JP2003239736A - Cooling device for water-cooled engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance an engine output by enhancing a volumetric efficiency and reducing a friction loss. <P>SOLUTION: In this cooling device for the water-cooled engine 15, a cooling water from a radiator is made to flow via a cylinder head 34 to a cylinder 33 thereby cooling is carried out. In this cooling device, after the cooling water from the radiator is made to enter a vicinity of an intake passage 43 of the cylinder head 34, the cooling water is made to flow in an exhaust side of the cylinder head 34 and introduced to the exhaust side of the cylinder 33 from a lower part of an exhaust passage 44, then, is returned to the radiator from an intake side of the cylinder 33. Accordingly, since the cooling water low in temperature from the radiator is first introduced to the vicinity of the intake passage 43 of the cylinder head 34, an intake air is efficiently cooled to increase its specific gravity rate. As a result, volumetric efficiency of the water-cooled engine 15 is enhanced, whereby the engine output is enhanced. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling device for a water-cooled engine that cools water by flowing cooling water from a radiator through a cylinder head to a cylinder. 2. Description of the Related Art In a water-cooled engine, a configuration is generally adopted in which cooling water from a radiator is caused to flow through a cylinder and then returned to the radiator through a cylinder head. [0003] In a motorcycle or the like equipped with a small engine such as a 50 cc engine, it is required to improve the engine output in order to obtain a performance capable of running along the traffic flow. Therefore, a cooling structure that can improve the frictional force and reduce the friction loss is required. In order to improve the volumetric efficiency of the engine, it is necessary to cool the cylinder head, especially in the vicinity of the intake passage, to lower the temperature of the intake air to increase the specific weight thereof, and to increase the friction of the engine. In order to reduce the loss, reduce the viscosity of the oil by keeping the temperature of the cylinder above a certain level,
It is necessary to keep the sliding resistance between the piston and the cylinder low. Therefore, cooling water from a radiator is first passed through a cylinder head to cool the cylinder head.
A configuration in which the cooling water having a high temperature is guided to a cylinder is employed. [0006] However, in a water-cooled engine employing the above-described cooling water path, the viscosity of oil is reduced by maintaining the temperature of the cylinder above a certain level, and the sliding of the piston and the cylinder is prevented. Although it is possible to reduce the resistance, the intake air flowing through the cylinder head was not cooled to increase the volumetric efficiency, and was insufficient to effectively increase the engine output. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a cooling device for a water-cooled engine capable of improving engine output by improving volumetric efficiency and reducing frictional loss. Is to do. In order to achieve the above object, the present invention relates to a cooling system for a water-cooled engine, in which cooling water from a radiator is passed through a cylinder head to a cylinder to cool them. After entering the cooling water from the vicinity of the intake passage of the cylinder head, the cylinder head flows to the exhaust side, is guided from the lower part of the exhaust passage to the exhaust side of the cylinder, and is returned to the radiator from the intake side of the cylinder. I do. Therefore, according to the present invention, since the low-temperature cooling water from the radiator is first guided to the vicinity of the intake port of the cylinder head, the intake air is effectively cooled and its specific weight is increased. The volumetric efficiency of the water-cooled engine is increased, and the engine output is improved. In addition, since the low-temperature cooling water from the radiator is first flowed to the cylinder head, a large amount of heat is dissipated, and the cylinder head which is particularly desired to be cooled is efficiently cooled, and the compression ratio may be increased to improve knock resistance. Thus, the engine output can be improved. Further, according to the present invention, since the cylinder head is cooled by cooling water whose temperature has been increased by cooling the cylinder head, the temperature of the cylinder and oil is maintained at a certain level or more, and the viscosity of the oil decreases. Further, the friction loss between the cylinder and the piston is suppressed low, and the engine output is increased. In addition, since the cooling water from the cylinder head is first guided to the exhaust side where the temperature of the cylinder is high and provided for cooling on the exhaust side, the temperature of the entire cylinder is substantially uniform, and deformation of the cylinder is suppressed. Thus, the gap between the cylinder and the piston is kept small, and the amount of blow-by gas passing through this gap is kept low. Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a side view of a scooter-type motorcycle 1, in which a head pipe 2 is located at a front upper portion of a vehicle body of the illustrated scooter-type motorcycle 1, and a steering shaft 3 is provided in the head pipe 2. It is inserted rotatably. A steering wheel 4 is attached to an upper end of the steering shaft 3, and a front fork 5 is attached to a lower end of the steering shaft 3. A front wheel 6 is rotatably mounted on a lower end of the front fork 5. Supported. A down tube 7 extends obliquely downward toward the rear of the vehicle body from the head pipe 2 and is then bent so as to extend substantially horizontally toward the vehicle body. A pair of right and left back stays 8 branch from each other and extend diagonally upward toward the rear of the vehicle body. The head pipe 2, the down tube 7 and the like at the front of the vehicle body are covered with a resin front cover 9, and the rear half of the front cover 9 also forms a resin leg shield 10. I have. The seat 1 is located behind the handle 4.
