A method for optimizing the structure of a low-leakage plunger assembly

Abstract

This invention relates to the field of internal combustion engine fuel injection system technology, specifically to a method for optimizing the structure of a low-leakage plunger assembly. Addressing the problems of increased clearance and fuel leakage due to plunger assembly deformation under high pressure, and the inadequacy and reliance on experience in traditional modification compensation methods, this invention establishes a two-way fluid-structure interaction model related to the plunger, plunger sleeve, and oil film. It extracts the deformation amount and designs the reverse deformation profiles of the plunger working cylindrical surface and the plunger sleeve inner bore. Simultaneously, it designs the plunger sleeve as a non-uniform wall thickness structure with increasing wall thickness at the high-pressure end. This method can significantly reduce leakage, optimize clearance, and improve the volumetric efficiency of the high-pressure pump, laying the foundation for improving the power and economy of internal combustion engines.

Description

Technical Field

[0001] This invention relates to the field of internal combustion engine fuel injection system technology, and specifically to a method for optimizing the structure of a low-leakage plunger assembly based on a reverse deformation profile and non-uniform wall thickness. 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 pressures, exceeding 200 MPa, to power fuel injection. A micrometer-level clearance 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] However, as the maximum fuel injection pressure of internal combustion engines continues to rise, the plunger assembly undergoes significant elastic deformation under ultra-high fuel pressure. Studies have shown that under high-pressure fuel, both the radial expansion of the plunger sleeve and the radial compression deformation of the plunger are significant, and their combined effect leads to a nonlinear increase in the assembly clearance during the high-pressure phase, resulting in a sharp increase in leakage. This has become one of the technical bottlenecks restricting further increases in fuel pressure.

[0005] To address the aforementioned problems, existing technologies typically employ methods such as modifying the plunger surface, for example, by imbuing the plunger surface with a fixed, minute taper, in order to counteract the plunger's own compressive deformation under high pressure and thus make the mating clearance more uniform. However, this traditional method has the following significant limitations:

[0006] Firstly, the deformation compensation mechanism is inadequate: existing modification schemes mainly compensate for the deformation of the plunger, but generally ignore the radial expansion deformation of the plunger sleeve under high pressure. As mentioned earlier, the deformation of the plunger sleeve is also one of the two major factors constituting the change in total clearance. Ignoring its influence makes the compensation measures inadequate and unable to further suppress the clearance of the mating parts.

[0007] Secondly, the design is based on theoretical flaws: the selection of the taper in existing technologies often relies on experience or simplified theoretical models. Traditional plunger assembly leakage models typically assume that the liquid pressure is linearly distributed along the gap. However, in reality, under high pressure, the coordinated elastic deformation of the plunger and plunger sleeve significantly alters the geometry of the fluid domain, causing the actual pressure field to deviate severely from the linear assumption. A fixed taper designed based on an erroneous model will inevitably struggle to achieve the ideal sealing effect under complex actual working conditions.

[0008] Third, the technical effect achieved solely through surface modification has its limitations: under ultra-high pressure environments, the combined deformation of the plunger and plunger sleeve may approach or even exceed the initial fit clearance. This means that, under the premise of maintaining a minimum clearance to ensure lubrication and prevent jamming, the deformation range that can be compensated and the leakage suppression effect achieved by simply modifying the surfaces of the mating parts to a limited extent are already saturated, and cannot fundamentally solve the problem of leakage surge caused by large synergistic deformation. Summary of the Invention

[0009] To address the problems existing in the prior art, the present invention aims to provide a method for optimizing the structure of a low-leakage plunger assembly based on a reverse deformation profile and non-uniform wall thickness. The method aims to significantly suppress fuel leakage under high-pressure operating conditions by optimizing the geometric characteristics of the plunger assembly itself.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for optimizing the structure of a low-leakage plunger assembly includes the following steps:

[0012] S1. Establish a two-way fluid-structure interaction simulation model related to the plunger, plunger sleeve and oil film;

[0013] S2, extract the deformation of the plunger assembly at different positions;

[0014] S3, determine the initial geometric profile of the plunger assembly;

