Capacitive self-sensing sealing device based on magnetorheological fluid

Abstract

The invention discloses a capacitive self-sensing sealing device based on magnetorheological fluid. The capacitive self-sensing sealing device comprises a shaft shell, a rotating shaft, a permanent magnet, a pole shoe unit, a magnetism isolating ring unit, a bearing unit and the magnetorheological fluid. A sealing gap is formed between the pole shoe unit and the rotating shaft, and the magnetorheological fluid is filled in the sealing gap to serve as a dielectric substance; the magnetism isolating ring unit forms a first electrode, a common-ground equipotential body formed by the rotating shaft, the pole shoe unit, the bearing unit and the shaft shell forms a second electrode, and the first electrode, the second electrode and the magnetorheological fluid form a sensing capacitor structure together. The impedance frequency spectrum of the capacitor is monitored in real time through the capacitance measuring circuit, the capacitance value change is analyzed, and the mechanical state change (such as vibration or abrasion) caused by the sealing gap change and the material state change (such as degradation or sealing pressure change) caused by the magnetorheological fluid dielectric constant change can be decoupled and distinguished; online sensing and fault early warning of the sealing state are achieved, and the reliability and the intelligent level of a sealing system are improved.

Description

Technical Field

[0001] This invention relates to a sealing device, specifically a capacitive self-sensing sealing device based on magnetorheological fluid, belonging to the field of magnetorheological sealing technology. Background Technology

[0002] Currently, commonly used rotary shaft seals include packing seals, mechanical seals, labyrinth seals, dry gas seals, and magnetorheological seals.

[0003] Magnetorheological (MR) sealing is a novel sealing technology utilizing magnetorheological fluids. Magnetorheological fluids are intelligent materials composed of magnetic particles, a base fluid, and additives; their viscosity and shear stress can undergo rapid, reversible, and controllable changes under an applied magnetic field. Through magnetic circuit design, MR seals confine the magnetorheological fluid within the sealing gap, forming a dynamic sealing ring. Compared to traditional sealing methods, MR seals offer advantages such as non-contact operation, low wear, long lifespan, simple structure, and controllable sealing performance, demonstrating broad application prospects in the field of rotary seals.

[0004] However, existing magnetorheological sealing technologies mainly focus on improving sealing performance, and their device functions are relatively limited. As a dynamic seal, magnetorheological seals face complex operating conditions during actual equipment operation. For example, prolonged rotational friction may cause the magnetorheological fluid to deteriorate; changes in ambient temperature leading to thermal expansion and contraction can alter the sealing gap; and severe vibrations or impacts on the equipment may cause the sealing components to vibrate or momentarily misalign.

[0005] The aforementioned factors can all lead to unpredictable changes in the sealing gap, thereby reducing the tightness of the seal and even causing sudden leakage. In existing technologies, such as the self-recovering enhanced magnetic fluid sealing device disclosed in CN117052907A, although the sealing stability is enhanced by elastic retaining rings and self-aligning roller bearings, its function is limited and lacks real-time monitoring capabilities for sealing conditions such as gap changes or magnetorheological fluid degradation. Another example is the magnetic fluid lubrication mechanical seal device proposed in CN104390012A, which controls the sealing pressure by adjusting the magnetic field strength to change the viscosity of the magnetorheological fluid, but it lacks an integrated sensing structure and cannot detect online changes in the sealing dielectric constant or gap mechanical properties. Magnetorheological sealing devices typically lack real-time monitoring capabilities for their own operating status. This inability to detect the sealing gap or sealing pressure online makes the sealing system unable to respond promptly to changes in operating conditions, resulting in high risk of sealing failure and insufficient reliability. These existing technologies focus on improving the sealing performance itself, neglecting the need for real-time diagnosis of the sealing status under complex operating conditions (such as vibration, wear, or temperature fluctuations). Specifically, in the long-term operation of traditional magnetorheological sealing devices, the magnetorheological fluid may deteriorate due to particle aggregation or degradation of the base fluid. At the same time, the sealing gap between the rotating shaft and the pole shoe may change due to vibration or thermal expansion and contraction. These factors can lead to the risk of seal failure, but existing devices cannot distinguish the root causes of these changes.

