Lightweight high-strength hydraulic oil cylinder suitable for aviation undercarriage

Abstract

The invention discloses a light-weight high-strength hydraulic oil cylinder suitable for an aircraft undercarriage, relates to a hydraulic control system technology, and particularly relates to a hydraulic oil cylinder suitable for an aircraft undercarriage, which has the excellent performances of light weight, high strength, long service life and the like. The oil cylinder comprises an oil cylinder shell, a piston, a piston rod and sealing rings, the piston and the piston rod are installed inside the oil cylinder shell after being connected with each other, and the sealing rings are arranged on an oil inlet and an oil outlet of the oil cylinder shell. The oil cylinder shell is made of high-strength aluminum alloy. A rough blank of the oil cylinder shell is subjected to die machining preparation through an extrusion method, and after the rough blank is extruded, the surface is subjected to rough treatment so as to remove an oxide layer and impurities on the surface; the common treatment method comprises acid pickling and sand blasting; shape processing; processing an inner cavity; thread machining; according to the technical scheme, through innovative materials, optimized structural design and an advanced manufacturing process, the comprehensive performance of the hydraulic oil cylinder is remarkably improved, the overall performance and safety of an aviation landing gear system are further improved, and a powerful guarantee is provided for efficient and safe operation of aircrafts.

Description

Technical Field

[0001] The present invention relates to a hydraulic control system technology, in particular to a hydraulic cylinder suitable for aircraft landing gear, which has excellent properties such as light weight, high strength and long life. Background Art

[0002] In modern aircraft design, the landing gear system is a critical component that ensures stability and safety during takeoff and landing. Its performance directly impacts the aircraft's safety, reliability, and service life. As a key actuator in the landing gear, the performance and durability of the hydraulic cylinder are crucial to the overall performance of the aircraft.

[0003] Currently, hydraulic cylinders for aircraft landing gear are generally made of steel or aluminum alloys. These materials have high strength and pressure resistance, which can meet certain load-bearing requirements. However, with the continuous development of aviation technology, the performance requirements for hydraulic cylinders are also constantly increasing.

[0004] Existing hydraulic cylinders still suffer from several major drawbacks: Existing hydraulic cylinders are typically made of steel or aluminum alloy, which have high density and result in a heavy overall cylinder weight. Weight is a significant factor affecting flight performance, particularly in aircraft. Excessively heavy hydraulic cylinders increase the aircraft's overall weight, thereby impacting fuel efficiency, takeoff and landing performance, and range. With the increasing demand for lightweight aircraft, existing hydraulic cylinders are no longer able to meet the lightweight requirements of modern aircraft.

[0005] Conventional hydraulic cylinders are susceptible to fatigue damage under conditions of long-term, high-pressure operation and frequent starts and stops, leading to seal failure, oil leakage, and cylinder surface wear. This not only increases maintenance costs but can also lead to premature cylinder failure, compromising the proper operation of the landing gear. Existing hydraulic cylinders are particularly susceptible to external influences in complex environments, such as high temperatures, low temperatures, and high humidity, which in turn affects their efficiency and reliability.

[0006] The manufacturing process for existing hydraulic cylinders is generally complex, often requiring multiple steps and processing, and often using traditional metalworking techniques. This not only increases production costs but also increases manufacturing time. As the aviation industry's demand for cost control increases, traditional hydraulic cylinder production processes are no longer able to meet cost-effectiveness requirements. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the present invention provides a lightweight and high-strength hydraulic cylinder suitable for aircraft landing gear. It solves the problems of excessive weight, poor durability, unreliable sealing system, etc. in the existing technology, improves the performance and service life of the hydraulic cylinder, and meets the high performance requirements of modern aircraft for hydraulic systems.

