INTERNAL COOLED AIR COMBUSTION ENGINE EQUIPPED WITH A SENSOR TO DETECT A STATE OF THE ENGINE Technical Field The present invention relates to an internal combustion engine cooled by air equipped with a sensor to detect a state of the engine and a shield which forms a passage of cooling air surrounding a motor body. This engine is mounted on a vehicle for example. BACKGROUND ART An air-cooled internal combustion engine equipped with a sensor for detecting the temperature of the motor is known as a state of the motor and a shield which forms a passage of cooling air surrounding a motor body (see, for example , Patent Document 1 [Japanese Patent Open to Public Inspection No. 2004-11436]). Further, an internal combustion engine equipped with an exhaust gas sensor for detecting the exhaust gas property as an engine condition is known (see, for example, Patent Document 2 [Japanese Patent Open to Public Inspection No. 2004-316430]). OBJECTIVE OF THE INVENTION An internal combustion engine cooled by air is provided which can ensure the capacity of
Protection and cooling performance for a sensor and an electrical cable connected to the sensor with a simple structure and has increased the flexibility of the placement of the sensor. Description of the Invention A sensor can be coupled to detect a state of the engine to one of the following: a cylinder, a cylinder head and a head cover which constitute a motor body. In this case, a part of the sensor exposed to the outside of the internal combustion engine and an electrical cable connected to the sensor in the exposed part are protected from being hit with a foreign object (eg, gravel agitated by a moving vehicle) by a body cover. In addition, in order to prevent the sensor and the electric cable from being heated excessively by the heat of the motor, it is necessary to cool them appropriately. Therefore, the placement of the sensor and the electrical cable or the placement of peripheral members arranged in the vicinity of the sensor and the electrical cable may be restricted. In view of these situations, the present invention has been made and an object of the invention of claims 1 to 3 is to provide an internal combustion engine cooled by air that can ensure
the protection capacity and the cooling performance for a sensor and an electric cable connected to the sensor with a simple structure and that can also present greater flexibility of the sensor arrangement. An object of the invention of claims 2 and 4 is to further improve the cooling performance for the electrical cable connected to the sensor, thereby improving the accuracy of sensor detection. An object of the invention of claim 3 is to place an exhaust gas sensor and an air passage for the exhaust purification air and further improve the cooling performance for the exhaust gas sensor and the exhaust purification performance. by the exhaust purification air. The invention set forth in claim 1 is an internal combustion engine cooled by air that includes: a motor body; a sensor coupled to the engine body to detect a state of the engine; and a shield that covers the motor body to define a passage of cooling air surrounding the motor body. In the motor, the sensor and an electrical cable connected to the sensor are arranged in the cooling air passage. According to the invention set forth in claim 1, since the sensor and the electric cable are arranged in the shield, they are protected
from being hit or getting in contact with a foreign object. The invention set forth in claim 1 is different from the technique where the placement of a sensor outside the shield 45 restricts the placement of the sensor and peripheral members located near the sensor. More specifically, the positioning of the sensor and the electric cable is not restricted by the member disposed outside the shield and neither the positioning of the member is restricted by the placement of the sensor and the electric cable. Since the sensor and the electric cable arranged in the cooling air passage are cooled by the cooling air in the shield, they are prevented from overheating by the heat of the internal combustion engine. The invention set forth in claim 2 is such that in the air-cooled internal combustion engine according to claim 1, a cooling fan covered by the shield is provided and cooling air is supplied to the cooling air passage and the cable The electric motor is arranged upstream of the motor body in terms of cooling air flow. According to the invention set forth in claim 2, in the internal combustion engine air-cooled in a forced manner by the air of