[0006] Therefore, how to integrate online monitoring functions into magnetorheological sealing devices to achieve self-sensing of the sealing status, so as to evaluate sealing performance in real time and provide early warning of potential leakage risks, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a capacitive self-sensing sealing device based on magnetorheological fluid in order to solve the problems of existing magnetorheological sealing devices having limited functions, lacking online real-time monitoring methods, and being unable to sense changes in their own operating conditions.

[0008] The present invention achieves the above objectives through the following technical solution: a capacitive self-sensing sealing device based on magnetorheological fluid, comprising a shaft housing, a rotating shaft rotatably disposed inside the shaft housing, and a sealing assembly sealing between the shaft housing and the rotating shaft. The two ends of the shaft housing are sealed with end cap units, and the sealing assembly is accommodated in the annular space between the shaft housing and the rotating shaft. The sealing assembly includes a permanent magnet, a pole shoe unit, a magnetic isolation ring unit, a bearing unit, and a magnetorheological fluid, all sleeved on the outside of the rotating shaft. The pole shoe unit surrounds the rotating shaft, and a sealed gap is formed between the pole shoe unit and the rotating shaft. The magnetorheological fluid fills the sealed gap to form a dielectric. The magnetic isolation ring unit forms the first electrode of the sealing device. The rotating shaft, pole shoe unit, bearing unit and shaft housing together form a common ground equipotential body to form the second electrode of the sealing device. The first electrode, the second electrode and the magnetorheological fluid form the sensing capacitor structure of the sealing device. The pressure resistance of the magnetorheological fluid seal includes the magnetization pressure generated by the magnetic properties of the magnetorheological fluid and the yield stress generated by the elastoplastic characteristics of the magnetorheological fluid.

[0009] As a further embodiment of the present invention: the end cover unit includes a front cover and a rear cover, the front cover and the rear cover are respectively sealed and fixedly connected to the two ends of the shaft housing by screws, and the rotating shaft is axially limited through the front cover and the rear cover.

[0010] As a further embodiment of the present invention: a permanent magnet is sleeved in the middle of the rotating shaft, and the pole shoe unit includes a first pole shoe and a second pole shoe symmetrically arranged. The first pole shoe and the second pole shoe are respectively located on both sides of the permanent magnet. Annular pole teeth are formed on the inner wall of the first pole shoe and the second pole shoe facing the rotating shaft. The magnetorheological fluid filled in the sealing gap forms a sealing ring structure under the action of the magnetic field, and the number of sealing ring structures depends on the number of annular pole teeth. The first pole shoe, the second pole shoe, the rotating shaft, and the shaft housing are all made of magnetically conductive materials, including but not limited to 2Cr13 stainless steel or electrical pure iron.

[0011] As a further embodiment of the present invention: a first magnetic isolation ring and a second magnetic isolation ring are symmetrically arranged in the magnetic isolation ring unit. The first magnetic isolation ring and the second magnetic isolation ring are respectively arranged on both sides of the permanent magnet. The first magnetic isolation ring and the adjacent first pole shoe, as well as the second magnetic isolation ring and the adjacent second pole shoe, are electrically isolated by an insulating layer. A first O-ring and a second O-ring are also arranged symmetrically inside the shaft housing. The first O-ring is embedded in the outside of the first pole shoe, and the second O-ring is embedded in the outside of the second pole shoe. The first magnetic isolation ring and the second magnetic isolation ring are both made of non-magnetic materials, including but not limited to 304 stainless steel and titanium alloy. The insulating layer is made of an insulating material with high dielectric strength and stable mechanical properties, including but not limited to polyetheretherketone or epoxy resin coating.

