A method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction and an optimized structure.

Abstract

This invention relates to the field of internal combustion engine fuel supply system technology, specifically to a method and optimized structure for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction. Addressing the problem of increased clearance and aggravated leakage caused by the comprehensive deformation of the plunger assembly under ultra-high pressure, this invention establishes a structural mechanical model and an oil film fluid dynamics model for the plunger assembly. Based on bidirectional fluid-structure interaction, it achieves bidirectional iteration of fluid pressure and structural displacement, accurately obtaining deformation, dynamic clearance distribution, and leakage. Based on this calculation method, a non-uniform wall thickness plunger sleeve is proposed, with its wall thickness decreasing functionally from the oil film inlet to the outlet, matching the pressure distribution to suppress radial expansion. This invention overcomes the shortcomings of inaccurate calculations and one-sided optimizations in traditional methods, significantly reducing leakage, improving fuel pump volumetric efficiency, adapting to high injection pressure requirements, and demonstrating strong manufacturing feasibility, thus providing support for high-efficiency and low-emission internal combustion engines.

Description

Technical Field

[0001] This invention relates to the field of internal combustion engine fuel supply system technology, specifically to a method and optimized structure for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The plunger assembly, consisting of a plunger and a plunger sleeve, is a core precision component of the high-pressure fuel pump in an internal combustion engine fuel supply system. Its working principle involves the plunger reciprocating within the plunger sleeve, periodically compressing the fuel and generating extremely high pressure, sometimes exceeding 200 MPa, to power fuel injection. A micrometer-level clearance, typically 1–5 μm, exists between the plunger and the plunger sleeve. This clearance serves two purposes: ensuring the plunger's flexible movement and providing lubrication, it also becomes the primary pathway for high-pressure fuel leakage. This leakage directly affects the fuel pump's volumetric efficiency and fuel supply stability, thus impacting the engine's power, fuel economy, and emissions levels.

[0004] As internal combustion engines develop towards higher power density and lower emissions, fuel injection pressure continues to rise. Under ultra-high fuel pressure, the plunger assembly undergoes significant elastic deformation. Traditional theory typically considers radial deformation of the plunger to be the primary cause of clearance changes. However, research shows that the radial expansion of the plunger sleeve under high pressure and the compressive deformation of the plunger body under axial pressure are equally significant. Furthermore, the combined effect of these three factors leads to a non-linear increase in the assembly clearance at high pressure, resulting in a sharp increase in leakage. This has become one of the technical bottlenecks restricting further increases in fuel pressure.

[0005] Existing technologies have proposed several solutions to the gap leakage problem under high pressure. The mainstream technical approach focuses on modifying the plunger surface, such as giving it a specific micro-taper or complex profile, aiming to counteract the plunger deformation under high pressure by pre-setting the profile, thereby forming a more uniform and ideal gap under working conditions and suppressing leakage.

[0006] However, the above methods have significant limitations:

[0007] First, the manufacturing process is difficult and the engineering feasibility is low: the fitting clearance of the plunger assembly is extremely small, only a few micrometers, making it extremely sensitive to any shape modification. The proposed complex profiles, such as micrometer-level tapers or curves, are difficult to achieve with existing manufacturing processes and are very costly, making it impossible to guarantee consistency in mass production.

[0008] Secondly, the design lacks sufficient basis and optimization efficiency: traditional designs often rely on experience or simplified mechanical models, failing to fully consider the complex interaction between high-pressure fuel and structural deformation. Therefore, the design results often deviate significantly from actual operating conditions, requiring repeated trials and experiments in the optimization process, resulting in long cycles and high costs.

[0009] Third, the solutions are one-sided: existing methods mainly focus on compensating for the deformation of the plunger, while generally ignoring the combined effects of the deformation of the plunger sleeve and the axial compression deformation of the plunger on the clearance. This results in limited compensation effect under high-pressure conditions and cannot fundamentally solve the leakage problem.

[0010] Therefore, there is an urgent need for a new structural design and optimization method that can effectively suppress the overall deformation of the plunger assembly, control the micron-level gap, and has good engineering feasibility. Summary of the Invention

[0011] To address the problems existing in the prior art, the present invention aims to provide a method for calculating the clearance of plunger assemblies based on bidirectional fluid-structure interaction, which is intended to solve the problems of uncontrolled deformation and increased leakage of high-pressure fuel pump plunger assemblies under ultra-high pressure conditions due to fluid-structure interaction.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction, wherein the plunger assembly includes a plunger and a plunger sleeve, comprising the following steps:

[0014] S1, Establish the geometric model of the plunger assembly and the oil film fluid domain;

[0015] S2, Structural mechanics modeling and parameter setting of plunger assembly;

[0016] S3, Oil film fluid dynamics modeling and parameter setting;

[0017] S4, construction of a two-way fluid-structure interaction system;

[0018] S5 extracts the calculation results of plunger assembly deformation, clearance, and leakage.