[0008] To achieve the above-mentioned purpose, the present invention provides the following technical solution: it includes a cylinder housing, a piston, a piston rod, and a sealing ring. The piston and the piston rod are connected to each other and installed inside the cylinder housing. The oil inlet and outlet of the cylinder housing are both provided with sealing rings. The cylinder housing is made of high-strength aluminum alloy (such as 7075-T6 or 6061-T6). The rough blank of the cylinder housing is prepared by die processing using an extrusion method. After the rough blank is extruded, the surface is rough-treated to remove the surface oxide layer and impurities. Common processing methods include pickling and sandblasting; shape processing; inner cavity processing; thread processing; surface anodizing treatment, placing the cylinder housing in an electrolyte, passing an electric current to oxidize the shell surface to form an oxide film. The thickness and hardness of the film can be adjusted according to the process requirements. The general thickness is between 5-25μm. A high-temperature resistant coating is added to the outer surface of the cylinder housing. The surface of the cylinder housing is sandblasted. Local polishing is performed. The present invention uses aluminum alloy extrusion technology to pressurize and extrude the aluminum alloy through a die. Pickling can remove the oxide film on the surface, while sandblasting helps to improve the surface roughness and provide a good foundation for subsequent processing. This method can ensure higher dimensional accuracy and is suitable for mass production. The surface of aluminum alloys is usually anodized to improve the hardness, corrosion resistance and wear resistance of the cylinder housing. Anodizing forms a strong oxide film, which makes the surface more corrosion-resistant and is particularly suitable for use in aircraft in high-humidity and high-temperature environments. High-temperature resistant coatings can enhance the durability of the cylinder housing in high-temperature environments. For parts that require high-precision matching, such as sealing groove positions, precision polishing is also required to ensure a smooth surface to avoid poor sealing due to rough surface.

[0009] The piston is made of a composite material of carbon fiber reinforced plastic (CFRP) or high-strength alloy steel. The specific preparation process is as follows: carbon fiber prepreg and resin are mixed, placed in a mold and formed through a hot pressing process. During the hot pressing process, the material is cured under specific temperature and pressure to form the desired piston shape; the prepreg is processed by hot pressing or vacuum bag curing to ensure that the resin is fully penetrated and cured; the curing temperature is generally between 100-150°C to ensure that the strength of the carbon fiber is not affected; the round alloy steel bar is rough-processed on a CNC lathe and cut into the desired piston core shape. The piston core is turned to remove excess material, ensuring the proper size and shape. The alloy steel portion undergoes a quenching and tempering process to enhance its mechanical properties. During quenching, the alloy steel is heated to a high temperature and then rapidly cooled to increase its hardness and tensile strength. Tempering eliminates post-quenching internal stresses and enhances the steel's toughness. The carbon fiber reinforced plastic portion is bonded to the alloy steel core using a high-strength epoxy resin. The bonding requires precise control of the bonding surface area and strength to ensure a strong bond between the composite and the metal. To ensure a good bond between the carbon fiber reinforced plastic and the alloy steel portion, the metal surface undergoes a surface roughening treatment. The piston surface is nitrided: The alloy steel portion of the piston is nitrided to form a hardened layer with a thickness typically ranging from 10 to 30 μm. The piston surface is chromium coated: For areas requiring enhanced surface hardness and corrosion resistance, the chromium coating is typically 10 to 20 μm thick. This process ensures that the piston meets lightweight requirements while maintaining high strength and fatigue resistance. The combination of composite materials and metals enables the piston to have both the excellent mechanical properties of carbon fiber materials and the compressive and wear-resistant properties of alloy steel, thus meeting the working requirements of aviation landing gear hydraulic systems in high-pressure and complex environments.

[0010] The piston rod is made of high-strength alloy steel; because the piston rod has a small diameter, high strength is required during long-term sports use, and the small diameter does not affect the overall weight.

[0011] The sealing ring is made of fluororubber (FPM) or polyurethane (PU) material, and the preparation of the sealing ring adopts the following process steps:

[0012] Compression Molding: The selected rubber or polymer material is heated to the appropriate temperature and then pressed into a mold. Common compression molding methods include hot press molding. The compression molding process allows for precise control of the seal's dimensions and, by controlling temperature, pressure, and time, ensures consistent density and performance.

[0013] Injection molding: For some types of seals, the injection molding process is used to inject thermoplastic material into a mold to ensure high-precision seal production. Injection molding has the advantages of efficient production and high dimensional accuracy.

[0014] Vulcanization: Rubber sealing materials (such as FPM, NBR, and PU) require vulcanization after compression or injection molding. The vulcanization process heats the rubber material to a certain temperature and maintains it for a certain period of time, causing the rubber molecules to cross-link and form a three-dimensional network structure, thereby improving the material's durability, elasticity, and high-temperature resistance.