[0012] As a further embodiment of the present invention: the bearing unit includes a first bearing and a second bearing located outside the pole shoe unit and arranged symmetrically, the inner rings of the first bearing and the second bearing are both fixedly sleeved on the shaft body of the rotating shaft, and the outer rings of the first bearing and the second bearing are both fixedly clamped on the inner wall of the shaft housing.

[0013] As a further aspect of the present invention, it also includes a capacitance measurement circuit, the two input terminals of which are electrically connected to the first electrode and the second electrode respectively, for real-time monitoring of the capacitance value of the sensing capacitor structure; the capacitance measurement circuit includes a multivibrator circuit, which uses a 555 timer chip to convert the capacitance value of the sensing capacitor structure into a frequency signal output; the capacitance measurement circuit includes an impedance conversion chip for measuring the impedance spectrum of the sensing capacitor structure at multiple frequencies, the impedance conversion chip being an AD5933.

[0014] As a further aspect of the present invention: the impedance conversion chip is connected to an external microcontroller and communicates via an I²C bus. The microcontroller is configured to perform impedance spectrum analysis to decouple the mechanical state changes caused by the change in sealing gap and the material state changes caused by the change in the dielectric constant of the magnetorheological fluid.

[0015] As a further aspect of the present invention: the monitoring of the sealing device by the capacitance measuring circuit includes the following steps: S1. The impedance spectrum of the sensing capacitor structure is measured at multiple different frequencies using a capacitance measurement circuit. S2. Obtain impedance spectrum data; S3. Analyze impedance spectrum data to decouple and distinguish mechanical state changes such as vibration or wear caused by changes in sealing gap, as well as material state changes such as deterioration and sealing pressure caused by changes in the dielectric constant of magnetorheological fluid.

[0016] As a further aspect of the present invention: the capacitance measurement circuit uses the AD5933 impedance conversion chip as the core component, and obtains the complex impedance amplitude and phase through frequency scanning.

[0017] As a further aspect of the present invention: impedance spectrum data is analyzed by the shape of the impedance spectrum curve. The impedance change caused by the change in sealing gap due to mechanical factors exhibits a nearly uniform translation characteristic across the entire spectrum, while the impedance change caused by the change in dielectric constant due to material factors exhibits obvious image distortion.

[0018] The beneficial effects of this invention are: 1) This invention integrates the sensing structure and the sealing structure into a single design, and cleverly utilizes magnetorheological fluid as both the sealing medium and the sensing dielectric. Without significantly increasing the complexity of the device structure, it endows the sealing device with the function of real-time sensing, and solves the technical defects of existing magnetorheological sealing devices that are single in function and lack online monitoring means. 2) This invention can reflect the actual working state of the sealing device in real time and comprehensively. The capacitance value of the sensing capacitor structure constructed by this invention is a function of the dielectric constant of the magnetorheological fluid and the sealing gap. Therefore, by monitoring the capacitance value in real time through the capacitance measurement circuit and analyzing the capacitance value change, it is possible to decouple and distinguish the mechanical state changes (such as vibration or wear) caused by the change of sealing gap and the material state changes (such as deterioration or sealing pressure changes) caused by the change of the dielectric constant of the magnetorheological fluid, and sensitively capture the state changes caused by multiple factors. 3) This invention significantly improves the reliability and intelligence level of the sealing system. Based on real-time monitoring capabilities, this invention can provide early warning of potential leakage risks such as excessive gaps by analyzing capacitance signals; it can also conduct online assessment of the aging and wear status of equipment; at the same time, it provides an effective experimental means for macroscopic analysis of the deterioration mechanism of magnetorheological fluids under complex working conditions. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall cross-sectional structure of the present invention; Figure 2 This is a schematic diagram of the first embodiment of the capacitance measurement circuit; Figure 3 A schematic diagram of a second preferred embodiment of the capacitance measurement circuit; Figure 4 This is a flowchart of a capacitive self-sensing monitoring method. In the figure: 1. Front end cover; 2. First bearing; 3. First magnetic shielding ring; 4. First O-ring; 5. First pole shoe; 6. Second O-ring; 7. Second pole shoe; 8. Rear end cover; 9. Second bearing; 10. Second magnetic shielding ring; 11. Permanent magnet; 12. Shaft housing; 13. Rotating shaft. Detailed Implementation

