Assembling and connecting method and structure of forced ignition type aviation piston engine combustion chamber

Abstract

The invention relates to an assembly connection method and structure of a forced ignition type aviation piston engine combustion chamber, the structure comprises a cylinder body, a cylinder cover, a screw and a gasket, the cylinder cover is provided with a taper hole corresponding to a threaded connection hole of the cylinder body, the screw comprises a threaded section, a taper rod section and a screw head, and the screw is connected with the cylinder body at the threaded section. And meanwhile, the conical rod section is attached to the conical hole, so that the stress contact area between the screw and the cylinder cover is increased, additional torque formed by uneven combustion stress of the cylinder cover on the screw can be decomposed through conical surface fit, the axial tension borne by the cylindrical screw is reduced, and the difference of the expansion amount of each screw group on the cylinder cover is reduced. According to the method, through optimized and innovative design of a connecting fastener and a matching part, on the basis of a temperature difference assembly method, a cylinder cover is heated to 110 DEG C in advance, primary assembly is completed in a near-vacuum environment, pre-tightening force is loaded step by step, secondary loading of screws is conducted after heat balance is achieved between the connecting piece and the cylinder cover, and then the cylinder cover is assembled. And it is ensured that the pre-tightening force meets the design requirement, and then the assembling quality and sealing reliability are improved. The sealing performance of the flange face of the combustion chamber is improved, the system assembling difficulty is reduced, the thermal shock resistance of the structure is enhanced, the structure adapts to the offset combustion chamber layout, and the safety and reliability of an engine are guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of piston engines and relates to an assembly connection method and structure of a combustion chamber of a forced ignition aviation piston engine. Background Art

[0002] In the aerospace field, spark ignition combustion is the main design method to improve the safety of large and medium-sized aviation piston engine systems and achieve a high power-to-weight ratio. The integration of the main structural parts of the combustion chamber is achieved by rigid connection with screws. However, the design of the connectors and the difference in assembly process are important factors affecting product performance.

[0003] As an important part of the engine power generation, the combustion chamber generally uses a torque limit to better ensure the tightness of the connecting bolts. However, the connection thread pair will not only produce deformation failure under the action of high temperature impact load for a long time, but also reduce the sealing performance of the combustion chamber; in addition, the combustion time difference of forced ignition combustion is larger than that of compression ignition, and the load unevenness is larger, resulting in different expansion and contraction amounts of the connecting flange screw group. In addition, there is a 30% error in the torque wrench loading process during the assembly process, and the effective preload applied to the multiple screws on the combustion chamber flange surface is quite different. The stress difference of the flange surface joint position with a larger preload torque is large. The working characteristics of the combustion chamber and the assembly method will jointly lead to differences in the circumferential force characteristics of the flange, affecting the sealing performance. During the long-term use of the combustion chamber, high-temperature flue gas leakage will burn the gasket and the joint surface of the cylinder block and cylinder head, and the sealing performance will be further deteriorated. Summary of the invention

[0004] In view of this, the purpose of the present invention is to solve the above problems and provide an assembly connection method and structure for a forced ignition aviation piston engine combustion chamber, which improves the sealing performance and assembly reliability of the combustion chamber by optimizing the screw design, reasonable assembly steps and special material processing technology. This solution overcomes the torque error and load unevenness problems in traditional connection methods and is suitable for the manufacture and assembly of various piston engines in the aerospace field.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A kind of assembly connection structure of the combustion chamber of forced ignition aviation piston engine comprises a cylinder body and a cylinder head, wherein the cylinder body is provided with a plurality of threaded connection holes, and the cylinder head is provided with tapered holes corresponding to the threaded connection holes; a screw is provided in each of the tapered holes; the screw comprises a threaded section, a tapered rod section and a screw head which are arranged in sequence; the screw head is located on the outer side of the cylinder head, and a gasket is provided between the screw head and the cylinder head; the screw is connected with the threaded connection hole on the cylinder body through the threaded section, and under the action of the threaded connection, the tapered rod section and the tapered hole on the cylinder head are fitted through a tapered surface, so that the additional torque formed on the screw by the uneven force of the cylinder head combustion is decomposed through the tapered surface cooperation, thereby reducing the axial tension on the cylindrical screw and reducing the difference in the expansion and contraction amount of each screw on the cylinder head.

[0007] Furthermore, the material of the screw is carbon steel with an elastic modulus ≮200GPa, which avoids excessive elongation difference of the screw caused by uneven combustion load in the combustion chamber, resulting in sealing failure; the thread section of the screw is a half-thread and is blackened to improve the consistency of force on the thread pair during the connection process between the screw groups and avoid uneven force on the flange surface.

