Method for measuring lift of valve core of oil injector

Abstract

The invention relates to the technical field of oil injector detection, and provides a measurement method based on optical fiber Fabry-Perot (F-P) interference and spectrum demodulation aiming at the defects that existing valve element lift measurement easily interferes with movement of a valve element, and is weak in pollution / temperature resistance and poor in adaptability in a narrow space. The method comprises the following steps: constructing a measurement system comprising a narrow linewidth laser and a miniature F-P sensing unit, and obtaining a displacement-spectrum model and a temperature correction matrix through calibration of a standard displacement table; a sensing unit is installed on the oil injector, interference spectrum and temperature signals are collected in real time, and after wavelet denoising, Gaussian fitting and temperature compensation are carried out, the signals are substituted into the model to calculate the lift of the valve element; non-contact measurement is achieved, the precision is smaller than or equal to + / -0.1 mu m, oil contamination / electromagnetic interference is resisted, the device is suitable for a narrow space and high-speed dynamic movement of the valve element, and the high-precision requirements for research and development, production calibration and fault diagnosis of a high-end oil injector are met.

Description

Technical Field

[0001] This invention relates to the field of fuel injector testing technology, and in particular to a method for measuring the lift of a fuel injector valve core. Background Technology

[0002] As a core component of the internal combustion engine's fuel supply system, the precise control of the injector's valve lift directly determines the fuel injection quantity, injection timing, and atomization effect, thus affecting the engine's power, economy, and emissions performance. Therefore, high-precision measurement of the valve lift is a crucial step in injector research and development, production calibration, and fault diagnosis.

[0003] Existing methods for measuring injector valve core lift are mainly divided into two categories: contact and non-contact. Contact measurement (such as dial indicator or displacement sensor contact measurement) has the drawbacks of easily wearing down the valve core surface, interfering with the valve core movement, and being unable to adapt to high-speed dynamic measurement. In non-contact measurement, laser displacement measurement is limited by the small space inside the injector and is easily affected by oil and mist, which can lead to measurement failure. Capacitive displacement measurement has strict requirements for installation clearance and is easily affected by electromagnetic interference, which can affect accuracy.

[0004] While fiber optic sensing technology has been applied to some precision measurement scenarios, there is still no mature measurement solution for the special operating conditions of fuel injector valve lift (confined space, high-speed reciprocating motion, oily environment, micron-level displacement). In particular, there is a lack of a measurement method that can simultaneously achieve non-contact, high precision, anti-interference, and miniaturized adaptability, failing to meet the stringent requirements of high-end fuel injectors for lift measurement. Therefore, developing a reasonable and feasible valve lift measurement method adapted to the special operating conditions of fuel injectors has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method for measuring the lift of an injector valve core to solve the above problems.

[0006] The technical solution of this invention is implemented as follows: A method for measuring the lift of an injector valve core includes the following steps: Step 1: Construct a fiber optic Fabry-Perot (FP) interferometry system. The system includes a narrow-linewidth laser, a fiber optic beam splitter, a miniature fiber optic FP sensing unit, a spectrometer, a temperature sensor, and a data processing unit. The miniature fiber optic FP sensing unit consists of a fiber optic probe fixed in a pre-set mounting hole in the injector housing and a valve core end face forming a closed FP interferometer cavity. The temperature sensor is attached to the injector housing near the FP interferometer cavity. Step 2: System calibration. Fix the fiber optic probe to the standard displacement stage. Use the valve core simulation component as the other reflecting surface of the FP interferometer cavity to obtain the interference spectrum signal under different displacement values. Extract the peak wavelength of the spectrum and calculate the spectral drift. Based on the FP interferometer principle, derive and correct the displacement-spectral drift correspondence model. Simultaneously collect calibration data at different temperatures to construct the temperature correction coefficient matrix. Step 3: Install the calibrated miniature fiber optic FP sensing unit onto the oil injector to be measured, adjust the position of the fiber optic probe so that the initial cavity length of the FP interferometer cavity is within the preset range, start the narrow linewidth laser and initialize the system parameters; Step 4: Start the fuel injector. The reciprocating motion of the valve core causes the length of the FP interference cavity to change. The spectrometer collects the interference spectrum signal in real time, and the temperature sensor collects the ambient temperature signal simultaneously. Step 5: The data processing unit preprocesses the interference spectrum signal, calculates the spectral drift, and performs temperature compensation through the temperature correction coefficient matrix. The compensated spectral drift is then substituted into the displacement-spectral drift correspondence model to obtain the real-time valve core lift and output the measurement data.