[0019] Preferably, in step S1, a parameterized geometric model is established that includes the plunger, the plunger sleeve, and the oil film fluid domain between them. The outer wall profile of the plunger sleeve is controlled by the wall thickness parameters at different axial positions, and the internal structure of the plunger is defined by parameters such as the diameter and depth of the pressure balance hole, laying the foundation for subsequent variable parameter optimization analysis.

[0020] In step S2, a structural mechanical model of the plunger assembly is established based on the finite element method; the mechanical properties of the material are defined, boundary constraints are applied, and a mesh is generated to calculate the structural deformation under fluid pressure.

[0021] In step S3, a computational fluid dynamics model of the oil film fluid domain is established; fuel physical property parameters are defined, pressure boundary conditions are set, a viscous model is selected, and dynamic mesh technology is enabled to adapt to the geometric deformation of the fluid domain during the fluid-structure interaction process;

[0022] In step S4, a two-way coupling relationship is established between the structural model and the fluid model. During the solution process, the fluid model transmits pressure field data to the structural model as a load. After calculating the deformation, the structural model returns the displacement data to the fluid model for mesh updating. Through iterative solution, accurate coupled simulation of fluid pressure and structural deformation is achieved.

[0023] In step S5, the coupled model is run under a given operating condition until convergence; the deformation and clearance distribution of the plunger and plunger sleeve are extracted from the structural model, and key performance parameters such as leakage flow rate are obtained from the fluid model, providing a quantitative basis for structural optimization.

[0024] Preferably, in step S1, firstly, an assembly model of the plunger and plunger sleeve is constructed according to the actual dimensions; then, the gap region between the plunger and plunger sleeve is extracted from the assembly model through Boolean operations to form an oil film fluid domain; the geometric model can be a two-dimensional axisymmetric model or a three-dimensional model.

[0025] Preferably, in step S2, the fundamental governing equations of linear elasticity are solved to obtain the displacement field of the structural field; the governing equations include:

[0026] Equilibrium equations for infinitesimal elements:

[0027]

[0028] Used to characterize the balance between internal and external forces; among them... Let f be the Cauchy stress tensor and f be the volume force vector.

[0029] Geometric equations:

[0030]

[0031] It is used to describe the relationship between strain and displacement; where ε is the strain tensor and u is the displacement vector;

[0032] Constitutive equation:

[0033]

[0034] Used to define the stress-strain relationship of a material; where σ is the stress tensor, ε is the strain tensor, and C is the fourth-order constitutive tensor;

[0035] The finite element method discretizes the above equations to solve for the displacement field u under given boundary conditions, thereby obtaining the deformation and stress of the structure.

[0036] Preferably, in step S3, the flow field within the oil film fluid domain is solved, and its dynamics are governed by the Navier-Stokes equations, specifically including:

[0037] mass conservation equation:

[0038]

[0039] For incompressible flow, the above equation can be simplified to:

[0040]

[0041] Where ρ is density and v is flow velocity. The rate of change of density over time. Net outflow;

[0042] Momentum conservation equation:

[0043]

[0044] Where v is the velocity vector, p is the pressure, and μ is the dynamic viscosity.

[0045] Preferably, in step S4, the mechanical equilibrium and geometric compatibility conditions are satisfied at the fluid-structure interaction interface, and the solution is iteratively obtained through data exchange until convergence; the coupling conditions are defined by the following equations:

[0046] Force equilibrium conditions:

[0047]

[0048] Where, σ s Let σ be the structural lateral stress tensor. f Let n be the fluid side stress tensor, and n be the interface normal vector.

[0049] Geometric compatibility condition:

[0050]

[0051] in, For the displacement of the fluid boundary mesh, This refers to the displacement on the structural boundary;

[0052] The system coupler ensures that the above conditions are met in each iteration step, thereby realizing the relationship between fluid pressure p and displacement structure. Precise two-way transmission between them.

[0053] Preferably, in step S2, based on the governing equations, the geometric model established in step one is imported into the finite element analysis software to construct a mechanical model. Specific implementation steps include:

[0054] S2a. Material property definition: Assign material parameters to the plunger and plunger sleeve respectively, including Young's modulus E, Poisson's ratio μ, yield strength σs and tensile strength σt;

[0055] S2b. Mesh generation: Discretize the geometric model using a hexahedral swept mesh. The starting and ending faces correspond to the two symmetry faces of 1 / 4 of the model, respectively.

