JP6636579B1 - Cooling structure of internal combustion engine - Google Patents

Abstract

Provided is a cooling structure for an internal combustion engine that can maintain the cooling efficiency of a cylinder block of the internal combustion engine at a high level, improve the rigidity of a fastening portion of the cylinder block to a crankcase, and maintain good sealing performance. A liquid passage (24W) in a cylinder block through which a coolant flows around a cylinder bore (24b) of a cylinder block (24) is formed by a partition wall (24P) and an upper liquid passage (24Wa) in an upper and lower cylinder block. The inner liquid passage (24Wb) is partitioned into inner and lower liquid passages, and the upper liquid passage (24Wa) inside the cylinder block is formed so as to pass through the inside of the stud bolt (40) and surround the outer periphery of the cylinder bore (24b). The lower liquid passage (24Wb) is a cooling structure of the internal combustion engine formed so as to surround the outer periphery of the cylinder bore (24b) through the swelling passage portion (24Wbf) bulging outside the stud bolt (40). is there. [Selection diagram] FIG.

Description

  The present invention relates to a cooling structure for a liquid-cooled internal combustion engine mounted on a vehicle.

  A water-cooled internal combustion engine, in which a cylinder block and a cylinder head are sequentially stacked on a crankcase and fastened by stud bolts to form an engine body, is a water passage in a cylinder block through which cooling water passes so as to surround an outer periphery of a cylinder bore of the cylinder block. (Water jacket) is formed.

  Usually, the water passage in the cylinder block is formed so as to pass through the inside of the stud bolt on the same side as the cylinder bore with respect to the stud bolt and surround the outer periphery of the cylinder bore (for example, see Patent Document 1).

JP 2014-47719 A

The water-cooled internal combustion engine disclosed in Patent Literature 1 is an in-line two-cylinder four-stroke internal combustion engine, in which a water jacket is formed so as to surround the outer periphery of parallel cylinder bores in a cylinder block.
Stud bolts for fastening the cylinder block and the cylinder head in order on the crankcase are inserted into bolt insertion holes formed at four corners around the cylinder bore and fastened.

  The water jacket passes through the inside of the stud bolt, i.e. between the cylinder bore and the stud bolt, on the same side as the cylinder bore with respect to the stud bolt, so as to surround the outer periphery close to the cylinder bore in order to effectively cool the cylinder block. And is formed so as to surround the outer periphery of the cylinder bore.

  Therefore, when it is desired to more securely fasten the cylinder block to the crankcase, the number of fastening locations increases and the thickness around the bolt insertion hole increases.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to improve the rigidity of a fastening portion of a cylinder block to a crankcase while maintaining a high cooling efficiency of a cylinder block of an internal combustion engine, and to perform sealing. Another object of the present invention is to provide a cooling structure for an internal combustion engine capable of maintaining good performance.

In order to achieve the above object, the present invention provides
An internal combustion engine is mounted in the center of the motorcycle between the front and rear wheels in the left and right vehicle width direction,
In the internal combustion engine, an engine body is configured by sequentially overlapping a cylinder block and a cylinder head on a crankcase and fastening them with stud bolts,
The cylinder block has a liquid passage in the cylinder block through which the coolant flows around the cylinder bore,
In the cooling structure of the internal combustion engine, the cylinder head has a liquid passage in the cylinder head through which a coolant flows around the combustion chamber.
The fluid passage in the cylinder block is divided into upper and lower fluid passages in the cylinder block and upper and lower fluid passages in the cylinder block, which are partitioned by a partition into upper and lower portions in an axial direction of a cylinder axis which is a center axis of the cylinder bore,
The cylinder block upper liquid passage is formed so as to pass through the inside of the stud bolt which is the same side as the cylinder bore with respect to the stud bolt, and to surround the outer periphery of the cylinder bore,
The lower liquid passage in the cylinder block is formed so as to pass through a swelling passage portion swelling outward of the stud bolt, which is opposite to the cylinder bore with respect to the stud bolt, and to surround the outer periphery of the cylinder bore. A cooling structure for an internal combustion engine is provided.

  According to this configuration, the upper liquid passage in the upper cylinder block which particularly requires cooling of the cylinder block passes through the inside of the stud bolt on the same side as the cylinder bore with respect to the stud bolt, and surrounds the outer periphery of the cylinder bore. Therefore, the cylinder block can be efficiently cooled.

  The lower fluid passage in the cylinder block formed on the lower side fastened to the crankcase of the cylinder block is a bulging passage portion bulging outside the stud bolt, which is opposite to the cylinder bore with respect to the stud bolt. Is formed so as to surround the outer periphery of the cylinder bore, so that the fastening portion to be fastened to the lower crankcase of the cylinder block has higher rigidity due to the bulging passage portion, and is firmly and firmly attached to the crankcase. At the same time, the rigidity of the packing surface with the crankcase is high, and the surface pressure can be made uniform to improve the sealing performance.

In a preferred embodiment of the present invention,
The cylinder block has a lower outer peripheral wall forming a lower liquid passage in the cylinder block and an upper outer peripheral wall forming an upper liquid passage in the cylinder block,
The lower outer peripheral wall extends outside the upper outer peripheral wall.

