An indirect method for measuring the internal fit dimensions of a positive overlap slide valve

Abstract

This invention relates to an indirect measurement method for the internal fit dimensions of a positively overlapping slide valve. The method includes the following steps: S1, conducting an experiment using a testing bench to obtain the static pressure characteristic curve of the slide valve; S2, obtaining the four axial positive overlap amounts of the slide valve based on the values ​​of four points on the straight segment of the static pressure characteristic curve; S3, obtaining the resulting radial clearance amount of the slide valve through an iterative method based on the value of one point on the non-straight segment of the static pressure characteristic curve, and obtaining the internal fit dimensions of the slide valve based on the radial clearance amount and the axial positive overlap amount. Compared with the prior art, this invention can predict and control the internal fit dimension chain of a positively overlapping slide valve based on the performance of the slide valve, improving the measurement efficiency in the slide valve manufacturing process.

Description

Technical Field

[0001] This invention relates to the field of hydraulic valves, and in particular to an indirect method for measuring the internal fit dimensions of a positive overlapping spool valve. Background Technology

[0002] A spool valve consists of two core components: a valve core and a valve sleeve or valve body. The relative movement between the valve core and valve sleeve forms and controls the flow area of ​​the valve orifice to achieve fluid flow control. The axial displacement control of the spool valve in an electro-hydraulic servo valve is typically in the range of tens to even several micrometers, and its performance has a crucial impact on the performance of the entire hydraulic system. The characteristics of a spool valve mainly depend on its internal fit dimensions, including axial and radial fit dimensions. The axial fit dimension is the axial overlap between the valve core shoulder and the corresponding flow distribution window of the valve sleeve, while the radial fit dimension is the radial clearance formed between the valve core and valve sleeve. Typically, hydraulic spool valves are ideal zero-opening valves, meaning the radial clearance between the valve core and valve sleeve is zero, and the axial overlap between the valve core shoulder and the corresponding flow distribution window of the valve sleeve is zero. However, due to the radial clearance between the valve core and valve sleeve, zero-position leakage occurs. Generally, the axial dimensions of the valve core and valve sleeve are made with a small positive overlap to reduce zero-position leakage, while maintaining spool valve performance close to that of an ideal zero-opening spool valve.

[0003] Currently, methods for measuring the axial overlap of spool valves typically include direct methods, pneumatic methods, and hydraulic methods. The direct method involves directly measuring the machining dimensions of the valve core and sleeve using measuring tools to calculate the overlap, but this method has significant errors and is only suitable for rough machining of the valve core. The pneumatic method uses gas as the working medium and indirectly measures the overlap by measuring changes in parameters such as gas flow rate or pressure. However, due to the low viscosity and high expansion coefficient of gas, the pneumatic method is only suitable for low flow rates; its accuracy is poor at high flow rates. In 2016, Yin Yaobao et al. proposed an indirect measurement method for the overlap of the valve core and sleeve in pneumatic servo valves and its application. This method uses the pneumatic method to measure the static pressure characteristics of the pneumatic servo valve, thereby determining the geometric overlap between the valve core and sleeve in the internal mating structure of the pneumatic servo valve (see patent literature: Yin Yaobao, Li Changming. Indirect Measurement Method for the Overlap of the Valve Core and Sleeve in Pneumatic Servo Valves and Its Application. ZL200810041108.X, 2008-07-29). The hydraulic method uses hydraulic oil as the working medium, which is closer to the actual working state of the spool valve. However, the current hydraulic method usually measures the overlap indirectly based on the flow rate through the valve orifice. The measured overlap needs to be compensated for to obtain an accurate value. The measurement of the radial clearance of a spool valve usually involves direct and indirect methods. In 2015, Qiao Jianjun et al. proposed a method for determining the annular clearance between the valve core and valve sleeve of an aircraft brake valve, determining the fitting clearance between the valve core and valve sleeve based on internal leakage (see patent literature: Qiao Jianjun, Peng Juan. Method for determining the annular clearance between the valve core and valve sleeve of an aircraft brake valve. ZL201510152588.7, 2015-04-01).