cooling the cooling fan, since the electric cable is effectively cooled by the cooling air that still does not cool the motor body, the change in electrical resistance resulting from the temperature increase attributable to the heat of the internal combustion engine is suppressed. The invention set forth in claim 3 is such that in the air-cooled internal combustion engine according to claim 1 or 2, a cylinder head constituting part of the engine body is provided with an exhaust hole; the sensor is an exhaust gas sensor which is coupled to the cylinder head to detect the property of the exhaust gas as the engine state in the exhaust port; the exhaust gas sensor is coupled in a position upstream of the exhaust port in terms of cooling air flow; and an adapted air passage is provided to direct the exhaust purification air to the exhaust port at a position downstream of the exhaust port in terms of cooling air flow. According to the invention set forth in claim 3, the exhaust gas sensor and the air passage can be arranged close to the exhaust port. In particular, the exhaust gas sensor is
cooled effectively by cooling air that is not yet heated by exhaust gas from the exhaust port. A part formed with the air passage is exposed to the cooling air that has cooled the cylinder head near the exhaust port, ie, which has been heated by the exhaust gas; therefore, the temperature of the exhaust purification air flowing through the air passage is suppressed or prevented from decreasing. This promotes the reaction of unburned components with the exhaust purification air. The invention set forth 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 the exhaust gas property as the state of the exhaust gas. motor and a temperature sensor which detects the temperature of the motor as the state of the motor; and the exhaust gas sensor and the temperature sensor each having a sensing part and a junction are coupled in such a way that the junction connected to the electrical cable is disposed closer to the cooling fan carried on an axle end of a crankshaft that the sensing part disposed inside the motor body. According to claim 4, since the
Exhaust gas sensor junctions and the temperature sensor are located closer to the cooling fan, the electrical wires connected to the sensors are cooled by the cooling air that has lower temperature. In this way, the change in electrical resistance resulting from the increase in temperature of the electric cables can be suppressed. Effect of the Invention In accordance with the invention set forth in claim 1, the following effect may be presented. The use of the shield in the internal combustion engine cooled by air can ensure the protection capacity and the cooling performance for the sensor and the cable connected to the sensor with a simple structure. In addition, the flexibility of the placement of the sensor and the electrical cable can be increased. According to the invention of claim 2, the following effect may be presented in addition to the effect of the invention set forth in the said claim. That is, since the cooling performance for the electrical cable connected to the sensor is improved, the change in electrical resistance is suppressed, which improves the accuracy of sensor detection. According to the invention of claim 3,
The following effect may be presented in addition to the effect of the invention set forth in the said claim. That is to say, the exhaust gas sensor and the air passage for the exhaust purification air are placed in a compact manner and in addition the cooling performance of the exhaust gas sensor and the exhaust purification performance by the purification air of Escape are improved. According to the invention of claim 4, the following effect may be presented in addition to the effect of the invention set forth in the said claim. That is, since the cooling performance for the electrical cables connected to the sensors can be improved, the change of the electrical resistance is suppressed, which improves the detection accuracy of each sensor. A preferred embodiment of the present invention will be described below with reference to Figures 1 to 6. Referring to Figures 1 and 2, an internal combustion engine E cooled by air representing the present invention is mounted on a motorcycle as a vehicle together with a power transmission apparatus that includes an automatic transmission M of trapezoidal belt type.
