilizing the inertia of intake air in the intake system effectively it is possible to produce a strong swirl of an air-fuel mixture in both combustion chamber and cylinder bore, making lean burn possible and permitting contribution to the improvement of fuel economy, and at the same time it is possible to obtain a high charging efficiency and improve the engine output. It is also possible to make contribution to the reduction of cost because it is not necessary for the intake system to be provided with a special swirler. In addition to the above first feature, the present invention is secondly characterized in that a timing drive chamber which receives therein a timing drive device in a valve operating mechanism is formed in an engine body on the same side as an opening end portion of the intake port which opening end portion is open to the combustion chamber with respect to the vertical plane. [OOlO] According to this second feature, the length of the intake system extending in a tangential direction of the peripheral edge of the combustion chamber can be ensured sufficiently without being interfered by the timing drive chamber. [0011] In addition to the above first or second feature, the present invention is thirdly characterized in that an air cleaner disposed on an upstream end of the intake system, as well as a water pump in the engine and a radiator communicating with the water pump, are disposed respectively on both sides of the vertical plane. [0012] According to this third feature, not only the air cleaner and the radiator can be disposed in a well-balanced state on both sides of the body frame, but also it is possible to shorten the communication path between the radiator and the water pump. Further, in a two- or three-wheeled motor vehicle wherein a timing drive chamber which receives therein a timing drive device in a valve operating mechanism is disposed on one side in the transverse direction of an engine body with a combustion chamber positioned below a vehicle body frame, an intake device according to the present invention is fourthly characterized in that an upstream end of an intake port contiguous to the combustion chamber is open to the engine body on the side opposite to the timing drive chamber, an air cleaner disposed at an upstream end of an intake system including the intake port is attached to a side face of the body frame on the same side as the intake port, and a radiator for cooling the engine is attached to a side face of the body frame on the side opposite to the intake port. According to this fourth feature, the intake system including the intake port can be made long, with minimum bending, without being interfered by the timing drive chamber and the radiator, and by utilizing the inertia of intake air in the intake system effectively it is made possible to increase the flowing velocity of intake air to a sufficient extent and attain a strong agitation of the mixture in both combustion chamber and cylinder bore and improvement of the charging efficiency. Thus, it is possible to satisfy both fuel economy and improved engine output. Besides, by adopting a water cooling method for the engine it is possible to prevent the occurrence of knocking caused by lean burn. Additionally, the air cleaner which is easily affected by dust and the radiator which utilizes running air for cooling can be disposed in a well-balanced state on the sides of the body frame, thus permitting contribution to the improvement in durability of the engine. [Mode for Carrying Out the Invention] The present invention will be described hereinunder by way of an embodiment thereof illustrated in the accompanying drawings. [Brief Description of the Drawings] [Fig. 1]— Fig. 1 is a side view of a two-wheeled motor vehicle with an engine mounted thereon in accordance with the present invention. [Fig. 2] Fig. 2 is an enlarged view as seen in the direction" of arrows 2-2 in Fig. 1. [Fig. 3] Fig. 3 is a sectional view taken on line 3-3 in Fig 2 . [Fig. 4]. Fig. 4 is an enlarged sectional view taken on line 4-4 in Fig. 3. [Fig. 5] Fig. 5 is a sectional view taken on line 5-5 in Fig 3. [Fig. 6] Fig. 6 is a sectional view taken on line 6-6 in Fig 5. [Fig. 7] Fig. 7 is a view as seen in the direction of arrows 7-7 in Fig. 2. [Fig. 8] Fig. 8 is a perspective view of a front cover. In Fig. 1, a vehicle body frame 15 of a two-wheeled motor vehicle is provided at a front end thereof with a head pipe 16, and a front fork 17 which supports a front wheel WF through an axle is connected to the head pipe 16 pivo.ta.lly and steerably. A steering stem is erected on an upper end of the front fork 17 and a bar handle 18 is connected to the steering stem. A front fender 19 which covers the front wheel WF from above is supported by the front fork 17. A rear