[0004] The internal fit dimensions of a spool valve directly affect and determine the basic working performance of high-end hydraulic components such as servo valves. Their manufacturing precision requirements are high, and the fit dimensions are difficult to measure. Therefore, accurately measuring the internal fit dimensions of spool valves, and thus understanding the dimensional chain information of the precision components inside high-end hydraulic components under service conditions (such as temperature and pressure), is one of the fundamental engineering problems that urgently needs to be solved. Currently, the axial overlap and radial clearance of spool valves are usually measured independently, resulting in low measurement efficiency and a lack of comprehensive measurement methods. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing an indirect measurement method for the internal fit dimensions of a positive overlapping slide valve. By observing the performance of the slide valve, the internal fit dimension chain of the positive overlapping slide valve can be predicted and understood, thereby improving the measurement efficiency in the slide valve manufacturing process.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for indirectly measuring the internal fit dimensions of a positive overlap slide valve, the method comprising the following steps:

[0008] S1. The static pressure characteristic curve of the slide valve is obtained by testing on the test bench. The static pressure characteristic curve of the slide valve is the characteristic curve of the pressure at the two load ports and the displacement of the valve core.

[0009] S2. Based on the values ​​of four points on the straight line segment of the static pressure characteristic curve, obtain the positive overlap of the four axes of the slide valve.

[0010] S3. Based on the value of a point on the non-linear segment of the static pressure characteristic curve, obtain the radial clearance of the slide valve through an iterative method, and obtain the internal fit dimensions of the slide valve based on the radial clearance and the axial positive overlap.

[0011] Furthermore, the straight line segment of the static pressure characteristic curve represents the linear relationship between the pressure at the two load ports and the valve core displacement when the valve core displacement is within the positive overlap range, the throttling orifice is a radial annular slit flow, and it is in laminar flow.

[0012] Furthermore, the expression for the straight line segment of the static pressure characteristic curve is:

[0013]

[0014]

[0015] Where p1 and p2 are the pressures at the two load ports when the valve core displacement is within the positive overlap range, respectively; x is the valve core displacement; p sis the oil supply pressure; U1 is the first axial positive overlap, U2 is the second axial positive overlap, U3 is the third axial positive overlap, and U4 is the fourth axial positive overlap.

[0016] Further, the specific method for obtaining the radial clearance of the spool valve by the iterative method is as follows:

[0017] Arbitrarily select a point on the non-linear segment of the static pressure characteristic curve, the pressure value at this point is p, set the initial radial clearance δ as δ0, determine the corresponding pressure value p0 at the same spool displacement according to the expression of the non-linear segment of the static pressure characteristic curve. If p0 < p, update the radial clearance δ to make δ = δ + Δδ, and calculate p0 again until p0 ≥ p. Take the finally obtained radial clearance as the result radial clearance δ' of the spool valve, where Δδ is the iteration step size.

[0018] Further, the non-linear segment of the static pressure characteristic curve represents the non-linear relationship between the pressures at the two load ports and the spool displacement when the spool displacement exceeds the positive overlap, and the throttle port is in turbulent flow.

[0019] Further, the expression of the non-linear segment of the static pressure characteristic curve is:

[0020]

[0021]

[0022] where p3 and p4 are the pressures at the two load ports when the spool displacement exceeds the positive overlap; C d is the flow coefficient; A1, A2, A3, and A4 are the flow areas of each throttle port; d is the spool diameter; μ is the dynamic viscosity; ρ is the oil density; x is the spool displacement; p s is the oil supply pressure; U1 is the first axial positive overlap, U2 is the second axial positive overlap, U3 is the third axial positive overlap, U4 is the fourth axial positive overlap; δ is the radial clearance.

[0023] Further, the four points on the linear segment of the static pressure characteristic curve are arbitrarily selected two points each on the linear segment of the characteristic curve of the pressures at the two load ports and the spool displacement.

[0024] Further, the internal mating dimensions of the spool valve include axial mating dimensions and radial mating dimensions.

[0025] Further, the axial mating dimension is the axial positive overlap between the spool shoulder and the corresponding flow distribution window of the valve sleeve.