The internal combustion engine E is an internal combustion engine with four strokes and a single cylinder, which is mounted on a vehicle body transversely in order to direct the central line of rotation Ll of a crankshaft 7 to the left and to the left. right. This motor has a motor body composed of a cylinder 1, a crankcase 2 connected to the cylinder 1 on the side of the crankshaft 7 in the direction of a cylinder axis L2 (hereinafter referred to as the "axial direction of the cylinder"), a head of cylinder 3 attached to cylinder 1 on the side opposite the crankshaft 7 in the axial direction of the cylinder and a head cover 4 attached to the cylinder head 3. Cylinder 1, crankcase 2, cylinder head 3 and The head cover 4 are made of metal, for example, an aluminum alloy, which is a material having high thermal conductivity. It should be noted that, in the mode, the top side and the bottom side, the front and rear or rear and the left and right are based on a motorcycle as a machine that has the internal combustion engine E. The address axial means a direction parallel to the center line of rotation Ll of the crankshaft 7. If the left side or the right side is one side in the axial direction, the other side is the other side
in the axial direction. The cylinder 1 is placed in the vehicle body in order to tilt a little upwards with respect to the horizontal plane so that the cylinder axis L2 extends slightly upwards obliquely towards the front. A piston 5 is provided with an inside cylinder diameter of the cylinder 1 in order to be able to oscillate. The piston 5 is connected to the crankshaft 7 via a connecting rod 6. The crankshaft 7 is rotatably articulated by the crankcase 2 through a pair of main bearings 8 including ball bearings. The left-right split crankcase 2 is composed of a left box half 2a and a right box half 2b in order to define a crankcase 9 which houses the crankshaft 7. The cylinder head 3 and cylinder 1 are attached together crankcase 2 with a plurality of, four in this case, head bolts 11 (see Figure 6) which are inserted into the through holes 10 (see Figure 4) formed in the cylinder 1 and the cylinder head 3. The cylinder head 3 is formed with a combustion chamber 12 which gives the piston 5 in the axial direction of the cylinder and an intake orifice 13 and an exhaust hole 14 which open to the chamber
combustion 12. A spark plug 15 is attached to the cylinder head 3 in order to face the combustion chamber 12. An intake valve 16 and an exhaust valve mounted on the cylinder head 3 open and close with force by means of 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 cam shaft 22 on the which is rotated forcefully by the energy of the crankshaft 7 transmitted through a transmission mechanism 18 to drive the valves. The valve system 20 is housed 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 swing arm 25 and an arm oscillating exhaust 26. The cam shaft 22 is rotatably articulated by the cylinder head 3 through bearings. The swinging inlet arm 25 and the exhaust swing arm 26 are pivoted about the 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 gear wheel 18a, a gearwheel
driven 18b and an endless chain 18c. The cogwheel of drive 18a is carried on a left axle end 7a of the crankshaft 7 which passes through the left main bearing 8 and protrudes to the left of the crankcase 9. The driven sprocket 18b is carried on a shaft end of the cam shaft 22 The chain 18c as an endless transmission belt extends between both sprockets 18a and 18b. Both sprockets 18a and 18b and the chain 18c are housed 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 box half 2a and communicates with the valve system chamber 21 and the crankcase 9. A transmission chamber 33 for housing the transmission M is formed on the side left of the crankcase 9 in the axial direction (the lateral direction) in order to put the chain chamber 27 between the transmission chamber 33 and the crankcase 9. The transmission M includes a drive pulley 31 and a driven pulley (not shown) ) wherein a trapezoidal belt 30 is wound and which is changed in the radius of the wind by a centrifugal weight 31a in accordance with the speed of the engine. The transmission case 32 defining the transmission chamber 33 is composed of a bodyof box 32a formed from the left box half 2a and a cover 32b attached to the box body 32a on the left side by means of a large number of pins. The shaft end 7a passing through the left housing half 2a and protruding to the left constitutes an actuation shaft of the drive pulley 31. An intake device of the internal combustion engine E includes an intake pipe 35 which connects a regulating body (not shown) equipped with a regulating valve for controlling the flow rate of the intake air of 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 a means of producing air-fuel mixture to produce a mixture of air and fuel by supplying fuel to the intake air flowing in an intake passage of the intake device ( see also Figure 3). The fuel injected from the fuel injection valve 36 into the intake port 13 enters as a mixture of air and fuel into the combustion chamber 12 through the intake port 13 when the intake valve 16 is opened. The mixture in the combustion chamber 12 is ignited by the spark plug of
