Device and method for simultaneously monitoring reciprocating dynamic seal contact stress and oil film thickness
By incorporating an optical fiber and ultrasonic probe within the piston rod, and combining a tunable laser with the ultrasonic reflection characteristics, simultaneous monitoring of the contact stress and oil film thickness of the reciprocating dynamic seal is achieved. This solves the problem of inaccurate monitoring in existing technologies and improves the reliability and predictive capability of the sealing system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-27
- Publication Date
- 2026-07-07
AI Technical Summary
In existing technologies, the contact stress and oil film thickness of reciprocating dynamic seals are mainly obtained through finite element simulation, which leads to a large discrepancy between the actual situation and the simulation results, and there is a lack of effective monitoring methods to accurately predict the amount of seal leakage.
Design a device that incorporates an optical fiber and an ultrasonic probe inside a piston rod. The optical fiber is connected to a tunable laser to monitor the contact stress between the seal and the piston rod. The ultrasonic probe is used to obtain the oil film thickness. By combining the tunable laser and the ultrasonic reflection characteristics, real-time monitoring of the sealing status can be achieved.
It enables comprehensive, real-time monitoring of the sealing status, improves measurement accuracy and sensitivity, can detect sealing failure trends early, guide preventive maintenance, extend sealing life, and improve system reliability. It is particularly suitable for measuring the oil film thickness of the dynamic seal of the landing gear buffer strut.
Smart Images
Figure CN122345446A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of reciprocating dynamic seal monitoring technology, and in particular to an apparatus and method for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal. Background Technology
[0002] In existing technologies, the contact stress and oil film thickness inside reciprocating dynamic seals are mainly obtained through finite element simulation. Various software is used to solve the control equations of the lubrication flow field under different working conditions to obtain the contact stress and oil film thickness, and then to calculate the theoretical leakage. However, due to the variability of actual working conditions and the precision of machining of mechanical parts, the data obtained from simulation differs greatly from the actual situation. Therefore, there is an urgent need for a device that can simultaneously monitor the stress and oil film thickness of reciprocating dynamic seals to provide data support for accurately predicting the leakage of seals. Summary of the Invention
[0003] The main objective of this application is to provide a device and method for simultaneously monitoring the contact stress and oil film thickness of reciprocating dynamic seals. This aims to solve the technical problem that the existing methods for obtaining contact stress and oil film thickness mainly rely on finite element simulation, which results in significant discrepancies between the actual data obtained and the actual working conditions due to the variability of real-world operating conditions.
[0004] To achieve the above objectives, in a first aspect, this application provides a device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal, comprising a piston cylinder having a piston chamber and a piston rod extending through the piston chamber; A sealing element is provided between the outer wall of the piston rod and the inner wall of the piston chamber; The piston rod has a positioning hole inside, and the inner wall of the positioning hole is provided with an optical fiber extending in a first direction. The optical fiber is connected to a tunable laser so that the contact stress between the seal and the piston rod can be obtained based on the tunable laser. An ultrasonic probe is also provided in the positioning hole. The ultrasonic probe is aligned with the position of the seal so that the oil film thickness at the seal can be obtained based on the ultrasonic probe.
[0005] Optionally, the inner wall of the positioning hole is provided with a plurality of positioning grooves extending along a first direction, all of which are arranged circumferentially, and the positioning grooves are used to install the optical fiber.
[0006] Optionally, the positioning hole passes through the first end of the piston rod, the ultrasonic probe is connected to a bracket, the bracket passes through the first end of the piston rod, and the second end of the piston rod is provided with an earring for connecting to a power mechanism to drive the piston rod to reciprocate along a first direction.
[0007] Optionally, the end of the ultrasonic probe near the seal is an arc-shaped surface adapted to the inner wall of the positioning hole.
[0008] Optionally, the piston chamber includes a through hole, with limiting grooves at both ends of the through hole. A set of bushings and end caps located on both sides of the through hole are sleeved on the piston rod. The bushings are located in the limiting grooves, and a portion of the end caps protrudes from the limiting grooves and abuts against the bushings. The bushings are provided with an annular receiving groove, which forms a sealing space with the outer wall of the piston rod for receiving a sealing element.
