Title of Invention

"AIR-COOLED INTERNAL COMBUSTION ENGINE EQUIPPED WITH SENSOR FOR DETECTING A ENGINE-STATE"

Abstract

An air-cooled internal combustion engine (E) comprising: an engine body; a sensor attached to the engine body to detect an engine-state; and a shroud (45) covering the engine body to define a cooling air passage (46) surrounding the engine body; characterized in that the sensor and electric cable (76) connected to the sensor is disposed in the cooling air passage (46); the sensor includes an exhaust gas sensor which detects exhaust gas property as the engine-state and a temperature sensor which detects engine temperature as the engine state; and the exhaust gas sensor and the temperature sensor each having a detecting portion and a joint are attached such that the joint connected to the electric cable (76) is disposed closer to the cooling fan (40) carried on a shaft end of a crankshaft (7) than the detecting portion disposed inside the engine body.

Full Text

[Name of Document] Specification [Title of the Invention] Air-cooled. Internal Combustion Engine Equipped with a Sensor for Detecting a Engine-state [Technical Field] [0001] The present invention relates to an air-cooled internal combustion engine equipped with a sensor for detecting an engine-state and a shroud which forms a cooling air passage surrounding an engine body. This engine is mounted on a vehicle for instance. [Background Art] [0002] There is known an air-cooled internal engine equipped with a sensor for detecting engine temperature as an engine-state and a shroud which forms a cooling air passage surrounding an engine body (see e.g., Patent Document I). In addition, there is known an internal combustion engine equipped with an exhaust gas sensor for detecting exhaust gas property as an engine-state (see e.g., Patent Document 2). [Patent Document 1] Japanese Patent Laid-Open No. 2004-11436 [Patent Document 2] Japanese Patent Laid-Open No. 2004-316430 [Disclosure of the Invention] [Problem to be Solved by the Invention] [0003] A sensor for detecting an engine-state may be attached to one of a cylinder, a cylinder head and a head cover which constitute an engine body. In this case, a portion of the sensor exposed to the outside of the internal combustion engine and an electric cable connected to the sensor at the exposed portion are protected from being hit with a foreign object (for example, gravel tossed up by a traveling vehicle) by a body cover. In addition, in order to prevent the sensor and the electric wire from being excessively heated by heat from the engine, it is necessary to appropriately cool them. Therefore, the arrangement of the sensor and electric wire may be restricted or the arrangement of peripheral members disposed in the vicinity of the sensor and electric wire may be restricted. [0004] In view of such situations, the present invention has been made and an object of the inventions of claims 1 to 3 is to provide an air-cooled internal combustion engine that can ensure protectional capability and cooling performance for a sensor and an electric wire connected to the sensor with simple structure and that can additionally exhibit increased flexibility of sensor arrangement. An object of the inventions of claims 2 and 4 is to further improve cooling performance for the electric wire connected to the sensor, thereby enhancing the detection accuracy of the sensor. An object of the invention of claim 3 is to arrange an exhaust gas sensor and an air passage for exhaust purification air and additionally enhance cooling performance for the exhaust gas sensor and exhaust purification performance by the exhaust purification air. [Means for Solving the Problem] [0005] The invention recited in claim 1 is an air-cooled internal combustion engine including: an engine body; a sensor attached to the engine body to detect an engine-state; and a shroud covering the engine body to define a cooling air passage surrounding the engine body. In the engine, the sensor and an electric cable connected to the sensor are disposed in the cooling air passage. [0006] According to the invention recited in claim 1, since the sensor and the electric cable are disposed in the shroud, they are protected from being hit or brought into contact with a foreign object. The invention recited in claim 1 is different from a technique in which the arrangement of a sensor outside the shroud 45 restricts the arrangement of the sensor and peripheral members located near the sensor. More specifically, the arrangement of the sensor and the electric cable is not restricted by the member disposed outside the shroud and also the arrangement of the member is not restricted by the arrangement of the sensor and the electric cable. Since the sensor and the