A device and method for preventing stiction of a brake pressure servo valve in an aircraft brake system

Abstract

The application provides a device and method for preventing brake pressure servo valve sticking in an airplane brake system, wherein the device comprises a filter joint and a process oil filter; the filter joint is arranged on a pipeline between the brake pressure servo valve and a doser, and a filter screen is arranged in the filter joint; the filter joint is designed according to the shape and size of the original brake pressure servo valve; and the process oil filter is arranged on a pipeline between the doser and inner brake wheels and outer brake wheels. Through hydraulic oil cleaning and brake system testing, the method can clean solid pollutants in the brake system, especially wear particles generated in the running-in stage and accumulated hydraulic oil in blind cavities of the brake device.

Description

Technical Field

[0001] This invention belongs to the field of aircraft maintenance technology, specifically relating to a device and method for preventing the brake pressure servo valve in an aircraft braking system from jamming. Background Technology

[0002] In a certain type of aircraft, the brake discs are installed at the left and right main landing gear wheels, located at the lowest point of the brake hydraulic system. In this type of brake hydraulic system, the pipeline from the brake valve through the brake pressure servo valve to the brake disc is a single chamber. When braking, hydraulic oil flows from the brake valve through the brake pressure servo valve to the brake disc. When releasing the brake, the hydraulic oil in the brake disc flows back through the brake pressure servo valve and the brake valve to the hydraulic oil tank.

[0003] The brake pressure servo valve is a precision electromechanical accessory in the braking system. Its internal parts have very small clearances; the minimum clearance for a plate valve is only 0.005mm, making it susceptible to blockage or jamming due to external contaminants. Currently, it is generally believed that these external contaminants are solid contaminants introduced during system assembly. The common practice is to drain the hydraulic oil containing solid contaminants from the brake unit's vent valve to prevent them from entering the brake pressure servo valve. However, we have found that after actual maintenance, especially after major aircraft overhauls such as replacing new brake units, even after replacing the hydraulic oil containing assembly-related solid contaminants, the brake pressure servo valve still quickly develops jamming problems. Summary of the Invention

[0004] In response to the problems identified in the background section, the applicant conducted research and analyzed the hydraulic fluid of the aircraft's braking system after a major aircraft overhaul and before ground adjustment tests. The analysis revealed that in addition to a small amount of contaminants introduced during assembly, the hydraulic fluid also contained a large number of solid particles. These solid particles caused the brake pressure servo valve to quickly develop a sticking failure after the aircraft overhaul. Further experimental research was conducted to investigate the source of these solid particles. The research found that because the brake piston friction pairs are made of aluminum and the brake assembly was a newly replaced product after maintenance, during the brake system's break-in period, wear particles were generated due to high temperature and pressure wear or friction between the piston friction pairs as the brake piston extended and retracted within the cylinder. As the brake hydraulic system operated, these solid particles accumulated at the brake disc. When the brakes were released, these solid contaminants would backflow and contaminate the brake pressure servo valve, causing it to stick or even resulting in abnormal brake pressure.

[0005] Based on the above analysis, this invention proposes a device to prevent the brake pressure servo valve in an aircraft braking system from jamming. The braking system includes brake branches respectively disposed between the brake valve and the inner brake wheel and the outer brake wheel. Each brake branch includes a brake pressure servo valve and a metering device connected in series via a brake conduit. The device is characterized in that it includes a filter connector, a process oil filter, and a process conduit. The filter connector is disposed between the brake pressure servo valve and the metering device and is connected to the metering device via the brake conduit.

[0006] The filter connector includes a coaxially connected tapered section and a cylindrical body, with a central hole along the axis as a hydraulic oil flow channel;

[0007] The column is provided with an external thread that matches the internal thread of the brake pressure servo valve housing interface.

[0008] The column is equipped with a filter screen;

[0009] The tapered segment includes a coaxially connected conical segment and a cylindrical segment;

[0010] The conical section has the same shape and size as the brake guide opening located between the metering device and the brake pressure servo valve;

[0011] The cylindrical section is provided with an external thread that is compatible with the nut on the brake guide tube;

[0012] The process oil filter is installed between the metering device and the inner brake wheel and the outer brake wheel. Both ends of the process oil filter are connected to the metering device, the inner brake wheel, and the outer brake wheel respectively through process conduits.

[0013] The process oil filter adopts a two-way oil filter, which can collect wear particles generated during the break-in period of the brake system due to high temperature and high pressure wear or piston friction when the brake piston extends and retracts in the oil cylinder.

[0014] Furthermore, the diameter of the bottom surface of the conical segment is equal to the outer diameter of the cylindrical segment.