[0009] Optionally, the limiting groove includes a first stepped groove and a second stepped groove arranged in a direction away from the through hole, wherein the inner diameter of the first stepped groove is smaller than the inner diameter of the second stepped groove. The bushing includes a first shaft segment and a second shaft segment. A stepped surface is formed at the connection between the first shaft segment and the second shaft segment. The first shaft segment is located in the first stepped groove. The receiving groove is disposed in the first shaft segment. The portion of the end cap protruding from the limiting groove abuts against the stepped surface.
[0010] Optionally, the end cap has an oil collection groove communicating with the limiting groove, and the end cap has an oil drain port communicating with the oil collection groove, and an oil collection cup is detachably provided at the oil drain port.
[0011] Optionally, a first sealing ring is provided between the outer wall of the first shaft segment and the inner wall of the first stepped groove, a second sealing ring is provided between the outer wall of the second shaft segment and the end cover, and a third sealing ring is provided between the piston rod and the end cover. The second sealing ring and the third sealing ring are respectively located on both sides of the oil collection groove along the first direction.
[0012] Optionally, the piston cylinder has an oil inlet and an oil return nozzle communicating with the piston chamber, for providing hydraulic pressure to the piston chamber and recovering oil.
[0013] Secondly, this application provides a method for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal, comprising the following steps: The linear sweep beam generated by the tunable laser is split into two optical paths via a coupler; After the first optical path enters the reference arm, it is reflected back to the coupler by the mirror and used as the local oscillator reference light. After the second optical path enters the optical fiber, it is scattered by Rayleigh. The scattered light carries local information of the optical fiber back to the coupler and interferes with the local oscillator reference light. The beat frequency signal is obtained through Fourier transform, and the contact stress is obtained based on the beat frequency signal. The reciprocating dynamic seal structure is simplified into a three-layer medium model, with the middle layer being the oil film to be tested, and the upper and lower layers being the sealing element and the metal contact pair, respectively. When there is no oil film at the seal, the ultrasonic wave is perpendicularly injected into the interface between the seal and the air, and the amplitude of the reflected echo is measured as a reference amplitude. When there is an oil film at the seal, ultrasonic waves are generated at the same position as when the reference amplitude is measured, and the amplitude of the reflected echo at the interface between the sealing ring and the oil film is used as the measurement amplitude. The reflection coefficient of ultrasonic waves at the interface between the sealing ring and the oil film is obtained by referencing the amplitude and using measurement aids. The thickness of the oil film is obtained by using the reflection coefficient, the acoustic impedance of the seal, the acoustic impedance of the metal contact pair, the ultrasonic frequency, the oil density, and the sound velocity.
[0014] The beneficial effects that this application can achieve are: This application proposes a device and method for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal. By installing an optical fiber and an ultrasonic probe inside the piston rod, with the optical fiber connected to a tunable laser, the device can simultaneously acquire the contact stress and oil film thickness between the seal and the piston rod. This enables comprehensive, real-time monitoring of the sealing status, avoiding the limitations of single-parameter monitoring. The optical fiber and ultrasonic probe are integrated into the positioning hole of the piston rod, occupying no external space and not affecting the original structure and motion function of the sealing system, thus having no interference with the sealing operation. The optical fiber, through the tunable laser, achieves contact stress measurement, offering high sensitivity and resistance to electromagnetic interference, making it suitable for dynamic reciprocating environments. The ultrasonic probe is directly aligned with the sealing area, ensuring accurate oil film thickness measurement and utilizing the ultrasonic reflection characteristics to improve thickness detection accuracy. By simultaneously monitoring contact stress and oil film thickness, the contact stress reflects the wear or compression state of the seal, while the oil film thickness reflects the lubrication status. This allows for early detection of seal failure trends, guiding preventative maintenance, extending seal life, and improving system reliability. It can simultaneously measure the contact stress and oil film thickness of the main sealing surface in reciprocating dynamic seals, and is particularly suitable for measuring the oil film thickness of the dynamic seal of the landing gear buffer strut, providing reliable data support for accurately predicting the amount of seal leakage. Attached Figure Description
[0015] Figure 1 This is a three-dimensional structural diagram of the device according to an embodiment of this application; Figure 2 This is a cross-sectional structural diagram of the device according to an embodiment of this application; Figure 3 for Figure 2 A schematic diagram of the cross-sectional structure of the piston cylinder; Figure 4 for Figure 2 Enlarged structural diagram at point A in the middle; Figure 5 This is a schematic diagram of the Michelson interferometer structure according to an embodiment of this application; Figure 6This is a schematic diagram of ultrasonic wave propagation in a three-layer medium model according to an embodiment of this application.