[0007] Preferably, the narrow linewidth laser in step 1 has a linewidth ≤ 0.1 nm, an output wavelength of 1550 nm, an optical fiber probe diameter ≤ 0.5 mm and an antireflection coating after polishing the end face, and a wavelength resolution of ≤ 0.01 nm for the spectrometer.

[0008] Preferably, the mounting hole in step 1 is processed by laser drilling, and the axis of the mounting hole is coaxial with the axis of the valve core; The initial cavity length of the FP interference cavity in step 3 is in the range of 50-100μm, which can ensure that the signal-to-noise ratio of the interference signal is ≥30dB.

[0009] Preferably, the standard displacement stage in step 2 is a high-precision piezoelectric displacement stage with a displacement accuracy ≤ ±0.05μm; The temperature correction coefficient matrix is ​​constructed in the range of -40℃ to 120℃ and is used to compensate for the effect of temperature on the refractive index of optical fiber and the cavity length of FP interferometer.

[0010] Preferably, the acquisition frequency of the spectrometer in step 4 is ≥1kHz to meet the dynamic measurement requirements of the high-speed movement of the valve core; The temperature sensor is a platinum resistance temperature sensor with an accuracy of ±0.1℃ and a distance of ≤5mm between it and the FP interferometer cavity.

[0011] Preferably, the preprocessing in step 5 includes using a wavelet threshold denoising algorithm to eliminate the interference of oil stains and vibrations on the spectral signal, and using a Gaussian fitting algorithm to extract the peak wavelength of the spectrum. The wavelet basis of the wavelet threshold denoising algorithm is db4, and the threshold is set to 0.01.

[0012] Preferably, the medium inside the FP interference cavity in step 1 is air, and the refractive index of the medium is n≈1; The theoretical basis formula for the displacement-spectral drift model described in step 2 is: ,in Initial displacement The peak wavelength of the spectrum at that time This represents the spectral peak shift. This represents the free spectral range of the interference spectrum.

[0013] Preferably, the displacement-spectral drift correspondence model in step 5 is as follows: ,in This is the sensitivity coefficient. This is the system zero drift correction value. This represents the spectral shift after temperature compensation. The data processing unit is equipped with LabVIEW data processing software, and the output parameters include the dynamic change curve of valve core lift, maximum lift value, minimum lift value and response time.

[0014] Preferably, the fiber optic beam splitter in step 1 is a 2×2 type with a splitting ratio of 1:1; The output power of the narrow linewidth laser is adjusted to 5-10mW to ensure that the spectrometer acquires a stable interference spectral signal.

[0015] Preferably, the fiber optic probe in step 3 is fixed in the mounting hole using a high-temperature resistant adhesive; The error of multiple measurements in step 5 is ≤ ±0.1μm, which meets the high-precision measurement requirements of high-end injector valve core lift.

[0016] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: I. The innovative measurement scheme combines fiber optic FP interferometry with spectral demodulation. This is a niche but reasonable application of precision measurement technology. It avoids the wear and interference to the valve core caused by traditional contact measurement and overcomes the measurement defects of laser and capacitance measurement in confined spaces and oily environments. It is suitable for the special working conditions of fuel injectors. II. High measurement accuracy: Through a narrow linewidth laser, a high-resolution spectrometer, and a temperature compensation algorithm, the valve core lift is measured at the micrometer level (error ≤ ±0.1μm), meeting the high-precision detection requirements of high-end fuel injectors; 3. Strong dynamic response capability: The spectral acquisition frequency is ≥1kHz, which can capture the lift change of the valve core in real time during high-speed reciprocating motion, and is suitable for dynamic performance testing of fuel injectors. IV. Strong anti-interference capability: The 1550nm wavelength laser is resistant to oil and fog interference, and the fiber optic sensing unit is not affected by electromagnetic interference, resulting in high measurement stability. V. Compact structure and good adaptability: The micro fiber optic probe has a diameter of ≤0.5mm and can be installed in the narrow space inside the injector through laser drilling. It does not require major modifications to the injector structure and is easy to apply in industrial applications.

