A backflow scavenged engine for a twin propeller aircraft

Abstract

This invention discloses a scavenging engine for twin-propeller aircraft, which adopts a symmetrical double-crankshaft structure with a combustion chamber in the middle and crankcases on both sides of the combustion chamber. Exhaust ports are opened at both ends of the combustion chamber near the crankcases, and pistons are slidably mounted at both ends of the combustion chamber. Connecting rods are rotatably mounted at the ends of both ends of the combustion chamber, and a crankshaft is rotatably mounted at the end of the connecting rod away from the combustion chamber. The combustion chamber synchronously drives the pistons, connecting rods, and crankshafts on both sides to rotate, realizing dual-path direct-drive power output. This invention is applicable to the field of aviation power plants, eliminating the external transmission system, reducing transmission weight increase and mechanical efficiency loss, and improving the engine power-to-weight ratio. The double-crankshaft opposed structure achieves self-balancing of inertial forces and torques, eliminating second-order vibrations and eliminating the need for a balance shaft, significantly reducing overall engine vibration. The single-combustion-chamber dual-power output design uses a single engine to achieve dual-path synchronous drive, simplifying the system structure and reducing control difficulty and manufacturing costs.

Description

Technical Field

[0001] This invention relates to the field of aviation power plants, and more particularly to a scavenging engine for twin-propeller aircraft. Background Technology

[0002] With the rapid development of the low-altitude economy, electric vertical take-off and landing aircraft, tiltrotor aircraft, twin-engine fixed-wing UAVs and other twin-propeller configuration aircraft are becoming increasingly popular in the industry. These aircraft place extremely high demands on the power-to-weight ratio, vibration control, structural compactness and layout flexibility of the power system.

[0003] Currently, the commonly used power solutions for twin-propeller aircraft fall into two categories. One type is a single crankshaft engine paired with a transmission system, which distributes power to the two propellers via gearboxes, synchronous belts, and other transmission mechanisms. This solution has inherent drawbacks such as significant weight increase in the transmission system (additional components account for 15% to 25% of the total power system weight), mechanical efficiency loss (5% to 10%), high structural complexity, and limited layout. The other type is a dual-engine independent power solution, in which an independent engine is arranged on each side to drive the corresponding propeller. Although this solution achieves independent control of the left and right sides, it suffers from problems such as the total weight of the power system, high control complexity, and high cost.

[0004] To address the aforementioned issues, existing technologies have introduced horizontally opposed engine solutions, which employ a single crankshaft and a 180° opposed layout of two cylinders. These solutions offer good balance, but still suffer from drawbacks such as a single output end (driving the twin propellers still requires an external transmission mechanism), residual vibration (second-order vibration exists, necessitating the addition of a balance shaft), and structural asymmetry.

[0005] Therefore, how to provide a power solution that can fundamentally eliminate the transmission system while possessing a high power-to-weight ratio, low vibration, and structural symmetry has become a pressing technical problem to be solved in the field of twin-propeller aircraft. Summary of the Invention

[0006] In view of the above problems, the present invention is proposed to provide solutions that overcome or at least partially solve the above problems.

[0007] According to one aspect of the present invention, a scavenging engine for a twin-propeller aircraft is provided, which adopts a dual-crankshaft symmetrical structure, with a combustion chamber in the middle and crankcases on both sides of the combustion chamber. Exhaust ports are provided at both ends of the combustion chamber near the crankcases. Pistons are slidably provided at both ends of the combustion chamber, and connecting rods are rotatably provided at the ends of both ends of the combustion chamber. A crankshaft is rotatably provided at the end of the connecting rod away from the combustion chamber. The combustion chamber synchronously drives the pistons, connecting rods and crankshafts on both sides to rotate, thereby realizing dual-path direct-drive power output. The crankcase consists of a lower crankcase and an upper crankcase, which are sealed and fastened together with fixing bolts to form a closed cavity. The crankcase intake port is used for fresh air to enter and complete pre-compression. The cylinder block is equipped with multiple sets of closed-loop scavenging passages. The scavenging passages are equipped with gas partition walls to guide the scavenging air flow to the combustion chamber and avoid interference between the intake and exhaust gases. The exhaust port and exhaust passage cooperate to form an exhaust passage. The engine outer wall is integrated with cooling fins to achieve air cooling. The crankshaft is equipped with crankshaft lubrication bearing assembly to ensure stable high-speed operation.