[0016] The numbers on the map are: 10-Piston cylinder, 11-Oil inlet, 12-Oil return nozzle, 13-Through hole, 14-Limiting groove, 141-First stepped groove, 142-Second stepped groove, 20-Piston rod, 21-Positioning hole, 22-Ear ring, 30-Seal, 31-Receiving groove, 40-Shaft sleeve, 41-First shaft section, 42-Second shaft section, 50-Ultrasonic probe, 60-End cap, 61-First sealing ring, 62-Second sealing ring, 63-Third sealing ring, 64-Oil collection groove, 70-Fiber optic cable, 71-Positioning groove, 80-Oil collection cup.
[0017] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0019] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.
[0020] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.
[0022] Example 1 Reference Figures 1-4 The first embodiment of this application provides a device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal, including a piston cylinder 10, a piston chamber inside the piston cylinder 10, and a piston rod 20 extending through the piston chamber. A seal 30 is provided between the outer wall of the piston rod 20 and the inner wall of the piston chamber; The piston rod 20 has a positioning hole 21 inside. The inner wall of the positioning hole 21 is provided with an optical fiber 70 extending in a first direction. The optical fiber 70 is connected to a tunable laser so that the contact stress between the seal 30 and the piston rod 20 can be obtained based on the tunable laser. An ultrasonic probe 50 is also provided in the positioning hole 21. The ultrasonic probe 50 is aligned with the position of the seal 30 so that the oil film thickness at the seal 30 can be obtained based on the ultrasonic probe 50.
[0023] In this embodiment, the piston cylinder 10 is mounted upside down on a support plate (not shown in the figure) using bolts and nuts. The piston cylinder 10 and piston rod 20 are fitted with a small clearance of H8 / f7. The first direction is the axial direction of the piston rod 20. The piston rod 20 is connected to a power mechanism, which drives the piston rod 20 to reciprocate along the first direction. During the reciprocating motion of the piston rod 20, the position of the piston cylinder 10 remains fixed. Two seals 30 are provided on the piston rod 20, and hydraulic oil is injected between the two seals 30. Ideally, the sealing performance of the seals 30 does not decrease, and the hydraulic oil remains within the space between the two seals 30. However, as the piston rod 20 reciprocates, the sealing performance of the seals 30 decreases, and the hydraulic oil may leak beyond the seals 30. The reciprocating dynamic seal contact stress and oil film thickness refer to the contact stress and oil film thickness between the seals 30 and the piston rod 20. By simultaneously monitoring contact stress and oil film thickness, early detection of seal failure trends can be achieved, guiding preventative maintenance, extending seal life, and improving system reliability. Contact stress reflects the wear or tightness of the seal 30, while oil film thickness reflects the lubrication status. An optical fiber 70 is installed inside the piston rod 20. The optical fiber 70 can be attached to the positioning hole 21 of the piston rod 20 by adhesive bonding or physical snap-fit. The optical fiber 70 is connected to a tunable laser (not shown in the figure). The tunable laser can be installed outside the piston rod 20, and its position remains fixed during the reciprocating movement of the piston rod 20. The optical fiber 70 has a length margin to ensure that it is not affected by the reciprocating movement of the piston rod 20. Similarly, the tunable laser can also be installed on the piston rod 20 so that it can reciprocate synchronously with the piston rod 20. An ultrasonic probe 50 is installed inside the positioning hole 21. The position of the ultrasonic probe 50 is fixed relative to the position of the piston cylinder 10, meaning that the ultrasonic probe 50 will not move synchronously with the piston rod 20 during its reciprocating motion. The position of the ultrasonic probe 50 is offset from the positioning groove 71. The ultrasonic probe 50 is connected to an ultrasonic generator and receiver, which is connected to a transducer. The data is transmitted to a PC via an oscilloscope acquisition card and saved for subsequent oil film thickness calculations.
[0024] Example 2 Based on Embodiment 1, this embodiment provides an installation structure for an optical fiber 70 and an ultrasonic probe 50, including: a plurality of positioning grooves 71 extending along a first direction are provided on the inner wall of the positioning hole 21, all positioning grooves 71 are arranged circumferentially, and the positioning grooves 71 are used to install the optical fiber 70.
[0025] Specifically, the inner wall of the positioning hole 21 is provided with a plurality of positioning grooves 71 arranged circumferentially, the distance between adjacent positioning grooves 71 is equal, and an optical fiber 70 can be installed in each positioning groove 71. The optical fiber 70 can be fixed in the positioning groove 71 by adhesive bonding.