On 15 to burn. The piston 5 is driven and oscillated by the pressure of the resulting combustion gas to forcefully rotate the crankshaft 7 through 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 energy of the crankshaft 7 is automatically adjusted in accordance with the speed of the engine by means of the transmission M and is then transmitted to a rear wheel as a drive wheel through a final reduction gear, thus turning the rear wheel strongly . Referring to Figures 1 and 3, on the right side of the crankcase 9, a fan chamber 41 is formed which houses an AC generator 39 and a cooling fan 40. The cooling fan 40 sucks the outside air and produces cooling air to forcefully cool the motor body. The fan chamber 41 is defined by the right case half 2b and a fan cover 42 that covers the cooling fan 40 from the right side. The alternating current generator 39 and the cooling fan 40 driven by the
crankshaft 7 are mounted on a right axle end 7b of the crankshaft 7. The right axle end 7b of the crankshaft 7 passes through the right box half 2b, extends cantilever to the right and ends in the fan chamber 41. With Referring to Figures 1 and 3, there is provided a fan cover 42 made of a synthetic resin for the internal combustion engine E and is attached to the right case half 2b with a plurality of bolts 43. The fan cover 42 includes a cylindrical air suction portion 42a which defines a suction port 41a through which the outside air flows into the fan chamber 41. A vent grill 42b is disposed within the air suction portion 42a to guide the air sucked 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 ventilation port 41b. This air vent port 41b is an outlet port of the fan chamber 41 that opens radially outward of the cooling fan 40 and the cylinder 1 in the axial direction of the cylinder. Referring further to Figures 2 and 4, a
shield 45 provided for the internal combustion engine E covers the entire cylinder 1 and the cylinder head 3 constituting the motor body to thereby define a cooling air passage 46 which surrounds the cylinder 1 and the cylinder head 3. More specifically, the shield 45 covers the entire circumference of the cylinder 1 and the cylinder head 3 in order to surround the cylinder axis L2 and also covers the complete lengths of the cylinder 1 and the cylinder head 3 in the axial direction of the cylinder. The cylinder 1 and the cylinder head 3 are formed with a large number of fins lf and 3f, respectively, on their outer surfaces in order to improve the cooling effect by the cooling air in the cylinder 1 and the cylinder head 3. The shield 45 made of a synthetic resin is divided into two parts with respect to a cutting plane almost parallel to the cylinder axis L2, that is, it is composed of an upper shield part 45a as a first shield part and a lower shield part 45b as a second shield part. Both shield parts 45a and 45b are joined together by retaining structures with hooks 47 and screws 48 and also to the fan cover 42 with screws 49. The lower shield part 45b is attached to the left box half 2a with bolts 50. The respective shore parts 45al,
45bl of the shield parts 45a, 45b to define an opening 51 through which the head cover 4 protrudes forward through the shield 45 are adapted to a flange portion 3a of the cylinder head 3. In this way , the shield 45 is mounted on the motor body. The shield 45 is formed on its front surface with the opening 51 extending over both shield parts 45a, 45b. In addition to the opening 51, the shield 45 is formed with other openings 52, 53, 54 and an air discharge port 55. An opening 52 is provided on a surface on the right side of the opening 51 so as to extend over both shield parts 45a, 45b and a spark plug cap 19 attached to the spark plug 15 is inserted into the opening 52. An opening 53 is provided in the upper shield portion 45a on a surface above the opening 52 and the tube of inlet 35 is inserted into the opening 53. An opening 54 is provided in the lower shield part 45b on a surface below the opening 53 and the exhaust pipe 37 and a forming part 83 described later are inserted through the opening 54. The air discharge port 55 is provided on a left surface and in the lower shield part 45b so as to open to the right.