[0015] Curing temperature and time control: Curing temperature and time are usually optimized according to the characteristics of the material, usually in the temperature range of 150-200℃, and the curing time is generally 15-30 minutes.

[0016] Quality Inspection: Use Shore hardness tester to test the hardness of the sealing ring to ensure that it meets the standard range of the selected material; perform leakage test on the sealing ring to simulate the use environment under working conditions to ensure that the sealing performance meets the requirements.

[0017] By utilizing high-performance sealing materials (such as fluororubber and polyurethane), this seal ring maintains a strong seal even under extreme pressures and temperature fluctuations, effectively preventing hydraulic oil leakage. Fluororubber can withstand high-temperature operating environments and offers excellent corrosion resistance, ensuring stable operation of hydraulic oil in long-term, high-temperature environments. Precise manufacturing processes and high-quality materials ensure the seal ring's wear and aging resistance, enabling long-term stable operation in harsh environments, thereby extending the overall service life of the hydraulic system. Precision machining and surface treatment ensure that the seal ring's dimensional accuracy and surface quality meet design standards, providing reliable sealing performance.

[0018] The lightweight, high-strength hydraulic cylinder technology proposed in this invention for aircraft landing gear has significant technical effects and advantages. Through innovative material selection, structural design, and manufacturing processes, the performance, reliability, and service life of the hydraulic cylinder can be significantly improved, specifically in the following aspects:

[0019] This cylinder utilizes lightweight materials such as high-strength aluminum alloy and carbon fiber reinforced plastic (CFRP), taking into account aircraft weight requirements. Compared to traditional steel or aluminum alloy cylinders, the cylinder weight is reduced by 30% to 40%. This lightweight design effectively improves the aircraft's fuel efficiency and range, enhances takeoff and landing performance, and reduces the burden on the landing gear system.

[0020] Through an optimized composite material design, combining carbon fiber reinforced plastics and high-strength alloy steel, the piston's compressive and fatigue resistance are significantly improved, allowing it to withstand higher operating pressures and mechanical loads. The use of composite materials not only ensures high strength and rigidity, but also enables the cylinder to operate stably under high-pressure and high-load conditions, extending the system's service life. Advanced surface treatment technologies (such as anodizing and nitriding) significantly increase the surface hardness of the cylinder, its piston, and its piston rod, significantly enhancing its resistance to wear, corrosion, and high temperatures, thereby reducing the risk of failure due to wear, corrosion, or high temperatures.

[0021] The dual-seal design and high-performance sealing materials (such as fluororubber and polyurethane) effectively prevent hydraulic oil leakage and ensure the cylinder's tightness under extreme operating conditions. The optimized sealing system not only improves the sealing effect, but also enhances the cylinder's operating stability, prevents hydraulic oil contamination, and improves the overall safety of the system.

[0022] Thanks to its design, which combines composite materials with metal, the piston exhibits improved fatigue resistance under high-pressure, high-frequency impact loading, enabling continuous and stable operation. The use of composite materials not only effectively reduces the piston's weight but also provides excellent impact resistance, enabling it to withstand the tremendous impact forces generated during aircraft takeoff and landing.

[0023] Through innovative material selection and surface treatment technology, the service life of this cylinder in harsh environments is significantly extended. The cylinder surface hardness is increased, wear resistance is enhanced, and it can operate stably in extreme environments such as high temperature, low temperature, and high humidity. This reduces malfunctions and system failures caused by environmental changes, thereby reducing aircraft maintenance costs.

[0024] Through innovative materials, optimized structural design, and advanced manufacturing processes, this technical solution significantly enhances the overall performance of hydraulic cylinders, meeting the requirements of modern aircraft for lightweight, high strength, and long-term reliability. Its lightweight design, enhanced strength, optimized sealing, and enhanced corrosion and fatigue resistance not only extend the cylinder's service life but also improve the overall performance and safety of aircraft landing gear systems, providing a strong guarantee for the efficient and safe operation of aircraft. DETAILED DESCRIPTION