[0017] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the fiber optic FP interferometric measurement system architecture of the present invention; Figure 2 This is a flowchart illustrating the overall workflow of the present invention; Figure 3 This is a flowchart of the system calibration sub-process of the present invention; Figure 4 This is a diagram illustrating the core data processing steps of the present invention. Detailed Implementation

[0020] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0021] It is important to note that terms such as "first," "second," "symmetric," and "array" are used only to distinguish between descriptive and positional descriptions and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features specified with terms such as "first" or "symmetric" may explicitly or implicitly include one or more of that feature; similarly, when the quantity of certain features is not limited by words such as "two" or "three," it should be noted that such features also explicitly or implicitly include one or more features. In this invention, unless otherwise explicitly specified and limited, terms such as "installation," "connection," and "fixation" should be interpreted broadly; for example, they can refer to a fixed connection, a detachable connection, or an integral molding; they can refer to a mechanical connection, a direct connection, a welding connection, or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the accompanying drawings and specific circumstances.

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0023] like Figure 1-4 As shown, the present invention provides a method for measuring the lift of an injector valve core, comprising the following steps: Step 1: Construct a fiber optic Fabry-Perot (FP) interferometry system. A narrow-linewidth laser is chosen as the light source due to its strong monochromaticity, which reduces stray light interference and improves the stability of the interference signal. The system includes a narrow-linewidth laser, a fiber beam splitter, a miniature fiber optic FP sensing unit, a spectrometer, a temperature sensor, and a data processing unit. The fiber beam splitter splits the laser into probe and reference beams, providing a dual-path foundation for interference signal formation. The miniature fiber optic FP sensing unit consists of a fiber probe fixed in a pre-drilled mounting hole in the injector housing, forming a closed FP interference cavity with the valve core end face. This "fiber probe + valve core end face" cavity design eliminates the need for additional reflective components, simplifying the sensing unit structure and fitting the compact internal space of the injector. The temperature sensor is attached to the injector housing near the FP interference cavity; this close proximity allows for more accurate capture of cavity temperature changes, improving the accuracy of temperature compensation.

[0024] Step 2: System calibration. Fix the fiber optic probe to the standard displacement stage. Use the valve core simulator as the other reflecting surface of the FP interferometer cavity. The advantage of using the valve core simulator is that it can simulate the end face characteristics of the actual valve core, avoiding wear caused by directly using the valve core under test. Obtain the interference spectrum signal at different displacement values, extract the peak wavelength of the spectrum and calculate the spectral drift. Based on the FP interferometry principle, derive and correct the displacement-spectral drift correspondence model. The advantage of correcting the model is that it can offset the inherent error of the system hardware and improve the accuracy of displacement conversion. Simultaneously collect calibration data at different temperatures to construct a temperature correction coefficient matrix. The advantage of simultaneously collecting temperature change data is that it allows subsequent measurements to adapt to temperature fluctuations under different operating conditions, expanding the applicability of the method.

[0025] Step 3: Install the calibrated miniature fiber optic FP sensing unit onto the oil injector to be measured, and adjust the position of the fiber optic probe so that the initial cavity length of the FP interferometer is within the preset range. The benefit of adjusting the initial cavity length is to ensure that the interference signal is in the optimal response range and to avoid signal distortion caused by the cavity length being too short / too long. Start the narrow linewidth laser and initialize the system parameters. The benefit of initializing the parameters is to unify the system reference and reduce the error between different measurement batches.