fork 20 which supports a rear wheel WR through an axle is pivotally connected to an intermediate portion of the body frame 15 and a rear cushion 21 is provided between a rear portion of the body frame 15 and the rear fork 20. [0018] At an intermediate portion of the body frame 15 is supported a power unit P which comprises a water-cooled four-cycle engine E and a transmission M. Output of the transmission M is transmitted to the rear wheel WR through a chain 22. A radiator 24, which is supported by an engine body 33 of the engine E and the body frame 15, is disposed above the engine E and an air cleaner 23 is also disposed above the engine E.. Further, a fuel tank 25 is disposed above the transmission M and a receptacle box 26 capable of receiving electric appliances therein is disposed above the fuel tank 25. The fuel tank 25 and the receptacle box 2 6 are supported by the body frame 15 An exhaust pipe 27 for conducting exhaust gas from the engine E is connected to an exhaust muffler 28 which is disposed between the power unit P and the rear wheel WR. A front portion of the body frame 15, engine E, air cleaner 23 and radiator 24 are covered with a leg shield 29 from above, the leg shield 29 being formed of a synthetic resin and attached to the body frame 15. Likewise, the rear portion of the body frame 15, fuel tank 25 and receptacle box 26 are covered with a rear cover 30, the rear cover 30 being formed of a synthetic resin and attached to the body frame 15. A rear fender 31 which covers a rear portion of the rear wheel WR from above is contiguous to the rear cover 30. A seat 32 is provided on the rear cover 3 0 so that it can open and close an upper-end opening of the receptacle box 26. A rider of the vehicle sits on the seat 32. As shown in Figs. 1 to 4 and Fig.7,the engine body 33 is provided with a cylinder block 35 disposed substantially horizontally with its head portion facing toward the front of the vehicle and a cylinder head 36 joined to a front end of the cylinder block 35. The engine body 33 is supported by a plurality of engine hangers 37 projected from the body frame 15. In the cylinder head 36 are formed a combustion chamber 36a which is coaxial with and contiguous to a cylinder bore 35a formed in the cylinder block 35, as well as an intake port 38 and an exhaust port 39 which are open to the combustion chamber 36a. The intake and exhaust ports 38, 39 are opened and closed with intake and exhaust valves 40 and 41, respectively, at respective open end portions which are open the combustion chamber 3 6a. A timing drive device 42 is provided in a valve operating mechanism of a known structure which actuates the intake and exhaust valves 40, 41 in their opening and closing directions, and a timing drive chamber 43 which accommodates the timing drive device 42 is formed in one side wall of the cylinder block 35 so as to be adjacent the cylinder bore 35a. As shown clearly in Figs 2 the engine E is disposed in such a manner that the axis of the cylinder bore 35a and combustion chamber 3 6a is substantially aligned with a vertical plane V including a center line of the body frame 15 which passes through the center of the head pipe 16. The intake port 38 is disposed in a substantially rectilinear shape with a steep gradient descending toward a downstream side along a tangent T of a peripheral edge of the combustion chamber 36a and across the vertical plane V. An open end portion of the intake port 3 8 which is open to the combustion chamber 36a is disposed close to one side of the vertical plane V and above the center of the combustion chamber 3 6a. On the other hand, an open end portion of the exhaust port 39 which is open to the combustion chamber 36a is disposed close to the opposite side of the vertical plane V and below the center of the combustion chamber 36a. A pair of spark plugs 44 and 44" having respective electrodes which face the combustion chamber 36a on both sides of a diametrical line L are threadedly engaged with the cylinder head 36 which diametrical line L joins the centers of open end portions of both ports 38 and 39 which are open to the combustion chamber 3 6a. The spark plugs 44 and 44" are energized simultaneously. An intake pipe 45 extends obliquely upward substantially along an extension of the axis of the intake port 38 and is connected to an upstream end of the intake port. A throttle body 46 is connected to an upstream end portion of the intake pipe 45 and the air cleaner 23 is connected to an upstream end of the throttle body 46. As known well, the throttle body 46 has an intake passage communicating with the air cleaner 23 and the intake pipe 45 and also has a throttle valve for opening and closing the passage. The intake port 38, intake pipe 45, throttle body 46 and air cleaner 23 