  According to this configuration, the cylinder block is formed such that the lower outer peripheral wall that forms the lower liquid passage in the cylinder block extends outside the upper outer peripheral wall that forms the upper liquid passage in the cylinder block. The rigidity of the fastening portion fastened to the lower crankcase of the cylinder block is further increased.

In a preferred embodiment of the present invention,
An oil passage extending in the axial direction of the cylinder axis is formed in the cylinder block,
The lower liquid passage in the cylinder block passes through the outside of the oil passage that is on the opposite side of the oil passage from the cylinder bore.

  According to this configuration, since the lower liquid passage in the cylinder block passes through the outside of the oil passage opposite to the cylinder bore with respect to the oil passage, the fastening portion fastened to the lower crankcase of the cylinder block. Rigidity increases more and more.

In a preferred embodiment of the present invention,
A coolant circulation path that circulates coolant through the cylinder block fluid path and the cylinder head fluid path by a coolant pump includes a radiator passage that passes through a radiator that cools the coolant and a bypass passage that bypasses the radiator. Interposed,
A thermostat that switches between circulation by the radiator passage and circulation by the bypass passage,
The lower liquid passage in the cylinder block forms a part of the bypass passage.

  According to this configuration, since the lower liquid passage in the cylinder block forms a part of the bypass passage bypassing the radiator, the bypass passage can be configured in the wall of the cylinder block, contributing to space saving and improvement in appearance. At the same time, when the internal combustion engine is started, the coolant passing through the bypass passage warms up quickly, and the internal combustion engine can be warmed up early.

  According to the present invention, the upper liquid passage in the upper cylinder block, which particularly requires cooling of the cylinder block, is formed so as to pass through the inside of the stud bolt on the same side as the cylinder bore with respect to the stud bolt and surround the outer periphery of the cylinder bore. Therefore, the cylinder block can be cooled efficiently.

  Further, the lower liquid passage in the lower cylinder block, which is fastened to the crankcase of the cylinder block, passes through a swelling passage that swells outside the stud bolt, which is the opposite side of the cylinder bore with respect to the stud bolt, Since it is formed so as to surround the outer periphery of the cylinder bore, the fastening portion to be fastened to the lower crankcase of the cylinder block is increased in rigidity by the bulging passage portion, and it is securely and firmly attached to the crankcase, and The rigidity of the packing surface with the case is high, and the surface pressure can be made uniform to improve the sealing performance.

1 is an overall side view of a motorcycle according to one embodiment of the present invention. FIG. 2 is a left side view of an internal combustion engine (power unit) and a radiator mounted on the motorcycle. It is the same right view. FIG. 2 is a front view of the internal combustion engine (power unit). FIG. 5 is a cross-sectional view of the internal combustion engine in the cylinder head as viewed from arrows VV in FIGS. 2 and 3. FIG. 6 is an enlarged sectional view of a thermostat in a different state in FIG. FIG. 7 is a cross-sectional view of the internal combustion engine in the cylinder block as viewed from arrows VII-VII in FIGS. 2 and 3. FIG. 8 is a cross-sectional view of the internal combustion engine in the cylinder block as viewed from arrows VIII-VIII in FIGS. 2 and 3. It is a top view of a cylinder block. It is a bottom view of the same cylinder block. FIG. 11 is a cross-sectional view of the cylinder block as viewed from arrows XI-XI in FIGS. 9 and 10. FIG. 9 is a sectional view of the internal combustion engine taken along the line XII-XII in FIGS. 5, 7 and 8. FIG. 9 is a cross-sectional view of the internal combustion engine taken along the line XIII-XIII in FIGS. 5, 7 and 8. FIG. 3 is a schematic diagram schematically showing a flow of cooling water in a cooling structure of the internal combustion engine.

An embodiment according to the present invention will be described below with reference to the drawings.
FIG. 1 is a side view of a motorcycle 1 which is a straddle-type vehicle according to an embodiment to which the present invention is applied.
In the description of the present specification, the front, rear, left, and right directions are based on a normal reference that the forward direction of the motorcycle 1 according to the present embodiment is forward, and in the drawings, FR indicates forward and RR indicates backward. , LH indicate the left side, and RH indicates the right side.

The body frame 2 of the straddle-type motorcycle 1 is divided into left and right sides from a head pipe 3 and main frames 4, 4 extend rearward, and rear center frame portions 4c, 4c are bent downward.
Down frames 5, 5 extend obliquely downward and rearward from the head pipe 3.
A seat rail 6 extends obliquely rearward and upward from a position closer to the front than the upper bent portion of the center frame portions 4c of the main frames 4 and 4.

  A front wheel 9 is pivotally supported at the lower end of a front fork 7 slidably supported by the head pipe 3, and a handle 8 is connected to the front fork 7 via a steering shaft (not shown) extending upward.

A rear fork 11 whose front end is pivotally supported by a pivot shaft 10 extends rearward on the center frame portion 4c, and a rear wheel 12 that is pivotally supported at its rear end is provided to be vertically swingable.
A link mechanism 13 is provided between a lower edge of the rear fork 11 and a lower end of the center frame 4c, and a rear cushion 14 is interposed between a part of the link mechanism 13 and an upper portion of the center frame 4c. Have been.