[0026] Step 4: Start the fuel injector. The reciprocating motion of the valve core causes the length of the FP interference cavity to change. The advantage of the cavity length changing synchronously with the valve core movement is that it enables dynamic real-time tracking of the valve core lift. The spectrometer collects interference spectrum signals in real time, and the temperature sensor collects ambient temperature signals simultaneously. The advantage of collecting dual signals simultaneously is that it provides real-time data support for subsequent temperature compensation, ensuring that the accuracy of the data is not affected by temperature changes.

[0027] Step 5: The data processing unit preprocesses the interference spectrum signal. The benefit of preprocessing is to filter out noise interference and improve the purity of the spectral signal. After calculating the spectral drift, temperature compensation is performed using a temperature correction coefficient matrix. The benefit of temperature compensation is to eliminate the influence of temperature on the refractive index and cavity length of the optical fiber, ensuring the consistency of measurement results under different temperature conditions. The compensated spectral drift is substituted into the displacement-spectral drift correspondence model to obtain the real-time valve core lift and output the measurement data. The benefit of outputting multi-dimensional measurement data is to provide a comprehensive quantitative basis for injector performance analysis.

[0028] The narrow linewidth laser mentioned in step 1 has a linewidth ≤ 0.1 nm and an output wavelength of 1550 nm. The advantage of a linewidth ≤ 0.1 nm is to ensure the monochromaticity of the laser and reduce the broadening and blurring of interference fringes. The advantage of choosing a wavelength of 1550nm is that this band has low transmission loss in optical fiber, which can improve signal strength. The fiber optic probe has a diameter ≤0.5mm and its end face is polished and coated with an anti-reflection film. The advantage of a diameter ≤0.5mm is that it can fit the compact installation space of the oil injector and avoid interference with other components. The benefits of end-face polishing and anti-reflection coating are to reduce light reflection loss and increase the optical power entering the interference cavity; The wavelength resolution of the spectrometer is ≤0.01nm. The advantage of a wavelength resolution of ≤0.01nm is that it can accurately capture spectral drift and improve the accuracy of displacement measurement. The mounting hole described in step 1 is processed using laser drilling technology, and the axis of the mounting hole is coaxial with the axis of the valve core. The advantage of using laser drilling technology is that it has high processing accuracy and can ensure the dimensional consistency of the mounting hole. The advantage of coaxiality is that it ensures that the fiber optic probe is parallel to the end face of the valve core and avoids signal errors caused by the tilt of the interference cavity. The initial cavity length of the FP interferometer cavity in step 3 is in the range of 50-100μm. This range can ensure that the signal-to-noise ratio of the interference signal is ≥30dB. The advantage of setting the initial cavity length to 50-100μm is to balance the intensity and resolution of the interference signal. The advantage of a signal-to-noise ratio of ≥30dB is to make the signal clearly distinguishable and reduce measurement errors caused by noise. The standard displacement stage mentioned in step 2 is a high-precision piezoelectric displacement stage with a displacement accuracy of ≤ ±0.05μm. The advantage of using a piezoelectric displacement stage is that it has high displacement control accuracy and fast response. The advantage of a displacement accuracy of ≤±0.05μm is that it provides a precise displacement reference for calibrating the model, thereby improving the reliability of the model. The temperature correction coefficient matrix is ​​constructed in the range of -40℃ to 120℃ to compensate for the influence of temperature on the refractive index of the optical fiber and the cavity length of the FP interferometer. The advantage of covering the temperature range of -40℃ to 120℃ is that it is compatible with the entire working range of the fuel injector from low temperature cold start to high temperature conditions, so that the measurement method can maintain accuracy in various environments.