[0008] Preferably, the scavenging passage includes scavenging passage one, scavenging passage two, and scavenging passage three, corresponding to scavenging outlet one, scavenging outlet two, and scavenging outlet three; wherein scavenging outlet one and scavenging outlet two are connected to scavenging inlet one through scavenging passage one and scavenging passage two, and scavenging outlet three is connected to scavenging inlet two through scavenging passage three.

[0009] Preferably, the gas partition wall divides the scavenging gas inlet into multiple independent gas flow channels.

[0010] Preferably, the top of the combustion chamber is provided with a spark plug and a fuel injector, and the included angle between the fuel injector and the spark plug is 30°.

[0011] Preferably, the heat dissipation fins are integrally formed on the outer wall of the cylinder block, combustion chamber and crankcase, and are cooled by forced air.

[0012] Preferably, the exhaust port opens before each scavenging outlet, in order to achieve an orderly air exchange process of exhausting first and then scavenging.

[0013] In this invention, the external transmission system is eliminated, reducing transmission weight gain and mechanical efficiency loss, and improving the engine's power-to-weight ratio. The dual-crankshaft opposed structure achieves self-balancing of inertial forces and torque, effectively eliminating second-order vibrations without the need for an additional balance shaft, significantly reducing overall vibration. The single-combustion-chamber dual-power-output design uses a single engine to achieve dual-path synchronous drive, simplifying the system structure and reducing control difficulty and manufacturing costs. Multiple scavenging ducts and gas partition walls work together to improve scavenging efficiency and combustion completeness, reducing fuel consumption and exhaust emissions. The integrated air-cooled heat dissipation structure is simple, lightweight, and highly reliable, eliminating the need for complex water-cooling circuits. The symmetrical layout of the entire machine allows for flexible installation and strong adaptability, making it widely applicable to various twin-propeller low-altitude aircraft and possessing outstanding engineering application value.

[0014] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the overall structure of the opposed piston two-stroke double crankshaft scavenging engine provided by the present invention; Figure 2 Three-dimensional design drawing of a two-stroke double-crankshaft scavenging engine with opposed pistons provided by the present invention; Figure 3 A schematic diagram of the double crank connecting rod mechanism and single combustion chamber structure of a two-stroke double-crankshaft scavenging engine with opposed pistons provided by the present invention. Figure 4 A schematic diagram of the cylinder block of a two-stroke double-crankshaft scavenging engine with opposed pistons provided by the present invention; Figure 5 A schematic diagram of the scavenging passage of a two-stroke, double-crankshaft, opposed-piston scavenging engine according to the present invention; Figure 6 It is along Figure 4 A cross-sectional view along line AA in the diagram; In the diagram: 1. Lower crankcase; 2. Crankcase inlet; 3. Upper crankcase; 4. Exhaust port; 5. Spark plug; 6. Combustion chamber; 7. Radiator fins; 8. Piston; 9. Connecting rod; 10. Crankshaft; 11. Crankshaft lubrication bearing assembly; 12. Fixing bolt; 13. Scavenging passage one; 14. Scavenging passage two; 15. Scavenging passage three; 16. Exhaust passage; 17. Gas partition wall; 18. Scavenging outlet one; 19. Scavenging outlet two; 20. Scavenging outlet three; 21. Scavenging inlet one; 22. Scavenging inlet two; 23. Injector. Detailed Implementation

[0017] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0018] The terms "comprising" and "having," and any variations thereof, in the specification, embodiments, claims, and drawings of this invention are intended to cover non-exclusive inclusion, such as including a series of steps or units.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] Opposed piston two-stroke double crankshaft scavenging engine, such as Figures 1-6 As shown, it adopts a double crankshaft symmetrical structure. The combustion chamber 6 is located symmetrically in the middle of the engine, and a spark plug 5 is installed on the top for ignition and power generation. Crankcases are provided on both sides of the combustion chamber 6. Exhaust ports 4 are opened at both ends of the combustion chamber 6 near the crankcases. Pistons 8 are slidably provided at both ends of the combustion chamber 6. Connecting rods 9 are rotatably provided at the ends of both ends of the combustion chamber 6. A crankshaft 10 is rotatably provided at the end of the connecting rod 9 away from the combustion chamber 6. Combustion chamber 6 is directly connected to the left and right sets of pistons 8 and connecting rods 9. The high-pressure gas generated by a single combustion can simultaneously push the pistons 8 on both sides downward, driving the connecting rods 9 to drive the double crankshaft 10 to rotate synchronously, realizing a single combustion chamber and synchronous output of dual power. The two ends of the double crankshaft 10 serve as power output ends and can be directly connected to the dual propellers without the need for external transmission mechanisms such as gearboxes and synchronous belts.