electric cable disposed in the cooling air passage are cooled by cooling air in the shroud, they are prevented from excessively heated by heat from the internal combustion engine. [0007] The invention recited in claim 2 is such that in the air-cooled internal combustion engine according to claim 1, a cooling fan covered by the shroud and supplying cooling air to the cooling air passage is provided, and the electric cable is disposed upstream of the engine body in terms of cooling air flow. [0008] According to the invention recited in claim 2, in the internal combustion engine forcibly air-cooled by cooling air from the cooling fan, since the electric cable is effectively cooled by the cooling air that does not yet cooled the engine body, the change of electric resistance resulting from temperature rise attributable to heat from the internal combustion engine is suppressed. [0009] The invention recited in claim 3 is such that in the air-cooled internal combustion engine according to claim 1 or 2, a cylinder head which constitutes part of the engine body is provided with an exhaust port; the sensor is an exhaust gas sensor which is attached to the cylinder head to detect exhaust gas property as the engine-state at the exhaust port; the exhaust gas sensor is attached at a position upstream of the exhaust port in terms of cooling air flow; and an air passage adapted to direct exhaust, purification air to the exhaust port is provided at a position downstream of the exhaust port in terms of the cooling air flow. [0010] According to the invention recited in claim 3, the exhaust gas sensor and the air passage can be disposed close to the exhaust port. In particular, the exhaust gas sensor is effectively cooled by the cooling air that is not yet heated by the exhaust gas of the exhaust port. A portion formed with the air passage is exposed to the cooling air that has cooled the cylinder head near the exhaust port, that is, that has been heated by exhaust gas; therefore, the temperature of the exhaust purification air flowing through the air passage is suppressed or prevented from lowering. This promotes the reaction of unburned components with the exhaust purification air. [0011] The invention recited in claim 4 is such that in the air-cooled internal combustion engine according to claim 1 or 2, the sensor includes an exhaust gas sensor which detects exhaust gas property as the engine-state and a temperature sensor which detects engine temperature as the engine state; and the exhaust gas sensor and the temperature sensor each having a detecting portion and a joint are attached such that the joint connected to the electric cable is disposed closer to the cooling fan carried on a shaft end of a crankshaft than the detecting portion disposed inside the engine body. [0012] According to the claim 4, since the joints of the exhaust gas sensor and the temperature sensor are located closer to the cooling fan, the electric cables connected to the sensors are cooled by the cooling air having lower temperature. Thus, the change of electric resistance resulting from temperature rise of the electric cables can be suppressed. [Effect of the Invention] [0013] According to the invention recited in claim 1, the following effect can be exhibited. Use of the shroud in the air-cooled internal combustion engine can ensure protectional capability and cooling performance for the sensor and the cable connected to the sensor with simple structure. In addition, the flexibility of the arrangement of the sensor and the electric cable can be increased. According to the invention in claim 2, the following effect can be exhibited in addition to the effect of the invention recited in the cited claim. That is, since the cooling performance for the electric cable connected to the sensor is further enhanced, the change of electric resistance is suppressed, which improves detection accuracy of the sensor. According to the invention in claim 3, the following effect can be exhibited in addition to the effect of the invention recited in the cited claim. That is, the exhaust gas sensor and the air passage for exhaust purification air are arranged in a compact manner, and further, the cooling performance of the exhaust gas sensor is enhanced and the exhaust purification performance by the exhaust purification air is improved. According to the invention recited in claim 4, the following effect can be exhibited in addition to the effect of the invention recited in the cited claim. That is, since the cooling performance for the electric cables connected to the sensors can be further enhanced, the change of electric resistance is suppressed, which improves the detection accuracy of each sensor. [Best Mode for Carrying out the Invention] [0014] A preferred embodiment