[0015] Through the above steps, the macroscopic profile of the working cylindrical surface of the plunger is fitted with a spline curve to form the plunger reverse deformation profile, and the macroscopic profile of the inner bore surface of the plunger sleeve is fitted with a spline curve to form the plunger sleeve inner bore reverse deformation profile. At the same time, the outer surface of the plunger sleeve is a conical surface, so that its wall thickness has a non-uniform wall thickness structure that linearly decreases from the high-pressure inlet end of the fuel gap to the low-pressure outlet end. By increasing the local wall thickness at the high-pressure inlet end to improve the structural stiffness, the radial expansion of this critical area is suppressed, thereby enhancing the compensation effect on the reverse deformation profile of the plunger sleeve inner bore.

[0016] Preferably, in step S1, the simulation model consists of a structural mechanics model in the solid domain and a computational fluid dynamics model in the fluid domain;

[0017] The solid domain constructs a structural mechanics model through a plunger and plunger assembly, while the fluid domain constructs a computational fluid dynamics model through a micron-level annular gap between the plunger and the plunger sleeve.

[0018] Preferably, in step S1, the interface between the fluid domain and the solid domain is defined as the fluid-structure interaction interface. During the simulation, the computational fluid dynamics model of the fluid domain transmits the calculated oil film pressure distribution as a load to the structural mechanics model through this interface. The structural mechanics model then feeds back the calculated deformation to the computational fluid dynamics model of the fluid domain to update the geometry of the fluid domain. This iterative process continues until the calculation results converge.

[0019] Preferably, in step S2, the deformation field of the plunger and plunger sleeve under the target fuel injection pressure is extracted, and then the radial deformation data of a series of discrete points are extracted at equal intervals along the mating length of the plunger assembly to complete the discretization of the deformation field.

[0020] Preferably, in step S2, under the action of high-pressure fuel, the clearance between the plunger components at different axial positions is:

[0021]

[0022] In the formula, The distance to the gap entrance. This refers to the clearance on one side of the plunger assembly when it is not deformed. For the radial deformation of the plunger, This represents the radial deformation of the plunger sleeve.

[0023] Preferably, in step S3, based on the deformation data of the plunger assembly under high-pressure fuel, the outer diameter of the plunger and the inner diameter of the plunger sleeve at different axial positions are compensated to determine the plunger assembly profile under the condition of no deformation.

[0024] Preferably, in step S3, the outer radius of the compensated plunger is optimized. It is derived from the following formula:

[0025]

[0026] Compensation optimization of the inner radius of the plunger sleeve It is derived from the following formula:

[0027]

[0028] In the formula, This is the plunger outer diameter compensation coefficient. This is the piston inner diameter compensation coefficient.

[0029] Preferably, in step S3, the single-sided clearance of the plunger assembly in the optimized, undeformed state is compensated according to the plunger assembly dimensions at different axial positions. The calculation formula is as follows:

[0030] .

[0031] Preferably, in step S3, the functional relationship between the plunger sleeve wall thickness H(z) and the oil film inlet distance is a piecewise function, and its expression is:

[0032] .

[0033] The present invention has at least the following beneficial effects:

[0034] This invention significantly suppresses high-pressure fuel leakage, providing key technical support for improving the volumetric efficiency and fuel supply stability of high-pressure pumps. Traditional surface modification techniques, which only address plunger deformation compensation and rely on empirical design, struggle to effectively control leakage. This invention, however, reduces the leakage path of high-pressure fuel at its source through the synergistic effect of reverse deformation profiles and non-uniform wall thickness: using reverse deformation profiles alone significantly reduces leakage compared to before optimization; using a plunger sleeve structure with non-uniform wall thickness alone also effectively reduces leakage; when both technologies are combined, leakage is drastically reduced, completely overcoming the bottleneck of traditional surface modification techniques in suppressing leakage and laying the foundation for improving the power, economy, and emissions performance of internal combustion engines.