The power unit 20 mounted on the body frame 2 of the motorcycle 1 is configured such that a transmission 31 is integrally accommodated in a rear portion of a crankcase 23 of an internal combustion engine 21. Is suspended between the down frame 5 and the main frame 4.
A fuel tank 15 is mounted on the main frame 4 above the power unit 20, and a seat 16 is provided behind the fuel tank 15 so as to be supported by the seat rail 6.

The internal combustion engine 21 is a water-cooled in-line four-cylinder four-stroke cycle internal combustion engine, and is mounted on the motorcycle 1 with its crankshaft 22 directed in the vehicle width direction (left-right direction).
2 is a left side view of the internal combustion engine 21, FIG. 3 is a right side view of the internal combustion engine 21, and FIG.

Referring to FIGS. 2 and 3, a cylinder axis is slightly inclined forward on a crankcase 23 which rotatably supports a crankshaft 22 so that a cylinder block 24 and a cylinder head 25 stand up so as to be sequentially overlapped. The engine body 21 </ b> H is configured by being fastened by the stud bolt 40 in the set posture, and the cylinder head cover 26 is covered on the cylinder head 25.
A gasket 25c is sandwiched between the cylinder block 24 and the cylinder head 25.
An oil pan 27 covers the lower part of the crankcase 23.

An intake pipe 50 extends upward from a forwardly inclined cylinder head 25 of the internal combustion engine 21 and is connected to an air cleaner 52 via a throttle body 51 (see FIG. 1).
The four exhaust pipes 55 extending forward and extending downward from the cylinder head 25 are gathered at a place where they are bent rearward, and extend rearward below the crankcase 23 via the catalyst device 56 so as to extend rearward. (See FIG. 1).

  A counter shaft 33 of the transmission 31, which is an output shaft of the power unit 20, penetrates the left bearing wall and protrudes leftward, and an output sprocket 34 is fitted to the left end thereof. The drive chain 36 is wound around the driven sprocket 35 fitted to the rear axle of the wheel 12, and the output of the power unit 20 is transmitted to the rear wheel 12 via the drive chain 36, so that the motorcycle 1 runs. (See FIG. 1).

In front of the internal combustion engine 21, a radiator 100 that is deployed in the left and right vehicle width direction is disposed in a posture inclined forward along the front surfaces of the cylinder block 24 and the cylinder head 25 of the engine main body H.
The radiator 100 has an upstream radiator tank 100U and a downstream radiator tank 100L on the left and right sides of the radiator core 100C.

Referring to FIGS. 7 to 10 showing the cylinder block 24, the cylinder block 24 is formed with four cylindrical cylinder bores 24b arranged side by side in the left-right vehicle width direction. A chain chamber 24c is formed.
The piston 28 reciprocates in the cylinder bore direction in the cylinder bore 24b (see FIG. 12).
An inner water passage (cylinder block water jacket) 24W is formed annularly above the crankcase 23 so as to surround the outer periphery of the four cylinder bores 24b arranged on the left and right sides of the cylinder block 24.

  As shown in FIGS. 12 and 13, the water passage 24 </ b> W in the cylinder block is vertically divided by a partition wall 24 </ b> P in the direction of the cylinder axis Lp, and an upper water passage 24 </ b> Wa in the cylinder block and a lower water passage 24 </ b> Wb in the cylinder block are formed. .

Referring to FIG. 12, a partition wall 24P defining a liquid passage 24W in the cylinder block is formed in the middle of a piston top surface moving range Dp in which a top surface 28t of a piston 28 sliding in the cylinder axis Lc direction in the cylinder bore 24b moves. It is formed more deviated toward the crankcase 23 side.
The width d of the lower water passage 24Wb in the cylinder block in the direction of the cylinder axis Lc is about 1/3 of the width D of the water passage 24W in the cylinder block in the direction of the cylinder axis Lc (see FIGS. 11 and 12).

  Referring to FIG. 7 showing the upper water passage 24Wa in the cylinder block and FIG. 8 showing the lower water passage 24Wb in the cylinder block, the inside of the cylinder block is formed annularly so as to surround the outer periphery of four cylinder bores 24b arranged on the left and right sides of the cylinder block 24. An upper channel 24Wa and a lower channel 24Wb in the cylinder block are formed.

Bolt holes 24s through which the stud bolts 40 penetrate are formed at four corners around the outer periphery of each cylinder bore 24b, and four stud bolts 40 are fastened around each cylinder bore 24b. .
A common bolt hole 24s is formed at a position where the outer periphery of both of the adjacent cylinder bores 24b, 24b overlaps with each other so as to slightly bite between the cylinder bores 24b, 24b, and the two front and rear stud bolts 40 penetrate. .

As shown in FIG. 5, a bolt hole 25s through which the stud bolt 40 penetrates is formed at a position corresponding to the cylinder head 25 as well.
Therefore, as shown in FIGS. 7 and 8, five bolt holes 24s are arranged on the left and right sides of the front wall and the rear wall of the cylinder block 24, respectively, and ten stud bolts 40 penetrate through each bolt hole 24s. As a result, the cylinder block 24 and the cylinder head 25 are fastened to the crankcase 23.

  As shown in FIG. 7 and FIG. 8, the front wall of the cylinder block 24 has the moving of the cylinder head 25 obliquely forward of the three inner bolt holes 24s among the five bolt holes 24s arranged on the left and right. An oil passage 24o for supplying oil to the valve system is formed.