constitute an intake system 47 in the engine E. The intake system 47 is constructed in a substantially rectilinear shape with a steep gradient descending toward the downstream steam across the foregoing vertical plane V. The intake pipe 45 has a connecting flange 45a at its downstream end portion and is connected to the cylinder head 36 through the flange 45a using bolts 45". A cylindrical mounting portion 49 is integral with the connecting flange 45a and an electromagnetic type fuel injection valve 50 of a known structure for the injection fuel toward the downstream side of the intake port 38 is mounted to the cylindrical mounting portion 49 so as to be positioned inwards of the vehicle body with respect to the intake pipe 45 (see Fig. 2). Thus, with the intake pipe 45, contact of the fuel injection pipe 50 with an object which approaches sideways from the exterior can be avoided. The timing drive chamber 43 formed in the cylinder block 35 at a position adjacent to one side of the cylinder bore 35a lies on the same side as the open end portion of the intake port 38 which is open to the combustion chamber 36a relative to the vertical plane V. As shown in Figs. 3 and 5, upper and lower portions of the cleaner case 70 of the air cleaner 23 disposed on one side of the vertical plane V are formed with support pieces 51 and 51", respectively. The support pieces 51 and 51" are fixed with bolts 52 to one side face of an upper portion of the body frame 15 positioned near the head pipe 16, whereby the air cleaner 23 is supported by the body frame 15 in the vicinity of the head pipe 16. On the other hand, the radiator 24 is disposed on the side opposite to the air cleaner 23 with respect to the vertical plane V and is secured to the opposite side face of the body frame 15. The radiator 24 is made up of an upper tank 24a, a lower tank 24b, and a core 24c which connects the tanks 24a and 24b. Using a bolt 56, a support piece 53 of the upper tank 24a and a support piece 54 of the body frame 15 are connected together with an elastic member 55 therebetween, whereby the radiator 24 is secured to the body frame 15. The interior of the lower tank 24b is partitioned into a first chamber Bl located on an outer side of the vehicle body and a second chamber B2 located on an inner side of the vehicle body. Both chambers Bl and B2 are in communication with the upper tank 24a through the core 24c. A water pump 57 is disposed in the cylinder head 36 at an end portion located on the same side as the radiator 24. A first hose 58a extending from a first chamber Bl of the lower tank 24b is connected to a suction pipe 59 of the water pump 57, a second hose 58b extending from a discharge pipe 60 of the water pump 57 is connected to a water jacket inlet pipe (not shown) in the cylinder block 35, and a third hose 58c extending from a water jacket outlet pipe 61 in the cylinder head 36 is connected to the second chamber B2 in the lower tank 24b. Thus, the cooling water which has entered the second chamber B2 through the third hose 58c rises through one half of the core 24c and enters the upper tank 24a, thence flows down through the other half of the core 24c and reaches the first chamber Bl. In this way it becomes possible to shorten the first and third hoses 58a, 58c. Through the three members - the hoses 58a, 58c and the elastic member 55 located at an upper position - the radiator 24 can be supported elastically by the body frame 15 and the engine E. As shown in Figs. 2 and 3, the leg shield 29 is made of a synthetic resin and comprises a central shield portion 29s which covers the front portion of the body frame 15 from above and a pair of overhanging shield portions 29a, 29b overhanging right and left from the central shield portion 29s to cover right and left legs of the rider from the front side. The right and left overhanging shield portions 29a, 29b overhang obliquely forward so as to cover the air cleaner 23 and the radiator 24 also from right and left outer sides. The overhanging shield portion 29a overhanging on the left-hand side (as seen from the rider sitting on the seat 32) which is the radiator 24 side is supported by the body frame 15 through a stay 62. More specifically, both end portions of the stay 62 are fixed with bolts 63 to the body frame 15 and also to the left-hand overhanging shield portion 29a. The overhanging shield portion 29b located on the right-hand side which is the air cleaner 23 side is supported by the body frame 15 through the air cleaner 23. To be more specific, the cleaner case 70 is fixed to the body frame 15 as described earlier and the right-hand overhanging shield portion 29b is fixed with a bolt 65 to a support piece 64 of the cleaner case 70. Thus, the cleaner case 70 also serves as a stay for supporting the