[0026] Optionally, the positioning hole 21 penetrates the first end of the piston rod 20, and the ultrasonic probe 50 is connected to a bracket that also penetrates the first end of the piston rod 20. An earring 22 is provided at the second end of the piston rod 20, which is used to connect to a power mechanism to drive the piston rod 20 to reciprocate along a first direction. For example, six shallow grooves with a radially uniform distribution of radius R0.08mm and a depth of 0.08mm can be formed inside the piston rod 20, and optical fibers 70 can be laid in the grooves and bonded with adhesive.
[0027] Specifically, such as Figure 2 As shown, the left end of piston rod 20 is the first end, and the right end is the second end. The first end of piston rod 20 has an open structure, through which both the optical fiber 70 and the bracket can pass. The cable of ultrasonic probe 50 can be used as a bracket to fix ultrasonic probe 50, or a separate bracket can be set to support ultrasonic probe 50 and its cable, ensuring that the optical fiber 70 moves back and forth with piston rod 20 during its reciprocating motion, while ultrasonic probe 50 does not move back and forth with piston rod 20. The second end of piston rod 20 is connected to an ear loop 22, which can be detachably connected to piston rod 20 via a threaded connection. Ear loop 22 is used to connect to a power mechanism to drive piston rod 20 to reciprocate at a certain speed and frequency. The power mechanism can be a hydraulic cylinder, a pneumatic cylinder, or other reciprocating drive mechanism.
[0028] Optionally, the end of the ultrasonic probe 50 near the seal 30 is an arc-shaped surface that fits the inner wall of the positioning hole 21.
[0029] Specifically, the ultrasonic probe 50 has a hemispherical or arc-shaped surface. The ultrasonic probe 50 matches the inner wall of the positioning hole 21 of the piston rod 20 and is coated with grease as a coupling agent to reduce the friction between the ultrasonic probe 50 and the inner wall of the piston rod 20.
[0030] Optionally, the piston chamber includes a through hole 13, with limiting grooves 14 at both ends of the through hole 13. A set of bushings 40 and end caps 60 located on both sides of the through hole 13 are sleeved on the piston rod 20. The bushings 40 are located in the limiting grooves 14, and part of the end caps 60 protrudes from the limiting grooves 14 and abuts against the bushings 40. The bushings 40 are provided with an annular receiving groove 31, which forms a sealing space with the outer wall of the piston rod 20 for receiving the sealing element 30.
[0031] Specifically, the limiting grooves 14 located on both sides of the through hole 13 have a symmetrical structure. A bushing 40 and an end cap 60 constitute a set of structures, with one set of structures provided on each side of the through hole 13. The bushing 40 and the end cap 60 cooperate to fix the seal 30, ensuring that the seal 30 does not move with the piston rod 20 during its reciprocating movement. The bushing 40 has an open structure, allowing the seal 30 to be installed directly from one side, avoiding deformation and restoration issues during installation. After installation, it is directly inserted into the piston cylinder 10 and limited by the end face of the limiting groove 14. The piston cylinder 10 and the piston rod 20 are fitted with a single-sided large clearance of 0.2mm; the inner hole of the bushing 40 and the end cover 60 is fitted with a small clearance of H8 / f8 between the inner hole and the outer circle of the piston rod 20; the outer circle of the bushing 40 and the end cover 60 is fitted with a small clearance of H8 / f8 between the inner hole of the piston cylinder 10 and the inner hole of the end cover 60.
[0032] Optionally, the limiting groove 14 includes a first stepped groove 141 and a second stepped groove 142 arranged in a direction away from the through hole 13, the inner diameter of the first stepped groove 141 being smaller than the inner diameter of the second stepped groove 142; the bushing 40 includes a first shaft section 41 and a second shaft section 42, a stepped surface is formed at the connection between the first shaft section 41 and the second shaft section 42, the first shaft section 41 is located in the first stepped groove 141, the receiving groove 31 is disposed in the first shaft section 41, and the portion of the end cap 60 protruding from the limiting groove 14 abuts against the stepped surface.
