Motorcycle engine

Abstract

The invention belongs to the technical field of motorcycle accessories, and relates to a motorcycle engine which comprises a crankcase, an air cylinder body and an air cylinder head, a crankshaft is arranged in the crankcase and filled with engine oil, one end of the crankshaft penetrates out of the crankcase and is sleeved with a fan, and a fan cover covers the fan. Two independent air outlets are formed in the circumferential side wall of the fan cover; the first air outlet is communicated with the radial extension part of the fan cover to cool engine oil, and the second air outlet is connected with the wind scooper to cool the air cylinder body and the air cylinder head; a three-dimensional heat dissipation fin array is arranged on the side, close to the fan cover, of the crankcase and located on an airflow path of the radial extending part, and the inner side of the three-dimensional heat dissipation fin array exchanges heat with engine oil. And an air guide rib is arranged in the cylinder head and is used for dividing cooling air flow and guiding the cooling air flow to the air inlet and the air outlet respectively. According to the motorcycle engine provided by the invention, the cooling uniformity and efficiency can be remarkably improved, and the performance requirement of the engine under high load is met.

Description

Technical Field

[0001] The invention belongs to the technical field of motorcycle accessories and relates to a motorcycle engine. Background Art

[0002] An air-cooled engine uses air as its cooling medium. Fins are cast onto the outer walls of the cylinder and cylinder head, and a cooling fan blows high-speed air across the fins, removing heat from the engine and cooling it. Air-cooled engines are a type of engine characterized by their simple structure and light weight. These engines are easily maintained and operated, highly adaptable to climate changes, start quickly, and do not require a radiator, making them widely used in motorcycles.

[0003] However, traditional air-cooled engines have a limited coverage. Chinese invention patent application CN119435189A (publication date: 2025.02.14) discloses an air-cooling system for an engine and an engine, including an engine body and a cooling system. The cooling system includes a fan assembly, including a fan and a fan cover provided with an air outlet I; an air guide cover, used to form a cooling air duct for cooling the engine body, and the cooling air duct is connected to the air outlet I; a flow guide member, arranged in the cooling air duct, is used to form a cooling air branch duct to divert the cooling air to the cylinder head spark plug I near the intake side; the air-cooling system for the engine and the engine of the present invention are provided with an air guide cover connected to the fan cover, thereby forming a cooling air duct for cooling the cylinder body and the cylinder head, which can achieve sufficient cooling of the cylinder body and the cylinder head. At the same time, by providing a flow guide member, the cooling air is diverted to the cylinder head spark plug area, which can improve the cooling effect of the spark plug, improve the utilization rate of the cooling air, and make the heat dissipation of various engine components uniform, thereby meeting the requirements of engine power, economy and reliability.

[0004] This structure directs cooling air toward the cylinder block and cylinder head, expanding the air-cooling coverage, particularly for the spark plug area. However, the lack of cooling structure for the oil in the engine crankcase results in poor cooling, and prolonged high temperatures can affect oil performance. Furthermore, the air-guiding structure only directs cooling air toward the spark plug area of ​​the cylinder head, lacking cooling structure for other areas. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a motorcycle engine that can significantly improve cooling uniformity and efficiency, and meet the performance requirements of the engine under high load.

[0006] In order to solve the above technical problems, the purpose of the present invention is achieved through the following technical solutions:

[0007] A motorcycle engine comprises a crankcase, a cylinder block and a cylinder head, wherein a crankshaft is arranged in the crankcase and stores engine oil, one end of the crankshaft passes through the crankcase and is fitted with a fan, the fan outer cover is provided with a fan cover, and two independent air outlets are provided on the circumferential side wall of the fan cover: the first air outlet is connected to a radial extension of the fan cover to cool the engine oil, and the second air outlet is connected to an air guide cover to cool the cylinder block and the cylinder head; a three-dimensional heat dissipation fin array is provided on a side of the crankcase close to the fan cover, the three-dimensional heat dissipation fin array is located on the air flow path of the radial extension and its inner side exchanges heat with the engine oil, the radial extension covers the three-dimensional heat dissipation fin array and an air outlet is provided at the end of the air flow path; air guide ribs are provided in the cylinder head for dividing the cooling air flow and guiding it to the air inlet and exhaust ports respectively.