[0056] S2c. Boundary Condition Setting: Based on the actual installation and stress state, apply constraints and loads, including setting the top surface of the plunger sleeve as a fixed constraint, applying fuel pressure to the fuel chamber wall, constraining the axial degree of freedom of the bottom surface of the plunger assembly, setting the two symmetry planes of the 1 / 4 model as frictionless constraints, and setting the wall surface of the plunger assembly in contact with the oil film as a fluid-structure interaction boundary to receive fluid pressure.

[0057] Preferably, in step S3, the Navier-Stokes equations are solved by establishing a computational fluid dynamics model of the oil film fluid domain to obtain the pressure distribution p and velocity field v within the oil film, wherein the pressure distribution is transmitted as a load to the structural model.

[0058] S3a. The steps for establishing a computational fluid dynamics model of the oil film fluid domain include:

[0059] Fluid domain mesh generation: suppress the geometry of the plunger and plunger sleeve structure, and retain the oil film fluid domain; use a hexahedral swept mesh to discretize the fluid domain, and set the number of mesh layers in the oil film thickness direction to meet the flow analysis requirements of micron-level gaps;

[0060] S3b. Physical Model and Material Definition: A laminar flow model is selected, and physical properties such as fuel density and viscosity are defined.

[0061] S3c. Boundary condition setting: Set the inlet of the oil film fluid domain as a pressure inlet and the outlet as a pressure outlet; define the wall surface corresponding to the plunger sleeve and the plunger as the fluid-structure interaction interface, and set the two symmetric planes as symmetric boundary conditions;

[0062] S3d. Dynamic Mesh Definition: Enable dynamic mesh technology and set all boundaries of the fluid domain as deformable walls; wherein, the displacement of the wall in contact with the plunger and plunger sleeve is driven by the structural model, which is used to ensure that the fluid domain moves in a coordinated manner as a whole with structural deformation during coupled calculation and to maintain the closure of the fluid domain.

[0063] Preferably, in step S4, based on the control equations, fluid-structure interaction data exchange is achieved, and the structural mechanics finite element model established in step S2 and the oil film hydrodynamic model established in step S3 are imported into the system coupler; the specific steps are as follows:

[0064] S4a. Define the data interface: The pressure data on the fluid-structure interaction interface in the fluid model is used as input and passed to the wall of the plunger assembly in the structural model established in step two, as a fluid load applied to the structure; at the same time, the displacement data of the wall in the structural model is used as input and passed back to the fluid model to drive the dynamic mesh update.

[0065] S4b. Set coupling calculation control parameters: In the system coupler, within each time step, the system coupler will transfer data between the fluid and structure solvers according to these settings until the maximum number of iterations is reached or the solvers of each physics field converge, and then automatically advance to the next time step to continue the calculation.

[0066] To better implement the above technical solutions, the present invention also provides an optimized plunger assembly structure based on bidirectional fluid-structure interaction. Based on the deformation and leakage laws obtained by the coupling analysis method, the wall thickness of the plunger sleeve varies non-uniformly along the axial direction, with the wall thickness being the largest at the oil film gap inlet and decreasing towards the outlet direction according to a certain function law. The non-uniform wall thickness design makes the structural stiffness match the fluid pressure distribution, providing greater rigidity in the high-pressure area to suppress radial expansion, while avoiding stress concentration and sudden increase in deformation caused by abrupt changes in wall thickness, thereby effectively controlling the change in the assembly gap and ultimately reducing leakage.

[0067] The present invention has at least the following beneficial effects:

[0068] Traditional methods employ unidirectional fluid-structure interaction or rigid body assumptions, assuming a constant fit clearance. This fails to capture the actual deformation of the plunger and plunger sleeve, and neglects the feedback of structural deformation to the fluid domain, leading to significant deviations from actual leakage calculations. This invention, through bidirectional fluid-structure interaction simulation, accurately reveals the deformation field (such as radial deformation of the plunger and radial expansion of the plunger sleeve) and the axial distribution of the dynamic clearance of the plunger assembly under ultra-high pressure, better reflecting actual operating conditions. Furthermore, it quantifies the nonlinear pressure distribution within the oil film, providing a reliable quantitative basis for fuel pump performance evaluation and reliability design.

[0069] Existing technologies rely on experience-driven processes, requiring repeated trials and experiments for optimization, resulting in long cycles and high costs. Furthermore, the complex micron-level shaping of the plunger surface is difficult to achieve with current processes, compromising consistency in mass production. This invention, through two-way fluid-structure interaction simulation, can directly extract the correlation data of deformation, clearance, and leakage, clearly defining the direction and parameter range for structural optimization. This eliminates the need for repeated trials, significantly shortening the design cycle and reducing R&D costs. Moreover, the optimization scheme focuses on the wall thickness variation of the plunger sleeve, rather than the complex shaping of the plunger itself. The processing technology is simple and mature, ensuring consistency in mass production while controlling manufacturing costs, demonstrating strong engineering feasibility.