of the present invention will be hereunder described with reference to Figs. 1 through 6. (Brief Description of the Drawings] [0042] [Fig. 1] Fig. 1 is a schematic cross-sectional view of an air-cooled internal combustion engine embodying the present invention, as taken along line I-I of Fig. 2. [Fig. 2] Fig. 2 is a cross-sectional view take along line II -II of Fig. I. [Fig. 3] Fig. 3 is a right side view of an essential portion of the air-cooled internal combustion engine of Fig. 1. [Fig. 41 Fig. 4 is a perspective view of the essential portion of the internal combustion engine of Fig. 1 with a lower shroud portion removed. [Fig. 5] Fig. 5 illustrates the essential portion of the cylinder and the cylinder head as viewed from arrow V of Fig. 3. [Fig. 6] Fig. 6 is a cross-sectional diagram taken along line Vla-VIa and line VIb-VIb of Fig. 5. Referring to Figs. 1 and 2, an air-cooled internal combustion engine E embodying the present invention is mounted on a motorcycle as a vehicle together with a power transmission apparatus including a V-belt type automatic transmission M. The internal combustion engine E is a single cylinder four-stroke internal combustion engine which is mounted on a vehicle body transversely so as to direct the rotational centerline LI of a crankshaft 7 leftward and rightward. This engine has an engine body composed of a cylinder 1, a crankcase 2 joined to the cylinder 1 on the side of the crankshaft 7 in the direction of a cylinder axis L2 (hereunder, referred to as "cylinder axial direction"), a head cover 3 joined to the cylinder 1 on the side opposite the side of the crankshaft 7 in the cylinder axial direction, and a head cover 4 joined to the cylinder head 3. The cylinder 1, crankcase: 2, cylinder head 3 and head cover 4 are made of metal, e.g., an aluminum alloy, which is a material having high thermal conductivity. [0015] It should be noted that, in the embodiment, the upside and downside, the front and rear or back, and the left and right are based on a motorcycle as a machine having the internal combustion engine E. The axial direction means a direction parallel to the rotational centerline LI of the crankshaft 7. If one of the left and right is one side in the axial direction, the other of the left and right is the other side in the axial direction. [0016] The cylinder 1 is arranged on the vehicle body so as to slant slightly upward with respect to the horizontal plane so that the cylinder axis L2 extends slightly-obliquely upwardly toward the front. A piston 5 is fitted in a cylinder bore la of the cylinder 1 so as to be able to reciprocate. The piston 5 is connected to the crankshaft 7 via a connecting rod 6. The crankshaft 7 is rotatably journaled by the crankcase 2 via a pair of main bearings 8 including ball bearings. The left-right split crankcase 2 is composed of a left case half 2a and a right, case half 2b so as to define a crank chamber 9 housing the crankshaft 7. The cylinder head 3 and the cylinder 1 are co-fastened to the crankcase 2 with a plurality of, four in this case, head bolts 11 (see Fig. 6) that are inserted into through-holes 10 (see Fig. 4) formed in the cylinder 1 and the cylinder head 3. [0017] The cylinder head 3 is formed with a combustion chamber 12 facing the piston 5 in the cylinder axial direction and an intake port 13 and an exhaust port 14 which open to the combustion chamber 12. An ignition plug 15 is attached to the cylinder head 3 so as to face the combustion chamber 12. An intake valve 16 and an exhaust valve 17 mounted to the cylinder head 3 are drivingly opened and closed by a valve system 20 to thereby open and close the intake port. 13 and the exhaust port 14, respectively, in synchronization with the rotation of the crankshaft 7 , The valve system 20 includes a earn shaft 22 which is drivingly rotated by the power of the crankshaft 7 transmitted via a transmission mechanism 18 for driving the valves. [0018] The valve system 20 is accommodated in a valve system chamber 21 defined by the cylinder head 3 and the head cover 4 . The valve system 20 includes the cam shaft 22 and an intake rocker arm 25 and an exhaust rocker arm 26. The cam shaft 22 is rotatably journaled by the cylinder head 3 via bearings. The intake rocker arm 25 and the exhaust rocker a.rm 26 pivotally move about rocker shafts 23 and 24 driven by an intake cam 22a and an exhaust cam 22b, respectively, carried on the cam shaft 22. The transmission mechanism 18 includes a drive sprocket 18a, a driven sprocket 18b and an endless chain 18c. The drive sprocket 18a is carried on a left-hand shaft end 7a of the crankshaft 7 which passes through the left-hand main bearing 8 and projects leftward of the crank chamber 9. The driven sprocket 18b is carried on a shaft, end of the