[0033] Specifically, two adjacent concentric circular grooves with different inner diameters are machined on the bore wall of the piston cylinder 10, together forming the limiting groove 14. Starting from the side near the piston cavity through hole 13, there is first a first stepped groove 141 with a smaller inner diameter; followed by a second stepped groove 142 with a larger inner diameter than the first stepped groove 141. The stepped structure formed by the first stepped groove 141 and the second stepped groove 142 creates an axial mechanical stop, the main function of which is to precisely limit the installation depth and radial position of the bushing 40, preventing it from moving away from the through hole 13 during operation and ensuring the geometric position of the sealing area is fixed. The bushing 40 is a stepped shaft that matches the limiting groove 14, consisting of a first shaft section 41 and a second shaft section 42. The outer diameter of the first shaft section 41 matches the inner diameter of the first stepped groove 141, and the outer diameter of the second shaft section 42 is usually less than or equal to the inner diameter of the second stepped groove 142. At the junction of the first shaft segment 41 and the second shaft segment 42, a radial stepped surface is naturally formed due to the difference in outer diameter. This stepped surface is a key load-bearing and positioning surface. The annular mounting groove 31 for installing the seal 30 is machined on the inner wall of the first shaft segment 41. This means that the seal 30 will be accommodated and work between the bushing 40 and the piston rod 20, which helps maintain the sealing shape. The end cap 60 is inserted into the second stepped groove 142 from the outside of the piston cylinder 10. The end cap 60 is not completely sunk in; a portion of its inner end face is designed as a raised structure. After assembly, the inner end face of the raised portion of the end cap 60 directly and tightly abuts against the stepped surface of the bushing 40. By fastening the end cap 60, such as by bolts or threads to the cylinder body, an axial clamping force is generated. This axial clamping force is transmitted through the raised portion of the end cap 60 to the stepped surface of the bushing 40, ultimately firmly pressing and positioning the entire bushing 40 along with the seal 30 within the first stepped groove 141, eliminating axial clearance.
[0034] Optionally, the end cap 60 has an oil collection groove 64 communicating with the limiting groove 14, and the end cap 60 has an oil drain port communicating with the oil collection groove 64. An oil collection cup 80 is detachably provided at the oil drain port.
[0035] Specifically, the oil collection groove 64 has an annular structure and a V-shaped cross-section. The hydraulic oil located between the two seals 30 will enter the oil collection groove 64 after passing through the seals 30. An oil leakage port communicating with the oil collection groove 64 is provided on the end cover 60. The oil leakage port can be detachably connected to the oil collection cup 80 by thread. A gravity sensor is installed in the oil collection cup 80, and the volume or weight of the oil leaking from the main sealing surface of the reciprocating dynamic seal is calculated by direct reading or weighing.
[0036] Optionally, a first sealing ring 61 is provided between the outer wall of the first shaft segment 41 and the inner wall of the first stepped groove 141, a second sealing ring 62 is provided between the outer wall of the second shaft segment 42 and the end cover 60, and a third sealing ring 63 is provided between the piston rod 20 and the end cover 60. The second sealing ring 62 and the third sealing ring 63 are respectively located on both sides of the oil collection groove 64 along the first direction.
[0037] Specifically, the first sealing ring 61, the second sealing ring 62, and the third sealing ring 63 are O-rings. Static sealing is achieved through these three sealing rings to prevent internal oil leakage through these connection gaps. This ensures that almost all oil leaking from the main sealing surface of the reciprocating dynamic seal can enter the oil collection cup 80, improving the accuracy of calculating oil leakage through the oil collection cup 80.
[0038] Optionally, the piston cylinder 10 has an oil inlet 11 and an oil return 12 communicating with the piston chamber for providing hydraulic pressure to the piston chamber and recovering oil.
[0039] Specifically, the piston cylinder 10 is designed according to HB4-59 and is equipped with an oil inlet nozzle and an oil outlet nozzle, which are used to provide the required hydraulic pressure to the reciprocating dynamic sealing device and to recover the oil.
[0040] Example 3 Based on Example 1, this example provides a method for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal, including the following steps: S101. The linear sweep beam generated by the tunable laser is split into two optical paths via a coupler.
[0041] Specifically, a tunable laser is activated, causing its output frequency to change linearly and continuously over time—that is, a linearly swept beam. This beam is then connected to a fiber optic coupler, such as a 1×2 type, where the beam is precisely split into two paths: one enters the reference arm, and the other enters the sensing arm, which is then connected to the fiber under test. The splitting ratio of the coupler needs to be optimized according to the system's signal-to-noise ratio, for example, 50:50, or adjusted based on the intensity of the reflected light.