[0026] Further, the radial mating dimension is the radial clearance formed between the spool and the valve sleeve.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] This invention addresses the problems of difficult measurement, low measurement efficiency, and lack of comprehensive measurement methods for the internal fit dimensions of positively overlapping slide valves. By measuring the static pressure characteristics of the slide valve, the radial clearance and axial positive overlap are obtained, thereby indirectly measuring the internal fit dimensions of the slide valve. In this invention, the correspondence between the basic characteristics of the slide valve and the internal fit dimensions is clear. The fit dimension chain inside the positively overlapping slide valve can be predicted and mastered by the performance of the slide valve, thus improving the measurement efficiency and economy in the slide valve manufacturing process. Attached Figure Description

[0029] Figure 1 This is a flowchart of the present invention;

[0030] Figure 2 This is a schematic diagram of the main parts of the present invention;

[0031] Figure 3 This is a schematic diagram of the detection stage portion of the present invention;

[0032] Figure 4 The diagram shows the pressure and valve core displacement characteristics of the two load ports of the slide valve with symmetrical and equal positive overlap of the present invention.

[0033] Figure 5 This is a graph showing the first characteristic curves of the pressure at the two load ports and the valve core displacement of the slide valve with symmetrical and uneven positive overlap of the present invention.

[0034] Figure 6 This is a graph showing the second characteristic curves of the pressure at the two load ports and the valve core displacement of the slide valve with symmetrical and uneven positive overlap of the present invention.

[0035] Figure 7 This is a curve showing the pressure and valve core displacement characteristics of the two load ports of the slide valve with irregular positive overlap according to the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0037] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0038] Example 1

[0039] This invention provides an indirect method for measuring the internal fit dimensions of a positive overlap slide valve, the flowchart of which is shown below. Figure 1 As shown. The method includes the following steps:

[0040] S1. Conduct tests using a testing bench to obtain the static pressure characteristic curve of the slide valve. The static pressure characteristic curve of the slide valve is the characteristic curve of the pressure at the two load ports versus the valve core displacement.

[0041] S2. Based on the values ​​of four points on the straight line segment of the static pressure characteristic curve, obtain the positive overlap of the four axes of the slide valve.

[0042] S3. Based on the value of a point on the non-linear segment of the static pressure characteristic curve, obtain the radial clearance of the slide valve through an iterative method, and obtain the internal fit dimensions of the slide valve based on the radial clearance and the axial positive overlap.

[0043] In S1, the test is conducted using a testing bench to complete the testing process without disassembling the spool valve, and the product is not damaged during the testing process. The testing bench has a constant pressure oil source that supplies oil to the oil inlet of the spool valve under test. The two load ports of the spool valve are independently connected to two oil pressure gauges or pressure sensors.

[0044] In S2, the four points on the straight line segment of the static pressure characteristic curve are two points arbitrarily selected from the straight line segments of the characteristic curves of the pressure at the two load ports and the valve core displacement.

[0045] The straight line segment of the static pressure characteristic curve represents the linear relationship between the pressure at both load ports and the valve core displacement when the valve core displacement is within the positive overlap range, indicating radial annular slit flow at the throttling orifice, which is laminar flow. The expression for the straight line segment of the static pressure characteristic curve is:

[0046]

[0047]

[0048] Where p1 and p2 are the pressures at the two load ports when the valve core displacement is within the positive overlap range, respectively; x is the valve core displacement; p s U1 is the oil supply pressure; U2 is the first axial positive overlap, U3 is the second axial positive overlap, U4 is the third axial positive overlap, and U4 is the fourth axial positive overlap.

[0049] In S3, the radial clearance of the slide valve is obtained through an iterative method as follows:

[0050] Arbitrarily select a point on the non-linear segment of the static pressure characteristic curve. The pressure value at this point is p, and the initial radial clearance δ is set as δ0. Determine the corresponding pressure value p0 at the same spool displacement according to the expression of the non-linear segment of the static pressure characteristic curve. If p0 < p, update the radial clearance δ such that δ = δ + Δδ, and calculate p0 again until p0 ≥ p. Take the finally obtained radial clearance as the result radial clearance δ' of the spool, where Δδ is the iteration step. The non-linear segment of the static pressure characteristic curve indicates that when the spool displacement exceeds the positive overlap amount, the throttle port is in turbulent flow, and the non-linear relationship between the pressures at the two load ports and the spool displacement.