[0008] In the above-mentioned motorcycle engine, the inner side of the three-dimensional heat dissipation fin array forms a heat-conducting surface with a curved structure, and the outer side forms a heat dissipation air guide groove with an arc-shaped bottom. The air outlet holes are arranged in a one-to-one correspondence with the heat dissipation air guide grooves, and the cooling air flow of the first air outlet flows along the heat dissipation air guide grooves and flows out of the air outlet holes.

[0009] In the aforementioned motorcycle engine, the three-dimensional cooling fin array is integrally formed with the crankcase and includes a plurality of spaced-apart three-dimensional fins. Cooling ducts are formed between adjacent three-dimensional fins. The inner sides of the three-dimensional fins corresponding to the three-dimensional fins form concave heat transfer surfaces, while the inner sides of the cooling ducts corresponding to the heat transfer ducts form convex heat transfer surfaces. In the present invention, the three-dimensional fins differ from traditional sheet-like fins in that they are sufficiently wide to form a curved heat transfer surface on the corresponding back surface.

[0010] In the above-mentioned motorcycle engine, an arc-shaped boss is provided at the bottom of the crankcase on the side away from the cylinder body, and the coverage range of the arc-shaped boss is 45°-90°. The arc-shaped boss forms a base structure of a three-dimensional heat dissipation fin array, and the heat dissipation air guide groove connects the outer side surface of the arc-shaped boss and the opposite surface of the arc-shaped boss and the crankshaft; the outer side surface of the arc-shaped boss refers to the axial outer side of the arc-shaped boss, and the opposite surface of the arc-shaped boss and the crankshaft refers to the radial inner side of the arc-shaped boss.

[0011] In the above-mentioned motorcycle engine, the air guide cover gradually converges along the air flow direction and enters the cylinder head from the spark plug of the cylinder head. The gaps on both sides of the spark plug form an air inlet flow channel, the gaps on both sides of the air inlet form an air inlet side air outlet flow channel, and the gaps on both sides of the exhaust port form an exhaust side air outlet flow channel.

[0012] In the above-mentioned motorcycle engine, air guide ribs are provided in the cylinder head for guiding the cooling air flow from the outside of the air inlet and exhaust port to the inside, and the air guide ribs are inclined toward the exhaust port side along the air flow direction; preferably, the ends of the air guide ribs form an arc structure that bends toward the exhaust port side.

[0013] In the above-mentioned motorcycle engine, the air guide ribs include a first air guide rib, a second air guide rib and a third air guide rib. The first air guide rib is arranged between the spark plug and the exhaust port, the second air guide rib is arranged between the air intake port and the exhaust port, and the third air guide rib is arranged between the air intake port and the side cylinder wall. The upper and lower ends of the second and third air guide ribs are respectively connected to the upper and lower cylinder walls and a wind gap is left between them and the side cylinder wall.

[0014] In the above-mentioned motorcycle engine, a main intake duct connected to the combustion chamber is provided on the air intake port, and an auxiliary intake duct connected to the main intake duct is provided on one side of the main intake duct. The diameter of the auxiliary intake duct is smaller than that of the main intake duct. The gas enters the main intake duct from the auxiliary intake duct and disturbs the gas in the main intake duct to enhance the tumble flow.

[0015] In the above-mentioned motorcycle engine, the intake openings of the main intake duct and the auxiliary intake duct are both arranged on the end face of the intake port, the auxiliary intake duct is located on the side close to the combustion chamber, the main intake duct is inclined toward the combustion chamber and connected to the combustion chamber, the auxiliary intake duct is arranged along the radial direction of the cylinder head and passes through the main intake duct, and the cross-section of the auxiliary intake duct is a flat structure; preferably, the long side of the flat structure extends in a direction parallel to the main intake duct; preferably, the auxiliary intake duct is arranged at a position corresponding to the middle of the main intake duct; preferably, an irregular variable diameter or curved surface structure is provided in the auxiliary intake duct.