[0042] S102. After the first optical path enters the reference arm, it is reflected back to the coupler by the mirror and used as the local oscillator reference light.
[0043] Specifically, a Faraday rotator or a high-reflectivity fiber end face is connected to the end of the first optical fiber to form a fixed reflecting end. After being reflected, the light returns to the coupler along the original path. The environmental interference experienced by this light during transmission should be as small and stable as possible, as its function is to provide a phase-stable local oscillator reference signal for subsequent interference.
[0044] S103. After entering the optical fiber, the second optical path generates Rayleigh scattering. The scattered light carries local information of the optical fiber back to the coupler and interferes with the local oscillator reference light. The beat frequency signal is obtained through Fourier transform. Based on the beat frequency signal, the contact stress is obtained.
[0045] Specifically, the second optical path is connected to the fiber under test, which is pre-embedded in the positioning hole of the piston rod. When the swept light propagates in the fiber, its inherent slight inhomogeneities generate backscattered Rayleigh light distributed along the entire length of the fiber. The scattered light carries information about the physical state of the fiber at its location, such as strain caused by contact stress. The scattered light returning from all locations returns to the coupler sequentially, merging with the local oscillator reference light returning from the reference arm, resulting in optical beat frequency interference. The mixed optical signal is converted into a time-domain electrical signal by a photodetector. A Fast Fourier Transform (FFT) is performed on the detected time-domain signal. Since the return time of the scattered light from different locations is different, the frequency of the beat frequency signal formed with the reference light is also different. Each frequency peak in the FFT spectrum corresponds to a specific spatial location on the fiber. The frequency peak corresponding to the location of the seal is identified and tracked. The axial strain of the fiber at that location can be obtained by wavelength demodulation (monitoring the peak frequency / wavelength shift) or phase demodulation (monitoring the phase change of the frequency component). Finally, according to the generalized Hooke's law, the strain is obtained using the formula... Calculate the contact stress between the seal and the piston rod, where, in the formula... The contact stress to be obtained is expressed in Pascals; E is the equivalent elastic modulus of the optical fiber, expressed in Pascals. The equivalent elastic modulus comprehensively reflects the overall mechanical properties of the optical fiber itself, the adhesive material, and the packaging structure, and is usually obtained through experimental calibration. This represents the axial strain of the optical fiber at the corresponding location in the seal. For example... Figure 5 As shown, Figure 5 This is a schematic diagram of the Michelson interferometer.
[0046] The axial strain is dimensionless and is calculated using optical frequency domain reflectance measurement technology. Its relationship can be further expressed as: or In the formula, This represents the phase change of the corresponding frequency component in the beat frequency signal, expressed in radians. The wavelength offset of the corresponding frequency component in the beat frequency signal, in meters; and The sensing sensitivity coefficient is related to the fiber Bragg grating parameters and optical system configuration, in units of 1 / meter, and L is the effective length of the sensing fiber, in meters.
[0047] S201. The reciprocating dynamic seal structure is simplified into a three-layer medium model, with the middle layer being the oil film to be tested, and the upper and lower layers being the seal and the metal contact pair, respectively.
[0048] Specifically, the problem of measuring the reciprocating dynamic seal oil film can be viewed as the propagation of ultrasonic waves in three media, such as... Figure 6 As shown, medium I is the seal, medium II is the oil film layer, and medium III is the metal contact pair, with the metal contact pair being the piston rod. When ultrasonic waves are incident perpendicularly on the interface between the seal and the oil film layer, the sound waves will be reflected and transmitted at that point. Similarly, when sound waves entering the oil film layer reach the interface between the oil film layer and the metal contact pair, they will also be reflected and transmitted. Compared to the thickness of the oil film layer and the wavelength of the ultrasonic waves in the middle, the seal and metal contact pair located on either side of the oil film layer are relatively thick and can be considered as semi-infinite media; therefore, their reflection and transmission at other interfaces can be ignored.
[0049] S202. When there is no oil film at the seal, the ultrasonic wave is perpendicularly injected into the interface between the seal and the air, and the amplitude of the reflected echo is measured as a reference amplitude.