[0051] The expression of the non-linear segment of the static pressure characteristic curve is:

[0052]

[0053]

[0054] where p3 and p4 are the pressures at the two load ports respectively when the spool displacement exceeds the positive overlap amount; C d is the flow coefficient; A1, A2, A3, A4 are the flow areas of each throttle port; d is the spool diameter; μ is the dynamic viscosity; ρ is the oil density; x is the spool displacement; p s is the supply pressure; U1 is the first axial positive overlap amount, U2 is the second axial positive overlap amount, U3 is the third axial positive overlap amount, U4 is the fourth axial positive overlap amount; δ is the radial clearance.

[0055] The internal mating dimensions of the spool valve in S3 include axial mating dimensions and radial mating dimensions. The axial mating dimension is the axial positive overlap amount between the spool shoulder and the corresponding flow distribution window of the valve sleeve, and the radial mating dimension is the radial clearance formed between the spool and the valve sleeve.

[0056] Figure 2 is a schematic diagram of the main part of an embodiment of the present invention. As Figure 2 shown, the spool 1 moves in the valve sleeve 2 to control the size of each throttle port. The supply pressure of the constant pressure oil source is p s , the return pressure p e is zero, the two load ports are A and B respectively, and their pressures are p1 and p2. The four-sided positive overlap amounts formed by the cylindrical spool valve spool and the valve sleeve are U1, U2, U3, U4 respectively, and the radial clearance between the spool and the valve sleeve is δ. When the positive overlap amounts U2 and U3 on the supply side of the spool valve are equal, and the positive overlap amounts U1 and U4 on the drain side are equal, this structure is defined as a spool valve with symmetric positive overlap amounts. When the four-sided positive overlap amounts of the spool valve are all equal, this structure is defined as a spool valve with symmetric and equal positive overlap amounts. When Figure 1When the two positive overlap amounts on the oil supply side and the two positive overlap amounts on the oil discharge side shown in [Figure] are not equal to each other, it is called a spool valve with irregular positive overlap amounts. In the manufacturing process of the spool valve, there are often phenomena of geometric symmetry equality, geometric symmetry inequality or irregularity in the overlap amount between the spool and the valve sleeve.

[0057] Figure 3 is a schematic diagram of a test bench part of an embodiment of the present invention. As Figure 3 shown, when the electromagnetic ball valve 11 is opened, a hydraulic oil source is generated by the hydraulic pump 7, and the hydraulic oil is supplied to the spool valve to be tested through the check valve 8, the filter 9, the oil supply port pressure gauge 10 and the electromagnetic ball valve 11. Among them, the overflow valve 14 plays a constant pressure role to maintain the constant outlet pressure of the hydraulic pump 7 and provide a stable input pressure for the spool valve to be tested; the filters 6 and 9 play a role in purifying the hydraulic oil. The pressure gauges 12 and 13 respectively detect the pressure values of the two load ports of the spool valve.

[0058] The flow law of the oil fluid at the valve port is in two states: laminar flow and turbulent flow. When the spool displacement is within the positive overlap amount range, the throttle port is a radial annular gap flow and is in laminar flow. Therefore, the load port pressure is linearly related to the spool displacement. When the spool displacement exceeds the positive overlap amount, the throttle port is in turbulent flow. Therefore, the load port pressure is non-linearly related to the spool displacement.

[0059] Figure 2 In [Figure], the relationship between the pressure at the load port A and the spool displacement is:

[0060] When -U1 < x < U2,

[0061] When x ≥ U2,

[0062] When x ≤ -U1,

[0063] x is the spool displacement; C d is the flow coefficient; A1, A2 are the flow areas of the throttle ports; d is the spool diameter; μ is the dynamic viscosity.

[0064] The relationship between the pressure at the load port B and the spool displacement is:

[0065] When -U3 < x < U4,

[0066] When x ≥ U4,

[0067] When x ≤ -U3,

[0068] A3, A4 are the flow areas of the throttle ports.