cam shaft 22. The chain 18c as an endless transmission belt is spanned between both the sprockets 18a and 18b. Both the sprockets 18a, 18b and the chain 18c ares accommodated in a chain chamber 27 as a transmission chamber. The chain chamber 27 is defined by the cylinder 1, the cylinder head 3, the head cover 4, and the left case; half 2a and communicates with the valve system chamber 21 and the crank chamber 9. [0019] A transmission chamber 33 for accommodating the transmission M is formed on the left side of the crank chamber 9 in the axial direction (the lateral direction) so as to put the chain chamber 27 between the transmission chamber 32 and the crank chamber 9. The transmission M includes a drive pulley 31 and a driven pulley (not shown) on which a V-belt 30 is wound and which is changed in wind-radius by a centrifugal weight 3la in accordance with engine speed. The transmission case 32 defining the transmission chamber 33 is composed of a case body 32a formed of the left case half 2a and a cover 32b fastened to the case body 32a from the left side by means of a large number of bolts. The shaft end 7a which passes through the left case half 2a and projects leftward constitutes a drive shaft of the drive pulley 31. [0020] An intake device of the internal combustion engine E includes an intake pipe 35 which connects a throttle body (not shown) equipped with a throttle valve to control a flow rate of intake air from an air cleaner, with the intake port 13 of the cylinder head 3. A fuel injection valve 36 is attached to the intake pipe 35. The fuel injection valve 36 serves as air-fuel mixture producing means for producing an air-fuel mixture by supplying fuel into intake air flowing in an intake passage of the intake device (also see Fig. 3). The fuel injected from the fuel injection valve 36 toward the intake port 13 enters as an air-fuel mixture the combustion chamber 12 via the intake port 13 when the intake valve 16 is opened. The mixture in the combustion chamber 12 is ignited by the ignition plug 15 to burn. The piston 5 is driven, and reciprocated by the pressure of the resulting combustion gas to drivingly rotate the crankshaft 7 via the connecting rod 6. The combustion gas is discharged to the outside of the internal combustion engine E through the exhaust port 14 and an exhaust device provided with an exhaust pipe 37 when the exhaust valve 17 is opened. The power of the crankshaft 7 is automatically adjusted in accordance with engine speed by the transmission M and then transmitted to a rear wheel as a drive wheel via a final reduction gear, thus drivingly rotating the rear wheel. [0021] Referring to Figs. I and 3, on the right side of the crank chamber 9, a fan chamber 41 is formed which accommodates an AC generator 39 and a cooling fan 40. The cooling fan 40 sucks outside air and produces cooling air for forcibly cooling the engine body. The fan chamber 41 is defined by the right case half 2b and a fan cover 42 which covers the cooling fan 40 from the right side. The AC generator 39 and the cooling fan 40 driven by the crankshaft 7 are mounted to a right shaft end 7b of the crankshaft 7. The right shaft end 7b of the crankshaft 7 passes through the right case half 2b, projectingly extends rightward and terminates in the fan chamber 41. [0022] With reference to Figs. 1 and 3, a fan cover 42 made of a synthetic resin is provided for the internal combustion engine E and fastened to the right case half 2b with a plurality of bolts 43. The fan cover 42 includes a cylindrical air suction portion 42a defining a suction port 4 la through which outside air flows into the fan chamber 41. A louver 42b is disposed inside the air suction portion 42a to guide the sucked air so that it flows in the axial direction. The air supplied under pressure by the cooling fan 40 is delivered as cooling air to an air passage 46 described later through an air vent port 41b. This air vent port 41b is an outlet port of the fan chamber 41 which opens toward the radial outside of the cooling fan 40 and the cylinder 1 in the cylinder axial direction. [0023] Referring additionally to Figs. 2 and 4, a shroud 45 provided for the internal combustion engine E covers the whole of the cylinder 1 and cylinder head 3 constituting the engine body to thereby define a cooling air passage 46 which surrounds the cylinder 1 and the cylinder head 3. More specifically, the shroud 45 covers over the entire circumference of the cylinder 1 and cylinder head 3 so as to encircle the cylinder axis L2 and also covers the full lengths of the cylinder 1 and cylinder head 3 in the cylinder axial direction. The cylinder I and the cylinder head 3 are formed with a large number of fins If and 3f, respectively, on the outer surfaces thereof in order to