[0029] The acquisition frequency of the spectrometer mentioned in step 4 is ≥1kHz to meet the dynamic measurement requirements of the high-speed movement of the valve core. The advantage of the acquisition frequency being ≥1kHz is that it can capture the instantaneous state of the high-speed reciprocating motion of the valve core, avoid data loss during the movement, and realize complete monitoring of the dynamic lift. The temperature sensor is a platinum resistance temperature sensor with an accuracy of ±0.1℃ and a distance of ≤5mm from the FP interferometer cavity. The advantage of choosing a platinum resistance temperature sensor is that it has high temperature measurement accuracy and good stability. The advantage of a spacing of ≤5mm is that it shortens the temperature conduction delay and improves the real-time performance of temperature change acquisition. The preprocessing described in step 5 includes using a wavelet threshold denoising algorithm to eliminate the interference of oil stains and vibrations on the spectral signal, and using a Gaussian fitting algorithm to extract the peak wavelength of the spectrum. The advantage of using wavelet threshold denoising is that it can specifically filter out random noise caused by oil stains and vibrations, while retaining the effective components of the signal. The advantage of using Gaussian fitting is that it can accurately extract spectral peaks and reduce peak location errors. The wavelet basis of the wavelet threshold denoising algorithm is db4, and the threshold is set to 0.01. The advantage of choosing the db4 wavelet basis is that it has good time-frequency localization characteristics and is suitable for processing non-stationary spectral signals. Setting the threshold to 0.01 has the advantage of balancing the denoising effect and signal fidelity, and avoiding excessive denoising that could lead to the loss of useful information.

[0030] The medium inside the FP interferometer cavity in step 1 is air, with a refractive index n≈1. The advantage of choosing air as the medium is that no additional filling material is needed, simplifying the cavity structure. At the same time, the refractive index of air is stable (at room temperature and pressure), reducing the additional influence of the medium on the interference. The theoretical basis formula for the displacement-spectral drift model described in step 2 is: ,in Initial displacement The peak wavelength of the spectrum at that time This represents the spectral peak shift. The free spectral range of the interference spectrum is defined by this theoretical formula. The advantage of this formula is that it relies on the mature FP interference principle, ensuring the theoretical reliability of the model and reducing the uncertainty of empirical fitting. The displacement-spectral drift model described in step 5 is as follows: Where k is the sensitivity coefficient and b is the system zero-drift correction value. The advantage of using a linear correction model for the spectral shift after temperature compensation is that it is easy to calculate, has strong real-time performance, and is suitable for rapid processing of dynamic data. The data processing unit is equipped with LabVIEW data processing software. The output parameters include the dynamic change curve of valve core lift, maximum lift value, minimum lift value and response time. The advantage of using LabVIEW is that the graphical programming interface facilitates data visualization and real-time processing. The advantage of outputting multi-dimensional parameters is that it provides comprehensive quantitative indicators for the dynamic performance evaluation of the injector; the fiber optic beam splitter mentioned in step 1 is a 2×2 type with a splitting ratio of 1:1. The advantage of selecting a 2×2 type beam splitter is to achieve equal power distribution between the two optical paths, and the advantage of a splitting ratio of 1:1 is to match the power of the probe light with that of the reference light, thereby improving the contrast of the interference fringes. The output power of the narrow linewidth laser is adjusted to 5-10mW to ensure that the spectrometer can acquire a stable interference spectrum signal. The advantage of adjusting the power to 5-10mW is that it ensures that the optical power is sufficient to support stable signal acquisition, while avoiding excessive power that may cause the device to overheat or the signal to saturate. The fiber optic probe described in step 3 is fixed in the mounting hole with a high-temperature resistant adhesive. The advantage of using a high-temperature resistant adhesive is that it is suitable for the high-temperature environment when the fuel injector is working, avoids the failure of the adhesive that would cause the probe to loosen, and improves the reliability of the measurement system. The error of multiple measurements in step 5 is ≤ ±0.1μm, which meets the high-precision measurement requirements of high-end injector valve core lift. The advantage of an error of ≤ ±0.1μm is that it meets the measurement accuracy standard of high-end injectors and can support the research and development and quality testing of high-precision injectors.

[0031] In this embodiment, the present invention operates as follows: The first step is system setup and preparation: From the precision equipment library, a narrow-linewidth laser with a linewidth ≤0.1nm and an output wavelength of 1550nm, a 2×2 type fiber optic beam splitter with a splitting ratio of 1:1, a fiber optic probe with a diameter ≤0.5mm and an anti-reflection coating of 1550nm on its end face, a spectrometer with a wavelength resolution ≤0.01nm, a platinum resistance temperature sensor with an accuracy of ±0.1℃, and a data processing unit equipped with LabVIEW software are selected and assembled into a fiber optic FP interferometry system. Simultaneously, a high-precision piezoelectric displacement stage with a displacement accuracy ≤±0.05μm and a valve core simulation component are prepared as calibration reference components. The target injector housing is machined with mounting holes using laser drilling technology to ensure that the axis of the mounting holes is completely coaxial with the axis of the valve core.