[0008] Furthermore, the screw head is a hexagonal cylindrical head, and the outer contour envelope size of the screw head should be as small as possible. As an option, a hexagonal cylindrical head specified in the standard is selected; burrs are removed from the contact part between the screw head and the gasket, and the surface roughness of the contact surface with the gasket does not exceed Ra3.2.

[0009] Furthermore, the taper of the tapered rod section is 1:10, and the surface is nickel-plated to increase the contact thermal resistance, reduce the heat transfer from the connected parts to the screws, and improve the surface insulation performance and wear resistance.

[0010] Furthermore, the gasket is a small flat washer, preferably a GB848 small flat washer, to ensure that each screw is pre-tightened and the force is uniform under the load, so as to avoid leakage due to poor circumferential sealing of the flange; the gasket is made of high-strength steel and the surface is carburized, with a surface hardness of ≥60HRC, which enhances the rigidity of the gasket while ensuring that the screw does not damage the gasket during the load application process; the surface roughness of the gasket does not exceed Ra3.2, and the surface roughness grade of the gasket needs to be focused on to avoid affecting the force on the surface of the thread pair due to excessive friction.

[0011] Furthermore, a sealing gasket is provided between the cylinder body and the cylinder cover, and the screw is connected to the cylinder body after passing through the cylinder cover and the sealing gasket.

[0012] Furthermore, the cylinder head is made of aluminum alloy, and a graphite printing layer is added to the inner surface of the tapered hole by a graphite printing process. The graphite printing layer increases the surface heat transfer resistance of the inner surface of each tapered hole, thereby extending the heat transfer time between the cylinder head and the screws during the assembly process, thereby reducing the difficulty of the assembly process.

[0013] A method for assembling and connecting a combustion chamber of a forced ignition type aviation piston engine, wherein the assembly and connection structure of the combustion chamber of a forced ignition type aviation piston engine as described above is adopted between a cylinder body and a cylinder head of the engine combustion chamber, and a temperature difference assembly method is adopted between the cylinder head and the screws to reduce heat transfer during the assembly process; the temperature difference assembly method comprises the following steps:

[0014] S1. Before assembly, place the cylinder head in an adiabatic heating environment and heat it in a constant power heating mode. The final temperature is controlled at 110℃±2℃. The cylinder head is preheated when the heating device is started no more than once within 5 minutes.

[0015] S2. The initial assembly process is carried out in a near-vacuum environment with an ambient temperature of 20℃±5℃, and an electric torque wrench with a small torque limit is used for rapid loading to ensure assembly quality;

[0016] S3. Place the assembled system in the assembly environment to cool for more than 20 minutes;

[0017] S4. Load the fully cooled screws again in a normal environment of 20℃±5℃, and use the specified lower limit of the screw pre-tightening torque.

[0018] Preferably, in S2, the tightening torque of the initial assembly process is 1 / 4 of the screw pre-tightening torque in S4, and the assembly of all screws is completed within 10 minutes.

[0019] Preferably, when the screw is an M6 carbon steel screw, the screw pre-tightening torque in S4 is 5 N·m, and when the screw is an M6 carbon steel screw, the screw pre-tightening torque is 10 N·m.

[0020] The beneficial effects of the present invention are:

[0021] 1. The tapered hole connection method in the present invention changes the force mode of the screw, effectively reduces the stress level of the thread pair and reduces the expansion and contraction difference of the screw group formed under the uneven force of the cylinder head.

[0022] 2. The carbon steel screws of the present invention have better rigidity than titanium alloy screws, better consistency of elongation under the same conditions, stronger adaptability to load fluctuations caused by time differences in local combustion in the combustion chamber, and better sealing.

[0023] 3. The present invention reduces the dependence of the system connection reliability on the assembly link, greatly improving the assembly qualification rate and ensuring the sealing performance of the combustion chamber during the working process.

[0024] 4. The present invention can be used in conjunction with an offset combustion chamber arrangement, which greatly ensures the safety of the engine combustion chamber and the reliability of the seal.

[0025] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 The figure is a schematic diagram of the assembly connection structure of the combustion chamber of the forced ignition aviation piston engine in the present invention.

[0028] Figure 2 A top view of the cylinder head.

[0029] Figure 3 It is a schematic diagram of the structure of the screw in the present invention.