As shown in FIG. 7, the upper water passage 24Wa in the cylinder block above the water passage 24W in the cylinder block defined by the partition wall 24P passes through the inside of the stud bolt 40 on the same side as the cylinder bore 24b with respect to the stud bolt 40. Are formed so as to surround the outer periphery of the cylinder bore 24b.
The upper water passage 24Wa in the cylinder block also passes through the oil passage 24o on the same side as the cylinder bore 24b with respect to the oil passage 24o.

On the other hand, as shown in FIG. 8, the lower water passage 24Wb inside the cylinder block 24W is a stud that is opposite to the cylinder bore 24b with respect to the six inner stud bolts 40 in the left-right direction as shown in FIG. It is formed so as to pass through the bulging passage portion 24Wbf bulging out of the bolt 40 and surround the outer periphery of the cylinder bore 24b.
Further, the swelling passage portion 24Wbf of the lower water passage 24Wb in the cylinder block also passes through the outside of the stud bolt 40 which is on the opposite side to the cylinder bore 24b with respect to the oil passage 24o.

  Therefore, as shown in FIGS. 11 and 13, the cylinder block 24 has a lower outer peripheral wall 24L in which the lower water passage 24Wb in the cylinder block is formed, and an upper outer peripheral wall 24U in which the upper water passage 24Wa in the cylinder block is formed. It is formed so as to extend outward.

  Referring to FIGS. 5 and 12, cylinder head 25 has a water passage (cylinder head water jacket) 25W formed around cylinder chamber 24b of cylinder block 24, around combustion chamber 25b.

An intake port 25i extends obliquely upward and backward from the combustion chamber 25b to the cylinder head 25, and the throttle body 51 is connected to an upstream end of the intake port 25i.
An exhaust port 25e extends obliquely upward and forward from the combustion chamber 25b, and the exhaust pipe 55 is connected to the exhaust port 25e.
The cylinder head inner water passage (cylinder head water jacket) 25W is also formed around the intake port 25i and the exhaust port 25e.

A water passage 25W in the cylinder head 25 of the cylinder head 25 is partially opened in a mating surface with the cylinder block 24.
The upper water passage 24Wa in the cylinder block of the water passage 25W in the cylinder head of the one cylinder block 24 is partially open to the mating surface with the cylinder head 25 (see FIG. 9).
The openings of the mating surfaces of the cylinder block 24 and the cylinder head 25 are opposed to each other, and when the cylinder block 24 and the cylinder head 25 are overlapped and fastened together with the gasket 25c interposed therebetween, the cylinder block upper water passage 24Wa and the cylinder head water passage 25W communicate with the gasket 25c communication hole. It communicates through 25 channels (see FIG. 12).

As shown in FIG. 3, a water pump 60 for circulating cooling water is provided below the transmission 31 on the right side of the crankcase 23 in the engine body 21H of the internal combustion engine 21 as described above (see FIG. 3). 1 and 2).
The water pump 60 is configured such that an impeller 60 a is housed in a pump body formed on the right side wall of the crankcase 23, and the impeller 60 a is covered from outside by a pump cover 61.

In the pump cover 61, a suction connection pipe 62 is formed so as to protrude from a suction chamber on the right side of the impeller 60a, and a pump inflow hose 65 connected to the suction connection pipe 62 extends forward along the right side of the crankcase 23. , Around the front surface of the front wall 24F of the cylinder block 24.
Further, a discharge connection pipe 63 that is curved and extends forward on the outer periphery of the impeller 60a is formed, and a pump outflow hose 66 connected to the discharge connection pipe 63 extends forward along the right side of the crankcase 23, It wraps around the front surface of the front wall 24F of the cylinder block 24.

Referring to FIGS. 2, 4 and 5, a thermostat 70 is provided integrally with the rear side wall of the cylinder head 25 at the left end of the rear surface of the cylinder head 25 of the engine body 21H.
As shown in FIGS. 5 and 6, the thermostat 70 has a thermostat case 71 integrally formed on the rear side wall of the cylinder head 25, a cover member 72 covering an opening opened to the left, and a first inside. Two valves, a valve 73 and a second valve 74, are housed.

Referring to FIG. 6, inside a thermostat 70, an annular valve seat 77 is fixed by being sandwiched between a thermostat case 71 and a cover member 72. The valve seat 77 has an annular seat having a valve opening in the center. And a band-shaped retainer 77b which is bent in a U-shape and has both ends connected to the periphery of the valve opening of the annular seat portion 77a.
The retainer portion 77b projects from the annular seat portion 77a of the valve seat 77 into the inner space of the left lid member 72.

A spring receiving support member 78 extends from the annular seat portion 77a of the valve seat 77 into the thermostat case 71 on the right side.
The spring support member 78 has a pair of support pieces 78a, 78a extending rightward from the valve seat 77, and has a ring-shaped spring support portion 78b formed at the right end.
The first valve 73 is urged by a coil spring 81 one end of which is supported by a spring receiving portion 78b of a spring receiving support member 78, and comes into contact with the annular seat portion 77a of the valve seat 77.

  The first valve 73 penetrates and is attached to the thermoelement 75, and the left end of the thermoelement 75 penetrates through a central valve opening of the annular valve seat 77 with a margin. When the valve seat 77 abuts on the annular seat portion 77a, the valve opening of the valve seat 77 is closed to close the valve, and the internal space of the thermostat case 71 and the internal space of the lid member 72 are partitioned.