[0032] The subsequent system calibration phase involved fixing the fiber optic probe to a piezoelectric displacement stage, using the valve core simulator as the other reflecting surface of the FP interference cavity, and gradually moving the displacement stage axially from 0 μm to 500 μm, stopping at 10 μm intervals and acquiring the corresponding interference spectrum signals; the peak wavelengths of the spectrum at each displacement value were extracted, and the spectral shift was calculated. Based on the FP interferometry theory formula ( The displacement-spectral drift correspondence model was obtained by fitting experimental data. Simultaneously, within the temperature range of -40℃ to 120℃, a set of calibration data is collected every 10℃ to construct a temperature correction coefficient matrix K(T), which is used to compensate for the influence of temperature on the refractive index and cavity length of the optical fiber.

[0033] Finally, the installation, measurement, and data output stage is as follows: The calibrated miniature fiber optic FP sensing unit is fixed to the preset mounting hole in the injector housing using high-temperature resistant adhesive. The position of the fiber optic probe is adjusted so that the initial cavity length of the FP interference cavity is 50-100μm (ensuring the interference signal signal-to-noise ratio ≥30dB). The laser is started and the output power is adjusted to 5-10mW. The calibration model and temperature correction matrix are loaded to complete the system initialization. The injector is started to make the valve core reciprocate. The spectrometer collects the interference spectrum signal in real time at a frequency ≥1kHz, and the temperature sensor collects the ambient temperature around the cavity simultaneously. The data processing unit uses a wavelet algorithm with a db4 wavelet basis and a threshold of 0.01 to denoise the spectral signal. The peak wavelength is extracted by Gaussian fitting. After calculating the spectral drift, the temperature correction matrix is ​​used for compensation. The displacement-spectral model is substituted to obtain the real-time valve core lift. The dynamic change curve of the lift, the maximum / minimum lift value, and the response time are output. At the same time, the error of multiple measurements is statistically analyzed to ensure ≤±0.1μm.

[0034] The following are several other specific embodiments of the application of this invention: Example 1: An Inert Gas Chamber Adapted to High Temperature and High Fluctuation Conditions The first stage involves system setup and media filling: Hardware equipment identical to that in the original embodiment is selected, the difference being that the internal medium of the FP interferometer cavity is replaced with argon gas with a purity ≥99.99%—argon gas is filled into the sealed cavity formed by the injector housing, fiber optic probe, and valve core end face through a micro-gas path, utilizing the chemical stability and refractive index temperature coefficient of argon gas. The argon gas pressure is much lower than that of air, which reduces the interference of temperature fluctuations on the equivalent refractive index of the cavity. At the same time, a micro-sealing gasket is added at the mounting hole to ensure that the argon pressure in the cavity is stable at 0.12MPa (slightly higher than atmospheric pressure to prevent outside air from seeping in).

[0035] The subsequent system calibration phase involves fixing the fiber optic probe to a piezoelectric displacement stage, using a valve core simulator as the reflective surface, and controlling the movement of the displacement stage at a reference temperature of 25°C to acquire interference spectral signals. The FP interference theory formula is then corrected using the argon refractive index (n=1.00028). The displacement-spectral drift model adapted to the argon medium was obtained by fitting the model; temperature calibration data were collected simultaneously in the range of -40℃ to 150℃ (covering ultra-high temperature conditions) to construct the temperature correction coefficient matrix K'(T) for the argon medium.

[0036] Finally, the installation, measurement, and data output stage: the sealed sensing unit is installed on the injector, and the initial cavity length is adjusted to 60-90 μm; after the injector is started, the spectrometer acquires the interference spectrum in real time. The data processing unit first corrects the spectral drift based on the argon refractive index, then compensates for the temperature effect through K'(T), and finally outputs the valve core lift data. This embodiment can control the measurement error under high-temperature conditions to ≤±0.07 μm, which is suitable for the measurement requirements of ultra-high temperature injectors for aero-engines.