[0015] Furthermore, the filter screen is made of copper wire mesh with a mesh size of 0.028 to 0.038 mm.

[0016] Furthermore, a hexagonal boss is provided between the tapered section and the column for installing or removing the filter connector using a wrench.

[0017] Furthermore, the maximum oil flow capacity of the process oil filter is 10L / min, and the oil flow resistance does not exceed 0.18MPa.

[0018] Furthermore, the filter connector is made of 45# steel.

[0019] A method for using a device to prevent the brake pressure servo valve in an aircraft braking system from sticking, wherein the method is performed during the ground adjustment test phase after an aircraft overhaul, and specifically includes the following steps:

[0020] Step 1: Remove the pipe joint installed on the brake pressure servo valve and install the filter joint on the pipeline between the brake pressure servo valve and the metering device;

[0021] Step 2: Remove the brake guide tubes between the metering device and the inner and outer brake wheels, and install process oil filters and process guide tubes between the metering device and the inner brake wheel, and between the metering device and the outer brake wheel;

[0022] Step 3: Supply pressurized hydraulic oil to the braking system to circulate and clean the hydraulic oil within the system;

[0023] Step 4: Test the contamination level of the hydraulic oil in the system after cleaning. If the contamination level of the hydraulic oil is better than the first set technical level requirement, proceed to the brake test; otherwise, return to step 3 and clean the brake system again.

[0024] Step 5: Conduct a brake test. After the test, sample and test the hydraulic oil. If the hydraulic oil contamination level is better than the second set technical level requirement, proceed to step 6. Otherwise, return to and repeat steps 3-5 until the second set technical level requirement is met.

[0025] The first set technical level requirement is different from the second set technical level requirement;

[0026] Step 6: Drain the hydraulic oil deposited in the blind cavity of the brake device through the vent valves inside the inner and outer brake wheels;

[0027] Step 7: Disassemble and remove the process oil filter, filter connector and process conduit, and restore the aircraft to its original installation state.

[0028] Furthermore, in step 3, the pressure of the hydraulic oil supplied to the braking system is 6-9 MPa, and the hydraulic oil circulates and cleans within the system for no less than 30 minutes.

[0029] Furthermore, in step 6, the specific process of draining the hydraulic oil deposited in the blind cavity of the brake device through the bleed valves inside the inner and outer brake wheels is as follows:

[0030] Step 6.1: Loosen the vent valves of the inner brake wheel and the outer brake wheel's inner brake device, and connect them to the hoses respectively;

[0031] Step 6.2: Depress the brake pedal all the way down and pull out the stop brake lever;

[0032] Step 6.3: Drain the hydraulic oil through the bleed valve, with a minimum of 3 liters of hydraulic oil drained from each brake wheel.

[0033] The advantages of this invention are:

[0034] The device of this invention includes a process oil filter and a filter connector. By installing the filter connector on the brake pressure servo valve and directly setting the process oil filter between the metering device and the inner and outer brake wheels, solid contaminants in the brake system can be collected by pressurizing and cleaning with a hydraulic source after aircraft overhaul. This ensures that the hydraulic oil in the brake system meets technical requirements and prevents backflow of contaminants from the aircraft brake system from contaminating the hydraulic servo valve during ground commissioning. This solves the problem of hydraulic oil backflow in the brake disc contaminating the brake pressure servo valve when the brake is released. Attached Figure Description

[0035] Figure 1 : This is a connection block diagram of the device of the present invention;

[0036] Figure 2 This is a schematic diagram of the filter connector in this invention; the external thread is not shown in the diagram.

[0037] Figure 3 : This is a cross-sectional view of the filter connector. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0039] The braking system includes brake branches respectively disposed between the brake valve and the inner and outer brake wheels. Each brake branch includes a brake pressure servo valve and a metering device connected in series via conduits. The brake pressure servo valve is connected to the brake conduit disposed between itself and the metering device via a pipe fitting.

[0040] Following an aircraft overhaul, during the break-in period, the braking system experiences wear due to high temperature and pressure, or wear particles generated by friction between the piston and hydraulic cylinder during piston extension and retraction. These particles accumulate at the brake disc as the brake hydraulic system operates, potentially causing the brake pressure servo valve to stick. (Refer to...) Figure 1 The present invention provides a device for preventing the brake pressure servo valve in an aircraft braking system from jamming, comprising a filter connector, a process oil filter and a process conduit, wherein the filter connector is disposed between the brake pressure servo valve and the metering device and is connected to the metering device through the brake conduit;

[0041] The filter connector includes a coaxially connected tapered section and a cylindrical body, with a central hole along the axis as a hydraulic oil flow channel;

[0042] The column is provided with an external thread that matches the internal thread of the brake pressure servo valve housing interface.