The right side portion of the thermoelement 75 whose diameter has been expanded is a temperature sensing portion 75t in which a thermal expansion body such as wax is sealed.
The thermo element 75 has a temperature sensing portion 75t slidably supported by an annular spring receiving portion 78b of a spring receiving supporting member 38, while a plunger 76 is provided with a left lid member from the left end of the thermo element 75. The tip of the plunger 76 protrudes into the valve seat 77 and is held in contact with a bent receiving portion 77bb of a retainer portion 77b formed integrally with the valve seat 77.

A second valve 74 is slidably fitted to and supported by a support rod 75a integrally projecting rightward from a temperature sensing portion 75t of the thermoelement 75.
The second valve 74 whose movement is restricted by the retaining ring 79 engaged with the support rod 75a is urged rightward by a conical coil spring 82 interposed between the second valve 74 and the temperature sensing part 75t.

The thermostat case 71 has a large-diameter cylindrical main body 71a on the lid member 72 side (left side), and a reduced-diameter cylindrical end 71b protruding from the right side of the cylindrical main body 71a.
The second valve 74 abuts on a step 71c between the cylindrical main body 71a and the small-diameter cylindrical end 71b to close the valve, thereby separating the internal space of the cylindrical main body 71a and the internal space of the small-diameter cylindrical end 71b. be able to.

  FIG. 5 shows a state in which the temperature of the cooling water around the temperature sensing portion 75t of the thermoelement 75 is low, and the first valve 73 and the thermoelement 75 are moved to the left by being urged by the coil spring 81. Then, the first valve 73 comes into contact with the valve seat 77 and closes, and the internal space of the thermostat case 71 and the internal space of the lid member 72 are separated from each other. At the same time, the first space is supported by the support rod 75 a of the thermoelement 75. The second valve 74 is opened apart from the step 71c between the cylindrical main body 71a and the small-diameter cylindrical end 71b of the thermostat case 71, and the internal space of the cylindrical main body 71a and the internal space of the small-diameter cylindrical end 71b are opened. Is in communication.

When the temperature of the cooling water around the temperature sensing portion 75t of the thermoelement 75 rises, the wax inside the temperature sensing portion 75t expands and pushes the plunger 76, and the tip of the plunger 76 is held by the retainer portion 77b of the valve seat 77. Therefore, the thermo-element 75 moves rightward against the coil spring 81 due to the reaction force, as shown in FIG.
Accordingly, the first valve 73 is opened to allow the internal space of the thermostat case 71 to communicate with the internal space of the lid member 72, and at the same time, the second valve 74 urged by the conical coil spring 82 abuts the step 71c. Then, the valve is closed to separate the internal space of the cylindrical main body 71a from the internal space of the small-diameter cylindrical end 71b.

An outflow connection pipe 72j is formed to project from the lid member 72 of the thermostat 70, and a radiator inflow hose 101 extending from an upstream radiator tank 100U of the radiator 100 is connected to the outflow connection pipe 72j.
The thermostat case 71 of the thermostat 70 is formed integrally with the rear side wall 25B of the cylinder head 25, and extends from the cylinder head inner water passage 25W of the cylinder head 25 into the internal space of the cylindrical main body 71a of the thermostat case 71. A wide outflow passage 84 is opened (see FIGS. 5 and 12).
That is, the thermostat case 71 is integrally formed at the outflow portion of the rear side wall 25B of the cylinder head 25 where the outflow passage 84 is formed.

A bypass communication passage 86 communicating with the internal space of the small-diameter cylindrical end portion 71b of the thermostat case 71 extends toward the lower cylinder block 24 on the rear wall 25B of the cylinder head 25, and opens at the mating surface with the cylinder block 24. It is formed.
The small-diameter cylindrical end 71b has a small leak passage 85 extending from the cylinder head water passage 25W, and a part of the cooling water from the cylinder head water passage 25W even when the second valve 74 is closed. Is leaked into the small-diameter cylindrical end 71b and flows into the bypass communication passage 86.

  Referring to FIG. 7, a bypass communication passage 87 communicating with the bypass communication passage 86 on the cylinder head 25 side on the rear side wall 24B of the cylinder block 24 is opened at a mating surface with the cylinder head 25 and extends downward. The bypass communication passage 86 on the cylinder head 25 side and the bypass communication passage 87 on the cylinder block 24 side communicate with each other through the communication hole of the gasket 25c.

Referring to FIGS. 7 and 8, bypass communication passage 87 formed in rear wall 24 </ b> B of cylinder block 24 has a lower end opening opening in lower water passage 24 </ b> Wb in the cylinder block to lower water passage 24 </ b> Wb in the cylinder block. The lower channel inlet 24 Wba.
The lower channel inlet 24Wba to the lower channel 24Wb in the cylinder block is formed on the rear wall 24B of the cylinder block 24.

With the configuration described above, when the temperature of the cooling water is low immediately after the start of the internal combustion engine, the first valve 73 closes and the second valve 74 opens, as shown in FIG. The cooling water circulated through the water passage 25W in the cylinder head flows from the internal space of the cylindrical main body 71a to the internal space of the small-diameter cylindrical end 71b, and from the internal space of the small-diameter cylindrical end 71b to the bypass communication passage 86 on the cylinder head 25 side. And, it flows down the bypass communication passage 87 on the cylinder block 24 side and flows into the lower water passage 24Wb in the cylinder block.
The lower water passage 24Wb in the cylinder block forms a part of a bypass passage.