1 is provided, and a low-floor footstep 12 is provided between the seat 11 and the handle 4. A radiator 13 is provided in a space obliquely below the foot step 12. A unit swing type engine 14 as a power unit is provided behind the foot step 12 and below the seat 11. The unit swing type engine 14 includes:
The transmission case 16 is provided on the left side of the vehicle body, and is integrally formed with a water-cooled engine 15 as a drive source and a transmission case 16 including a V-belt type automatic transmission and a reduction mechanism (not shown). 15 extends rearward from the left side of the vehicle body, and a rear wheel 17 is rotatably supported at the rear end thereof. An air cleaner 18 is disposed on the left side of the water-cooled engine 15. An intake pipe 19 extending from an upper portion of the air cleaner 18 is bent upward and then rearwardly, and has a carburetor at its end. 20 are attached. An intake pipe 21 extending from the carburetor 20 toward the vehicle body is bent downward and connected to the intake system of the water-cooled engine 15. On the other hand, an exhaust pipe 22 extending from the exhaust system below the water-cooled engine 15 extends rearward on the right side of the vehicle body toward the rear of the vehicle body, and has an exhaust muffler 23 attached to its end. Further, cooling water pipes 24 and 25 extending substantially horizontally from the radiator 13 disposed in front of the engine 15 toward the rear of the vehicle are connected to the water-cooled engine 15 as shown. The unit swing type engine 14 having the above configuration is supported by an engine suspension bracket 26 fixed to the back stay 8 so as to be vertically swingable via a link 27, and a rear end of the rear wheel 17 is provided. Also supported by the back stay 8 via a rear cushion 28. On the other hand, a portion of the vehicle body below the seat 11 is covered with a resin body cover 29, and the unit swing type engine 14
A storage box 30 having an open top is disposed above the fuel cell, and a fuel tank 31 is disposed behind the storage box 30. Here, the storage box 30 is for storing the helmet 32, and the front half of the bottom wall thereof is formed into an arcuate curved shape according to the outer shape of the helmet 32. Then, the sheet 11 is placed on the storage box 30.
The front end of the seat 11 pivots up and down around a hinge (not shown) to open and close the storage box 30. Here, the configuration of the water-cooled engine 15 will be described in detail with reference to FIGS. 2 and 3 are longitudinal sectional views of the engine. The water-cooled engine 15 is a four-stroke single-cylinder DOHC engine, and its cylinder 33 and cylinder head 34 are inclined substantially horizontally forward. Specifically, as shown in FIG. 2, an axial center line (hereinafter, referred to as a cylinder axis) M of a bore 35 formed in the cylinder 33 is:
While being inclined upward by an angle θ with respect to the horizontal line H,
Offset by ε below the crank center O. In the DOHC engine 15, the angle θ is set to a value that allows oil to return from the lowest position in the chain chamber 36 shown in FIG. A piston 37 is slidably fitted in a bore 35 formed in the cylinder 33. The piston 37 is connected to a crankshaft 39 via a connecting rod 38. Here, the crankshaft 39 is rotatably disposed in the crankcase 40 formed integrally with the transmission case 16 in a direction perpendicular to the paper surface of FIG. 2 (in the vehicle width direction). Is connected at the large end of the connecting rod 38 by a crank pin 41,
The small end of the connecting rod 38 is connected to the piston 37 via a piston pin 42. The reciprocating linear movement of the piston 37 in the cylinder bore 35 is performed by a connecting rod 38.
Is converted into the rotational motion of the crankshaft 39 via. The upper and lower portions of the cylinder head 34 attached to the end surface of the cylinder 33 are provided with intake passages 43, respectively.