[0070] The non-uniform wall thickness plunger sleeve proposed in this invention can effectively suppress the comprehensive elastic deformation under ultra-high pressure. Under working pressure, the nonlinear increase in the mating clearance is significantly suppressed, and the fuel leakage is greatly reduced. This improves the volumetric efficiency of the high-pressure fuel pump, which can effectively improve the power and economy of the internal combustion engine, avoid power loss due to insufficient fuel supply, reduce fuel waste, and improve emission levels. It provides key technical support for the development of internal combustion engines towards high power density and low emissions.

[0071] Traditional technologies focus solely on compensating for the radial deformation of the plunger, generally neglecting the radial expansion of the plunger sleeve and the axial compression deformation of the plunger. This leads to the failure of compensation under ultra-high pressure conditions, becoming a bottleneck restricting further increases in injection pressure. This invention, through a two-way fluid-structure interaction model, comprehensively quantifies the synergistic effects of plunger radial deformation, plunger sleeve radial expansion, and plunger axial compression. The structural optimization scheme also specifically controls the combined influence of these three types of deformation, fundamentally solving the problem of nonlinear increase in clearance. This allows the plunger assembly to adapt to higher fuel injection pressures, breaking through technical limitations for the continuous improvement of internal combustion engine injection pressure. Attached Figure Description

[0072] Figure 1 This is a cross-sectional view of the non-uniform wall thickness structure plunger sleeve in this invention;

[0073] Figure 2 This is a curve showing the change in diameter of the plunger assembly as a function of the oil film inlet distance in this invention;

[0074] Figure 3 This is a curve showing the variation of the plunger assembly clearance with the oil film inlet distance in this invention;

[0075] Figure 4 These are the curves showing the change of oil film pressure with inlet distance obtained from the two models in this invention;

[0076] Figure 5 This invention optimizes the relationship between the gap between the front and rear plunger components and the inlet distance.

[0077] Figure 6This is a schematic diagram of the planar structure of the geometric model of the plunger assembly and the oil film fluid domain in this invention;

[0078] Figure 7 This is a three-dimensional structural schematic diagram of the geometric model of the plunger assembly and the oil film fluid domain in this invention. Detailed Implementation

[0079] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0080] Example 1

[0081] Figures 1 to 7 A method for calculating the clearance of a plunger assembly based on two-way fluid-structure interaction is presented. The plunger assembly includes a plunger and a plunger sleeve. The core of this method lies in accurately obtaining the deformation, clearance distribution, and leakage of the plunger assembly under high-pressure fuel through two-way fluid-structure interaction simulation, providing a quantitative basis for structural optimization. The specific steps are as follows:

[0082] Step 1: Establish the geometric model of the plunger assembly and the oil film fluid domain:

[0083] The plunger assembly includes a plunger and a plunger sleeve. First, an assembly model of the plunger and plunger sleeve is constructed based on actual dimensions. Then, Boolean operations are used to extract the gap region between the plunger and plunger sleeve from the assembly model, forming an oil film fluid domain. To improve computational efficiency, non-critical structures such as the internal flow channels, external surface chamfers, and fillets of the plunger sleeve can be appropriately simplified.

[0084] The geometric model can be either a two-dimensional axisymmetric model or a three-dimensional model. In the three-dimensional model, a complete model or a symmetrical simplified model (such as a 1 / 2 model or a 1 / 4 model) can be selected based on computational resources. In this embodiment, a 1 / 4 three-dimensional model is preferred to improve computational efficiency while ensuring computational accuracy. Finally, after the computational model is input into the computational analysis software, its geometric structure is as follows: Figure 6 and Figure 7 As shown.

[0085] Step 2: Establish the structural mechanics finite element model of the plunger assembly;

[0086] The core of this step is to solve the fundamental governing equations of linear elasticity to obtain the displacement field of the structural field.

[0087] The governing equations include:

[0088] The equilibrium equations (stress divergence equations) of a infinitesimal element characterize the balance between internal and external forces:

[0089]

[0090] Where σ is the Cauchy stress tensor and f is the volume force vector.

[0091] Geometric equations used to describe the relationship between strain and displacement:

[0092]

[0093] Where ε is the strain tensor and u is the displacement vector.

[0094] The constitutive equation (generalized Hooke's law) defines the stress-strain relationship of a material:

[0095]

[0096] Where σ is the stress tensor, ε is the strain tensor, and C is the fourth-order constitutive tensor (the elastic stiffness tensor of the material).

[0097] The finite element method discretizes the above set of equations to solve the displacement field u under given boundary conditions (such as fixed constraints or pressure loads), thereby obtaining the deformation and stress of the structure.