[0016] In the above-mentioned motorcycle engine, the ratio of the cross-sectional area of ​​the main intake duct to the auxiliary intake duct is 10:1-5:1; the connection point between the auxiliary intake duct and the main intake duct is located on the side of the main intake duct close to the combustion chamber.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The motorcycle engine provided by the present invention has an independent oil cooling structure. In order to solve the problem of insufficient oil cooling in the crankcase, an independent cooling path and a three-dimensional heat dissipation fin array structure are designed. The first air outlet of the fan cover is used to guide the airflow through the radial extension to cover the three-dimensional heat dissipation fin array on one side of the crankcase. The inner side of the fin array performs efficient heat exchange with the oil through the curved heat-conducting surface. The outer airflow flows through the heat dissipation guide groove and is discharged through the air outlet, taking away the heat exchanged by the fin array, thereby efficiently reducing the oil temperature, avoiding the influence of long-term high temperature on the oil performance, and ensuring the reliability of the lubrication system. The unique three-dimensional heat dissipation fin array structure of the present invention ensures excellent heat exchange efficiency both inside and outside.

[0019] 2. The motorcycle engine provided by this invention features an optimized cylinder head cooling structure. To cool the cylinder head and cylinder block, the fan cover's second air outlet connects to the air guide, directing air into the cylinder head. Air guide ribs then divide the airflow, directing it towards the spark plugs, intake, and exhaust ports. This ensures uniform cooling of key areas such as the spark plugs, intake, and exhaust ports, addressing the shortcomings of conventional air cooling systems, particularly the lack of cooling structures on the intake side.

[0020] 3. The present invention further improves the air duct structure of the engine air intake, adopts dual-air duct intake, increases the intake volume, and more importantly: the designed auxiliary air intake duct disturbs the main air intake duct airflow through a small-diameter channel, enhances the tumble effect, indirectly improves combustion efficiency, and provides further support for the engine's power and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a perspective view of the present invention;

[0022] Figure 2 It is a three-dimensional diagram of the present invention (excluding the fan cover and the air guide cover);

[0023] Figure 3 It is a three-dimensional diagram of the fan cover and the air guide cover of the present invention;

[0024] Figure 4 is a perspective view of a crankcase of the present invention;

[0025] Figure 5 is another perspective view of the crankcase of the present invention;

[0026] Figure 6 is a perspective view of a cylinder head of the present invention;

[0027] Figure 7 is a cross-sectional view of a cylinder head of the present invention;

[0028] Figure 8 is another cross-sectional view of the cylinder head of the present invention;

[0029] Figure numerals: 1. crankcase; 2. cylinder block; 3. cylinder head; 4. crankshaft; 5. fan; 6. fan cover; 7. first air outlet; 8. radial extension; 9. second air outlet; 10. air guide cover; 11. three-dimensional heat dissipation fin array; 12. air outlet; 13. air guide ribs; 14. air inlet; 15. exhaust port; 16. heat transfer surface; 17. heat dissipation air guide groove; 18. three-dimensional fin; 19. concave heat transfer surface; 20. convex heat transfer surface; 21. arc-shaped boss; 22. spark plug; 23. first air guide rib; 24. second air guide rib; 25. third air guide rib; 26. combustion chamber; 27. main air intake duct; 28. auxiliary air intake duct. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to specific embodiments of the present invention. Figure 1-8 :

[0031] A motorcycle engine comprises a crankcase 1, a cylinder block 2 and a cylinder head 3, wherein a crankshaft 4 is arranged in the crankcase 1 and stores engine oil, one end of the crankshaft 4 passes through the crankcase 1 and is fitted with a fan 5, the outer cover of the fan 5 is provided with a fan cover 6, and two independent air outlets are provided on the circumferential side wall of the fan cover 6: a first air outlet 7 is connected to a radial extension 8 of the fan cover 6 to cool the engine oil, and a second air outlet 9 is connected to an air guide cover 10 to cool the cylinder block 2 and the cylinder head 3; a three-dimensional heat dissipation fin array 11 is provided on the side of the crankcase 1 close to the fan cover 6, the three-dimensional heat dissipation fin array 11 is located on the air flow path of the radial extension 8 and its inner side exchanges heat with the engine oil, the radial extension 8 covers the three-dimensional heat dissipation fin array 11 and an air outlet 12 is provided at the end of the air flow path; an air guide rib 13 is provided in the cylinder head 3 for dividing the cooling air flow and guiding it to an air inlet 14 and an exhaust port 15 respectively.

[0032] With reference to the accompanying drawings, the structure of the three-dimensional heat dissipating fin array 11 of this embodiment is specifically as follows: a heat-conducting surface 16 with a curved structure is formed on the inner side of the three-dimensional heat dissipating fin array 11, and a heat dissipating air guide groove 17 with an arc-shaped bottom is formed on the outer side. The air outlet holes 12 are arranged in a one-to-one correspondence with the heat dissipating air guide groove 17, and the cooling air flow of the first air outlet 7 flows along the heat dissipating air guide groove 17 and flows out from the air outlet holes 12.