[0025] This specific embodiment adopts the following technical scheme: it includes a cylinder housing, a piston, a piston rod, and a sealing ring. The piston and the piston rod are connected to each other and installed inside the cylinder housing. The inlet and outlet oil ports of the cylinder housing are both provided with sealing rings; the cylinder housing is made of high-strength aluminum alloy (such as 7075-T6 or 6061-T6); the rough blank of the cylinder housing is prepared by die processing using an extrusion method, and the surface is roughened after extrusion to remove the surface oxide layer and impurities; commonly used processing methods include pickling and sandblasting; shape processing; inner cavity processing; thread processing; surface anodizing treatment, the cylinder housing is placed in an electrolyte, and an electric current is passed to oxidize the shell surface to form an oxide film. The thickness and hardness of the film can be adjusted according to the process requirements, and the general thickness is between 5-25μm; a high-temperature resistant coating is added to the outer surface of the cylinder housing; the surface of the cylinder housing is sandblasted; and local polishing work is done.

[0026] The piston is made of a composite material of carbon fiber reinforced plastic (CFRP) or high-strength alloy steel. The specific preparation process is as follows: carbon fiber prepreg and resin are mixed, placed in a mold and formed through a hot pressing process. During the hot pressing process, the material is cured under specific temperature and pressure to form the desired piston shape; the prepreg is processed by hot pressing or vacuum bag curing to ensure that the resin is fully penetrated and cured; the curing temperature is generally between 100-150°C to ensure that the strength of the carbon fiber is not affected; the round alloy steel bar is rough-processed on a CNC lathe and cut into the desired piston core shape. Through the turning process, the excess parts are removed to ensure that the piston core has the appropriate size and shape; for the alloy steel part, the quenching and tempering process is used to improve its mechanical properties; during the quenching process, the alloy steel is heated to a high temperature and then rapidly cooled to increase its hardness and tensile strength; tempering is used to eliminate the internal stress after quenching and enhance the toughness of the steel; the carbon fiber reinforced plastic part and the alloy steel core are bonded and fixed with high-strength epoxy resin. The bonding part needs to precisely control the area and strength of the bonding surface to ensure a strong bond between the composite material and the metal; to ensure good bonding between the carbon fiber reinforced plastic and the alloy steel part, the metal surface needs to be roughened; piston surface nitriding treatment: for the alloy steel part of the piston, a nitriding treatment process is used to form a hardened layer, and the thickness of the nitriding layer is generally 10-30μm; the piston surface is chromium coated: for the part that needs to enhance the surface hardness and corrosion resistance, the chromium coating thickness is usually controlled between 10-20μm.

[0027] The piston rod is made of high-strength alloy steel; because the piston rod has a small diameter, high strength is required during long-term sports use, and the small diameter does not affect the overall weight.

[0028] The sealing ring is made of fluororubber (FPM) or polyurethane (PU) material, and the preparation of the sealing ring adopts the following process steps:

[0029] Compression Molding: The selected rubber or polymer material is heated to the appropriate temperature and then pressed into a mold. Common compression molding methods include hot press molding. The compression molding process allows for precise control of the seal's dimensions and, by controlling temperature, pressure, and time, ensures consistent density and performance.

[0030] Injection molding: For some types of seals, the injection molding process is used to inject thermoplastic material into a mold to ensure high-precision seal production. Injection molding has the advantages of efficient production and high dimensional accuracy.

[0031] Vulcanization: Rubber sealing materials (such as FPM, NBR, and PU) require vulcanization after compression or injection molding. The vulcanization process heats the rubber material to a certain temperature and maintains it for a certain period of time, causing the rubber molecules to cross-link and form a three-dimensional network structure, thereby improving the material's durability, elasticity, and high-temperature resistance.

[0032] Curing temperature and time control: Curing temperature and time are usually optimized according to the characteristics of the material, usually in the temperature range of 150-200℃, and the curing time is generally 15-30 minutes.

[0033] Quality Inspection: Use Shore hardness tester to test the hardness of the sealing ring to ensure that it meets the standard range of the selected material; perform leakage test on the sealing ring to simulate the use environment under working conditions to ensure that the sealing performance meets the requirements.

[0034] Through innovative materials, optimized structural design, and advanced manufacturing processes, this technical solution significantly enhances the overall performance of hydraulic cylinders, meeting the requirements of modern aircraft for lightweight, high strength, and long-term reliability. Its lightweight design, enhanced strength, optimized sealing, and enhanced corrosion and fatigue resistance not only extend the cylinder's service life but also improve the overall performance and safety of aircraft landing gear systems, providing a strong guarantee for the efficient and safe operation of aircraft.