right-hand overhanging shield portion 29b, whereby it is possible to simplify the support structure for the leg shield 29. As shown in Figs. 5 and 8, a front cover 66 is connected to a front side of the leg shield 29. The front cover 66, which is also made of a synthetic resin, comprises a central cover portion 66s which covers the head pipe 16 from the front side and a pair of side cover portions 6 6a and 6 6b extending downward from both right and left ends of the central cover portion 66s to cover the front sides of the right and left overhanging shield portions 29a, 29b. Using a large number of machine screws 67, the side cover portions 66a and 66b are fixed to outer edges of the right and left overhanging shield portions 29a, 29b. At this time, an auxiliary device chamber 68 for receiving the air cleaner 23 therein is formed between the right-hand overhanging shield portion 29b and the side cover portion 66b. As shown in Fig. 8, both end portions of a radiator grill 78 for introducing running air into the radiator 24 are fixed to the right and left side cover portions 66a, 66b with plural bolts 79, whereby both side cover portions 66a and 66b are reinforced with respect to each other. Referring again to Figs. 5 and 6, the air cleaner 23 is made up of the cylindrical cleaner case 70 whose underside is open, a lid 71 connected to the open side of the cleaner case 70 removably, and a cylindrical cleaner element 72 received and supported within the cleaner case 70. The cleaner case 70 is formed so that its cross section is laterally long in the width direction of the right-hand overhanging shield portion 29b and so that the front-to-rear width of the cross section is large in one half located on an inner side of the vehicle body and small in the other half. A front wall of the cleaner case 70 is formed with a stepped portion 70a for avoiding interference with the front fork 17 when the front fork rotates. Further, the cylindrical cleaner element 72 is disposed in the large front-to-rear width portion within the cleaner case 70. In the interior of the cleaner case 70, the outside of the cleaner element 72 serves as an uncleaned chamber 73 and the inside as a cleaned chamber 74. An air inlet pipe 75 is open to a portion of the uncleaned chamber 73 which portion is small in the front-to-rear width, while an air outlet pipe 76 is open to a central portion of the uncleaned chamber 73, the air inlet and outlet pipes 75, 76 being formed in the lid 71. The air outlet pipe 76 is connected to an upstream end portion of the throttle valve 46 with a band 77. Next, the operation of this embodiment will be described below. During operation of the engine E, when an intake stroke begins in which the intake valve 40 opens, the outside air which has entered the uncleaned chamber 73 from the air inlet pipe 75 in the air cleaner 23 is filtered with the cleaner element 72 and shifts to the cleaned chamber 74, then passes through the air outlet pipe 76, intake passage in the throttle body 46, the intake pipe 45 and the intake port 38 in this order, and is sucked into the combustion chamber 3 6a and the cylinder bore 35a. In the meantime, the fuel injection valve 50 injects a predetermined amount of fuel toward a downstream side of the intake port 38, which injected fuel is sucked into the combustion chamber 36a and the cylinder bore 35a while producing a mixture together with the air. Since the intake system 47 extending from the air cleaner 23 to the intake port 38 is constituted in a generally rectilinear shape extending in the tangential direction T of the peripheral edge of the combustion chamber 36a and descending downstream with a steep gradient while crossing the vertical plane V which includes the center line of the body frame 15, it is possible to decrease the intake resistance of the intake system 47 and at the same time ensure a sufficient length of the intake system without being interfered by the body frame 15 and vehicle body components attached thereto. Therefore, it is possible to effectively utilize the inertia of intake air within the intake system 47, thereby cause the air-fuel mixture to flow along the inner peripheral surfaces of the combustion chamber 3 6a and the cylinder bore 35a, and attain a high charging efficiency while inducing a powerful swirl (see arrow A in Fig. 4). Consequently, at the time of ignition it is possible to effect lean burn, whereby it is possible to improve both fuel economy and engine output. Besides, it is not necessary that a special swirler be provided in the intake system 47, and therefore it is also possible to make contribution to the reduction of cost. Moreover, since the timing drive chamber 43 formed in the cylinder block 35 is located on the same side as the open end portion of the intake port 