When the temperature of the cooling water rises to a certain degree due to the operation of the internal combustion engine, as shown in FIG. 5, the first valve 73 opens and the second valve 74 closes, as shown in FIG. The cooling water having circulated 25 W flows from the internal space of the cylindrical main body 71a to the radiator inflow hose 101 via the internal space of the cover member 72, and flows into the upstream radiator tank 100U.
Note that even when the second valve 74 is closed, a part of the cooling water leaks from the narrow leakage passage 85 into the small-diameter cylindrical end 71b from the water passage 25W in the cylinder head and flows to the bypass communication passage 86.
Note that the leakage passage 85 may be formed as a groove in which a portion of the stepped portion 71c that contacts the second valve 74 is partially cut away.

Referring to FIG. 7, an upper channel inlet for injecting cooling water into cylinder block upper channel 24Wa is provided on the right side of the front wall of upper outer peripheral wall 24U in which cylinder block upper channel 24W of cylinder block 24 is formed. 24 Waa is formed.
Referring to FIG. 8, cooling water is supplied from lower water passage 24Wb in the cylinder block to the right side of front wall 24F of lower outer peripheral wall 24L in which lower water passage 24Wb in the cylinder block of cylinder block 24 is formed. An outflow lower channel outlet 24Wbb is formed.

Referring to FIG. 4 which is a front view of the internal combustion engine 21, the upper channel inlet 24Waa and the lower channel outlet 24Wbb are provided on the right side of the front wall 24F of the cylinder block 24 adjacent to each other and on the left and right sides. I have.
An upper channel inlet connection pipe 91 connected to the upper channel inlet 24Waa and a lower channel outlet connection pipe 92 connected to the lower channel outlet 24Wbb have a common mounting seat plate portion 93, and a cylinder block. By screwing the mounting seat plate portion 93 to the front wall 24F of the cylinder 24 with bolts, the upper channel inflow connection pipe 91 and the lower channel outflow connection pipe 92 are integrally attached to the front wall 24F of the cylinder block 24.

Referring to FIG. 4, a pump outlet hose 66 extending forward from the water pump 60 and wrapping around the front surface of the front wall 24F of the cylinder block 24 is connected to the upper channel inlet connection pipe 91.
Another pump inflow hose 65 extending forward from the water pump 60 and wrapping around the front surface of the front side wall 24F of the cylinder block 24 is a radiator outflow hose for guiding cooling water flowing out of the radiator 100 downstream radiator tank 100L. It is connected to 102 by a branch connection pipe 94.

As shown in FIG. 4, the lower channel outflow connection pipe 92 is branched from the branch connection pipe 94 to be integrally formed.
That is, the branch pipe portion of the branch connection pipe 94 is the lower waterway outflow connection pipe 92.
Therefore, the upper pipe inlet connection pipe 91, the lower water outlet connection pipe 92, and the branch connection pipe 94 constitute a connection pipe structure 90 (a hatched portion in FIG. 4) integrally formed.

FIG. 14 schematically shows the flow of the cooling water in the cooling structure of the internal combustion engine 1 described above.
The thermostat 70 and the water pump 60 are separately arranged on the left and right sides of the engine body 21H, and the thermostat 70 on the left side of the engine body 21H and the upstream radiator tank 100U on the same left side of the radiator 100 are connected by a radiator inflow hose 101. Have been.
The water pump 60 on the right side of the engine body 21H and the downstream radiator tank 100L on the same right side of the radiator 100 are connected by a radiator outflow hose 102 and a pump inflow hose 65.

  A radiator passage passage Pr passing through the radiator 100 includes a radiator inflow hose 101 for flowing cooling water from the left thermostat 70 to the radiator tank 100U on the upstream side of the radiator 100, and a water pump 60 on the right side from the radiator tank 100L on the downstream side of the radiator 100. A radiator outlet hose 102 and a pump inlet hose 65 that allow the cooling water to flow out is opened and closed by the first valve 73 of the thermostat 70.

  A bypass passage Pb that bypasses the radiator 100 between the thermostat 70 and the water pump 60 includes bypass communication passages 86 and 87, a lower water passage 24Wb in the cylinder block, and a lower water passage outflow connection pipe 92. The passage Pb is opened and closed by the second valve 74 of the thermostat 70.

As described above, since the bypass passage Pb is configured using the lower water passage 24Wb in the cylinder block, only the lower water passage outflow connection pipe 92 is used as the external piping, and the external piping is greatly reduced.
Therefore, since a part of the bypass passage Pb is constituted by the lower water passage 24Wb in the cylinder block of the cylinder block 24, the formation of the bypass passage is facilitated, the external piping of the bypass passage Pb is reduced, and the number of parts is reduced. And the cost can be reduced and the weight of the internal combustion engine can be reduced, and the periphery of the engine body can be simplified to maintain a good appearance.