[0020] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1, as Figure 1As shown, a capacitive self-sensing sealing device based on magnetorheological fluid includes a housing 12, a rotating shaft 13 rotatably disposed inside the housing 12, and a sealing assembly sealing between the housing 12 and the rotating shaft 13. The two ends of the housing 12 are sealed with end cap units, and the sealing assembly is accommodated in the annular space between the housing 12 and the rotating shaft 13. The sealing assembly includes permanent magnets 11, pole shoe units, magnetic isolation ring units, bearing units, and magnetorheological fluid, all sleeved on the outside of the rotating shaft 13. The pole shoe unit surrounds the rotating shaft 13, and a sealed gap is formed between the pole shoe unit and the rotating shaft 13. The magnetorheological fluid fills the sealed gap to form a dielectric. The magnetic isolation ring unit forms the first electrode of the sealing device. The rotating shaft 13, the pole shoe unit, the bearing unit and the shaft housing 12 together form a common ground equipotential body to form the second electrode of the sealing device. The first electrode, the second electrode and the magnetorheological fluid form the sensing capacitor structure of the sealing device.

[0022] By filling the sealing gap between the pole shoe unit and the rotating shaft 13 with magnetorheological fluid to form a dielectric, and using a magnetic isolation ring unit as the first electrode of the sealing device, and a common equipotential body composed of the rotating shaft 13, pole shoe unit, bearing unit, and shaft housing 12 as the second electrode, a sensing capacitor structure is formed. This allows the sealing device to monitor changes in the sealing state in real time. For example, by detecting changes in capacitance value through a capacitance measurement circuit, the change in the dielectric constant of the magnetorheological fluid or the change in the sealing gap can be inferred, thereby achieving online evaluation of sealing performance and fault early warning. This solves the technical defects of existing magnetorheological sealing devices, such as single function and lack of online monitoring means. At the same time, by using magnetorheological fluid as both a sealing medium and a sensing dielectric, real-time self-sensing of the sealing state is achieved, which can sensitively capture changes in operating conditions caused by vibration, wear, magnetorheological fluid deterioration, or changes in sealing pressure.

[0023] Example 2, in addition to all the technical features included in Example 1, also includes: The end cap unit includes a front cover 1 and a rear cover 8. The front cover 1 and the rear cover 8 are sealed and fixedly connected to both ends of the shaft housing 12 by screws, and the rotating shaft 13 is axially limited through the front cover 1 and the rear cover 8. The front cover 1 and the rear cover 8 ensure that the components inside the shaft housing 12 are effectively sealed and fixed, preventing external contaminants from entering and internal magnetorheological fluid from leaking. At the same time, the rotating shaft 13 is axially limited to ensure the stable rotation of the rotating shaft 13.

[0024] The permanent magnet 11 is fitted in the middle of the rotating shaft 13. The pole shoe unit includes a first pole shoe 5 and a second pole shoe 7 arranged symmetrically. The first pole shoe 5 and the second pole shoe 7 are respectively located on both sides of the permanent magnet 11. The first pole shoe 5 and the second pole shoe 7 are provided with annular pole teeth on the inner wall facing the rotating shaft 13. The magnetorheological fluid filled in the sealing gap forms a sealing ring structure under the action of the magnetic field. The number of sealing ring structures depends on the number of annular pole teeth, so that the sealing device can form multiple dynamic sealing rings, improving the sealing performance. It is especially suitable for high pressure or variable working conditions. At the same time, the number and shape of the annular pole teeth can be adjusted according to different application scenarios, enhancing the adaptability and flexibility of the device, thereby ensuring effective sealing under various working conditions.