3 8 open to the combustion chamber 36a with respect to the vertical plane V, even in the case of a four-cycle engine E, the length of the intake system 47 extending in the tangential direction T of the peripheral edge of the combustion chamber 36a can be ensured sufficiently without being interfered by the timing drive chamber 43. Besides, by adopting a water cooling system for the engine E it is possible to prevent the occurrence of knocking in a lean burn condition. Further, since the air cleaner 23 mounted at an upstream end of the intake system 47, as well as the water pump 57 in the engine E and the radiator 24 communicating therewith, are disposed respectively on both sides of the vertical plane V, the air cleaner 23 which is apt to be affected by dust and the radiator 24 which utilizes the running air for cooling can be disposed in a well-balanced state on both sides of the body frame 15. Besides, it is possible to shorten the first and third hoses 58a, 58c which connect the radiator 24 with the water pump 57 and the cylinder head 36. Although the air cleaner 23 is disposed in a narrow space formed between the body frame 15 and the right-hand overhanging shield portion 29b, since the cleaner case 70 is formed laterally long along the width of the overhanging shield portion 29b, it is possible to ensure a sufficient volume of the cleaner case 70 and decrease the intake resistance and intake noise. In this case, that the air outlet pipe 76 in the air cleaner 23 is disposed on an inner side of the vehicle body within the oblong cleaner case 70 and is drawn as close as possible to the position just above the cylinder head 36 which is disposed on the vertical plane V, is effective in making steep the downward gradient of the intake system 47 and thereby decreasing the intake resistance. The present invention is not limited to the above embodiment, but various modifications may be made within the scope not departing from the gist of the invention. For example, if the agitation of the air-fuel mixture is done to a satisfactory extent in the combustion chamber 36a and cylinder bore 35a, it is not always necessary that the intake port 3 8 be disposed in the tangential direction T of the combustion chamber 3 6a. Moreover, the air inlet pipe 75 of the air cleaner 23 may be connected to the body frame 15 which is a hollow pipe open to the atmosphere at one end portion thereof, thereby allowing the clean air present within the body frame 15 to flow into the air cleaner 23. Further, the present invention is applicable not only to the two-wheeled motor vehicle referred to in the above embodiment but also to a three-wheeled motor vehicle. [Effects of the Invention] As set forth above, according to the first feature of the present invention, in a two- or three-wheeled motor vehicle wherein an engine is disposed in such a manner that the axes of a cylinder bore and a combustion chamber contiguous thereto are substantially aligned with a vertical plane including a center line of a vehicle body frame, an intake system including an intake port which is open to the combustion chamber and an intake pipe which is contiguous to an upstream side of the intake port, is disposed so as to extend in a tangential direction of a peripheral edge of the combustion chamber and cross the vertical plane. With this arrangement, the length of the intake system extending in a tangential direction of the peripheral edge of the combustion chamber can be ensured sufficiently without being interfered by the body frame and vehicle body components attached thereto. Consequently, by utilizing the inertia of intake air in the intake system effectively it is possible to create a strong swirl of an air-fuel mixture within the combustion chamber and hence possible to effect lean burn and contribute to the improvement of fuel economy. At the same time it is possible to obtain a high charging efficiency and improve the engine output. Besides, contribution can also be made to the reduction of cost because the provision of a special swirler is not needed in the intake system. According to the second feature of the present invention, since a timing drive chamber which receives therein a timing drive device in a valve operating mechanism is formed in the cylinder block on the same side as an opening end portion of the intake port which opening end portion is open to the combustion chamber with respect to the vertical plane, the length of the intake system extending in a tangential direction of the peripheral edge of the combustion chamber can be ensured sufficiently without being interfered by the timing drive chamber. According to the third feature of the present invention, since an air cleaner disposed on an upstream end of the intake system, as well as a water pump in