[0035] This invention effectively suppresses the elastic deformation of plunger components under high pressure, achieving precise control and uniform optimization of the mating clearance, and solving the technical problem of nonlinear clearance increase under high-pressure conditions. In high-pressure environments, the radial compression of the plunger and the radial expansion of the plunger sleeve easily lead to an increase in the mating clearance. However, this invention, through synchronous compensation of bidirectional reverse deformation profiles and the strengthening of the stiffness of key areas by non-uniform wall thickness, not only effectively reduces the maximum mating clearance of the components and significantly reduces the deformation at specific locations of the plunger sleeve, but also significantly improves the consistency of clearance distribution and greatly optimizes the clearance differences at different axial positions. This optimization ensures the minimum lubrication clearance required for the reciprocating motion of the plunger, avoiding the risk of jamming, while maintaining the clearance within a uniform and small range, significantly improving sealing conditions and extending the service life of the plunger components.

[0036] The optimization system constructed in this invention possesses both precision and versatility, providing a scientifically feasible solution for the design of high-pressure plunger assemblies. Traditional techniques often rely on experience to select modification parameters, resulting in low design accuracy and poor adaptability. In contrast, this invention, based on real deformation data obtained from two-way fluid-structure interaction simulation, achieves flexible control of optimization parameters through quantitative compensation logic and segmented wall thickness design. Its reverse deformation profile and non-uniform wall thickness design approach can be adjusted according to different fuel injection pressures, assembly lengths, and other operating conditions, adapting to the design requirements of various high-pressure fuel pumps. This eliminates reliance on empirical models and promotes the transformation of plunger assembly design from experience-based to precise and systematic. Attached Figure Description

[0037] Figure 1 This is a schematic diagram showing the radius distribution of the plunger assembly before and after deformation according to the present invention;

[0038] Figure 2 This is a schematic diagram of the initial profile of the optimized plunger assembly of the present invention;

[0039] Figure 3 This is a schematic diagram of the optimized plunger assembly profile under a non-uniform wall thickness plunger sleeve structure.

[0040] Figure 4 This is a schematic diagram of the gap distribution of the deformed components of the present invention;

[0041] Figure 5 This is a schematic diagram showing the leakage amount under different optimization schemes of the present invention. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0043] Figures 1 to 5 A low-leakage plunger assembly structure based on a reverse deformation profile is presented, and its specific implementation is as follows:

[0044] Step 1: Establish a two-way fluid-structure interaction simulation model of plunger-plunger sleeve-oil film.

[0045] The simulation model consists of a structural mechanics model in the solid domain and a computational fluid dynamics (CFD) model in the fluid domain.

[0046] The solid domain in the simulation model includes a plunger and a plunger assembly, used to construct the structural mechanics model. A three-dimensional model is created in finite element analysis software, assigning material properties such as elastic modulus and Poisson's ratio, and applying displacement constraints.

[0047] The fluid domain in the simulation model is the micron-sized annular gap between the plunger and the plunger sleeve, used to construct the computational fluid dynamics model. An oil film geometry model is established in finite element software, defining its material properties such as density and viscosity, as well as defining boundary conditions such as inlet and outlet pressures, wall surfaces, and dynamic mesh regions.

[0048] The interface between the fluid domain and the solid domain is defined as the fluid-structure interaction interface. During the simulation, the CFD model transmits the calculated oil film pressure distribution as a load to the structural mechanics model through this interface; the structural mechanics model, in turn, feeds back the calculated deformation to the CFD model to update the geometry of the fluid domain. This iterative process continues until the calculation results converge.

[0049] To simplify the calculation process, this embodiment uses a 1 / 8 symmetric model to establish a two-way fluid-structure interaction simulation model of the plunger-plunger sleeve-oil film.

[0050] Step 2: Extract the deformation of the plunger assembly at different positions.

[0051] The solution is performed under the target fuel injection pressure, which is 220 MPa in this embodiment. After the solution is completed, the deformation field of the plunger and plunger sleeve is extracted. Then, radial deformation data of a series of discrete points are extracted at equal intervals along the mating length of the plunger assembly to complete the discretization of the deformation field.

[0052] Axial position, i.e., the distance from the gap inlet, is denoted as , Where i is a subscript index, representing the i-th sampling point arranged sequentially along the axial direction. For example, This indicates the axial position of the nth sampling point.