[0037] Example 2: High-frequency response example adapted to high-speed piezoelectric fuel injectors First, the system hardware upgrade and preparation phase was carried out: a high-speed spectrometer with a sampling frequency of ≥2kHz (replacing the original 1kHz model) and a high-speed platinum resistance temperature sensor with a response time of ≤2μs were selected, and the motion response time of the piezoelectric injector valve core was matched with ≤0.03ms; the antireflection film on the end face of the fiber optic probe was upgraded to "1550nm band ultra-wideband antireflection film" to make the light reflection loss ≤0.1% and improve the signal strength in low light environment.

[0038] The system calibration phase then proceeds: a dynamic calibration method is adopted in which the movement frequency of the displacement stage is consistent with the working frequency of the piezoelectric injector valve core (20kHz). The displacement stage is controlled to simulate the high-speed reciprocating motion of the valve core, and dynamic interference spectrum signals are acquired synchronously. In view of the noise characteristics of high-frequency signals, the denoising algorithm is upgraded to "wavelet packet threshold denoising" (the number of decomposition layers is increased to 6 layers) to improve the denoising accuracy of dynamic signals. A displacement-spectral drift correspondence model adapted to high-speed dynamic scenarios is obtained by fitting, and the sampling interval of the temperature correction matrix is ​​optimized (a set of data is collected every 5℃).

[0039] Finally, the installation, measurement, and data output stage: The sensing unit is installed on the piezoelectric injector. After startup, the spectrometer acquires signals at a frequency of 2kHz. The data processing unit extracts the peak wavelength through wavelet packet denoising and high-speed Gaussian fitting (computation time ≤ 5μs), substitutes it into the dynamic calibration model to obtain the lift data, and outputs the high-frequency dynamic curve of the valve core lift (sampling point density increased by 1 time). This embodiment can accurately capture the microsecond-level motion details of the piezoelectric injector valve core, adapting to the fuel injection control requirements of high-end new energy hybrid engines.

[0040] Example 3: High-Reliability Example of Dual-Cavity Redundancy Verification The first step is to build the dual-cavity system: two coaxial mounting holes are machined on the injector housing (symmetrically distributed on both sides of the valve core axis), and two independent miniature fiber optic FP sensing units are installed on them (sharing the same laser, spectrometer and data processing unit) to form a dual FP interferometric cavity measurement system; the fiber optic probe end faces of the two sensing units are parallel to the valve core end face, and the initial cavity lengths are set to 70μm and 80μm respectively.

[0041] The subsequent dual-cavity calibration phase involves independently calibrating both sets of sensing units to obtain their respective displacement-spectral drift correspondence models. ), A temperature correction matrix was used; simultaneously, collaborative calibration data of the two cavities were collected, and a deviation threshold (≤±0.05μm) for the dual-cavity measurements was established as a basis for verifying the validity of the data.

[0042] Finally, in the dual-cavity measurement and redundant output stage: after the injector is started, the two sets of sensing units synchronously acquire spectral signals, and the data processing unit calculates the results respectively. and If the deviation between the two chamber measurements is less than or equal to the threshold, the weighted average of the two measurements is output (the weights are assigned based on their respective calibration accuracy). If the deviation is greater than the threshold, the data output is automatically switched to the chamber with the higher calibration accuracy. This embodiment can improve the measurement reliability under harsh operating conditions (such as partial oil contamination) and is suitable for the long-term online monitoring requirements of heavy-duty fuel injectors in commercial vehicles.