[0030] Figure numerals: 1-screw; 2-gasket; 3-cylinder head; 4-sealing gasket; 5-cylinder body; 6-taper hole; 7-combustion chamber. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0032] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0033] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0034] See also Figures 1 to 3 , is an assembly connection structure of a combustion chamber of a forced ignition aviation piston engine, comprising a cylinder body 5 and a cylinder head 3, wherein the cylinder body 5 is provided with a plurality of threaded connection holes, and the cylinder head 3 is provided with a tapered hole 6 corresponding to the threaded connection hole; a screw 1 is provided in the tapered hole 6; the screw 1 comprises a threaded section, a tapered rod section, and a screw 1 head which are arranged in sequence; the screw 1 head is located on the outer side of the cylinder head 3, and a gasket 2 is provided between the screw 1 head and the cylinder head 3; the screw 1 is connected to the threaded connection hole on the cylinder body 5 through the threaded section, and under the action of the threaded connection, the tapered rod section and the tapered hole 6 on the cylinder head 3 are fitted through the tapered surface, thereby increasing the force contact area between the screw 1 and the cylinder head 3, thereby dispersing the force applied to the screw 1 by the deformation of the cylinder head 3, and at the same time, the force is decomposed through the tapered surface cooperation, further reducing the axial tension on the screw 1, thereby reducing the difference in the expansion and contraction amount of each screw 1 on the cylinder head 3.

[0035] The material of screw 1 is carbon steel with elastic modulus ≮200GPa, which can avoid excessive elongation difference of screw 1 caused by uneven combustion load in combustion chamber 7 and cause sealing failure; the thread section of screw 1 is a half-thread and is blackened to improve the consistency of force on the thread pair during the connection process between screw groups 1 and avoid uneven force on the flange surface.

[0036] The screw head is a hexagonal cylindrical head, and the outer contour envelope size of the screw head should be as small as possible. As an option, the hexagonal cylindrical head specified in the standard is selected; the burrs on the contact part between the screw head and the gasket 2 are removed, and the roughness does not exceed Ra3.2.

[0037] The taper of the tapered rod section is 1:10, the outer diameter close to the screw head is larger than the outer diameter close to the thread side, and the surface is nickel-plated to increase the contact thermal resistance, reduce the heat transfer from the connected parts to the screw 1, and improve the surface insulation performance and wear resistance.

[0038] The utilization efficiency and stress concentration level of the connecting thread pair are important aspects of the connection reliability. The design process should avoid using spring washers. Therefore, the gasket 2 in this embodiment uses GB848 small and medium flat washers to ensure that each screw 1 is pre-tightened and the force is uniform under load, while improving the utilization efficiency of the thread pair; the material of the gasket 2 is high-strength steel such as S50CM and S70CM and is carburized, with a surface hardness of ≥60HRC. By increasing the rigidity of the gasket, it is ensured that the screw 1 does not cause damage to the gasket 2 during the load application process; the surface roughness grade of the gasket 2 needs to be strictly controlled and does not exceed Ra3.2 to avoid the effect of excessive friction on the surface of the thread pair.

[0039] A sealing gasket 4 is provided between the cylinder body 5 and the cylinder cover 3 , and the screw 1 passes through the cylinder cover 3 and the sealing gasket 4 and is connected to the cylinder body 5 .

[0040] Among them, the cylinder head 3 is made of aluminum alloy, and the inner surface of the tapered hole 6 has a graphite printing layer to increase the surface heat transfer resistance, which prolongs the heat transfer time between the cylinder head and the screws during the assembly process, thereby reducing the difficulty of the assembly process.

[0041] A method for assembling and connecting a combustion chamber of a forced ignition aviation piston engine is disclosed. The assembly and connection structure of the combustion chamber of a forced ignition aviation piston engine in this embodiment is adopted between the cylinder body 5 and the cylinder head 3 of the engine combustion chamber 7. The cylinder head 3 and the screw 1 adopt a temperature difference assembly method to reduce heat transfer during the assembly process. The temperature difference assembly method includes the following steps:

[0042] S1,

[0043] Before assembly, the cylinder head 3 is placed in an adiabatic heating environment and heated in a constant power heating mode. The final temperature is controlled at 110°C ± 2°C. The preheating of the cylinder head is completed when the heating device is started no more than once within 5 minutes.

[0045] S2. The initial assembly process is carried out in a near-vacuum environment with an ambient temperature of 20℃±5℃, and an electric torque wrench with a small torque limit is used for rapid loading to ensure assembly quality. The tightening torque of the initial assembly process is 1 / 4 of the screw pre-tightening torque in S4, and the assembly of all screws 1 is completed within 10 minutes.