[0053] Assuming for each axial position The single-sided clearance when the plunger assembly is not deformed Same. In this embodiment .

[0054] Assuming for each axial position In this embodiment, the plunger radius r0 and the plunger sleeve radius R0 are both constant values ​​when they are not deformed. , .

[0055] In this embodiment, the sign of deformation is defined as follows: deformation along the radial outward direction (such as expansion) is positive, and deformation along the radial inward direction (such as compression) is negative.

[0056] For each axial position The radial deformation of the plunger is denoted as .

[0057] For each axial position The radial deformation of the plunger sleeve is denoted as .

[0058] Under the action of high-pressure fuel The radius of the outer side of the upper plunger is .

[0059] Under the action of high-pressure fuel The radius of the inner side of the upper plunger sleeve is .

[0060] Before optimization, under high-pressure fuel, the clearance of the plunger assembly at different axial positions was:

[0061]

[0062] The relationship between the radius of the plunger assembly before and after deformation and the gap inlet distance is as follows: Figure 1 As shown, the leakage rate is approximately 0.01057 kg / s.

[0063] Step 3: Determine the initial geometry of the plunger assembly.

[0064] Based on the deformation data of the plunger assembly under high-pressure fuel, the outer diameter of the plunger and the inner diameter of the plunger sleeve at different axial positions are compensated to determine the plunger assembly profile under the condition of no deformation.

[0065] For each axial position Optimized outer radius of the plunger It is derived from the following formula:

[0066]

[0067] For each axial position Optimized inner radius of the plunger sleeve It is derived from the following formula:

[0068]

[0069] In the above formula, For the plunger outer diameter compensation coefficient, This is the plunger inner diameter compensation coefficient, which can be adjusted appropriately based on the compensation effect. In this embodiment, Take 0.5, Take 0.2.

[0070] Based on the dimensions of the plunger assembly at different axial positions, the optimized single-sided clearance of the assembly in its undeformed state is obtained. The calculation formula is as follows:

[0071]

[0072] Based on the above compensation method, the axial position under undeformed conditions is obtained. The outer diameter of the plunger and the inner diameter of the plunger sleeve, as well as the clearance on one side when no deformation occurs, such as Figure 2 As shown.

[0073] Through the above process, the plunger assembly proposed in this invention needs to possess the following structural features:

[0074] (a) Plunger reverse deformation profile structure

[0075] The macroscopic profile of the working cylindrical surface of the plunger is obtained from discrete data points [z] calculated by the aforementioned method. i, r(z i A smooth curve fitted by spline curves, the radius of which, in its radial projection, varies with its axial position. It exhibits a non-monotonic and non-linear variation pattern. This specific profile is used to precisely counteract the radial compressive deformation of the plunger itself under high pressure. Therefore, this profile is not a traditional conical surface or a surface with a constant diameter, but a profile uniquely determined by a physical compensation process.

[0076] (ii) Reverse deformation profile structure of the plunger sleeve inner bore

[0077] The macroscopic profile of the inner surface of the plunger sleeve is also composed of discrete data points [z]. i, R(z i A smooth curve obtained by spline curve fitting. This profile matches the outer contour of the plunger, together forming a systematic sealing solution. Its variation law is mainly used to compensate for the non-uniform radial expansion of the plunger sleeve itself under the action of high-pressure fuel. This ensures that a uniform gap is formed as much as possible with the compensated plunger during operation.

[0078] (iii) Non-uniform wall thickness structure of plunger sleeve

[0079] The outer surface of the plunger sleeve is designed and machined into a conical surface, so that its wall thickness decreases linearly from the high-pressure inlet end of the fuel gap to the low-pressure outlet end. This simplified design is directly derived from the "deformation-wall thickness" correlation law revealed by simulation results. Its purpose is to increase the structural stiffness by increasing the local wall thickness in the high-pressure area (inlet end), thereby helping to suppress the radial expansion of this critical area and enhancing the compensation effect of the reverse deformation profile of the inner hole.