[0098] Based on the above equations, the geometric model established in step one is imported into the finite element analysis (FEA) software to construct a mechanical model. The specific implementation steps include:

[0099] a) Material property definition: Assign material parameters to the plunger and plunger sleeve respectively, including Young's modulus E, Poisson's ratio μ, and yield strength σ. s and tensile strength σ t wait;

[0100] b) Mesh generation: The geometric model is discretized using a hexahedral swept mesh. The starting and ending faces correspond to the two symmetry faces (cutting faces) of 1 / 4 of the model.

[0101] c) Boundary condition settings: Based on the actual installation and stress state, apply constraints and loads, including setting the top surface of the plunger sleeve as a fixed constraint, applying fuel pressure to the fuel chamber wall, constraining the axial degree of freedom of the bottom surface of the plunger assembly, setting the two symmetry planes (cutting planes) of the 1 / 4 model as frictionless constraints, and setting the wall surface of the plunger assembly in contact with the oil film as a fluid-structure interaction (FSI) boundary to receive fluid pressure.

[0102] Step 3: Establish an oil film hydrodynamic model;

[0103] This step aims to solve for the flow field within the oil film fluid domain. Given the low Reynolds number at the micrometer scale, the flow is laminar, and its dynamics are governed by the Navier-Stokes (NS) equations, specifically including:

[0104] Mass conservation equation (continuity equation):

[0105]

[0106] Where ρ is density and v is flow velocity. The rate of change of density over time. This represents the net outflow (divergence term).

[0107] For incompressible flow (where density ρ is constant), the above equation can be simplified to:

[0108]

[0109] Momentum conservation equation:

[0110]

[0111] Where v is the velocity vector, p is the pressure, and μ is the dynamic viscosity.

[0112] This step involves solving the above equations by establishing a CFD model of the oil film fluid domain to obtain the pressure distribution p and velocity field v within the oil film. The pressure distribution will be transferred as a load to the structural model. The key steps in establishing the CFD model of the oil film fluid domain include:

[0113] a) Fluid Domain Mesh Generation: Suppress the geometry of the plunger and plunger sleeve structure while preserving the oil film fluid domain. A hexahedral swept mesh is used to discretize the fluid domain, and the number of mesh layers is set in the oil film thickness direction (radial) to meet the flow analysis requirements for micrometer-level gaps (in this embodiment, the nominal oil film thickness is 5 μm, and the number of layers is 5).

[0114] b) Physical model and material definition: It was estimated that the Reynolds number of oil film flow at the micron scale is much lower than the critical value, and the flow is in a laminar state. Therefore, a laminar flow model was selected, and physical property parameters such as fuel density and viscosity were defined.

[0115] c) Boundary condition setting: Set the inlet of the oil film fluid domain as a pressure inlet and the outlet as a pressure outlet (in this embodiment, the inlet pressure is 220 MPa and the outlet pressure is 0.5 MPa). Define the wall surface corresponding to the plunger sleeve and the plunger as the fluid-structure interaction (FSI) interface, and set the two symmetric planes as symmetric boundary conditions.

[0116] d) Dynamic mesh definition: Enable dynamic meshing technology, and set all boundaries of the fluid domain (including fluid-structure interaction interfaces, inlets, outlets, and symmetry planes) as deformable walls. Among them, the displacement of the wall in contact with the plunger / plunger sleeve is driven by the structural model. This is intended to ensure that the fluid domain moves in a coordinated manner with the structural deformation during coupled calculations and to maintain the closed nature of the fluid domain.

[0117] Step four: Establish system coupling relationships;

[0118] This step achieves bidirectional coupling between the fluid and the structure. Essentially, it satisfies mechanical equilibrium and geometric compatibility conditions at the fluid-structure interaction interface, and iteratively solves the problem through data exchange until convergence. The coupling conditions are defined by the following equations:

[0119] Force equilibrium condition (stress continuity), that is, at the fluid-structure interaction interface, the stress applied by the fluid is equal to the stress inside the structure:

[0120]

[0121] Where, σ s Let σ be the structural lateral stress tensor. f For the fluid side stress tensor (σ) f =-pI+τ, where τ is the viscous stress and n is the interface normal vector. In scenarios where pressure is the primary load, this can be simplified to the fluid pressure load acting directly on the structure.

[0122] Geometric compatibility conditions (displacement continuity / no slip): At the fluid-structure interaction interface, the displacement of the fluid domain mesh is consistent with the displacement of the structure.

[0123]

[0124] in, For the displacement of the fluid boundary mesh, This represents the displacement at the structural boundary.