[0025] The magnetic isolation ring unit includes a first magnetic isolation ring 3 and a second magnetic isolation ring 10 symmetrically arranged on both sides of the permanent magnet 11. The first magnetic isolation ring 3 and the second magnetic isolation ring 10 are respectively disposed on both sides of the permanent magnet 11. The first magnetic isolation ring 3 is electrically isolated from the adjacent first pole shoe 5, and the second pole shoe 7 is electrically isolated from the adjacent second pole shoe 7 through an insulating layer. The shaft housing 12 also contains a first O-ring 4 and a second O-ring 6 symmetrically arranged. The first O-ring 4 is embedded in the outside of the first pole shoe 5, and the second O-ring 6 is embedded in the outside of the second pole shoe 7, so that the first electrode and the second electrode are completely electrically isolated, ensuring the accurate measurement of the sensing capacitance structure and avoiding signal interference or short circuit. At the same time, the first O-ring 4 and the second O-ring 6 provide a reliable static seal to prevent the magnetorheological fluid from leaking from the pole shoe and the shaft housing 12, thereby improving the sealing performance of the entire sealing device and the stability of the sensing signal.

[0026] The bearing unit includes a first bearing 2 and a second bearing 9 located symmetrically arranged outside the pole shoe unit. The inner rings of the first bearing 2 and the second bearing 9 are fixedly sleeved on the shaft body of the rotating shaft 13, and the outer rings of the first bearing 2 and the second bearing 9 are fixedly clamped on the inner wall of the shaft housing 12, so that the rotating shaft 13 is effectively supported and positioned radially, ensuring the stable rotation of the rotating shaft 13 inside the shaft housing 12, reducing the change in sealing gap caused by vibration or eccentricity, thereby reducing wear and energy loss.

[0027] The first magnetic isolation ring 3 and the second magnetic isolation ring 10 are both made of non-magnetic materials, including but not limited to 304 stainless steel and titanium alloy. This ensures that the magnetic isolation ring unit does not interfere with the magnetic field distribution in the magnetic circuit. At the same time, due to its conductivity, it can effectively serve as the first electrode of the sensing capacitor structure, ensuring accurate acquisition of the capacitor signal. The non-magnetic material avoids magnetic short circuits and maintains the magnetic field strength required for the sealing of the magnetorheological fluid, thereby improving the sealing performance and sensing reliability.

[0028] The first pole shoe 5, the second pole shoe 7, the rotating shaft 13, and the shaft housing 12 are all made of magnetically conductive materials, including but not limited to 2Cr13 stainless steel or electrical pure iron, which enables the magnetic circuit to efficiently conduct magnetic flux. The magnetic field generated by the permanent magnet 11 is concentrated on the magnetorheological fluid in the sealing gap through the magnetically conductive materials, which enhances the curing effect of the magnetorheological fluid and forms a more stable sealing ring structure, thereby improving the pressure resistance and sealing performance of the sealing device.

[0029] The insulation layer is made of insulating materials with high dielectric strength and stable mechanical properties, including but not limited to polyetheretherketone or epoxy resin coatings.

[0030] The pressure resistance of magnetorheological fluid seals includes the magnetization pressure generated by the magnetic properties of the magnetorheological fluid and the yield stress generated by the elastoplastic characteristics of the magnetorheological fluid.

[0031] Example 3, as Figures 2 to 4 As shown, a capacitive self-sensing sealing device based on magnetorheological fluid is disclosed. The device also includes a capacitance measurement circuit, the two input terminals of which are electrically connected to the first electrode and the second electrode, respectively, for real-time monitoring of the capacitance value of the sensing capacitor structure.

[0032] The capacitance measurement circuit uses a 555 timer chip to construct a multivibrator circuit to measure the capacitance value. Convert to frequency signal Output.

[0033] The circuit connection method involves using the second magnetic isolation ring 10 as the first electrode, the common ground body as the second electrode, and the magnetorheological fluid as the dielectric in the constructed sensing capacitor. The resulting capacitor serves as the main timing capacitor in this circuit. Connection. Specifically, the first electrode is connected to the Thres pin and the Trig pin of the 555 timer U1. The second electrode is connected to pin 1 of the circuit, i.e., GND.