[0069] In the above two relationships between the pressure at the load ports and the valve core displacement, there are five undetermined parameters: four positive overlap quantities U1, U2, U3, and U4 of the spool valve and the radial clearance quantity δ. Therefore, two points can be arbitrarily selected on the straight segments of the two load port pressure characteristic curves, and their values ​​can be substituted into the corresponding relationships to solve the equation system and obtain the four axial positive overlap quantities of the spool valve. Then, one point can be arbitrarily selected on the non-straight segments of the two load port pressure characteristic curves, and the radial clearance quantity of the spool valve can be obtained by iterative method.

[0070] Figure 4 This is a curve showing the pressure and valve core displacement characteristics of a spool valve with symmetrical and equal positive overlap at its two load ports, according to an embodiment of the present invention. In this embodiment, the hydraulic oil is HLP46, and the supply pressure is p. s =10MPa, valve core diameter d=12mm. For example... Figure 3 As shown, curve A is the pressure-valve core displacement characteristic curve at load port A, and curve B is the pressure-valve core displacement characteristic curve at load port B. Taking two points on the straight segments of curves A and B respectively, and substituting their values ​​into the corresponding relational formulas, the equation system can be solved to obtain the positive overlap of the four sides of the slide valve in this embodiment: U1 = U2 = U3 = U4 = 0.2 mm. It can be seen that the slide valve in this embodiment has a symmetrical and equal positive overlap. Taking any point on the non-straight segment, the radial clearance of the slide valve in this embodiment is obtained by iterative method: δ = 10 μm, that is, the final result is radial clearance δ' = 10 μm.

[0071] Figure 5 This is a graph showing the pressure at the two load ports and the first characteristic curve of the valve core displacement of a spool valve with symmetrical, uneven positive overlap, according to an embodiment of the present invention. In this embodiment, the hydraulic oil is HLP46, and the supply pressure is p. s =10MPa, valve core diameter d=12mm. For example... Figure 4 As shown, curve A is the pressure-valve core displacement characteristic curve at load port A, and curve B is the pressure-valve core displacement characteristic curve at load port B. Taking two points on the straight segments of curves A and B respectively, and substituting their values ​​into the corresponding relational formulas, we can solve the equation system to obtain the positive overlap of the four sides of the slide valve in this embodiment: U1 = U4 = 0.2 mm, U2 = U3 = 0.4 mm. It can be seen that the slide valve in this embodiment has a symmetrical but uneven positive overlap. Taking any point on the non-straight segment, we can obtain the radial clearance of the slide valve in this embodiment as δ = 10 μm through the iterative method, that is, the final result is the radial clearance δ' = 10 μm.

[0072] Figure 6 This is a curve showing the pressure and valve core displacement characteristics of a spool valve with symmetrical, uneven positive overlap, according to an embodiment of the present invention. In this embodiment, the hydraulic oil is HLP46, and the supply pressure is p. s=10MPa, valve core diameter d=12mm. For example... Figure 5 As shown, curve A is the pressure-valve core displacement characteristic curve at load port A, and curve B is the pressure-valve core displacement characteristic curve at load port B. Taking two points on the straight segments of curves A and B respectively, and substituting their values ​​into the corresponding relational formulas, we can solve the equation system to obtain the positive overlap of the four sides of the slide valve in this embodiment: U1 = U4 = 0.17 mm, U2 = U3 = 0.07 mm. It can be seen that the slide valve in this embodiment has a symmetrical but uneven positive overlap. Taking any point on the non-straight segment, we can obtain the radial clearance of the slide valve in this embodiment as δ = 10 μm through the iterative method, that is, the final result is the radial clearance δ' = 10 μm.

[0073] Figure 7 This is a curve showing the pressure and valve core displacement characteristics of a spool valve with irregular positive overlap, according to an embodiment of the present invention. In this embodiment, the hydraulic oil is HLP46, and the supply pressure is p. s =10MPa, valve core diameter d=12mm. For example... Figure 5 As shown, curve A is the pressure-valve core displacement characteristic curve at load port A, and curve B is the pressure-valve core displacement characteristic curve at load port B. Taking two points on the straight segments of curves A and B respectively, and substituting their values ​​into the corresponding relational formulas, the equation system can be solved to obtain the positive overlap of the four sides of the slide valve in this embodiment: U1 = 0.15mm, U2 = 0.35mm, U3 = 0.3mm, U4 = 0.1mm. It can be seen that the slide valve in this embodiment has an irregular positive overlap. Taking any point on the non-straight segment, the radial clearance of the slide valve in this embodiment is obtained by iterative method: δ = 10μm, that is, the final result is radial clearance δ' = 10μm.