[0125] The system coupler ensures that the above conditions are met in each iteration step, thereby realizing the relationship between fluid pressure p and displacement structure. Precise two-way transmission between them.

[0126] Based on the above governing equations, this embodiment establishes system coupling relationships using the SystemCoupling component in the ANSYS Workbench platform to achieve fluid-structure interaction data exchange. The structural mechanics finite element model established in step two (S2) and the oil film hydrodynamic model established in step three (S3) are imported into this module. The key steps are as follows:

[0127] a) Define the data interface: The pressure data on the fluid-structure interaction interface in the fluid model is used as input and passed to the wall of the plunger assembly in the structural model established in step two, as a fluid load applied to the structure; at the same time, the displacement data of the wall in the structural model is used as input and passed back to the fluid model to drive the dynamic mesh update.

[0128] b) Setting Coupling Calculation Control Parameters: In the system coupling module, this embodiment sets the minimum number of data exchange iterations to 10 and the maximum number of iterations to 100 for each coupling time step. Within each time step, the system coupler will transfer data between the fluid and structural solvers according to these settings until the maximum number of iterations is reached or the solvers for each physics field converge, at which point it will automatically advance to the next time step to continue the calculation. At this point, the bidirectional fluid-structure interaction model of the plunger assembly has been completed.

[0129] Step 5: Result Extraction and Analysis;

[0130] After the two-way fluid-structure interaction model calculation converges, the output data of the system coupling solver is post-processed. The key steps are as follows:

[0131] a) Extracting the deformation and clearance of the plunger assembly: Obtain the deformation contour maps of the plunger and plunger sleeve from the structural mechanics model. Through data processing, extract the radial deformation of the plunger and plunger sleeve at different positions along the plunger axis (represented by the axial length from the oil film inlet). Subtracting the inner wall displacement of the plunger sleeve from the outer wall displacement of the plunger at the same position yields the actual axial distribution curve of the clearance under working conditions, i.e., the "relationship between the assembly clearance and the inlet distance".

[0132] b) Extracting the leakage of the plunger assembly under high-pressure fuel: The mass flow rate of the oil film fluid domain outlet after calculation convergence is directly read from the fluid dynamics model.

[0133] Example 2

[0134] Based on the above embodiments and the analysis and verification of the aforementioned two-way fluid-structure interaction steady-state calculation method, the embodiments improve the structure of the plunger assembly and propose a plunger sleeve with a non-uniform wall thickness structure. The specific implementation is as follows:

[0135] The wall thickness of the plunger sleeve is optimized along its axial direction, exhibiting a continuous, non-uniform variation. Specifically, the wall thickness is greatest at the oil film gap inlet, decreases along the axial direction towards the outlet according to a certain functional law, and is smallest at the outlet.

[0136] The functions include, but are not limited to, polynomial functions (linear functions, quadratic functions, etc.), power functions, exponential functions, logarithmic functions, composite functions, and piecewise functions.

[0137] In this embodiment, the distance between the oil film inlet and outlet is 42 mm, and the functional relationship between the plunger sleeve wall thickness and the oil film inlet distance is a piecewise function, the expression of which is:

[0138]

[0139] Where x is the distance from the oil film inlet end, in mm; H is the plunger sleeve wall thickness, in mm.

[0140] The continuously varying wall thickness distribution ensures that the structural stiffness roughly matches the fluid pressure distribution. In the inlet region, which experiences the highest pressure, the wall thickness is increased to enhance rigidity and effectively resist radial expansion deformation in that region.

[0141] In addition, this continuous transition wall thickness design effectively avoids stress concentration and sudden drop in local stiffness that may be caused by abrupt changes in wall thickness, thereby suppressing the sudden increase in radial deformation that may occur at the abrupt change in wall thickness of the plunger sleeve inner wall.

[0142] The above structure reduces leakage by suppressing radial expansion deformation inside the plunger sleeve.

[0143] Compared with existing technologies, the plunger assembly clearance calculation method and optimized structure based on bidirectional fluid-structure interaction provided by this invention bring significant and multifaceted technical improvements, specifically reflected in the following three aspects:

[0144] Firstly, it enables the calculation of leakage and deformation: Traditional one-way fluid-structure interaction or rigid body assumption methods fail to account for structural deformation caused by high-pressure fluids and assume that the fitting clearance remains constant during operation, resulting in leakage calculations that deviate significantly from reality (usually significantly lower) and completely fail to provide deformation data for the plunger and plunger sleeve. This invention, through two-way fluid-structure interaction simulation, accurately reveals the true deformation field of the plunger and plunger sleeve under operating conditions, such as... Figure 2 As shown, the distribution law of dynamic fit clearance along the axial direction was further obtained, as follows: Figure 3 As shown in the figure. The leakage calculated based on this gap is more consistent with the actual situation, providing a reliable basis for product performance evaluation and reliability design.