[0043] The column is equipped with a filter screen;

[0044] The tapered segment includes a coaxially connected conical segment and a cylindrical segment;

[0045] The conical section has the same shape and size as the conduit opening connecting the metering device and the brake pressure servo valve;

[0046] The cylindrical section is provided with an external thread that matches the nut on the conduit.

[0047] The process oil filter is installed between the metering device and the inner brake wheel and the outer brake wheel. Both ends of the process oil filter are connected to the metering device and the inner brake wheel or the outer brake wheel through process conduits, respectively.

[0048] The process oil filter adopts a two-way oil filter, which can collect wear particles generated during the break-in period of the brake system due to high temperature and high pressure wear or piston friction when the brake piston extends and retracts in the oil cylinder, thus preventing the brake pressure servo valve from being stuck due to back-contamination of the servo valve by wear particles.

[0049] Reference Figure 2 and Figure 3 The diameter of the bottom surface of the conical section of the filter connector is equal to the outer diameter of the cylindrical section. A hexagonal boss is provided between the conical section and the cylindrical body for installing or removing the filter connector using a wrench.

[0050] The filter screen is selected according to standard HB1862, and in this embodiment, a copper wire mesh with a mesh diameter of 0.028–0.038 mm is used. The center hole of the filter connector is a double-hole design, and the filter screen is placed in the countersunk hole within the column. The filter connector is made of 45# steel.

[0051] The process oil filter is a bidirectional oil filter with a maximum oil flow rate of 10 L / min and an oil flow resistance of no more than 0.18 MPa. In this embodiment, the YL-7A process oil filter is selected, with a filtration accuracy of 10 μm, which can filter solid impurities with a diameter of not less than 10 μm.

[0052] The present invention provides a method for preventing the brake pressure servo valve in an aircraft braking system from jamming, comprising the following steps:

[0053] Step 1: Remove the pipe joint installed between the brake pressure servo valve and the metering device, and install the filter joint on the brake pressure servo valve and the brake conduit between it and the metering device.

[0054] During installation, the cylindrical end of the filter connector is threadedly connected to the internal thread of the brake pressure servo valve housing interface, the tapered section is embedded in the brake conduit interface, and the external thread of the tapered section is fastened to the nut set on the brake conduit.

[0055] Step 2: Install process oil filters on the conduits between the metering device and the inner brake wheel, and between the metering device and the outer brake wheel; the process oil filters can be used for oil flow in both directions.

[0056] Step 3: Pressurize the aircraft using a ground-based hydraulic power source, applying 6-9 MPa of hydraulic pressure to the braking system. This allows the hydraulic oil to circulate and clean within the system for at least 30 minutes. The presence of filter connectors and process oil filters effectively removes contaminants from the braking system piping.

[0057] Step 4: Test the contamination level of the hydraulic oil after cleaning. It should be better than the GJB-420B Level 6 requirement. If it does not meet the requirement, return to Step 3 and clean again.

[0058] Step 5: Conduct a brake system test. During braking, hydraulic oil flows from the brake valve through the brake pressure servo valve, filter connector, metering device, and process oil filter to the brake disc. The filter connector and process oil filter clean contaminants in the brake system pipeline.

[0059] When the brake is released, the hydraulic oil in the brake disc flows in reverse order through the process oil filter, metering device, filter connector, brake pressure servo valve and brake valve back to the hydraulic oil tank. Due to the function of the process oil filter, wear particles generated by high temperature and high pressure wear or piston friction when the brake piston extends and retracts in the cylinder during the break-in period of the brake system will not enter the brake pressure servo valve.

[0060] Repeat the above process to perform multiple brake system tests. After the test, sample the hydraulic oil from the brake devices of the inner brake wheel and the outer brake wheel and test it. The contamination level of the hydraulic oil should be better than GJB-420B Grade 7. If the contamination level of the hydraulic oil does not meet the technical requirements, return to step 3-5 and repeat until the technical requirements are met.

[0061] Step 6: After the test, drain the accumulated hydraulic oil from the brake system through the bleed valves inside the inner and outer brake wheels. The specific process is as follows:

[0062] First, loosen the air vents of the inner brake wheel and the inner brake device of the outer brake wheel, and connect them to the hoses respectively;

[0063] Then, press the brake pedal all the way down and pull out the stop brake lever;

[0064] Finally, drain the hydraulic oil deposited in the blind cavity of the brake device through the vent. Generally, drain no less than 3 liters of hydraulic oil from each brake wheel to ensure that the hydraulic oil deposited in the blind cavity of the brake device is completely drained.