And an exhaust passage 44 are formed. The intake pipe 21 is connected to the intake passage 43, and the exhaust pipe 22 is connected to the exhaust passage 44. An intake port and an exhaust port, which are openings of the intake passage 43 and the exhaust passage 44 to the combustion chamber S, are opened and closed at appropriate timings by an intake valve 45 and an exhaust valve 46, respectively. Gas exchange is performed. An ignition plug 48 is screwed to the cylinder head 34, and an electrode portion of the ignition plug 48 faces the top of the combustion chamber S. Here, in the water-cooled engine 15, a DOHC (twin cam) type is employed as a valve mechanism for opening and closing the intake valve 45 and the exhaust valve 46. The structure and operation of this valve mechanism will be described below. explain. The intake valve 45 and the exhaust valve 46 are
Valve guides 49 and 5 press-fitted into cylinder head 34
0 are slidably inserted and supported, respectively, and are constantly biased to the closing side by valve springs 51 and 52. Rocker arms 53 and 54 are rotatably supported on upper and lower portions of the cylinder head 34 by rocker shafts 55 and 56, respectively.
The tips of 3 and 54 are in contact with the tops of intake valve 45 and exhaust valve 46, respectively. And the cylinder head 3
In the vicinity of the upper and lower rocker arms 53 and 54, an intake cam shaft 57 and an exhaust cam shaft 58 extending in the vehicle width direction (perpendicular to the plane of FIG. 2) are rotatably supported, respectively.
The intake cam 57a and the exhaust cam 5 formed integrally therewith.
Reference numeral 8a abuts on the back of the rocker arms 53 and 54, respectively. The intake cam shaft 57 and the exhaust cam shaft 58 are covered by a head cover 59 attached to the cylinder head 34. As shown in FIG. 3, chain sprockets 60 and 61 having the same diameter are attached to each end of the intake cam shaft 57 and the exhaust cam shaft 58 by bolts 62 and 63, respectively. An endless cam chain 65 is wound around the chain sprockets 60 and 61 and the small-diameter chain sprocket 64 attached to one end of the crankshaft 39. In FIG. 3, 66 is a chain tensioner for applying a predetermined tension to the cam chain 65, and 67 and 68 are chain guides for preventing the cam chain 65 from swinging. During the operation of the water-cooled engine 15, the rotation of the crankshaft 39 is reduced by half through the chain sprocket 64, the cam chain 65, and the chain sprockets 60 and 61, and the intake camshaft 57 and the exhaust camshaft are reduced. The intake camshaft 57 and the exhaust camshaft 58 are driven to rotate. Then, the intake cam 57a and the exhaust cam 5 formed on the intake cam shaft 57 and the exhaust cam shaft 58
8a are the rocker arms 53,
As the rocker arms 53 and 54 rotate about the rocker shafts 55 and 56 to push and open the intake valve 45 and the exhaust valve 46, respectively, necessary gas exchange is performed in the cylinder bore 35 as described above. Done. Next, the operation of the water-cooled engine 15 will be described. When the water-cooled engine 15 is started, the fresh air is sucked into the air cleaner 18 by the intake negative pressure generated in the intake stroke in which the piston 37 is obliquely descended in the cylinder bore 35, and the fresh air is sucked. After the air is purified in the air cleaner 18, the air is introduced into the carburetor 20 through the intake pipe 19. In the carburetor 20, a fuel-air mixture having a predetermined air-fuel ratio (A / F) is formed by mixing fuel in a spray state with fresh air flowing therethrough.
The air-fuel mixture flows into the cylinder bore 35 through the intake pipe 21, the intake passage 43 of the cylinder head 34, and the intake valve 45 in an open state. In the intake stroke,
The exhaust valve 46 is closed. Then, the piston 37 is moved to the bottom dead center (BDC).
Is shifted to the compression stroke that rises after
5 is closed, the air-fuel mixture is compressed by the piston 37 in the cylinder bore 35, and the piston 37 is moved to the top dead center (TD
Immediately before reaching (C), the fuel is ignited and burned by the spark plug 48. Then, receiving the high pressure generated by the combustion of the air-fuel mixture, the piston 37 shifts to an explosion (work) stroke in which the piston 37 descends in the cylinder bore 35, and the exhaust valve 46 is opened in an exhaust stroke in which the piston 37 rises past the bottom dead center. Then, the high-temperature and high-pressure exhaust gas is discharged to the exhaust passage 44 of the cylinder head 34, and the exhaust gas is discharged into the atmosphere through the exhaust pipe 22 and the exhaust muffler 23. Thereafter, the same process is repeated to continuously operate the water-cooled engine 15. As described above, the reciprocating linear motion of the piston 37 in the cylinder bore 35 is controlled by the connecting rod 38.