[0035] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A lightweight, high-strength hydraulic cylinder suitable for aircraft landing gear, characterized by: It includes a cylinder housing, a piston, a piston rod, and a sealing ring. The piston and the piston rod are connected to each other and installed inside the cylinder housing. The oil inlet and outlet of the cylinder housing are both provided with sealing rings. The cylinder housing is made of high-strength aluminum alloy. The rough blank of the cylinder housing is prepared by die processing using the extrusion method. After the rough blank is extruded, the surface is roughened to remove the surface oxide layer and impurities. Common treatment methods include pickling and sandblasting. Shape processing; Inner cavity processing; Thread processing; Surface anodizing treatment: the cylinder shell is placed in an electrolyte and an electric current is passed through the shell surface to oxidize and form an oxide film. The thickness and hardness of the film can be adjusted according to the process requirements. The general thickness is between 5-25μm. A high-temperature resistant coating is added to the outer surface of the cylinder shell. The surface of the cylinder shell is sandblasted and partially polished.

2. The lightweight, high-strength hydraulic cylinder suitable for aircraft landing gear according to claim 1, characterized in that: The piston is made of a composite material of carbon fiber reinforced plastic or high-strength alloy steel. The specific preparation process is as follows: carbon fiber prepreg and resin are mixed and placed in a mold for forming through a hot pressing process. During the hot pressing process, the material is cured under specific temperature and pressure to form the desired piston shape. The prepreg is processed by hot pressing or vacuum bag curing to ensure that the resin is fully penetrated and cured. The curing temperature is usually between 100-150℃ to ensure that the strength of the carbon fiber is not affected. The round bars of alloy steel are roughly processed by CNC lathe and cut into the required piston core shape. The excess part is removed through the turning process to ensure that the piston core has the appropriate size and shape. For alloy steel, quenching and tempering processes are used to improve its mechanical properties. During the quenching process, the alloy steel is heated to a high temperature and then rapidly cooled to increase its hardness and tensile strength. Tempering is used to eliminate the internal stress after quenching and enhance the toughness of the steel. The carbon fiber reinforced plastic part is fixed to the alloy steel core with high-strength epoxy resin. The bonding part requires precise control of the bonding surface area and strength to ensure a strong bond between the composite material and the metal. To ensure good bonding between carbon fiber reinforced plastic and alloy steel parts, the metal surface needs to be roughened; Nitriding treatment of piston surface: For the alloy steel part of the piston, a nitriding treatment process is used to form a hardened layer. The thickness of the nitrided layer is generally 10-30μm. The piston surface is chromium coated: For parts that need to enhance surface hardness and corrosion resistance, the thickness of the chromium coating is usually controlled between 10-20μm.

3. The lightweight, high-strength hydraulic cylinder suitable for aircraft landing gear according to claim 1, characterized in that: The piston rod is made of high-strength alloy steel.

4. The lightweight, high-strength hydraulic cylinder suitable for aircraft landing gear according to claim 1, characterized in that: The sealing ring is made of fluororubber or polyurethane, and the preparation of the sealing ring adopts the following process steps: Compression molding: The selected rubber or polymer material is heated to the appropriate temperature and placed in a mold for compression molding. Common compression molding methods include hot pressing. The compression molding process can accurately control the size of the seal ring and ensure the stability of the seal ring's density and performance by controlling the temperature, pressure and time. Injection molding: For some types of seals, the injection molding process is used to inject thermoplastic material into the mold to ensure high-precision seal production. Injection molding has the advantages of efficient production and high dimensional accuracy. Vulcanization treatment: For rubber sealing materials, vulcanization treatment is required after molding or injection molding. The vulcanization process is to heat the rubber material to a certain temperature and maintain it for a certain period of time to cross-link the rubber molecules and form a three-dimensional network structure, thereby improving the durability, elasticity and high temperature resistance of the material; Curing temperature and time control: Curing temperature and time are usually optimized according to the characteristics of the material, usually in the temperature range of 150-200℃, and the curing time is generally 15-30 minutes; Quality Inspection: Use Shore hardness tester to test the hardness of the sealing ring to ensure that it meets the standard range of the selected material; perform leakage test on the sealing ring to simulate the use environment under working conditions to ensure that the sealing performance meets the requirements.