[0034] After the circuit is started, the sensing capacitor The capacitor is charged through resistors R2 and R1 until the voltage reaches its maximum value; subsequently, the capacitor... Discharge is supplied to discharge pin 7 through resistor R1 until the voltage drops to its minimum value. This process repeats continuously, generating a continuous square wave signal at the output pin. The oscillation frequency of this square wave signal... With timing capacitor The capacitance is strictly inversely proportional to the frequency, which can be approximated as: ; When the sealing conditions change, it will cause changes in the sensing capacitance. Changes in capacitance cause a corresponding change in the oscillation frequency. The frequency is measured at the COMA and COMB ports using a microprocessor. The real-time value can be used to deduce the change in the sensing capacitance, thus enabling online monitoring of the sealing status.

[0035] Example 4 is a preferred embodiment of the capacitance measurement circuit in Example 3. Since in reality, factors causing changes in the target sensor capacitance include mechanical factors, and in Example 2, coupling occurred, making it difficult to distinguish the specific cause of the change, an optimized solution is adopted. This solution uses impedance spectrum analysis technology to achieve precise decoupling monitoring of the sealed state. The circuit system of this embodiment is based on a high-precision impedance converter chip AD5933, and is controlled by an external microcontroller. The AD5933 integrates a frequency generator (DDS), a 12-bit analog-to-digital converter (ADC), and a digital signal processing (DSP) core. The MCU is connected to pins 16 (SCL) and 15 (SDA) of the AD5933 via an I²C serial bus to send control commands and read data. The excitation signal output pin VOUT of the AD5933 is connected to an external circuit amplifier, i.e., an external amplifier, whose low-impedance output terminal is connected to the sensing capacitance of this invention. First electrode The second electrode of the sensing capacitor Connect to the signal measurement input pin VIN of the AD5933. A high-precision external feedback resistor R6 is connected between pin 4 RFB and pin 5 VIN to set the gain of the internal current-voltage amplifier.

[0036] The workflow of this embodiment is as follows: Figure 4 First, the MCU programs the AD5933's frequency scan parameters via the I²C bus, including the starting frequency, frequency increment, and number of increment points. Then, the MCU issues a command to start the frequency scan. At each frequency point during the scan, the AD5933's DDS core generates an excitation signal to stimulate the sensor. The sensor's response signal is sampled by the ADC, and the on-chip DSP performs a 1024-point Discrete Fourier Transform (DFT) on it, satisfying... ; In the formula, It is the signal at the frequency point energy, It's the output of the ADC. and The frequency point is provided by the DDS kernel. The sampling test vector.

[0037] The product values ​​corresponding to 1024 samples at each frequency point are accumulated, and the result is stored in two 16-bit registers, representing the real part and the imaginary part of the result, respectively.

[0038] The MCU performs impedance calculations off-chip. First, the MCU calculates the system gain coefficient using a known calibration impedance, satisfying: ; In the formula, the amplitude is determined by the result stored in the register.

[0039] Subsequently, the MCU uses this gain coefficient to calculate the complex impedance amplitude and phase of the sensing capacitor at each frequency point. The unknown impedance satisfies: ; Phase full of unknown impedance: ； In the formula, It is the system phase measured by connecting a calibration resistor between VIN and VOUT; It is the system phase measured by connecting an unknown impedance between VIN and VOUT; It is the phase caused by the impedance, that is, the impedance phase.

[0040] Through the above iterative scanning, this embodiment obtained a complete impedance spectrum curve. The decoupling principle of this invention is based on the analysis of this spectrum morphology, where mechanical factors cause sealing gaps. The impedance change caused by the change exhibits a nearly uniform translation characteristic across the entire spectrum; while the dielectric constant caused by material factors... The impedance changes caused by the changes exhibit obvious image distortion. Therefore, this embodiment successfully decouples the effects of mechanical and material changes on the total capacitance through multi-frequency impedance spectrum analysis, and realizes high-precision, multi-dimensional self-sensing monitoring of the sealing state.