Is converted into rotational motion of the crankshaft 39 by
The rotation of the crankshaft 39 is transmitted to the rear wheel 17 via a not-shown V-belt type automatic transmission and a reduction mechanism built in the transmission case 16. As a result, the rear wheel 17 is driven to rotate, and the scooter-type motorcycle 1 runs at a predetermined speed. Next, the details of the cooling device for the water-cooled engine 15 will be described with reference to FIGS. FIG. 4 is a longitudinal sectional view of a water-cooled engine showing a cooling water path of the cooling device according to the present invention, FIG.
6 is a sectional view taken along line AA of FIG. 4, FIG. 7 is a sectional view taken along line BB of FIG. 4, FIG. 8 is a sectional view taken along line CC of FIG. 4, and FIG.
FIG. 10 is a sectional view taken along line D-E of FIG. 8. As shown in FIGS. 5 and 6, the engine 15
A cooling water pump 70 is arranged coaxially with the exhaust cam shaft 58 on one end face (right end face) of the head cover 59.
Here, the cooling water pump 70 is configured by directly connecting an impeller 72 to one end of a pump shaft 71 disposed coaxially with the exhaust cam shaft 58, and the pump shaft 71 is incorporated into one end surface of the head cover 59. The other end is rotatably supported by the pump housing 73 and is connected to one end of the exhaust camshaft 58 by means of a concave and convex fit. Note that a seal member 74 is in sliding contact with the outer periphery of the pump shaft 71. The impeller 72 is covered by a pump cover 75 attached to a pump housing 73. The pump cover 75 is integrally provided with a cooling water passage 75a for guiding cooling water to the impeller 72 in the axial direction. The cooling water passage 75a is connected to the cooling water pipe 24 (see FIG. 1) extending from the outlet side of the radiator 13. A scroll chamber 76 is formed around the impeller 72 of the pump cover 75, and the outlet of the scroll chamber 76 is connected to the pump housing 7.
3 is connected to a cooling water passage 73a formed in the cooling water passage 73.
The scroll chamber 76 is sealed by the seal member 74 that slides on the outer periphery of the pump shaft 71. On the other hand, as shown in FIGS. 4 and 7 to 10, the intake passage 43 and the exhaust passage 44 of the cylinder head 34 are provided.
And a water jacket 77 around the spark plug 48.
Are formed, and the cylinder bore 3 of the cylinder 33 is formed.
A water jacket 78 is formed around 5. The lower portion on the exhaust side of the water jacket 77 formed in the cylinder head 34 communicates with the lower portion on the exhaust side of the water jacket 78 formed in the cylinder 33. As shown in FIG. 8, ribs 34a for deflecting the flow of the cooling water flowing through the water jacket 77 toward the spark plug 48 are formed on the left and right sides of the cylinder head 34. On the intake side (upper side) of the cylinder head 34, a cooling water inlet 77a having a circular hole opening to the water jacket 77 is formed. The cooling water passage 73a formed in the pump housing 73 is connected. On the intake side (upper side) of the cylinder 33, a cooling water outlet 78a having a circular hole opening to the water jacket 78 is formed. As shown in FIG. A plug 79 is attached. One end of the cooling water pipe 25 (see FIG. 1) is connected to the plug 79, and the other end of the cooling water pipe 25 is connected to the radiator 13 (see FIG. 1).
Connected to the entrance. In the cooling water apparatus having the above-described cooling water path, the cooling water from the radiator 13 is introduced into the vicinity of the intake passage 43 of the cylinder head 34 and then exhausted from the water jacket 77 of the cylinder head 34. The fluid flows downward toward the side, is introduced from the lower part of the exhaust passage 44 to the exhaust side of the water jacket 78 of the cylinder 33, and is returned to the radiator 13 from the intake side of the cylinder 33. That is, when the water-cooled engine 15 is started and the exhaust cam shaft 58 is driven to rotate as described above, the pump shaft 71 of the cooling water pump 70 connected to the exhaust cam shaft 58
And the impeller 72 directly connected thereto are driven to rotate at the same speed, and the low-temperature cooling water cooled in the radiator 13 passes through the cooling water pipe 24 from the cooling water passage 75a of the pump cover 75 to the impeller of the cooling water pump 70. 72 suctions in the axial direction. Then, the pressure of the cooling water is increased by the impeller 72 and flows from the outlet of the scroll chamber 76 to the cooling water passage 73 a of the pump housing 73, and firstly into the cylinder head 34 from a cooling water inlet 77 a formed on the intake side of the cylinder head 34. It is led. In the cylinder head 34, the low-temperature cooling water flows through the water jacket 77 from the intake side (upper side) to the exhaust side (lower side), and first cools the vicinity of the intake passage 43, and then cools the exhaust side. To cool the vicinity of the spark plug 48 and the exhaust passage 44. As described above, the high-temperature cooling water that flows through the water jacket 77 of the cylinder head 34 from the intake side to the exhaust side and cools each part is discharged from the lower part of the exhaust passage 44 of the cylinder head 33 to the water jacket 78 of the cylinder 33. (See FIGS. 9 and 10), and cools around the cylinder bore 35 of the cylinder 33 in the process of flowing through the water jacket 78 from the exhaust side to the intake side (from below to above).