The cooling air, from the cooling fan 40, having a component of the direction of rotation of the fan 40 on the radial exterior of the fan 40 flows into the cooling air passage 46 from the air vent port 41b of the chamber of fan 41 (the flow of cooling air is denoted by just the short-line arrows in Figure 3). In the cooling air passage 46, the cooling air flows around the cylinder 1 and the cylinder head 3 to cool them. Then, the cooling air is discharged from the air discharge port 55 to the exterior of the shield 45. The cooling air flows from the air discharge port 55 to the exhaust pipe 38 and cools it. Referring to Figure 1, a drive gear 60 is carried on the shaft end 7b between the right main bearing 8 and the alternating current 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 energy of the crankshaft 7 transmitted through a transmission mechanism including a pair of gears including the drive gear 60. The oil pump driven in this way supplies the oil lubricant pumped from a crankcase
of lubricating oil formed in the lower part of the crankcase 2, up to the lubricated parts in the internal combustion engine E, through a large number of oil passages. The lubricated parts include the main bearings 8, the crankshaft 7 and the valve system 20. With reference to Figures 2 and 4 to 6, the lubricating oil discharged from the oil pump is supplied to the lubricated parts such as the valve system 20, provided in 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 10a. Part of the lubricating oil in the oil passage 61 is directed towards an oil passage 62 (see Figure 2) formed in the head cover 4 and is ejected towards the valve system chamber 21 from an ejection port 62a of the passage of oil 62. In addition, the rest of the lubricating oil in the oil passage 61 is ejected into the valve system chamber 21 from an oil passage 63 (see Figure 2) on the rocker shaft 23 through a part sliding with the intake swing arm 25. The lubricating oil that has lubricated the parts to be lubricated flows down from the valve system chamber 21 into a return oil passage 64 (see
also Figure 4) including a through hole, then flowing to the crankcase 9 and returning to the lubricating oil sump. The aforementioned through hole passes through the lower circumferential wall 3b of the cylinder head 3 and the lower circumferential wall Ib of the cylinder 1 and opens to the crankcase 9. With reference to Figures 1 to 6, the internal combustion engine E is equipped with, as sensors for detecting an engine condition, an exhaust gas sensor to detect the property of exhaust gas as a state of the engine and a temperature sensor for detecting the temperature of the engine as a state of the engine. 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 in the exhaust port 14. In addition, the sensor The temperature is an oil temperature sensor 75 for detecting the temperature of the lubricating oil. 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 substantially columnar and is disposed approximately parallel to the axial direction . In addition, this sensor 70 has a
connecting part 70a including a threaded part which is screwed into the cylinder head 3 for attachment, a detection part 70b located inside the cylinder head 3 in order to face towards the inside of the exhaust hole 14 and a joint 70c connected to an electrical 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 arranged to be exposed to the passage of cooling air 46 from the cylinder 1 while it is covered by the shield 45. 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 14a is opened. This sensor 75 is substantially columnar and is arranged approximately parallel to the axial direction . In addition, this sensor 75 has a connecting part 75a that includes a threaded part that is screwed into the cylinder 1 for attachment, a sensing part 75b disposed inside the cylinder 1 in order to look toward the return oil passage 64 and a junction 75c connected to an electrical cable 76 used to transmit a detected signal to the controller. The union 75c is connected to a coupler 77 as a connection part attached to the tip of the electric cable 76. In addition, the union 75c is
arranged to expose the passage of cooling air 46 from the cylinder 1 while it is covered by the shield 45. Furthermore, the oil temperature sensor 75 is arranged to extend from the detection part 75b to the side opposite the side of the chamber of chain 27 in the axial direction. In addition, the entire oil temperature sensor 75 overlaps cylinder 1 (see Figure 1) as seen from the direction perpendicular to a plane H (see Figure 1). Therefore, the oil temperature sensor 75 will not protrude from the cylinder 1 in the axial direction, so that it can be placed in the cylinder 1 in a compact manner. By the way, the plane H is a plane that includes the cylinder axis L2 and is parallel to the central line of rotation Ll or includes it. The sensors 70 and 75 are positioned in such a way that the joints 70c and 75c are positioned axially closer to the cooling fan 40 carried on the shaft end 7b than the sensing parts 70b and 75b, respectively. In this way, the connections 70c and 75c are positioned upstream of the cooling air in the sensors 70 and 75, respectively. The oxygen concentration sensor 70 and the oil temperature sensor 75 are placed