[0046] S3. Place the assembled system in an environment not exceeding 20°C to cool for more than 20 minutes;

[0047] S4. Load the fully cooled screw 1 again in an environment of 20℃±5℃, and use the lower limit of the specified torque for the screw pre-tightening torque.

[0048] Among them, when the screw 1 is an M6 carbon steel screw 1, the screw pre-tightening torque in S4 is 5 N·m, and when the screw 1 is an M6 carbon steel screw 1, the screw pre-tightening torque is 10 N·m.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. An assembly connection structure of a forced ignition aviation piston engine combustion chamber, comprising a cylinder block and a cylinder head, characterized in that: The cylinder body is provided with a plurality of threaded connection holes, and the cylinder head is provided with tapered holes corresponding to the threaded connection holes; a screw is provided in each of the tapered holes; the screw comprises a threaded section, a tapered rod section and a screw head which are arranged in sequence; the screw head is located on the outer side of the cylinder head, and a gasket is provided between the screw head and the cylinder head; the screw is connected to the threaded connection hole on the cylinder body through the threaded section, and under the action of the threaded connection, the tapered rod section and the tapered hole on the cylinder head are fitted through the tapered surface, so that the additional torque formed on the screw by the uneven force of the cylinder head combustion is decomposed through the tapered surface cooperation, thereby reducing the axial tension on the cylindrical screw and reducing the difference in the expansion and contraction amount of each screw on the cylinder head.

2. The assembly connection structure of the combustion chamber of a forced ignition aviation piston engine according to claim 1 is characterized in that: The material of the screw is carbon steel, and the elastic modulus is ≮200GPa; the thread section of the screw is a half-thread and is blackened.

3. The assembly connection structure of the combustion chamber of a forced ignition aviation piston engine according to claim 1, characterized in that: The screw head is a hexagonal cylindrical head, burrs are removed from the contact area between the screw head and the gasket, and the surface roughness of the contact area between the screw head and the gasket does not exceed Ra3.

2.

4. The assembly connection structure of the combustion chamber of a forced ignition aviation piston engine according to claim 1, characterized in that: The taper of the tapered rod section is 1:10, and the surface is nickel-plated.

5. The assembly connection structure of the combustion chamber of a forced ignition aviation piston engine according to claim 1, characterized in that: The gasket is a small flat washer, the material of the gasket is high-strength steel and is carburized, the surface hardness is ≥60HRC, and the surface roughness does not exceed Ra3.

2.

6. The assembly connection structure of the combustion chamber of a forced ignition aviation piston engine according to claim 1, characterized in that: A sealing gasket is arranged between the cylinder body and the cylinder cover, and the screw is connected with the cylinder body after passing through the cylinder cover and the sealing gasket.

7. The assembly connection structure of the combustion chamber of a forced ignition aviation piston engine according to claim 1, characterized in that: The cylinder head is made of aluminum alloy, and a graphite printing layer is added to the inner surface of the tapered hole by a graphite printing process.

8. A method for assembling and connecting a combustion chamber of a forced ignition aviation piston engine, characterized in that: The cylinder body and the cylinder head of the engine combustion chamber adopt the assembly connection structure of the forced ignition type aviation piston engine combustion chamber as claimed in any one of claims 1 to 7, and the cylinder head and the screws adopt the temperature difference assembly method to reduce the heat transfer during the assembly process; the temperature difference assembly method comprises the following steps: S1. Before assembly, place the cylinder head in an adiabatic heating environment and heat it in a constant power heating mode. The final temperature is controlled at 110℃±2℃. The cylinder head is preheated when the heating device is started no more than once within 5 minutes. S2. The initial assembly process is carried out in a near-vacuum environment with an ambient temperature of 20℃±5℃, and an electric torque wrench with a small torque limit is used for rapid loading to ensure assembly quality; S3. Place the assembled system in an assembly environment at 20℃±5℃ to cool for more than 20 minutes; S4. Load the fully cooled screws again in a normal environment of 20℃±5℃, and use the specified lower limit of the screw pre-tightening torque.

9. The assembly and connection method of the combustion chamber of a forced ignition aviation piston engine according to claim 8, characterized in that: In S2, the tightening torque during the initial assembly process is 1 / 4 of the screw pre-tightening torque in S4, and the assembly of all screws is completed within 10 minutes.

10. The assembly and connection method of the combustion chamber of a forced ignition aviation piston engine according to claim 8, characterized in that: When the screw is an M6 carbon steel screw, the screw pre-tightening torque in S4 is 5N·m, and when the screw is an M8 carbon steel screw, the screw pre-tightening torque is 10N·m.

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