[0050] Specifically, with the system initially lubricated without oil or with the sealed area ensured to be dry, the ultrasonic probe located inside the piston rod is driven to emit a short-pulse ultrasonic wave of known frequency towards the seal. After propagating through medium III, i.e., the piston rod, the ultrasonic wave undergoes near total reflection at the piston rod surface, at which point the piston rod surface comes into contact with air. The ultrasonic probe receives the first reflected echo from this solid-gas interface and records its voltage amplitude. This value serves as a reference auxiliary value for subsequent calculations, at which point the reflection coefficient... .
[0051] S203. When there is an oil film at the seal, ultrasonic waves are generated at the same position as when the reference amplitude is measured, and the amplitude of the reflected echo at the interface between the sealing ring and the oil film is used as the measurement amplitude.
[0052] Specifically, under normal system oil supply and oil film conditions, the piston rod is moved to the exact same position as in step S202, which can be located using a displacement sensor or encoder. At this position, the ultrasonic probe emits an ultrasonic pulse with the same parameters again. This time, the ultrasonic wave passes through the oil film layer and is reflected at the seal-oil film interface. The probe receives this reflected echo and records its voltage amplitude. This is the measured amplitude.
[0053] S204. Obtain the reflection coefficient of ultrasonic waves at the interface between the sealing ring and the oil film by using reference amplitude and measurement assistance.
[0054] Specifically, according to the principle of ultrasonic reflection, under the same excitation and reception conditions, the interface reflection coefficient is directly proportional to the echo amplitude. Therefore, using the formula... In the formula, The reflection coefficient of the solid-gas interface tends to be 1. The value measured in step S202 is... And measured in step S203 Substitute and take This allows for the direct calculation of the actual acoustic reflection coefficient R at the seal-oil film interface when the current oil film is present.
[0055] S205. The thickness of the oil film is obtained by using the reflection coefficient, the acoustic impedance of the seal, the acoustic impedance of the metal contact pair, the ultrasonic frequency, the density of the oil, and the sound velocity.
[0056] Since the thickness of the oil film layer in the middle is very small compared to the ultrasonic wavelength, it can be used as a reflective layer. When calculating the reflectivity of the oil film layer, the equivalent spring stiffness can be used to replace the reflectivity. That is, the reflection coefficient R is determined by its stiffness K, and can be expressed mathematically as: In the formula, For the acoustic impedance of the seal, Let be the acoustic impedance of the piston rod, which is the product of wave velocity and density. The imaginary unit, ω is the angular frequency of ultrasound. , where f is the ultrasonic frequency.
[0057] Acoustic impedance is the ratio of the pressure of a sound wave on an equiphase surface to the volume velocity passing through that surface, describing the degree to which a medium impedes the sound wave. Since the meaning of volume velocity is ambiguous, particle velocity is usually used instead; that is, the ratio of sound pressure to particle velocity is defined as acoustic impedance, i.e.: In the formula, z is the acoustic impedance at a certain location, and v is the particle velocity at that location; for a plane wave, its acoustic impedance can be written in another form, namely: In the formula Let be the density of the oil film medium, and c be the propagation speed of ultrasonic waves in the oil film. For the same medium, It is a constant that remains unchanged and is called the characteristic impedance of the medium, which can be obtained by looking up a table. If the bulk modulus of a given oil is B, the bulk modulus is the density of the oil. The stiffness coefficient K of the liquid layer is obtained by multiplying the product of the square of the sound velocity c in the oil and the product of ... Combining the above formulas, the mathematical expression for oil film thickness can be obtained as follows:
[0058] In the formula, The oil film thickness to be measured is located between the seal and the piston rod. The density of the oil film layer. The speed at which ultrasound propagates in oil. ω is the angular frequency of the ultrasound. The acoustic impedance of the sealing material, Let R be the acoustic impedance of the piston rod material, and R be the interface reflection coefficient of the seal-oil film interface, which is calculated using step S204. The characteristic impedance of the seal material can be obtained from a material handbook or through experimental calibration. Piston rod material characteristic impedance Oil density and speed of sound The center frequency of the ultrasound wave is determined from the signal emitted by the ultrasound probe. The angular frequency is calculated. The calculated h value is the current monitoring position, such as the instantaneous oil film thickness aligned with the fiber optic stress monitoring point. Combined with the synchronously obtained contact stress, comprehensive monitoring and evaluation of reciprocating dynamic sealing conditions, such as friction and lubrication status, can be achieved, providing reliable data support for accurately predicting seal leakage.