[0074] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for indirectly measuring the internal fit dimensions of a positive overlapping slide valve, characterized in that, The method comprises the following steps: S1. Conduct tests through a test bench to obtain the static pressure characteristic curve of the spool valve. The static pressure characteristic curve of the spool valve is the characteristic curve of the pressures of two load ports and the spool displacement. S2. Obtain four axial positive overlap amounts of the spool valve according to the values of four points on the straight-line segment of the static pressure characteristic curve. S3. Obtain the resulting radial clearance amount of the spool valve by the iterative method according to the value of one point on the non-straight-line segment of the static pressure characteristic curve, and obtain the internal fitting dimensions of the spool valve based on the resulting radial clearance amount and the axial positive overlap amount. The straight-line segment of the static pressure characteristic curve represents the linear relationship between the pressures of two load ports and the spool displacement when the spool displacement is within the positive overlap amount range, the throttle port is in the form of radial annular slit flow and in laminar flow. The expression of the straight-line segment of the static pressure characteristic curve is: Where p1 and p2 are the pressures at the two load ports when the valve core displacement is within the positive overlap range, respectively; x is the valve core displacement; p s U1 is the oil supply pressure; U2 is the first axial positive overlap, U3 is the second axial positive overlap, U4 is the third axial positive overlap, and U4 is the fourth axial positive overlap. The four-sided positive overlap amounts formed by the cylindrical spool valve spool and the valve sleeve in structure are the first axial positive overlap amount U1, the second axial positive overlap amount U2, the third axial positive overlap amount U3 and the fourth axial positive overlap amount U4 respectively. The internal fitting dimensions of the spool valve include axial fitting dimensions and radial fitting dimensions. The axial fitting dimension is the axial positive overlap amount between the spool shoulder and the corresponding flow distribution window of the valve sleeve. The radial fitting dimension is the radial clearance amount formed between the spool and the valve sleeve.

2. The method for indirectly measuring the internal fit dimensions of a positive overlapping slide valve according to claim 1, characterized in that, The specific process of obtaining the resulting radial clearance amount of the spool valve by the iterative method is as follows: Arbitrarily select a point on the non-straight-line segment of the static pressure characteristic curve. The pressure value of this point is p. Set the initial radial clearance amount δ as δ0. Determine the corresponding pressure value p0 at the same spool displacement according to the expression of the non-straight-line segment of the static pressure characteristic curve. If p0 < p, update the radial clearance amount δ to make δ = δ + Δδ, and calculate p0 again until p0 ≥ p. Take the finally obtained radial clearance amount as the resulting radial clearance amount δ' of the spool valve, where Δδ is the iteration step size.

3. The method for indirectly measuring the internal fit dimensions of a positive overlapping slide valve according to claim 2, characterized in that, The non-straight-line segment of the static pressure characteristic curve represents the non-linear relationship between the pressures of two load ports and the spool displacement when the spool displacement exceeds the positive overlap amount, and the throttle port is in turbulent flow.

4. The method for indirectly measuring the internal fit dimensions of a positive overlapping slide valve according to claim 3, characterized in that, The expression of the non-straight-line segment of the static pressure characteristic curve is: Where p3 and p4 are the pressures at the two load ports when the valve core displacement exceeds the positive overlap, respectively; C d A1 is the flow coefficient; A2, A3, and A4 are the flow areas of each throttling orifice; d is the valve core diameter; μ is the dynamic viscosity; ρ is the oil density; x is the valve core displacement; p s U1 is the oil supply pressure; U2 is the first axial positive overlap, U3 is the second axial positive overlap, U4 is the third axial positive overlap, and δ is the radial clearance.

5. The method for indirectly measuring the internal fit dimensions of a positive overlapping slide valve according to claim 1, characterized in that, The four points on the straight-line segment of the static pressure characteristic curve are arbitrarily selected two points each on the straight-line segment of the characteristic curve of the pressures of two load ports and the spool displacement.

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