[0033] Furthermore, the three-dimensional heat dissipation fin array 11 is integrally formed with the crankcase 1 and includes a plurality of spaced-apart three-dimensional fins 18. Cooling ducts 17 are formed between adjacent three-dimensional fins 18. Concave heat-conducting surfaces 19 are formed on the inner sides of the three-dimensional fins 18, while convex heat-conducting surfaces 20 are formed on the inner sides of the cooling ducts 17. Together, the concave heat-conducting surfaces 19 and the convex heat-conducting surfaces 20 form the curved heat-conducting surface 16. In this embodiment, the three-dimensional fins 18 differ from traditional sheet fins in that they are sufficiently wide to form the curved heat-conducting surface 16 at the corresponding back surface.

[0034] In this embodiment, after the motorcycle engine is started, the crankshaft 4 drives the fan 5 at one end thereof to rotate at high speed. The cooling airflow generated by the fan 5 (the cooling airflow is formed by the entry of low-temperature external air through the axial air inlet at the end of the fan cover 6) is constrained and diverted by the fan cover 6. Specifically:

[0035] Oil cooling path: Part of the air flow enters the radial extension portion 8 from the first air outlet 7, and the air flow is guided to the surface of the three-dimensional heat dissipation fin array 11 on the side wall of the crankcase 1 4. The air flow flows along the heat dissipation air guide groove 17 formed by the adjacent three-dimensional fins 18. The air flow contacts the three-dimensional fins 18 and the heat dissipation air guide groove 17 at the same time to efficiently exchange heat. At the same time, the curved heat-conducting surface 16 (the curved heat-conducting surface 16 has a larger heat exchange area) on the inner side of the three-dimensional heat dissipation fin array 11 (facing the inside of the crankcase 1) performs efficient heat exchange with the oil in the box, absorbs the heat of the oil, and the air flow carrying the heat is finally discharged through the air outlet 12 at the end, thereby realizing continuous forced air cooling of the oil.

[0036] Cooling path of the cylinder block 2 and the cylinder head 3: Another part of the air flow enters the air guide hood 10 from the second air outlet 9, and the air guide hood 10 guides it to the cylinder block 2 and the cylinder head 3, and takes away the heat on the surface of the cylinder block 2 and the cylinder head 3 during the flow. The cooling air flow then flows through the spark plug 22 area of ​​the cylinder head 3, cools the spark plug 22 area, and then enters the interior of the cylinder head 3. It is guided by the air guide ribs 13 and is split again. Part of the air flow is directed to the exhaust port 15 area and finally flows out, and part of the air flow is directed to the air intake port 14 area and finally flows out.

[0037] The specific configuration of the three-dimensional cooling fin array 11 is as follows: an arcuate boss 21 is provided at the bottom of the crankcase 1 on the side away from the cylinder block 2. The arcuate boss 21 covers a range of 45°-90° and forms the base structure of the three-dimensional cooling fin array 11. The heat dissipation air guide 17 connects the outer side of the arcuate boss 21 and the surface of the arcuate boss 21 facing the crankshaft 4. The outer side of the arcuate boss 21 refers to the axial outer side of the arcuate boss 21, and the surface of the arcuate boss 21 facing the crankshaft 4 refers to the radial inner side of the arcuate boss 21. The provision of the arcuate boss 21 extends the axial distance between the three-dimensional fins 18 and the cooling airflow, significantly enhancing the heat dissipation effect.

[0038] Furthermore, the air guide hood 10 gradually converges along the air flow direction, which can accelerate the cooling air flow to the cylinder head 3 area, and enter the cylinder head 3 from the spark plug 22 of the cylinder head 3. The gaps on both sides of the spark plug 22 form an air inlet flow channel, the gaps on both sides of the air inlet 14 form an air inlet side air outlet flow channel, and the gaps on both sides of the exhaust port 15 form an exhaust side air outlet flow channel. The above flow channel design can increase the coverage range of the cooling air flow and improve the cooling effect.