approximately parallel to each other in the axial direction of the cylinder in a part of the motor body on the side where the outlet 14a of the exhaust hole 14 is opened towards the plane H, that is, in the lower circumferential walls 3b and Ib forming the lower surfaces of the cylinder head 3 and cylinder 1, respectively (see Figure 1). In addition, the sensors 70 and 75 are in respective positions overlapping each other as seen from the axial direction of the cylinder (see Figure 6). The electrical cables 71, 76 extend from the links 70c, 75c, respectively, through the cooling air passage 46 to the cooling fan 40. Then, the cables 71, 76 pass through a ring 79 adapted to and retained by notches. of the shield parts 45a, 45b, extending outward from the shield 45 and 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 still does not reach the cylinder 1 and the cylinder head 3. The detected values by the oxygen concentration sensor 70 is used to control the fuel quantity of the injection valve of
fuel 16 for the purpose of improving the purification performance of the exhaust gas of a catalytic device included in the exhaust system. The value detected by the oil temperature sensor 75 is used to control the fuel quantity of the fuel injection valve 36 in accordance with the heating state of the internal combustion engine. In addition, this value is used to control the amount of air in idle for the control of the idling speed of the engine during the heating operation. Referring to Figures 3 and 4, the internal combustion engine E includes a secondary air supply device for the exhaust system which supplies 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 amount of air supplied to the exhaust gas and an air supply tube 82 which connects the control valve 81 to the cylinder head 3 to direct the air of the air. exhaust purification controlled by the control valve 81 to the exhaust port 14. The control valve 81 supplies the exhaust purification air in the exhaust gas.
exhaust in the operating state of the engine where control of the fuel quantity is not exercised based on the detected value, for example, by the oxygen concentration sensor 70. The air supply tube 82 is composed of a tube of upper supply 82a made of a rubber hose connected to the control valve 81 and a lower metallic supply tube 82b placed along the shield 45. The lower supply tube 82b protrudes from the outer surface of the cylinder head 3, crossing the cooling air passage 46 and connecting with a passage forming part 83. This passage forming part 83 is formed of a projecting portion extending from the opening 54 of the shield 45 to the exterior of the shield 45. The step forming part 83 formed integrally with the cylinder head 3 is provided with an air passage 84 that opens to the exhaust port 14. After flowing into the air supply tube 8 2, the exhaust purification air flows in the air passage 84 and is supplied to the exhaust port 14. The passage formation part 83 is downstream of the exhaust port 14 and the exhaust pipe 38 in terms of flow of cooling air so that the air passage 84 is downstream of the exhaust port 14 in the air passage of
cooling 46 with respect to the cooling air flow. Afterwards, the function and effect of the above described modality will be described. The electric cable 71 connected to the oxygen concentration sensor 70 attached to the cylinder head 3 and the electric cable 76 connected to the oil temperature sensor 75 attached to the cylinder 1 are placed in the cooling air passage 46. In this way , since the sensors 70, 75 and the electric cables 71, 76 are placed on the shield 45, are protected from being hit or coming into contact with a foreign object, for example, gravel agitated during a journey. The present embodiment is different from the technique where, since a sensor is disposed outside the shield 45, the positioning of the sensor and the peripheral components near the sensor is restricted. That is, the present embodiment is such that the positioning of the sensors 70, 75 and the electrical cables 71, 76 is not restricted by the members disposed outside the shield 45. Neither the sensors 70, 75 and the electrical cables 71, 76 restrict the placement of the members. Since the sensors 70, 75 and the electric cables 71, 76 arranged in the cooling air passage 46 are cooled by the air of