[0021] The crankcase consists of a lower crankcase 1 and an upper crankcase 3, sealed and fastened together by fixing bolts 12 to form a closed cavity. The cylinder block is equipped with multiple closed-loop scavenging passages, each with a gas partition wall 17 to direct the scavenging airflow to the combustion chamber 6, preventing interference between intake and exhaust gases. The exhaust port 4 and exhaust passage 16 cooperate to form an exhaust passage. Integrated cooling fins 7 are installed on the engine's outer wall for air cooling. The engine adopts a symmetrical layout with two opposing crankshafts, a centrally located single combustion chamber, and left-right alignment. The upper and lower crankcases are sealed and fastened together by fixing bolts 12, forming a rigid support and a sealed working chamber, providing a stable mounting reference for the two crankshafts 10 and ensuring the coaxiality and operational accuracy of the dual power output ends. A crankcase intake port 2 is provided on the crankcase for fresh air to enter and be pre-compressed by the upward and downward movement of the pistons.

[0022] In one possible implementation, the scavenging duct includes scavenging duct one 13, scavenging duct two 14, and scavenging duct three 15, corresponding to scavenging outlet one 18, scavenging outlet two 19, and scavenging outlet three 20. Scavenging outlet one 18 and scavenging outlet two 19 are connected to scavenging inlet one 21 via scavenging duct one 13 and scavenging duct two 14, respectively, while scavenging outlet three 20 is connected to scavenging inlet two 22 via scavenging duct three 15. A gas partition wall 17 is installed inside the scavenging duct to orderly separate and guide the multiple scavenging gas streams, preventing mutual interference or short-circuiting with exhaust gas, thereby improving scavenging uniformity and combustion efficiency. All scavenging ducts adopt a closed structure, forming a complete sealed airflow channel with the crankcase and combustion chamber to ensure stable scavenging pressure.

[0023] In one possible implementation, the gas partition wall 17 divides the scavenging gas inlet 21 into multiple independent airflow channels.

[0024] In one possible implementation, the top of the combustion chamber 6 is provided with a spark plug 5 and an injector 23, with the angle between the injector and the spark plug being 30°.

[0025] In one possible implementation, the heat dissipation fins 7 are integrally formed on the outer wall of the engine block, combustion chamber, and crankcase. The heat dissipation fins 7 are evenly distributed over a large area, utilizing the oncoming airflow during flight to achieve forced air cooling. This eliminates the need for additional components such as water-cooled pumps, water pipes, and water tanks, resulting in a simpler structure, lighter weight, and higher reliability, meeting the high power-to-weight ratio requirements of aviation. The crankshaft 10 is equipped with a crankshaft lubrication bearing assembly 11 to reduce frictional losses during high-speed rotation and improve the engine's continuous operating stability and service life.

[0026] In one possible implementation, the exhaust port 4 opens before each scavenging outlet, in order to achieve an orderly air exchange process of exhausting first and then scavenging.

[0027] The working cycle of this engine is as follows: Taking the single-output operation mode as an example: Upward compression and intake: Piston 8 moves upward, closing exhaust port 4 and each scavenging outlet, increasing the internal volume of the crankcase to form a negative pressure, and fresh air is drawn into the crankcase through crankcase intake port 2 to complete the intake; at the same time, the air-fuel mixture in combustion chamber 6 is compressed, and spark plug 5 ignites when it is close to top dead center.