[0041] During operation, the device generates a constant magnetic field through the permanent magnet 11. This magnetic field forms a closed magnetic circuit via the first pole piece 5, the second pole piece 7, the rotating shaft 13, and the shaft housing 12, all made of magnetically conductive material. Magnetic lines of force concentrate through the sealed gap formed between the pole piece units and the rotating shaft 13. This causes the magnetorheological fluid filling this gap to undergo a rheological effect under the influence of the magnetic field, resulting in the chaining of internal magnetic particles to form a solid or semi-solid structure with high shear yield strength. This constructs a series of dynamic, O-ring-like sealing ring structures within the sealed gap, effectively preventing leakage of the sealed medium and achieving non-contact active sealing. Simultaneously, the device integrates a self-sensing function. Its core lies in using the same magnetorheological fluid as the sensing dielectric, which, together with the magnetically shielding ring unit as the first electrode and the common-ground equipotential body as the second electrode, constitutes a unique sensing capacitor structure. The capacitance value of this sensing capacitor structure is determined by the dielectric constant of the magnetorheological fluid and the geometric dimensions of the sealed gap. By using an external capacitance measurement circuit, such as one employing the AD5933 impedance conversion chip, the impedance spectrum of the capacitor can be monitored in real time. When the sealing conditions change, such as changes in the sealing gap due to vibration or wear, or changes in the dielectric constant of the magnetorheological fluid due to temperature, pressure, or material degradation, the capacitance value or frequency response characteristics of the sensing capacitor will change accordingly. By analyzing these capacitance signals, especially the impedance spectrum at multiple frequencies, the state changes from different sources can be effectively decoupled and distinguished: gap changes caused by purely mechanical factors usually lead to an overall shift in the impedance spectrum, while changes in the dielectric constant caused by changes in material properties lead to distortion of the impedance spectrum morphology.

[0042] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0043] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A capacitive self-sensing sealing device based on magnetorheological fluid, comprising a shaft housing (12), a rotating shaft (13) rotatably disposed inside the shaft housing (12), and a sealing assembly sealing between the shaft housing (12) and the rotating shaft (13), characterized in that: The two ends of the shaft housing (12) are sealed with end cap units. The sealing assembly is housed in the annular space between the shaft housing (12) and the rotating shaft (13). The sealing assembly includes a permanent magnet (11) sleeved on the outside of the rotating shaft (13), a pole shoe unit, a magnetic isolation ring unit, a bearing unit, and a magnetorheological fluid. The pole shoe unit surrounds the rotating shaft (13), and a sealing gap is formed between the pole shoe unit and the rotating shaft (13). The magnetorheological fluid fills the sealing gap to form a dielectric. The magnetic isolation ring unit forms the first electrode of the sealing device. The rotating shaft (13), the pole shoe unit, the bearing unit and the shaft housing (12) together form the common ground equipotential body to form the second electrode of the sealing device. The first electrode, the second electrode and the magnetorheological fluid form the sensing capacitor structure of the sealing device. The pressure resistance of the magnetorheological fluid seal includes the magnetization pressure generated by the magnetic properties of the magnetorheological fluid and the yield stress generated by the elastoplastic characteristics of the magnetorheological fluid.

2. The capacitive self-sensing sealing device according to claim 1, characterized in that: The end cap unit includes a front end cap (1) and a rear end cap (8). The front end cap (1) and the rear end cap (8) are sealed and fixedly connected to both ends of the shaft housing (12) by screws, and the rotating shaft (13) is axially limited through the front end cap (1) and the rear end cap (8).