the engine and a radiator communicating with the water pump, are disposed respectively on both sides of the foregoing vertical plane, the air cleaner and the radiator can be disposed in a well-balanced state on both sides of the body frame and it is possible to shorten the communication path between the radiator and the water pump. According to the fourth feature of the present invention, in a two- or three-wheeled motor vehicle wherein a timing drive chamber which receives therein a timing drive device in a valve operating mechanism is disposed on one side in the transverse direction of an engine body with a combustion chamber positioned below a vehicle body frame, an upstream end of an intake port contiguous to the combustion chamber is open to the engine body on the side opposite to the timing drive chamber, an air cleaner disposed at an upstream end of an intake system including the intake port is attached to a side face of the body frame on the same side as the intake port, and a radiator for cooling the engine is attached to a side face of the body frame on the side opposite to the intake port. With this arrangement, the intake system including the intake port can be made long, with minimum bending, without being influenced by the timing drive chamber and the radiator, and by utilizing the inertia of intake air in the intake system effectively it is possible to effect a strong agitation of the mixture within both combustion chamber and cylinder bore and improve the charging efficiency. Besides, it is possible to effect lean burn and contribute to the improvement of fuel economy. At the same time it is possible to obtain a high charging efficiency and thereby improve the engine output. Further, by adopting a water cooling method for the engine it is possible to prevent the occurrence of knocking caused by lean burn. Additionally, the air cleaner which is easily affected by dust and the radiator which utilizes running air for cooling can be disposed in a well-balanced stated on both sides of the body frame, thus permitting contribution to the improvement in durability of the engine. [Explanation of Reference Numerals] E ... engine T ... tangential direction We claim 1. An intake device for an engine, in a two- or three-wheeled motor vehicle wherein the engine (E) is disposed in such a manner that the axes of a cylinder bore (35a) and a combustion Chamber (36a) contiguous thereto are substantially aligned with a vertical plane (V) including a center line of a vehicle body frame (15), characterized in that: an intake system (47) including an intake port (38) which is open to the combustion chamber (36a) and an intake pipe (45) which is contiguous to an upstream side of the intake port (38) , is disposed so as to extend in a tangential direction (T) of a peripheral edge of the combustion chamber (36a) and cross the vertical plane (V). 2. An intake device for an engine in a two -or three- wheeled motor vehicle according to claim 1, wherein a timing drive chamber (43) which receives therein a timing drive device (42) in a valve operating mechanism is formed in an engine body (33) on the same side as an opening end portion of the intake port (38) which opening end portion is open to the combustion chamber (36a) with respect to said vertical plane (V). 3. An intake device for an engine in a two-or three-wheeled motor vehicle according to claim 1 or claim 2, wherein an air cleaner (23) disposed on an upstream end of the intake system (47), as well as a water pump (57) in the engine (E) and a radiator (24) communicating with the water pump (57), are disposed respectively on both sides of said vertical plane (V). 4. An intake device for an engine, in a two-or three-wheeled motor vehicle wherein a timing drive chamber (43) which receives therein a timing drive device (42) in a valve operating mechanism is disposed on one side in the transverse direction of an engine body (33) with a combustion chamber (36a) positioned below a vehicle body frame, characterized in. that*. an upstream end of an intake port (38) contiguous to the combustion chamber (36a) is open to the engine body (33) on the side opposite to said timing drive chamber (43), an air cleaner (23) disposed at an upstream end of an intake system (47) including the intake port (38) is attached to a side face of the body frame (15) on the same side as the intake port (38), and a radiator (24) for cooling the engine is attached to a side face of the body frame (15) on the side opposite to the intake port (38). 5. An intake device for an engine substantially as hereinbefore described with reference to the accompanying drawings. Dated this 12th day of July, 2001. [RANJNA MEHTA DUTT] OF REMFRY & SAGAR AGENT FOR THE APPLICANTS

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