  During the warm-up operation when the temperature of the cooling water at the time of starting the engine is low, the thermostat 70 closes the first valve 73 and opens the second valve 74, so that the cooling water discharged from the water pump 60 flows out of the pump. The water flows into the upper water passage 24 Wa in the cylinder block through the hose 66, enters the water passage 25 W in the cylinder head from the upper water passage 24 Wa in the cylinder block through the communication hole 25 ch, and circulates through the upper water passage 24 Wa in the cylinder block and the water passage 25 W in the cylinder head. Then, it flows into the cylindrical main body 71a of the thermostat 70 from the outflow passage 84, flows from the opened second valve 74 to the bypass communication passages 86 and 87, and is a lower water passage 24Wb in the cylinder block which is a part of the bypass passage Pb. Through the lower waterway outflow connection pipe 92 and back to the water pump 60.

  Therefore, when the cooling water flowing through the upper water passage 24Wa in the cylinder block and the water passage 25W in the cylinder head and passing through the bypass passage Pb bypassing the radiator 100, only the short lower water passage outflow connection pipe 92 is reduced due to the reduction of external piping. Is further suppressed in the lower water passage 24Wb in the cylinder block, and the temperature can be further increased to further promote warm-up.

  When the temperature of the cooling water rises to some extent due to the warm-up operation of the internal combustion engine 21, the thermostat 70 closes the second valve 74, opens the first valve 73, and enters a normal operation. The cooling water circulates from the pump outflow hose 66 through the upper water passage 24 Wa in the cylinder block and the water passage 25 W in the cylinder head, flows into the cylindrical main body 71 a of the thermostat 70 from the outflow passage 84, and from the opened first valve 73. The air passes through a radiator passage Pr passing through the radiator 100 and passes through a circulation path returning to the water pump 60.

Therefore, the cooling water cooled by the radiator 100 flows through the upper water passage 24 Wa in the cylinder block and the water passage 25 W in the cylinder head to cool the cylinder block 24 and the cylinder head 25.
During the normal operation after the warm-up operation of the internal combustion engine 21, even if the second valve 74 of the thermostat 70 is closed, the cooling water leaks to the bypass communication passage 86 through the narrow leakage passage 85, and even if the bypass passage is small. The cooling water is prevented from stagnating in the lower water passage 24Wb in the cylinder block by flowing.

As described above, the embodiment of the cooling structure for an internal combustion engine according to the present invention has the following advantages.
As shown in FIG. 7, the upper water passage 24 Wa in the upper cylinder block which particularly requires cooling of the cylinder block 24 passes through the inside of the stud bolt 40 on the same side as the cylinder bore 24 b with respect to the stud bolt 40, and Since the cylinder block 24 is formed so as to surround the outer periphery of the cylinder block 24b, the cylinder block 24 can be cooled efficiently.

  As shown in FIG. 8, the lower water passage 24Wb in the cylinder block formed on the lower side fastened to the crankcase 23 of the cylinder block 24 is opposite to the cylinder bore 24b with respect to the stud bolt 40. Since it is formed so as to pass through the swelling passage portion 24Wbf bulging out of the stud bolt 40 and surround the outer periphery of the cylinder bore 24b, the fastening portion to be fastened to the lower crankcase 23 of the cylinder block 24 bulges. The swelling of the passage portion 24Wbf increases the rigidity, and it is firmly and firmly attached to the crankcase 23, and the packing surface with the crankcase 23 has high rigidity and uniform surface pressure to improve sealing performance. .

  As shown in FIGS. 11 and 13, in the cylinder block 24, the lower outer peripheral wall 24L in which the lower water passage 24Wb in the cylinder block is formed is higher than the upper outer peripheral wall 24U in which the upper water passage 24Wa in the cylinder block is formed. Since it is formed to expand outward, the rigidity of the fastening portion to be fastened to the lower crankcase 23 of the cylinder block 24 is further increased.

  As shown in FIG. 8, the lower water passage 24Wb in the cylinder block passes through the outside of the oil passage 24o opposite to the cylinder bore 24b with respect to the oil passage 24o. The rigidity of the fastening portion to be fastened becomes higher.

  As shown in FIGS. 5 and 14, the lower water passage 24Wb in the cylinder block forms a part of the bypass passage Pb bypassing the radiator 100, so that the bypass passage Pb can be formed in the wall of the cylinder block 24, and In addition to contributing to space and improvement in appearance, the cooling water passing through the bypass passage Pb warms up quickly when the internal combustion engine is started, so that the internal combustion engine can be warmed up early.

  As described above, the cooling structure of the internal combustion engine according to one embodiment of the present invention has been described. However, aspects of the present invention are not limited to the above-described embodiment, and may be implemented in various forms within the scope of the present invention. This includes those that are performed.

For example, the cooling structure of an internal combustion engine in which the flow of cooling water is different, such as when the thermostat and the water pump are disposed on the same side on either the left or right side of the engine body, is also included.
Further, the present invention also includes aspects such as a cooling structure of an internal combustion engine in which a thermostat is arranged separately from a cylinder head and connected by a cooling hose.