3. The capacitive self-sensing sealing device according to claim 1, characterized in that: The permanent magnet (11) is sleeved in the middle part of the rotating shaft (13). The pole shoe unit includes a first pole shoe (5) and a second pole shoe (7) arranged symmetrically. The first pole shoe (5) and the second pole shoe (7) are respectively located on both sides of the permanent magnet (11). The first pole shoe (5) and the second pole shoe (7) are provided with annular pole teeth on the inner wall facing the rotating shaft (13). The magnetorheological fluid filled in the sealing gap forms a sealing ring structure under the action of the magnetic field. The number of sealing ring structures depends on the number of annular pole teeth. The first pole shoe (5), the second pole shoe (7), the rotating shaft (13) and the shaft shell (12) are all made of magnetically conductive materials. The magnetically conductive materials include, but are not limited to, 2Cr13 stainless steel or electrical pure iron.

4. The capacitive self-sensing sealing device according to claim 3, characterized in that: The magnetic isolation ring unit is symmetrically arranged with a first magnetic isolation ring (3) and a second magnetic isolation ring (10). The first magnetic isolation ring (3) and the second magnetic isolation ring (10) are respectively arranged on both sides of the permanent magnet (11). The first magnetic isolation ring (3) and the adjacent first pole shoe (5) and the second magnetic isolation ring (10) and the adjacent second pole shoe (7) are electrically isolated by an insulating layer. The shaft housing (12) is also provided with a first O-ring (4) and a second O-ring (6) arranged symmetrically. The first O-ring (4) is embedded in the outside of the first pole shoe (5), and the second O-ring (6) is embedded in the outside of the second pole shoe (7). The first magnetic isolation ring (3) and the second magnetic isolation ring (10) are both made of non-magnetic materials, including but not limited to 304 stainless steel and titanium alloy. The insulating layer is made of an insulating material with high dielectric strength and stable mechanical properties, including but not limited to polyether ether ketone or epoxy resin coating.

5. The capacitive self-sensing sealing device according to claim 1, characterized in that: The bearing unit includes a first bearing (2) and a second bearing (9) located outside the pole shoe unit and arranged symmetrically. The inner rings of the first bearing (2) and the second bearing (9) are fixedly sleeved on the shaft body of the rotating shaft (13), and the outer rings of the first bearing (2) and the second bearing (9) are fixedly clamped on the inner wall of the shaft housing (12).

6. The capacitive self-sensing sealing device according to claim 1, characterized in that: It also includes a capacitance measurement circuit, whose two input terminals are electrically connected to the first electrode and the second electrode, respectively, for real-time monitoring of the capacitance value of the sensing capacitor structure; the capacitance measurement circuit includes a multivibrator circuit, which uses a 555 timer chip to convert the capacitance value of the sensing capacitor structure into a frequency signal output; the capacitance measurement circuit includes an impedance conversion chip, namely AD5933, for measuring the impedance spectrum of the sensing capacitor structure at multiple frequencies.

7. The capacitive self-sensing sealing device according to claim 6, characterized in that: The impedance conversion chip is connected to an external microcontroller and communicates via an I²C bus. The microcontroller is configured to perform impedance spectrum analysis to decouple the mechanical state changes caused by the change in sealing gap and the material state changes caused by the change in the dielectric constant of the magnetorheological fluid.

8. The capacitive self-sensing sealing device according to claim 7, characterized in that: The capacitance measurement circuit monitors the sealing device through the following steps: S1. The impedance spectrum of the sensing capacitor structure is measured at multiple different frequencies using a capacitance measurement circuit. S2. Obtain impedance spectrum data; S3. Analyze impedance spectrum data to decouple and distinguish mechanical state changes such as vibration or wear caused by changes in sealing gap, as well as material state changes such as deterioration and sealing pressure caused by changes in the dielectric constant of magnetorheological fluid.

9. The capacitive self-sensing sealing device according to claim 8, characterized in that: The capacitance measurement circuit uses the AD5933 impedance conversion chip as the core component and obtains the complex impedance amplitude and phase through frequency scanning.

10. The capacitive self-sensing sealing device according to claim 8, characterized in that: Impedance spectrum data were analyzed by morphological analysis of the impedance spectrum curves. The impedance change caused by the change in sealing gap due to mechanical factors showed a nearly uniform translation characteristic across the entire spectrum, while the impedance change caused by the change in dielectric constant due to material factors showed obvious image distortion.

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