[0065] Step 7: When the aircraft enters the flight test preparation phase, disassemble and remove the process oil filter and filter connector, and restore the aircraft to its original installation state.

[0066] The above-described usage method is performed during the aircraft adjustment and testing phase after the aircraft overhaul to ensure that the brake pressure servo valve will not get stuck during the later test flights due to wear particles generated by high temperature and high pressure wear during the brake system break-in period or by piston friction particles generated when the brake piston extends and retracts in the cylinder.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and such modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for preventing the brake pressure servo valve in an aircraft braking system from jamming, characterized in that, The method is based on a device to prevent the brake pressure servo valve in the aircraft braking system from jamming, and the method is carried out during the aircraft ground adjustment test phase after the aircraft overhaul. The braking system includes brake branches respectively disposed between the brake valve and the inner brake wheel and the outer brake wheel. The brake branches include a brake pressure servo valve and a metering device connected in series through a brake conduit. The device is characterized by including a filter connector, a process oil filter and a process conduit. The filter connector is located between the brake pressure servo valve and the metering device, and is connected to the metering device through a brake conduit. The filter connector includes a conical section and a cylindrical body connected coaxially, with a central hole along the axis as a hydraulic oil flow channel; the cylindrical body is provided with an external thread that matches the internal thread of the brake pressure servo valve housing interface. The column is equipped with a filter screen; the conical section includes a conical section and a cylindrical section connected coaxially; the conical section has the same shape and size as the inner hole of the brake guide provided between the brake pressure servo valve and the metering device; The cylindrical section is provided with an external thread that matches the nut on the brake guide tube; The process oil filter is installed between the metering device and the inner and outer brake wheels. Both ends of the process oil filter are connected to the metering device, the inner brake wheel, and the outer brake wheel through process conduits, respectively. The process oil filter is a bidirectional oil filter, which can collect wear particles generated during the break-in period of the brake system due to high temperature and high pressure wear or piston friction when the brake piston extends and retracts in the oil cylinder. The method includes the following steps: Step 1: Remove the pipe joint installed on the brake pressure servo valve and install the filter joint on the pipeline between the brake pressure servo valve and the metering device; Step 2: Remove the brake guide tubes between the metering device and the inner and outer brake wheels, and install process oil filters and process guide tubes between the metering device and the inner brake wheel, and between the metering device and the outer brake wheel; Step 3: Supply pressurized hydraulic oil to the braking system to circulate and clean the hydraulic oil within the system; Step 4: After cleaning, test the contamination level of the hydraulic oil in the system. If the contamination level of the hydraulic oil is better than the first set technical level requirement, proceed to the brake test; otherwise, return to step 3 and clean the brake system again. Step 5: Conduct a brake test. After the test, sample and test the hydraulic oil. If the hydraulic oil contamination level is better than the second set technical level requirement, proceed to step 6. Otherwise, return to and repeat steps 3-5 until the second set technical level requirement is met. The first set technical level requirement is superior to the second set technical level requirement; Step 6: Drain the hydraulic oil deposited in the blind cavity of the brake device through the vent valves inside the inner and outer brake wheels; Step 7: Disassemble and remove the process oil filter, filter connector and process conduit, and restore the aircraft to its original installation state.

2. The method according to claim 1, characterized in that, In step 3, the pressure of the hydraulic oil supplied to the braking system is 6-9 MPa, and the hydraulic oil circulates and cleans within the system for no less than 30 minutes.

3. The method according to claim 2, characterized in that, In step 6, the specific process of draining the hydraulic oil deposited in the blind cavity of the brake device through the bleed valves inside the inner and outer brake wheels is as follows: Step 6.1: Loosen the vent valves of the inner brake wheel and the outer brake wheel's inner brake device, and connect them to the hoses respectively; Step 6.2: Depress the brake pedal all the way down and pull out the stop brake lever; Step 6.3: Drain the hydraulic oil through the bleed valve, with a minimum of 3 liters of hydraulic oil drained from each brake wheel.

4. The method according to claim 1, characterized in that, The diameter of the bottom surface of the conical section is equal to the outer diameter of the cylindrical section.

5. The method according to claim 4, characterized in that, The filter screen is made of copper wire mesh with a mesh diameter of 0.028 to 0.038 mm.

6. The method according to claim 5, characterized in that, The maximum oil flow capacity of the process oil filter is 10L / min, and the oil flow resistance does not exceed 0.18MPa.

7. The method according to claim 6, characterized in that, A hexagonal boss is provided between the tapered section and the column, which facilitates the installation or removal of the filter connector by means of a wrench.

8. The method according to claim 1, characterized in that, The filter connector is made of 45# steel.

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