DESCRIPTION OF SYMBOLS 1 ... Motorcycle, 2 body frame, 3 ... Head pipe, 4 ... Main frame, 5 ... Down frame, 6 ... Seat rail, 7 ... Front fork, 8 ... Handle, 9 ... Front wheel, 10 ... Pivot shaft, 11 ... Rear Fork, 12 rear wheel, 13 link mechanism, 14 rear cushion, 15 fuel tank, 16 seat,
20 ... power unit, 21 ... internal combustion engine, 21 H ... engine body, 22 ... crankshaft, 23 ... crankcase,
24 ... Cylinder block, 24F ... Front side wall, 24B ... Rear side wall, 24U ... Upper outer peripheral wall, 24L ... Lower outer peripheral wall, 24b ... Cylinder bore, 24W ... Cylinder block water passage (cylinder block water jacket), 24Wa ... Cylinder block Upper channel, 24Waa: Upper channel inlet, 24Wb: Lower channel inside cylinder block, 24Wba: Lower channel inlet, 24Wbb: Lower channel outlet, 24P: Partition wall, 24o: Oil channel,
25 ... Cylinder head, 25B ... Rear wall, 25W ... Cylinder head inner water passage (cylinder head water jacket), 25c ... Gasket, 25ch ... Communication hole,
26… Cylinder head cover, 27… Oil pan, 28… Piston, 29…,
31 ... transmission, 32 ... main shaft, 33 ... counter shaft (output shaft), 34 ... output sprocket, 35 ... driven sprocket, 36 ... drive chain, 40 ... stud bolt,
50 ... intake pipe, 51 ... throttle body, 52 ... air cleaner, 55 ... exhaust pipe, 56 ... catalyst device, 57 ... muffler,
60… water pump, 61… pump cover, 62… suction connection pipe, 63… discharge connection pipe, 65… pump inflow hose, 66… pump outflow hose,
70 ... thermostat, 71 ... thermostat case, 71a ... cylindrical body, 71b ... small-diameter cylindrical end, 71c ... step, 72 ... lid member, 73 ... first valve, 74 ... second valve, 75 ... thermoelement, 75t … Temperature sensing part, 76… Plunger, 77… Valve seat, 78… Spring support member, 79… Retaining ring,
81: Coil spring, 82: Conical coil spring, 84: Outflow passage, 85: Leakage passage, 86: Bypass communication passage, 87: Bypass communication passage,
90 ... connecting pipe structure, 91 ... upper channel inflow connecting pipe, 92 ... lower channel outflow connecting pipe, 93 ... mounting seat plate, 94 ... branch connecting pipe,
100: radiator, 100C: radiator core, 100U: upstream radiator tank, 100L: downstream radiator tank, 101: radiator inflow hose (cooling fluid piping), 102: radiator outflow hose (cooling fluid piping).

Claims (4)

An internal combustion engine (21) is mounted between the front wheel (9) and the rear wheel (12) of the motorcycle (1) in the center of the vehicle body in the left and right vehicle width direction,
In the internal combustion engine (21), an engine body (21H) is configured by sequentially stacking a cylinder block (24) and a cylinder head (25) on a crankcase (23) and fastening them with stud bolts (40),
The cylinder block (24) has a liquid passage (24W) in the cylinder block through which the coolant passes around the cylinder bore (24b),
The cylinder head (25), in the cooling structure of the internal combustion engine having a liquid passage (25W) in the cylinder head through which the coolant passes around the combustion chamber,
The liquid passage (24W) in the cylinder block is divided into upper and lower liquid passages (24Wa) in the cylinder block by being partitioned vertically by a partition wall (24P) in the axial direction of a cylinder axis (Lc) that is a center axis of the cylinder bore (24b). It consists of a lower liquid path (24 Wb) inside the cylinder block,
The upper liquid passage inside the cylinder block (24Wa) passes through the inside of the stud bolt (40), which is on the same side as the cylinder bore (24b) with respect to the stud bolt (40), and surrounds the outer periphery of the cylinder bore (24b). Is formed to surround the
The lower liquid passage (24Wb) in the cylinder block is a swelling passage portion swelling outside the stud bolt (40), which is opposite to the cylinder bore (24b) with respect to the stud bolt (40). 24. A cooling structure for an internal combustion engine, which is formed so as to pass through 24Wbf) and surround the outer periphery of the cylinder bore (24b). The cylinder block (24) includes a lower outer peripheral wall (24L) forming a lower liquid passage (24Wb) in the cylinder block and an upper outer peripheral wall (24U) forming an upper liquid passage (4Wa) in the cylinder block. Has,
The cooling structure for an internal combustion engine according to claim 1, wherein the lower outer peripheral wall (24L) extends outside the upper outer peripheral wall (24U). An oil passage (24o) extending in the axial direction of the cylinder axis (Lc) is formed in the cylinder block (24),
The lower liquid passage (24Wb) inside the cylinder block passes through the outside of the oil passage (24o) opposite to the oil passage (24o) from the cylinder bore (24b). The cooling structure for an internal combustion engine according to claim 1 or 2. A coolant is circulated through a radiator (100) that cools the coolant through a coolant circulation path that circulates coolant through the coolant passage (24W) in the cylinder block and the fluid passage (25W) in the cylinder head by a coolant pump (60 ). A radiator passage (Pr) and a bypass passage (Pb) bypassing the radiator (100) are interposed,
A thermostat (70) for switching between circulation by the radiator passage (Pr) and circulation by the bypass passage (Pb),
The cooling structure for an internal combustion engine according to any one of claims 1 to 3, wherein the lower liquid passage (24Wb) in the cylinder block forms a part of the bypass passage (Pb).

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