enhance a cooling effect by cooling air on the cylinder 1 and the cylinder head 3, [0024] The shroud 45 made of a synthetic resin is split into two portions with respect to a splitting plane almost parallel to the cylinder axis L2, that is, composed of an upper shroud portion 45a as a first shroud portion and a lower shroud portion 45b as a second shroud portion. Both the shroud portions 45a and 45b are fastened to each other by retaining structures with claws 47 and screws 48 and also to the fan cover 42 with screws 49. The lower shroud portion 45b is fastened to the left case half 2a with bolts 50. Respective edge portions 45al, 45bl of the shroud portions 45a, 45b for defining an opening 51 through which the head cover 4 projects forwardly through the shroud 45 are fitted to a flange portion 3a of the cylinder head 3. In this way, the shroud 45 is mounted to the engine body. [0025] The shroud 45 is formed on its front surface with the opening 51 extending over both the shroud portions 45a, 45b. In addition to the opening 51 the shroud 45 is formed with other openings 52, 53, 54 and an air discharge port 55. An opening 52 is provided in a surface on the right side of the opening 51 so as to extend over both the shroud portions 45a, 45b and a plug cap 19 attached to the ignition plug 15 is inserted into the opening 52. An opening 53 is provided in the upper shroud portion 45a in a surface above the opening 52 and the intake pipe 35 is inserted into the opening 53. An opening 54 is provided in the lower shroud portion 45b in a surface below the opening 53 and the exhaust pipe 37 and a passage forming portion 83 described later are inserted through the opening 54. The air discharge port 55 is provided in a left, surface and in the lower shroud portion 45b so as to be open rightward. [0026] Cooling air, from the cooling fan 40, having a component of the rotational direction of the fan 40 on the radial outside of the fan 40 flows into the cooling air passage 46 from the air vent port 41b of the fan chamber 41 (the flow of cooling air is roughly denoted by broken line arrows in Fig. 3) . In the cooling air passage 46, the cooling air flows around the cylinder 1 arid cylinder head 3 to cool them. Then, the cooling air is discharged from the air discharge port 55 to the outside of the shroud 45. The cooling air flows out from the air discharge port 55 toward the exhaust pipe 38 and cools it. [0027] Referring to Fig. 1, a drive gear 60 is carried on the shaft end 7b between the right main bearing 8 and the AC generator 39 to drive an oil pump (not shown) constituting a lubricating system for the internal combustion engine E. The oil pump is driven by the power of the crankshaft 7 transmitted via a transmission mechanism including a gear pair including the drive gear 60. The thus-driven oil pump feeds the lubricating oil pumped from an oil sump formed on the bottom portion of the crankcase 2, to lubricated portions in the internal combustion engine E, through a large number of oil passages. The lubricated portions include the main bearings 8, the crankshaft 7 and the valve system 20. [0028] With reference to Figs. 2, and 4 to 6, the lubricating oil discharged from the oil pump is fed to lubricated portions such as the valve system 20, provided on the cylinder head 3, in the valve system chamber 21 in the following manner. The lubricating oil flows in an oil passage 61 formed using an insertion hole lOa. Part of the lubricating oil in the oil passage 61 is directed into an oil passage 62 (see Fig. 2) formed in the head cover 4 and ejected into the valve system chamber 21 from an ejecting port 62a of the oil passage 62. In addition, the remainder of the lubricating oil in the oil passage 61 is ejected into the valve system chamber 21 from an oil passage 63 (see Fig. 2) in the rocker shaft 23 through a sliding portion with the intake rocker arm 25. The lubricating oil that has lubricated the lubricated portions flows down, from the valve system chamber 21, in a return oil passage 64 (also see Fig. 4) including a through-hole, then flowing into the crank chamber 9, and returns to the oil sump. The above-mentioned through-hole passes through the lower circumferential wall 3b of the cylinder head 3 and the lower circumferential wall Ib of the cylinder I and opens to the crank chamber 9. [0029] With reference to Figs 1 through 6, the internal combustion engine E is equipped with, as sensors for detecting an engine state, an exhaust gas sensor for detecting exhaust gas property as an engine-state and a temperature sensor for detecting engine temperature as an engine state. For example, the exhaust gas sensor is an oxygen concentration sensor 70 which is attached to the cylinder head 3 to detect the concentration of oxygen in the