[0080] 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 H(z) and the oil film inlet distance is a piecewise function, the expression of which is:

[0081]

[0082] After completing the model modification, following steps one through three above, the further optimized plunger assembly profile is obtained as follows: Figure 3 As shown in Appendix 1, the outer and inner radii of the plunger at each axial position are as follows:

[0083] Appendix 1: Plunger assembly profile after optimization of plunger sleeve

[0084] <![CDATA[Axial position z i / mm]]> plunger radius / mm plunger sleeve radius / mm Piston sleeve outer radius / mm 0.0 5.9943204 5.9994112 11.5 1.0 5.994396875 5.99938027 12 2.0 5.994542693 5.9993188 12.5 3.0 5.994694318 5.99925015 13 4.0 5.994832845 5.99918183 13.5 5.0 5.994953513 5.99911673 14 6.0 5.995056893 5.99905597 14.5 7.0 5.99514535 5.99899986 15 8.0 5.995221618 5.99894839 15.5 9.0 5.99528834 5.99890122 16 10.0 5.99534764 5.998858 16.5 11.0 5.995401078 5.99881837 17 12.0 5.995449728 5.99878203 17.5 13.0 5.995494685 5.99874854 18 14.0 5.9955367 5.99871754 18.5 15.0 5.99557625 5.99868875 19 16.0 5.9956137 5.99866192 19.5 17.0 5.99564935 5.99863681 20 18.0 5.9956834 5.99861325 20.5 19.0 5.995716025 5.99859106 21 20.0 5.9957473 5.99857014 21.5 21.0 5.995777425 5.99855035 22 22.0 5.9958064 5.9985316 22.5 23.0 5.995834325 5.9985138 23 24.0 5.9958614 5.99849687 23.5 25.0 5.9958876 5.99848076 24 26.0 5.99591305 5.99846539 24.5 27.0 5.995937825 5.99845073 25 28.0 5.995961925 5.99843677 25.5 29.0 5.995985425 5.99842349 26 30.0 5.996008325 5.99841085 26.5 31.0 5.996030725 5.99839889 27 32.0 5.996052625 5.99838761 27.5 33.0 5.99607405 5.99837704 28 34.0 5.996095075 5.99836719 28.5 35.0 5.996115725 5.99835816 29 36.0 5.996136 5.99835001 29 37.0 5.9961559 5.99834287 29 38.0 5.996175375 5.99833687 29 39.0 5.996194325 5.99833217 29 40.0 5.996212425 5.99832899 29 41.0 5.996229225 5.99832731 29 42.0 5.9962433 5.9983333 29

[0085] Compared with existing conventional plunger assemblies, the technical solution provided by this invention can significantly suppress leakage and improve the sealing performance of the plunger assembly, specifically in the following two aspects:

[0086] Firstly, it significantly reduces fuel leakage from the plunger assembly.

[0087] This invention, through structural optimization, fundamentally reduces the leakage paths of high-pressure fuel, resulting in a significant reduction in leakage.

[0088] By employing a reverse deformation profile design alone, leakage is reduced by 23.3% compared to before optimization through deformation compensation; by employing a plunger sleeve with a non-uniform wall thickness structure alone, leakage is reduced by approximately 19.6% by enhancing local stiffness and suppressing expansion; when both technologies are applied simultaneously, the overall leakage reduction reaches as high as 60.1%, providing technical support for improving the volumetric efficiency of high-pressure pumps.

[0089] Secondly, it effectively suppresses elastic deformation of mating parts and controls the mating clearance.

[0090] This invention effectively alleviates the technical bottleneck of nonlinear increase in fit clearance under high pressure, and significantly optimizes the size and uniformity of the clearance:

[0091] The maximum clearance is effectively suppressed: the reverse deformation profile reduces the maximum clearance of the plunger assembly by 0.14 μm; the non-uniform wall thickness structure of the plunger sleeve reduces the maximum clearance of the assembly by 2.4 μm; when both technologies are applied simultaneously, the maximum clearance of the assembly is reduced by 3.1 μm, and the deformation of the plunger sleeve at a specific axial position is reduced by up to 29.5%.