cooling on the shield 45, it is prevented from overheating by the heat of the internal combustion engine E. In consequence thereof, the use of the shield 45 in the internal combustion engine E can ensure the protection capacity and the cooling performance for the sensors 70, 75 and the electric cables 71 and 76 connected to the respective sensors 70 and 75 with a simple structure and increase the flexibility of the positioning of the sensors 70, 75 and the electric cables 71, 76. In the internal combustion engine E which includes the cooling fan 40 covered by the shield 45 and which supplies cooling air to the air passage of cooling 46 and the electric cables 71 and 76 arranged upstream of the cylinder 1 and the cylinder head 3 in terms of cooling air flow and therefore forcedly cooled by the cooling air of the cooling fan 40, the electric cables 71 , 76 are effectively cooled by cooling air that still does not cool cylinder 1 and cylinder head 3. The change of the resulting electrical resistance d the temperature rise of the electric cables 71, 76 attributable to the heat of the internal combustion engine E can be suppressed. The oxygen concentration sensor 70 and the temperature sensor of
oil 75 are attached in such a way that the connections 70c and 75c are closer to the cooling fan 40 carried by the shaft end 7b of the crankshaft 7 than the sensing parts 70b and 75b positioned inside the cylinder head 3 and the cylinder 1, respectively. That is, the respective junctions 70c and 75c of the oxygen concentration sensor
70 and the oil temperature sensor 75 are located near the cooling fan 40. Accordingly, the electric cables 71 and 76 connected to the sensors 70 and 75, respectively, are cooled by the cooling air with low temperature. Also in this aspect, the change in electrical resistance resulting from the temperature rise of the electric cables 71, 76 is suppressed. As a result, cooling performance for electric cables
71 and 76 connected to the sensors 70 and 75, respectively, is improved, which suppresses the change of the electrical resistance, thus improving the detection accuracy of the sensors 70, 75. The oxygen concentration sensor 70 is linked in a position upstream of the exhaust port 14 in terms of the cooling air flow. In addition, the air passage 84 which directs the exhaust purification air to the exhaust port 14 is provided in a
position downstream of the exhaust port 14 with respect to the flow of cooling air. In this way, the oxygen concentration sensor 70 and the air passage 84 can be arranged close to the exhaust port 14. In addition, the oxygen concentration sensor 70 is effectively cooled by the cooling air that is not yet heated by the air. Exhaust gas from the exhaust hole 1. The passage forming part 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, it 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 decreasing, which promotes the reaction of the unburned components in the exhaust gas with the purification air of the exhaust gas. escape. As a result, the oxygen concentration sensor 70 and the air passage 84 for the exhaust purification air are placed in a compact manner and the cooling performance for the oxygen concentration sensor 70 and the purification performance of Exhaust purification exhaust air are improved. The configuration modifications of the modality described above will be described later.
The exhaust gas sensor can be an LAF sensor which detects an air-fuel ratio in the exhaust gas or a sensor that detects unburned components. The temperature of the motor can be the temperature of the motor body itself or the combustion temperature, or the temperature of cooling water in a case of an internal combustion engine cooled by air and cooled by water. The step forming part 83 may be formed of a member separate from the cylinder head 3. In this case, the step forming part 83 is made of a material having high thermal conductivity, such as metal, as with the head of cylinder 3 made of a light alloy, such as an aluminum alloy. The internal combustion engine can be one having a cylinder and a cylinder head formed integrally with each other, it can also be a multi-cylinder internal combustion engine. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view of an air-cooled internal combustion engine depicting the present invention, taken along line II of FIG. 2. FIG. 2 is a cross-sectional view taken along the lines of FIG. the
along the line II-II of Figure 1. Figure 3 is a right-side view of an essential part of the internal combustion engine of Figure 1. Figure 4 is a perspective view of the essential part of the engine of internal combustion of Figure 1 with a lower shield part removed. Figure 5 illustrates the essential part of the cylinder and the cylinder head as seen from the arrow V of Figure 3. Figure 6 is a cross-sectional diagram taken along the line Vla-VIa and the line VIb-VIb of Figure 5. Description of Reference Symbols 1 ... cylinder, 3 ... cylinder head, 7 ... crankshaft, 20 ... valve system, 40 ... cooling fan, 45 ... shield, 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 ... internal combustion engine cooled by air.