[0059] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. A device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal, comprising a piston cylinder having a piston chamber, and a piston rod extending through the piston chamber; characterized in that, A sealing element is provided between the outer wall of the piston rod and the inner wall of the piston chamber; The piston rod has a positioning hole inside, and the inner wall of the positioning hole is provided with an optical fiber extending in a first direction. The optical fiber is connected to a tunable laser so that the contact stress between the seal and the piston rod can be obtained based on the tunable laser. An ultrasonic probe is also provided in the positioning hole. The ultrasonic probe is aligned with the position of the seal so that the oil film thickness at the seal can be obtained based on the ultrasonic probe.
2. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 1, characterized in that, The inner wall of the positioning hole is provided with a plurality of positioning grooves extending along a first direction, all of which are arranged circumferentially, and the positioning grooves are used to install the optical fiber.
3. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 1, characterized in that, The positioning hole passes through the first end of the piston rod. The ultrasonic probe is connected to a bracket, which passes through the first end of the piston rod. The second end of the piston rod is provided with an earring, which is used to connect to a power mechanism to drive the piston rod to reciprocate along a first direction.
4. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 1, characterized in that, The end of the ultrasonic probe near the seal is an arc-shaped surface that fits the inner wall of the positioning hole.
5. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 1, characterized in that, The piston chamber includes a through hole, and limiting grooves are provided at both ends of the through hole. A set of bushings and end caps located on both sides of the through hole are sleeved on the piston rod. The bushings are located in the limiting grooves, and a portion of the end caps protrudes from the limiting grooves and abuts against the bushings. The bushings are provided with an annular receiving groove, and the receiving groove and the outer wall of the piston rod form a sealing space for receiving a sealing element.
6. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 5, characterized in that, The limiting groove includes a first stepped groove and a second stepped groove arranged in a direction away from the through hole, wherein the inner diameter of the first stepped groove is smaller than the inner diameter of the second stepped groove. The bushing includes a first shaft segment and a second shaft segment. A stepped surface is formed at the connection between the first shaft segment and the second shaft segment. The first shaft segment is located in the first stepped groove. The receiving groove is disposed in the first shaft segment. The portion of the end cap protruding from the limiting groove abuts against the stepped surface.
7. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 6, characterized in that, The end cap has an oil collection groove communicating with the limiting groove, and the end cap has an oil drain port communicating with the oil collection groove. An oil collection cup is detachably installed at the oil drain port.
8. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 7, characterized in that, A first sealing ring is provided between the outer wall of the first shaft segment and the inner wall of the first stepped groove, a second sealing ring is provided between the outer wall of the second shaft segment and the end cover, and a third sealing ring is provided between the piston rod and the end cover. The second sealing ring and the third sealing ring are respectively located on both sides of the oil collection groove along the first direction.
9. The device for simultaneously monitoring the contact stress and oil film thickness of a reciprocating dynamic seal as described in claim 1, characterized in that, The piston cylinder has an oil inlet and an oil return nozzle that communicate with the piston chamber, for providing hydraulic pressure to the piston chamber and recovering oil.
10. A method for simultaneously monitoring reciprocating dynamic seal contact stress and oil film thickness using the apparatus described in any one of claims 1-9, characterized in that, include: The linear sweep beam generated by the tunable laser is split into two optical paths via a coupler; After the first optical path enters the reference arm, it is reflected back to the coupler by the mirror and used as the local oscillator reference light. After the second optical path enters the optical fiber, it is scattered by Rayleigh. The scattered light carries local information of the optical fiber back to the coupler and interferes with the local oscillator reference light. The beat frequency signal is obtained through Fourier transform, and the contact stress is obtained based on the beat frequency signal. The reciprocating dynamic seal structure is simplified into a three-layer medium model, with the middle layer being the oil film to be tested, and the upper and lower layers being the sealing element and the metal contact pair, respectively. When there is no oil film at the seal, the ultrasonic wave is perpendicularly injected into the interface between the seal and the air, and the amplitude of the reflected echo is measured as a reference amplitude. When there is an oil film at the seal, ultrasonic waves are generated at the same position as when the reference amplitude is measured, and the amplitude of the reflected echo at the interface between the sealing ring and the oil film is used as the measurement amplitude. The reflection coefficient of ultrasonic waves at the interface between the sealing ring and the oil film is obtained by referencing the amplitude and using measurement aids. The thickness of the oil film is obtained by using the reflection coefficient, the acoustic impedance of the seal, the acoustic impedance of the metal contact pair, the ultrasonic frequency, the oil density, and the sound velocity.