exhaust gas at the exhaust port 14. In addition, the temperature sensor is an oil temperature sensor 75 for detecting the temperature of lubricating oil. [0030] The oxygen concentration sensor 70 is attached to the lower circumferential wall 3b of the cylinder head 3 in the vicinity of an outlet 14a of the exhaust port 14. This sensor 70 is virtually columnar and is disposed approximately parallel to the axial direction. In addition, this sensor 70 has an attachment•portion 70a including a threaded part threaded into the cylinder head 3 for attachment, a detecting portion 70b located inside the cylinder head 3 so as to face the inside of the exhaust port 14, and a joint 70c connected to an electric cable 71 used to transmit a detected signal to a controller. The joint 70c is connected to a coupler 72 as a connection part attached to the tip of the electric cable 71. In addition, the joint 70c is disposed to be exposed to the cooling air passage 46 from the cylinder 1 while being covered by the shroud 45. [0031] The oil temperature sensor 75 is attached to the lower circumferential wall Ib of the cylinder 1 on the side where the outlet 14a of the exhaust port 14 opens. This sensor 75 is virtually columnar and is disposed approximately parallel to the axial direction. In addition, this sensor 75 has an attachment portion 75a including a threaded part threaded into the cylinder 1 for attachment, a detecting portion 75b disposed inside the cylinder 1 so as to face the return oil passage 64, and a joint 75c connected to an electric cable 76 used to transmit a detected signal to the controller. The joint 75c is connected to a coupler 77 as a connection part attached to the tip of the electric cable 76. In addition, the joint 75c is disposed to be exposed to the cooling air passage 46 from the cylinder 1 while being covered by the shroud 4 5. [0032] Further, the oil temperature sensor 75 is disposed to extend from the detecting portion 75b to the side opposite the side of the chain chamber 27 in the axial direction. In addition, the whole of the oil temperature sensor 75 overlaps the cylinder 1 (see Fig. 1) as viewed from the direction perpendicular to a plane H (see Fig. 1) . Therefore, the oil temperature sensor 75 will not project from the cylinder 1 in the axial direction, so that it can be arranged on the cylinder 1 in a compact manner. Incidentally, the plane H is a plane including the cylinder axis L2 and being parallel to or including the rotational centerline LI. The sensors 70 and 75 are arranged such that: the joints 70c and 75c are positioned axially closer to the cooling fan 40 carried on the shaft end 7b than the detecting portions 70b and 75b, respectively. Thus, the joints 70c and 75c are positioned upstream of cooling air in the sensors 70 and 75, respectively. [0034] The oxygen concentration sensor 70 and the oil temperature sensor 75 are arranged approximately parallel to each other in the cylinder axial direction at a portion of the engine body on the side where the outlet 14a of the exhaust port 14 opens toward the plane H, that is, in the lower circumferential walls 3b and Ib forming the lower surfaces of cylinder head 3 and the cylinder 1, respectively (see Fig. 1) . In addition, the sensors 70 and 75 are located at respective positions overlapping each other as viewed from the cylinder axial direction (see Fig. 6) . [0035] The electric cables 71, 76 extend from the joints 70c, 75c, respectively, across the cooling air passage 46 toward the cooling fan 40. Then, the cables 71, 76 pass through a grommet 79 fitted to and retained by notches of the shroud portions 45a, 45b, extending toward the outside of the shroud 45, and is connected to the controller. In this way, the electric cables 71, 76 are located upstream of the cylinder 1 and the cylinder head 3, so that they are exposed to the cooling air that does not yet reach the cylinder 1 and the cylinder head 3. [0036] The value detected by the oxygen concentration sensor 70 is used to control the amount of fuel of the fuel injection valve 36 in order to enhance the exhaust gas purifying performance of a catalytic device included in the exhaust device. The value detected by the oil temperature sensor 75 is used to control the amount of fuel of the fuel injection valve 36 in accordance with the warm-up state of the internal combustion engine. In addition, this value is used to control the amount of idling air for idling engine speed control during warm-up operation. [0037] Referring to Figs. 3 and 4, the internal combustion engine E includes an exhaust system secondary air supply device which feeds exhaust purification air in the exhaust gas in order to burn unburned components (HC, CO) in the exhaust gas for exhaust purification. The secondary