[0043] 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 variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for measuring the lift of an injector valve core, characterized in that, Includes the following steps: Step 1: Construct a fiber optic Fabry-Perot interferometry system, which includes a narrow linewidth laser, a fiber optic beam splitter, a miniature fiber optic FP sensing unit, a spectrometer, a temperature sensor, and a data processing unit; The miniature fiber optic FP sensing unit consists of a closed FP interference cavity formed by a fiber optic probe fixed in a preset mounting hole in the injector housing and a valve core end face, and a temperature sensor is attached to the injector housing near the FP interference cavity. Step 2: System calibration. Fix the fiber optic probe to the standard displacement stage. Use the valve core simulation component as the other reflecting surface of the FP interferometer cavity to obtain the interference spectrum signal under different displacement values. Extract the peak wavelength of the spectrum and calculate the spectral drift. Based on the FP interferometer principle, derive and correct the displacement-spectral drift correspondence model. Simultaneously collect calibration data at different temperatures to construct the temperature correction coefficient matrix. Step 3: Install the calibrated miniature fiber optic FP sensing unit onto the oil injector to be measured, adjust the position of the fiber optic probe so that the initial cavity length of the FP interferometer cavity is within the preset range, start the narrow linewidth laser and initialize the system parameters; Step 4: Start the fuel injector. The reciprocating motion of the valve core causes the length of the FP interference cavity to change. The spectrometer collects the interference spectrum signal in real time, and the temperature sensor collects the ambient temperature signal simultaneously. Step 5: The data processing unit preprocesses the interference spectrum signal, calculates the spectral drift, and performs temperature compensation through the temperature correction coefficient matrix. The compensated spectral drift is then substituted into the displacement-spectral drift correspondence model to obtain the real-time valve core lift and output the measurement data.

2. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The narrow linewidth laser mentioned in step 1 has a linewidth ≤ 0.1 nm, an output wavelength of 1550 nm, an optical fiber probe diameter ≤ 0.5 mm, and an anti-reflection coating after polishing the end face. The wavelength resolution of the spectrometer is ≤ 0.01 nm.

3. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The mounting hole described in step 1 is processed using laser drilling technology, and the axis of the mounting hole is coaxial with the axis of the valve core; The initial cavity length of the FP interference cavity in step 3 is in the range of 50-100μm, which can ensure that the signal-to-noise ratio of the interference signal is ≥30dB.

4. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The standard displacement stage mentioned in step 2 is a high-precision piezoelectric displacement stage with a displacement accuracy of ≤ ±0.05μm; The temperature correction coefficient matrix is ​​constructed in the range of -40℃ to 120℃ and is used to compensate for the effect of temperature on the refractive index of optical fiber and the cavity length of FP interferometer.

5. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The acquisition frequency of the spectrometer mentioned in step 4 is ≥1kHz to meet the dynamic measurement requirements of the high-speed movement of the valve core. The temperature sensor is a platinum resistance temperature sensor with an accuracy of ±0.1℃ and a distance of ≤5mm between it and the FP interferometer cavity.

6. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The preprocessing described in step 5 includes using a wavelet threshold denoising algorithm to eliminate the interference of oil stains and vibrations on the spectral signal, and using a Gaussian fitting algorithm to extract the peak wavelength of the spectrum. The wavelet basis of the wavelet threshold denoising algorithm is db4, and the threshold is set to 0.

01.

7. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The medium inside the FP interferometer cavity in step 1 is air, and the refractive index of the medium is n≈1; The theoretical basis formula for the displacement-spectral drift model described in step 2 is: ,in Initial displacement The peak wavelength of the spectrum at that time This represents the spectral peak shift. This represents the free spectral range of the interference spectrum.

8. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The displacement-spectral drift model described in step 5 is as follows: ,in This is the sensitivity coefficient. This is the system zero drift correction value. This represents the spectral shift after temperature compensation. The data processing unit is equipped with LabVIEW data processing software, and the output parameters include the dynamic change curve of valve core lift, maximum lift value, minimum lift value and response time.

9. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The fiber optic beam splitter mentioned in step 1 is a 2×2 type with a splitting ratio of 1:1; The output power of the narrow linewidth laser is adjusted to 5-10mW to ensure that the spectrometer acquires a stable interference spectral signal.

10. The method for measuring the lift of an injector valve core according to claim 1, characterized in that: The fiber optic probe described in step 3 is fixed in the mounting hole using a high-temperature resistant adhesive. The error of multiple measurements in step 5 is ≤ ±0.1μm, which meets the high-precision measurement requirements of high-end injector valve core lift.

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