[0028] Downward power stroke and pre-compression: The high-pressure gas generated by combustion pushes the piston 8 downward, and the crankshaft 10 rotates to output power; the downward movement of the piston reduces the volume of the crankcase and the internal mixture is pre-compressed; when the piston approaches the bottom dead center, the exhaust port 4 opens first, and the high-temperature exhaust gas is quickly discharged through the exhaust passage 16.

[0029] Scavenging and scavenging: As the piston continues to move downward, scavenging outlet 18, scavenging outlet 29, and scavenging outlet 320 open in sequence. The pre-compressed mixture is injected into the combustion chamber 6 through the three sets of scavenging channels. Under the guidance of the gas dividing wall 17, an orderly scavenging airflow is formed, which completely pushes the residual exhaust gas out of the exhaust port 4, completing the scavenging process.

[0030] Cycle continues: the piston moves upward and closes the air port again, entering the next compression-combustion-power-scavenging cycle. The dual crankshafts rotate synchronously continuously, stably outputting dual-path power and directly driving the twin propellers.

[0031] Compared with existing power solutions, this implementation eliminates transmission losses and residual vibrations from a structural perspective through dual crankshaft self-balancing, single combustion chamber dual output, closed multi-channel scavenging, and integrated air-cooling, significantly improving the power-to-weight ratio, reducing vibration, and simplifying control. It can be stably adapted to low-altitude equipment such as electric vertical take-off and landing aircraft, tiltrotor aircraft, and twin-engine fixed-wing UAVs, with advantages such as high efficiency, low fuel consumption, and high reliability.

[0032] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A scavenging engine for a twin-propeller aircraft, characterized in that: It adopts a double crankshaft symmetrical structure, with a combustion chamber (6) in the middle and crankcases on both sides of the combustion chamber (6). Exhaust ports (4) are opened at both ends of the combustion chamber (6) near the crankcases. Pistons (8) are slidably provided at both ends of the combustion chamber (6). Connecting rods (9) are rotatably provided at the ends of both ends of the combustion chamber (6). A crankshaft (10) is rotatably provided at the end of the connecting rod (9) away from the combustion chamber (6). The combustion chamber (6) synchronously drives the pistons (8), connecting rods (9) and crankshaft (10) on both sides to rotate, realizing dual-path direct drive output. The crankcase is formed by sealing and fastening the lower crankcase (1) and the upper crankcase (3) with fixing bolts (12) to form a closed cavity. The crankcase intake port (2) is used for fresh air to enter and complete pre-compression. The cylinder block is equipped with multiple closed return scavenging passages. The scavenging passages are equipped with gas partition walls (17) to guide the scavenging air flow to the combustion chamber (6) in a directional manner to avoid interference between intake and exhaust gas. The exhaust port (4) and the exhaust passage (16) cooperate to form an exhaust passage. The engine outer wall is equipped with integrated heat dissipation fins (7) to achieve air cooling. The crankshaft (10) is equipped with crankshaft lubrication bearing assembly (11) to ensure stable high-speed operation.

2. The scavenging engine for a twin-propeller aircraft as described in claim 1, characterized in that: The scavenging passage includes scavenging passage one (13), scavenging passage two (14), and scavenging passage three (15), corresponding to scavenging outlet one (18), scavenging outlet two (19), and scavenging outlet three (20); wherein scavenging outlet one (18) and scavenging outlet two (19) are connected to scavenging inlet one (21) through scavenging passage one (13) and scavenging passage two (14), and scavenging outlet three (20) is connected to scavenging inlet two (22) through scavenging passage three (15).

3. The scavenging engine for a twin-propeller aircraft as described in claim 1, characterized in that: The gas partition wall (17) divides the scavenging gas inlet (21) into multiple independent airflow channels.

4. The scavenging engine for a twin-propeller aircraft as described in claim 1, characterized in that: The combustion chamber (6) is equipped with a spark plug (5) and an injector (23) at the top, and the angle between the injector and the spark plug is 30°.

5. A scavenging engine for a twin-propeller aircraft as described in claim 1, characterized in that: The heat dissipation fins (7) are integrally formed on the outer wall of the cylinder block, combustion chamber and crankcase, and are cooled by forced air.

6. A scavenging engine for a twin-propeller aircraft as described in claim 1, characterized in that: The exhaust port (4) opens before each scavenging outlet, which is used to realize an orderly air exchange process of exhausting first and then scavenging.

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