air supply device has a control valve 81 for controlling the ijmount of air supplied to exhaust gas and an air supply pipe 82 which connects the control valve 81 with the cylinder head 3 to direct the exhaust purification air controlled by the control valve 81 to the exhaust port 14. The control valve 81 feeds the exhaust purification air in the exhaust gas in the engine operation state where fuel amount control is not exercised based on the value detected by e.g. the oxygen concentration sensor 70. The air supply pipe 82 is composed of an upper supply pipe 82a made of a rubber hose connected to the control valve 81 and a metallic lower supply pipe 82b arranged along the shroud 45. The lower supply pipe 82b projects from the outer surface of the cylinder head 3, traversing the cooling air passage 46, and connects with a passage forming portion 83. This passage forming portion 83 is formed of a projecting portion which extends from the opening 54 of the shroud 45 to the outside? of the shroud 45. The passage forming portion. 83 formed integrally with the cylinder head 3 is provided with an air passage 84 opening to the exhaust port 14. After flowing in the air supply pipe 82, the exhaust purification air flows in the air passage 84 and is fed to tl'ie exhaust port 14. The passage forming portion 83 is located downstream of the exhaust port 14 and the exhaust pipe 38 in terms of cooling air flow so that the air passage 84 is located downstream of the exhaust port 14 in the cooling air passage 46 with respect of the cooling air f 1 ow. [0038] Next, the function and effect of the embodiment described above will be described. The electric wire 71 connected to the oxygen concentration sensor 70 attached to the cylinder head 3 and the electric wire 76 connected to the oil temperature sensor 75 attached to the cylinder 1 are arranged in the cooling air passage 46. In this way, since the sensors 70, 75 and the electric cables 71, 76 are arranged in the shroud 45, they are protected from being hit or brought into contact with a foreign object, e.g., gravel tossed up during traveling. The present embodiment is different from the technique in which since a sensor is disposed outside the shroud 45, the arrangement of the sensor and peripheral components near the sensor is restricted. That is to say, the present embodiment is such that the arrangement of the sensors 70, 75 and the electric cables 71, 76 is not restricted by the members disposed outside the shroud 45. Also the sensors 70, 75 and the electric cables 71, 76 do not restrict the arrangement of the members. Since the sensors 70, 75 and the electric wires 71, 76 disposed in the cooling air passage 46 are cooled by the cooling air in the shroud 45, they are prevented from being excessively heated by heat from the internal combustion engine E. Consequently, use of the shroud 45 in the internal combustion engine E can ensure the protective capability and cooling performance for the sensors 70, 75 and the electric cables 71 and 76 connected to the respective sensors 70 and 75 with simple structure, arid increase the flexibility of the arrangement of the sensors 70, 75 and the electric wires 71, 76. [0039] In the internal combustion engine E that includes the cooling fan 40 covered by the shroud 45 and supplying cooling air to the cooling air passage 46 and the electric cables 71 and 76 disposed upstream of the cylinder 1 and the cylinder head 3 in terms of cooling air flow and thus forcibly air-cooled by cooling air from the cooling fan 40, the electric cables 71, 76 are effectively cooled by the cooling air that does not: yet cool the cylinder 1 and the cylinder head 3. The change of electric resistance resulting from temperature rise of the electric cables 71, 76 attributable to heat from the internal combustion engine E can be suppressed. The oxygen concentration sensor 70 and the oil temperature sensor 75 are attached such that the joints 70c and 75c are located closer to the cooling fan 40 carried by the shaft end 7b of the crankshaft 7 than the detecting portions 7Ob and 75b positioned inside the cylinder head 3 and the cylinder 1, respectively. That is, the respective joints 70c and 75c of the oxygen concentration sensor 70 and the oil temperature sensor 75 are located close to the cooling fan 40. Accordingly, the electric wires 71 and 76 connected to the sensors 70 and 75, respectively, are cooled by cooling air with low temperature. Also in this aspect, the change of electric resistance resulting from the temperature rise of the electric cables 71, 76 are suppressed. As a result, cooling performance for the electric cables 71 and 76 connected to the sensors 70 and 75, respectively, are further enhanced, which suppresses the change of the electric resistance, thereby