Finally, the cooling water is discharged from the cooling water outlet 78 a formed on the side of the cylinder 33 to the outside of the cylinder 33, returned to the radiator 13 through the cooling water pipe 25, and generated by the radiator 13 with the traveling wind. After that, the cooling water flows continuously through the same cooling water path as described above to cool each part of the water-cooled engine 15. As described above, in the cooling device according to the present invention, since the low-temperature cooling water from the radiator 13 is first guided to the vicinity of the intake passage 43 of the cylinder head 34, the intake air (air-fuel mixture) is effectively reduced. The water-cooled engine 15 is cooled and its specific weight is increased. As a result, the volumetric efficiency of the water-cooled engine 15 is increased, and the engine output is improved. Since the low-temperature cooling water from the radiator 13 is first passed through the cylinder head 34, the amount of heat radiation is large, and the cylinder head 34 that is particularly desired to be cooled is efficiently cooled and the knock resistance is enhanced. The compression ratio can be increased, which can also improve the engine output. Further, according to the present invention, the cylinder head 3
4 is cooled and the cylinder 3
3 is cooled, the temperature of the cylinder 33 and the oil is maintained at a certain level or higher, and the viscosity of the oil is reduced, so that the friction loss (sliding resistance) between the cylinder 33 and the piston 37 is suppressed low, and the engine output is reduced. Enhanced. The cooling water from the cylinder head 34 is
Since it is first guided to the exhaust side where the temperature of the cylinder 33 is high and used for cooling on the exhaust side, the temperature of the entire cylinder 33 becomes substantially uniform and deformation of the cylinder 33 is suppressed, and the cylinder bore 35 and the piston 37 Is kept small, and the amount of blow-by gas passing through this gap is kept low. In this embodiment, the cooling water pump 70
Is driven by the exhaust camshaft 58, but the cooling water pump 70 may be driven by the intake camshaft 57. As is apparent from the above description, according to the present invention, in the cooling system of a water-cooled engine for cooling water from a radiator through a cylinder head to a cylinder to cool them, After the cooling water from the cylinder head is introduced into the vicinity of the intake passage of the cylinder head, the cylinder head flows to the exhaust side, is guided from the lower part of the exhaust passage to the exhaust side of the cylinder, and is returned to the radiator from the intake side of the cylinder. The effect that the engine output can be improved by the improvement, the reduction of the friction loss and the like is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a scooter type motorcycle. FIG. 2 is a longitudinal sectional view of a water-cooled engine. FIG. 3 is a longitudinal sectional view of a water-cooled engine. FIG. 4 is a longitudinal sectional view of a water-cooled engine showing a cooling water path of the cooling device according to the present invention. FIG. 5 is a right side view in which a part of the water-cooled engine is broken. FIG. 6 is a sectional view taken along line AA of FIG. 4; FIG. 7 is a sectional view taken along line BB of FIG. 4; FIG. 8 is a sectional view taken along line CC of FIG. 4; FIG. 9 is a sectional view taken along the line DD in FIG. 8; FIG. 10 is a sectional view taken along line EE of FIG. 8; [Description of Signs] 13 Radiator 15 Water-cooled engine 33 Cylinder 34 Cylinder head 43 Intake passage 44 Exhaust passage 70 Cooling water pump 77, 78 Water jacket

Claims (1)

Claims: 1. A cooling device for a water-cooled engine, wherein cooling water from a radiator flows through a cylinder head to a cylinder to cool the cooling water, wherein the cooling water from the radiator is provided near an intake passage of the cylinder head. A cooling device for a water-cooled engine, wherein the cylinder head is caused to flow to the exhaust side after being inserted, guided to the exhaust side of the cylinder from a lower portion of the exhaust passage, and returned to the radiator from the intake side of the cylinder.