[0039] Air guide ribs 13 are provided within the cylinder head 3 to guide the cooling airflow from the outside of the air intake 14 and the exhaust 15 toward the inside. These air guide ribs 13 are inclined toward the exhaust 15 along the airflow direction. Preferably, the ends of these air guide ribs form an arc-shaped structure that bends toward the exhaust 15. The air guide ribs 13 divide the airflow and direct it toward the air intake 14 and exhaust 15, respectively. The inclined structure of these air guide ribs 13 increases the distribution of air toward the exhaust 15.

[0040] The above-mentioned air guide ribs 13 include a first air guide rib 23, a second air guide rib 24 and a third air guide rib 25. The first air guide rib 23 is arranged between the spark plug 22 and the exhaust port 15, the second air guide rib 24 is arranged between the air intake port 14 and the exhaust port 15, and the third air guide rib 25 is arranged between the air intake port 14 and the side cylinder wall. The upper and lower ends of the second air guide rib 24 and the third air guide rib 25 are respectively connected to the upper and lower cylinder walls and a wind gap is left between them and the side cylinder wall. The second air guide rib 24 and the third air guide rib 25 form a partitioned flow channel on both sides to obtain a better diversion effect.

[0041] This embodiment further improves the air intake structure. Specifically:

[0042] The above-mentioned air intake port 14 is provided with a main air intake duct 27 connected to the combustion chamber 26, and an auxiliary air intake duct 28 connected to the main air intake duct 27 is provided on one side of the main air intake duct 27. The diameter of the auxiliary air intake duct 28 is smaller than that of the main air intake duct 27. The gas enters the main air intake duct 27 through the auxiliary air intake duct 28 and disturbs the gas in the main air intake duct 27 to enhance the tumble flow; when the engine intake valve is started, the gas mainly enters the combustion chamber 26 through the main air intake duct 27. At the same time, part of the gas enters through the auxiliary air intake duct 28 with a smaller diameter. The airflow entering the auxiliary air intake duct 28 disturbs the mainstream gas in the main air intake duct 27, disrupts the laminar flow state, and significantly enhances the tumble intensity of the gas entering the combustion chamber 26, that is, forms a stronger air rotation motion. The enhanced tumble promotes the mixing of fuel and air, increases the turbulence intensity in the combustion chamber 26, thereby indirectly improving the combustion efficiency and speed.

[0043] The intake openings of the above-mentioned main intake duct 27 and auxiliary intake duct 28 are both arranged on the end face of the intake port 14, and the auxiliary intake duct 28 is located on the side close to the combustion chamber 26. The main intake duct 27 is inclined toward the combustion chamber 26 and is connected to the combustion chamber 26. The auxiliary intake duct 28 is arranged along the radial direction of the cylinder head 3 and passes through the main intake duct 27. The cross-section of the auxiliary intake duct 28 is a flat structure; preferably, the long side of the flat structure extends in a direction parallel to the main intake duct 27; preferably, the auxiliary intake duct 28 is arranged at a position corresponding to the middle of the main intake duct 27; preferably, an irregular diameter change or curved surface structure is provided in the auxiliary intake duct 28.

[0044] The ratio of the cross-sectional areas of the main air intake duct 27 and the auxiliary air intake duct 28 is 10:1-5:1; the connection point between the auxiliary air intake duct 28 and the main air intake duct 27 is located on the side of the main air intake duct 27 close to the combustion chamber 26.

[0045] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A motorcycle engine, comprising a crankcase (1), a cylinder block (2) and a cylinder head (3), wherein a crankshaft (4) is provided in the crankcase (1) and stores oil, one end of the crankshaft (4) passes through the crankcase (1) and is provided with a fan (5), and the fan (5) is provided with a fan cover (6) on its outer cover, characterized in that: Two independent air outlets are provided on the circumferential side wall of the fan cover (6): the first air outlet (7) is connected to the radial extension (8) of the fan cover (6) to cool the engine oil, and the second air outlet (9) is connected to the air guide cover (10) to cool the cylinder block (2) and the cylinder head (3); a three-dimensional heat dissipation fin array (11) is provided on the side of the crankcase (1) close to the fan cover (6), the three-dimensional heat dissipation fin array (11) is located on the air flow path of the radial extension (8) and its inner side exchanges heat with the engine oil, the radial extension (8) covers the three-dimensional heat dissipation fin array (11) and an air outlet (12) is provided at the end of the air flow path; an air guide rib (13) is provided in the cylinder head (3) for dividing the cooling air flow and guiding it to the air inlet (14) and the exhaust port (15) respectively.