enhancing detection accuracy of the sensors 70, 75. [0040] The oxygen concentration sensor 70 is attached at a position upstream of the exhaust port 14 in terms of cooling air flow. In addition, the air passage 84 which directs exhaust purification air to the exhaust port 14 is provided at a position downstream of the exhaust port 14 with respect to cooling air flow. Thus, the oxygen concentration sensor 70 and the air passage 84 can be disposed close to the exhaust port 14. Further, the oxygen concentration sensor 70 is effectively cooled by the cooling air that is not yet heated by the exhaust gas of the exhaust port 14 . The passage forming portion 83 formed with the air passage 84 is exposed to the cooling air that has cooled the cylinder head 3 near the exhaust port 14, that: is, has been heated by the exhaust gas. Therefore, the temperature of the exhaust purification air flowing through the air passage 84 is suppressed or prevented from lowering, which promotes reaction of the unburned components in the exhaust gas with the exhaust purification air. As a result, the oxygen concentration sensor 70 and the air passage 84 for exhaust purification air are arranged in a compact manner, the cooling performance for the oxygen concentration sensor 70 is enhanced, and exhaust purification performance of exhaust purification air is improved. [0041] Configurative modifications of the embodiment described above will be below described. The exhaust gas sensor may be an LAP sensor which detects an air-fuel ratio in the exhaust gas or a sensor that detects unburned components. The engine temperature may be temperature of the engine body itself or combustion temperature, or cooling water temperature in a case of an air-cooled and water-cooled internal combustion engine. The passage forming portion 83 may be formed of a member separate from the cylinder head 3. In this case, the passage forming portion 83 is made of a material having high thermal conductivity, such as made of metal, as with the cylinder head 3 made of a light alloy, such as an aluminum alloy. The internal combustion engine may be one having a cylinder and a cylinder head formed integrally with each other, also may be a multi-cylinder internal combustion engine. [Description of Reference Symbols] 1 ... cylinder, 3 ... cylinder head, 7 ... crankshaft, 20 ... valve system, 40 ... cooling fan, 45 ... shroud, 46 ... cooling air passage, 64 ... return oil passage, 70 ... oxygen concentration sensor, 71, 76 ... electric cable, 75 ... oil temperature sensor, 82 ... air supply pipe, E ... air-cooled internal combustion engine. We claim: 1. An air-cooled internal combustion engine (E) comprising: an engine body; a sensor attached to the engine body to detect an engine-state; and a shroud (45) covering the engine body to define a cooling air passage (46) surrounding the engine body; characterized in that the sensor and electric cable (76) connected to the sensor is disposed in the cooling air passage (46); the sensor includes an exhaust gas sensor which detects exhaust gas property as the engine-state and a temperature sensor which detects engine temperature as the engine state; and the exhaust gas sensor and the temperature sensor each having a detecting portion and a joint are attached such that the joint connected to the electric cable (76) is disposed closer to the cooling fan (40) carried on a shaft end of a crankshaft (7) than the detecting portion disposed inside the engine body. 2. The air-cooled internal combustion engine (E) as claimed in claim 1, wherein a cylinder head (3) which constitutes part of the engine body is provided with an exhaust port; the sensor is an exhaust gas sensor which is attached to the cylinder head (3) to detect exhaust gas property as the engine-state at the exhaust port; the exhaust gas sensor is attached at a position upstream of the exhaust port in terms of cooling air flow; and an air passage adapted to direct exhaust purification air to the exhaust port is provided at a position downstream of the exhaust port in terms of the cooling flow.

Documents:

2426-del-2006- abstract.pdf

2426-del-2006- claims.pdf

2426-del-2006- description (complete).pdf

2426-del-2006- form-1.pdf

2426-del-2006- form-18.pdf

2426-del-2006- form-2.pdf

2426-del-2006- form-3.pdf

2426-del-2006- form-5.pdf

2426-del-2006- gpa.pdf

2426-DEL-2006-Abstract-(02-12-2011).pdf

2426-DEL-2006-Claims-(02-12-2011).pdf

2426-DEL-2006-Correspondence Others-(02-12-2011).pdf

2426-del-2006-correspondence-others.pdf

2426-DEL-2006-Drawings-(02-12-2011).pdf

2426-DEL-2006-Drawings.pdf

2426-DEL-2006-Form-3-(02-12-2011).pdf

2426-DEL-2006-GPA-(02-12-2011).pdf

2426-DEL-2006-Petition-137-(02-12-2011).pdf

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