[0092] Significant improvement in clearance uniformity: The synergistic effect of both significantly enhances the consistency of clearance distribution, optimizing the clearance range at different axial positions from 9.4 μm to 7.0 μm. This demonstrates that the present invention successfully suppresses the mating clearance under high pressure to a smaller and more uniform level, resulting in a substantial improvement in sealing conditions.

[0093] 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.

[0094] 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.

[0095] 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 optimizing the structure of a low-leakage plunger assembly, characterized in that: Includes the following steps: S1. Establish a two-way fluid-structure interaction simulation model related to the plunger, plunger sleeve and oil film; S2, extract the deformation of the plunger assembly at different positions; S3, determine the initial geometric profile of the plunger assembly; Through the above steps, the macroscopic profile of the working cylindrical surface of the plunger is fitted with a spline curve to form the plunger reverse deformation profile, and the macroscopic profile of the inner bore surface of the plunger sleeve is fitted with a spline curve to form the plunger sleeve inner bore reverse deformation profile. At the same time, the outer surface of the plunger sleeve is a conical surface, so that its wall thickness has a non-uniform wall thickness structure that linearly decreases from the high-pressure inlet end of the fuel gap to the low-pressure outlet end. By increasing the local wall thickness at the high-pressure inlet end to improve the structural stiffness, the radial expansion of this critical area is suppressed, thereby enhancing the compensation effect on the reverse deformation profile of the plunger sleeve inner bore.

2. The low-leakage plunger assembly structure optimization method as described in claim 1, characterized in that: In step S1, the simulation model consists of a structural mechanics model in the solid domain and a computational fluid dynamics model in the fluid domain; The solid domain constructs a structural mechanics model through a plunger and plunger assembly, while the fluid domain constructs a computational fluid dynamics model through a micron-level annular gap between the plunger and the plunger sleeve.

3. The low-leakage plunger assembly structure optimization method as described in claim 2, characterized in that: In step S1, the interface between the fluid domain and the solid domain is defined as the fluid-structure interaction interface. During the simulation, the computational fluid dynamics model of the fluid domain transmits the calculated oil film pressure distribution as a load to the structural mechanics model through this interface. The structural mechanics model feeds back the calculated deformation to the computational fluid dynamics model of the fluid domain to update the geometry of the fluid domain. This iterative process continues until the calculation results converge.

4. The low-leakage plunger assembly structure optimization method as described in claim 1, characterized in that: In step S2, the deformation field of the plunger and plunger sleeve under the target fuel injection pressure is extracted. Then, along the mating length of the plunger assembly, a series of discrete points are extracted at equal intervals to complete the discretization of the deformation field.

5. The low-leakage plunger assembly structure optimization method as described in claim 4, characterized in that: In step S2, under the action of high-pressure fuel, the clearance of the plunger assembly at different axial positions is: In the formula, The distance to the gap entrance. This refers to the clearance on one side of the plunger assembly when it is not deformed. For the radial deformation of the plunger, This represents the radial deformation of the plunger sleeve.

6. The low-leakage plunger assembly structure optimization method as described in claim 4, characterized in that: In step S3, based on the deformation data of the plunger assembly under high-pressure fuel, the outer diameter of the plunger and the inner diameter of the plunger sleeve at different axial positions are compensated to determine the plunger assembly profile under the condition of no deformation.

7. The low-leakage plunger assembly structure optimization method as described in claim 6, characterized in that: In step S3, the outer radius of the compensated plunger is optimized. It is derived from the following formula: Compensation optimization of the inner radius of the plunger sleeve It is derived from the following formula: In the formula, This is the plunger outer diameter compensation coefficient. This is the piston inner diameter compensation coefficient.

8. The low-leakage plunger assembly structure optimization method as described in claim 7, characterized in that: In step S3, based on the dimensions of the plunger assembly at different axial positions, the single-sided clearance of the assembly in its optimized, undeformed state is compensated. The calculation formula is as follows: .

9. The method for optimizing the structure of a low-leakage plunger assembly as described in claim 8, characterized in that: In step S3, the functional relationship between the plunger sleeve wall thickness H(z) and the oil film inlet distance is a piecewise function, and its expression is: .

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