2. A motorcycle engine according to claim 1, characterized in that: The inner side of the three-dimensional heat dissipation fin array (11) forms a heat-conducting surface (16) with a curved structure, and the outer side forms a heat dissipation air guide groove (17) with an arc-shaped bottom. The air outlet holes (12) are arranged in a one-to-one correspondence with the heat dissipation air guide groove (17). The cooling airflow of the first air outlet (7) flows along the heat dissipation air guide groove (17) and flows out from the air outlet holes (12).

3. A motorcycle engine according to claim 2, characterized in that: The three-dimensional heat dissipation fin array (11) is integrally formed with the crankcase (1), and includes a plurality of three-dimensional fins (18) arranged at intervals, heat dissipation air guide grooves (17) are formed between adjacent three-dimensional fins (18), the inner sides corresponding to the three-dimensional fins (18) form concave heat conduction surfaces (19), and the inner sides corresponding to the heat dissipation air guide grooves (17) form convex heat conduction surfaces (20).

4. A motorcycle engine according to claim 2, characterized in that: An arc-shaped boss (21) is provided at the bottom of one side of the crankcase (1) away from the cylinder block (2), and the coverage range of the arc-shaped boss (21) is 45°-90°. The arc-shaped boss (21) forms a base structure of the three-dimensional heat dissipation fin array (11), and the heat dissipation air guide groove (17) connects the outer side surface of the arc-shaped boss (21) and the opposite surface of the arc-shaped boss (21) and the crankshaft (4).

5. A motorcycle engine according to claim 1, characterized in that: The air guide cover (10) gradually converges along the air flow direction and enters the cylinder head (3) from the spark plug (22) of the cylinder head (3). The gaps on both sides of the spark plug (22) form an air inlet flow channel, the gaps on both sides of the air inlet (14) form an air inlet side air outlet flow channel, and the gaps on both sides of the exhaust port (15) form an exhaust side air outlet flow channel.

6. A motorcycle engine according to claim 5, characterized in that: An air guide rib (13) is provided in the cylinder head (3) for guiding the cooling air flow from the outside of the air inlet (14) and the exhaust port (15) to the inside. The air guide rib (13) is inclined toward the exhaust port (15) along the air flow direction.

7. A motorcycle engine according to claim 6, characterized in that: The air guide rib (13) comprises a first air guide rib (23), a second air guide rib (24) and a third air guide rib (25), wherein the first air guide rib (23) is arranged between the spark plug (22) and the exhaust port (15), the second air guide rib (24) is arranged between the air intake port (14) and the exhaust port (15), and the third air guide rib (25) is arranged between the air intake port (14) and the side cylinder wall, and the upper and lower ends of the second air guide rib (24) and the third air guide rib (25) are respectively connected to the upper and lower cylinder walls as a whole, and a wind clearance is left between the second air guide rib (24) and the side cylinder wall.

8. A motorcycle engine according to claim 1, characterized in that: The air intake port (14) is provided with a main air intake passage (27) connected to the combustion chamber (26); an auxiliary air intake passage (28) connected to the main air intake passage (27) is provided on one side of the main air intake passage (27); the aperture of the auxiliary air intake passage (28) is smaller than that of the main air intake passage (27); gas enters the main air intake passage (27) through the auxiliary air intake passage (28) and forms a disturbance on the gas in the main air intake passage (27) to enhance tumble flow.

9. A motorcycle engine according to claim 8, characterized in that: The intake openings of the main intake duct (27) and the auxiliary intake duct (28) are both arranged on the end surface of the intake port (14); the auxiliary intake duct (28) is located on a side close to the combustion chamber (26); the main intake duct (27) is inclined toward the combustion chamber (26) and is connected to the combustion chamber (26); the auxiliary intake duct (28) is arranged along the radial direction of the cylinder head (3) and penetrates into the main intake duct (27); and the cross section of the auxiliary intake duct (28) is a flat structure.

10. A motorcycle engine according to claim 8, characterized in that: The ratio of the cross-sectional area of ​​the main air intake duct (27) to the auxiliary air intake duct (28) is 10:1-5:1; the connection point between the auxiliary air intake duct (28) and the main air intake duct (27) is located on a side of the main air intake duct (27) close to the combustion chamber (26).

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