[0145] Secondly, it improves the accuracy of leakage and pressure distribution calculations: the assumption of linearly decreasing oil film pressure along the axial direction, commonly used in traditional methods, deviates from physical reality under ultra-high pressure micron-sized gap conditions. The leakage calculated using the traditional method (one-way coupling model) is 0.0018865 kg / s, while the leakage obtained using the method of this invention is 0.0022665 kg / s. The analysis results in the embodiments of this invention show that, due to the feedback effect of structural deformation on the fluid domain, the pressure distribution within the oil film exhibits significant nonlinear characteristics.

[0146] Thirdly, structural optimization reduces leakage in the plunger assembly: Simulation and experimental data confirm that the plunger sleeve with a non-uniform wall thickness structure proposed in this invention can effectively suppress comprehensive elastic deformation under high pressure. At the same working pressure of 220 MPa, it can significantly reduce the gap between the components, such as... Figure 5 As shown, the fuel leakage rate was ultimately reduced from 0.0022665 kg / s to 0.0021237 kg / s, with the leakage rate under the optimized structure being approximately 6.3% lower than that under the original uniform wall thickness structure. This performance improvement can be directly translated into an increase in the volumetric efficiency of the high-pressure fuel pump.

[0147] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0148] The terms "upper," "lower," "outer," "inner," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish relative positional relationships and are not necessarily qualitative. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0149] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction, wherein the plunger assembly includes a plunger and a plunger sleeve, characterized in that: Includes the following steps: S1, Establish the geometric model of the plunger assembly and the oil film fluid domain; S2, Structural mechanics modeling and parameter setting of plunger assembly; S3, Oil film fluid dynamics modeling and parameter setting; S4, construction of a two-way fluid-structure interaction system; S5 extracts the calculation results of plunger assembly deformation, clearance, and leakage.

2. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 1, characterized in that: In step S1, a parameterized geometric model is established, which includes the plunger, the plunger sleeve, and the oil film fluid domain between them. The outer wall profile of the plunger sleeve is controlled by the wall thickness parameters at different axial positions, and the internal structure of the plunger is defined by parameters such as the diameter and depth of the pressure balance hole, laying the foundation for subsequent variable parameter optimization analysis. In step S2, a structural mechanical model of the plunger assembly is established based on the finite element method; the mechanical properties of the material are defined, boundary constraints are applied, and a mesh is generated to calculate the structural deformation under fluid pressure. In step S3, a computational fluid dynamics model of the oil film fluid domain is established; fuel physical property parameters are defined, pressure boundary conditions are set, a viscous model is selected, and dynamic mesh technology is enabled to adapt to the geometric deformation of the fluid domain during the fluid-structure interaction process; In step S4, a two-way coupling relationship is established between the structural model and the fluid model. During the solution process, the fluid model transmits pressure field data to the structural model as a load. After calculating the deformation, the structural model returns the displacement data to the fluid model for mesh updating. Through iterative solution, accurate coupled simulation of fluid pressure and structural deformation is achieved. In step S5, the coupled model is run under a given operating condition until convergence; the deformation and clearance distribution of the plunger and plunger sleeve are extracted from the structural model, and key performance parameters such as leakage flow rate are obtained from the fluid model, providing a quantitative basis for structural optimization.

3. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 1, characterized in that: In step S1, firstly, an assembly model of the plunger and plunger sleeve is constructed according to the actual dimensions; then, the gap region between the plunger and plunger sleeve is extracted from the assembly model through Boolean operations to form an oil film fluid domain; the geometric model can be a two-dimensional axisymmetric model or a three-dimensional model.

4. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 1, characterized in that: In step S2, the fundamental governing equations of linear elasticity are solved to obtain the displacement field of the structural field; the governing equations include: Equilibrium equations for infinitesimal elements: Used to characterize the balance between internal and external forces; among them... Let f be the Cauchy stress tensor and f be the volume force vector. Geometric equations: It is used to describe the relationship between strain and displacement; where ε is the strain tensor and u is the displacement vector; Constitutive equation: Used to define the stress-strain relationship of a material; where... σ For stress tensor, ε C is the strain tensor, and C is the fourth-order constitutive tensor; The finite element method discretizes the above equations to solve for the displacement field u under given boundary conditions, thereby obtaining the deformation and stress of the structure.

5. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 1, characterized in that: In step S3, the flow field within the oil film fluid domain is solved, and its dynamics are governed by the Navier-Stokes equations, specifically including: mass conservation equation: For incompressible flow, the above equation can be simplified to: in, ρ For density, v For flow rate, The rate of change of density over time. Net outflow; Momentum conservation equation: in, v It is a velocity vector. p For pressure, μ This refers to dynamic viscosity.

6. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 1, characterized in that: In step S4, the mechanical equilibrium and geometric compatibility conditions are satisfied at the fluid-structure interaction interface, and the solution is iteratively obtained through data exchange until convergence; the coupling conditions are defined by the following equations: Force equilibrium conditions: Where, σ s Let σ be the structural lateral stress tensor. f Let n be the fluid side stress tensor, and n be the interface normal vector. Geometric compatibility condition: in, For the displacement of the fluid boundary mesh, This refers to the displacement on the structural boundary; The system coupler ensures that the above conditions are met in each iteration step, thereby realizing the relationship between fluid pressure p and displacement structure. Precise two-way transmission between them.

7. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 4, characterized in that: In step S2, based on the governing equations, the geometric model established in step one is imported into the finite element analysis software to construct a mechanical model. Specific implementation steps include: S2a. Material property definition: Assign material parameters to the plunger and plunger sleeve respectively, including Young's modulus E, Poisson's ratio μ, yield strength σs and tensile strength σt; S2b. Mesh generation: Discretize the geometric model using a hexahedral swept mesh. The starting and ending faces correspond to the two symmetry faces of 1 / 4 of the model, respectively. S2c. Boundary Condition Setting: Based on the actual installation and stress state, apply constraints and loads, including setting the top surface of the plunger sleeve as a fixed constraint, applying fuel pressure to the fuel chamber wall, constraining the axial degree of freedom of the bottom surface of the plunger assembly, setting the two symmetry planes of the 1 / 4 model as frictionless constraints, and setting the wall surface of the plunger assembly in contact with the oil film as a fluid-structure interaction boundary to receive fluid pressure.

8. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 5, characterized in that: In step S3, the Navier-Stokes equations are solved by establishing a computational fluid dynamics model of the oil film fluid domain to obtain the pressure distribution p and velocity field v within the oil film, wherein the pressure distribution is transmitted as a load to the structural model. S3a. The steps for establishing a computational fluid dynamics model of the oil film fluid domain include: Fluid domain mesh generation: suppress the geometry of the plunger and plunger sleeve structure, and retain the oil film fluid domain; use a hexahedral swept mesh to discretize the fluid domain, and set the number of mesh layers in the oil film thickness direction to meet the flow analysis requirements of micron-level gaps; S3b. Physical Model and Material Definition: A laminar flow model is selected, and physical properties such as fuel density and viscosity are defined. S3c. Boundary condition setting: Set the inlet of the oil film fluid domain as a pressure inlet and the outlet as a pressure outlet; define the wall surface corresponding to the plunger sleeve and the plunger as the fluid-structure interaction interface, and set the two symmetric planes as symmetric boundary conditions; S3d. Dynamic Mesh Definition: Enable dynamic mesh technology and set all boundaries of the fluid domain as deformable walls; wherein, the displacement of the wall in contact with the plunger and plunger sleeve is driven by the structural model, which is used to ensure that the fluid domain moves in a coordinated manner as a whole with structural deformation during coupled calculation and to maintain the closure of the fluid domain.

9. The method for calculating the clearance of a plunger assembly based on bidirectional fluid-structure interaction as described in claim 5, characterized in that: In step S4, based on the governing equations, fluid-structure interaction data exchange is achieved by importing the structural mechanics finite element model established in step S2 and the oil film hydrodynamic model established in step S3 into the system coupler; the specific steps are as follows: S4a. Define the data interface: The pressure data on the fluid-structure interaction interface in the fluid model is used as input and passed to the wall of the plunger assembly in the structural model established in step two, as a fluid load applied to the structure; at the same time, the displacement data of the wall in the structural model is used as input and passed back to the fluid model to drive the dynamic mesh update. S4b. Set coupling calculation control parameters: In the system coupler, within each time step, the system coupler will transfer data between the fluid and structure solvers according to these settings until the maximum number of iterations is reached or the solvers of each physics field converge, and then automatically advance to the next time step to continue the calculation.

10. An optimized plunger assembly structure in the plunger assembly clearance calculation method based on bidirectional fluid-structure interaction as described in claim 1, characterized in that: Based on the deformation and leakage patterns obtained by the coupling analysis method, the wall thickness of the plunger sleeve varies non-uniformly along the axial direction, with the maximum wall thickness at the oil film gap inlet and decreasing towards the outlet according to a certain functional law. The non-uniform wall thickness design makes the structural stiffness match the fluid pressure distribution, providing greater rigidity in the high-pressure area to suppress radial expansion, while avoiding stress concentration and sudden increase in deformation caused by abrupt changes in wall thickness, thereby effectively controlling the change in the gap between the components and ultimately reducing leakage.

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