Low-pressure-loss segmented differential pressure type flow metering device

Abstract

The invention relates to a low-pressure-loss segmented differential pressure type flow metering device, and belongs to the field of flow adjustment. The flow metering device comprises a differential pressure sensor (1), a controller (2), a port (3) and one or more cascaded metering sections (4), each metering section structurally comprises a throttling body (5), a control coil (6) and a shell (7), a permanent magnet is embedded in the throttling body and can slide along a guide shaft (8) under the control of the control coil, and the shell (7) is arranged in an inner cavity of the throttling body. Two limiting and positioning feedback mechanisms (9) are arranged on the guide shaft, the controller calculates flow according to pressure difference and positioning feedback signals, current control is conducted on the control coil, the limiting state of the throttling body is adjusted, the metering device is kept in a low-pressure-difference state, the number of metering sections can be increased according to the measuring range, and the metering efficiency is improved. And low-pressure-loss high-precision segmented fuel oil metering in a large-flow range is realized. The flow regulating valve is low in metering pressure loss, high in precision, low in power consumption and capable of meeting the wide-range flow regulating requirement.

Description

Technical Field

[0001] The invention relates to a low-pressure-loss segmented pressure-differential flow metering device, belonging to the field of flow regulation. Background Art

[0002] Flow metering devices play a crucial role in industrial measurement. Based on their operating principles, flow metering devices can be primarily categorized into three types: differential pressure, positive displacement, and velocity. Differential pressure flow metering devices are a common type. Their core principle is to use a differential pressure transmitter to measure differential pressure, thereby measuring the flow rate of the fluid being measured. However, the accuracy characteristics of differential pressure transmitters have certain limitations. Specifically, the accuracy of a differential pressure transmitter is defined based on its full measurement range, i.e., full-scale accuracy. This means that the larger the differential pressure measurement range, the lower the measurement accuracy at low differential pressures. At high flow rates, laminar flow meters struggle to maintain laminar flow in the flow channel. At these conditions, the fluid velocity is high, leading to turbulence. Conversely, at low flow rates, the differential pressure cannot generate a sufficient differential pressure to meet the measurement requirements of the differential pressure transmitter. This significantly limits the measurement range of differential pressure fuel metering devices, making them unable to cover the full range of measurement requirements.

[0003] Limited by the accuracy of differential pressure transmitters, differential pressure flowmeters cannot achieve a large range while maintaining measurement accuracy. To overcome this, invention patents such as publication number CN111896059A propose a differential pressure adaptive metering section. Utilizing the concept of laminar flow, the metering differential pressure is inversely proportional to the flow path length. By shifting the spindle-shaped throttle body, the flow path length measured by the differential pressure transmitter is changed, ensuring a larger differential pressure at low flow rates and a smaller differential pressure at high flow rates. However, due to the friction between the spindle-shaped throttle body and the guide shaft, the device creates a dead zone, resulting in a decrease in metering accuracy and a large pressure drop in the metering section. Publication number CN115307693B uses two throttle plates, each with a function hole. By changing the relative position of the holes on the two throttle plates, the flowmeter's piezoresistance is adjusted to accommodate the pressure difference at different flow rates within an appropriate range. However, it only has two working ranges and cannot meet the requirements of a larger range and higher accuracy.

[0004] In summary, there is currently no differential pressure metering device that can meet high precision and wide range while also having small errors, and the cascaded metering sections of the low-pressure-loss segmented differential pressure flow metering device can adapt to a variety of practical applications. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the existing differential pressure flowmeter, and propose a low pressure loss segmented differential pressure flowmeter, which is characterized by comprising a differential pressure sensor (1), a controller (2), a port (3) and one or more cascaded metering sections (4), wherein the metering section structure comprises: a throttle body (5), a control coil (6), and a shell (7), wherein a permanent magnet is embedded in the throttle body and can slide along a guide shaft (8) under the control of the control coil, and two limit and positioning feedback mechanisms (9) are arranged on the guide shaft in the inner cavity of the throttle body; the guide shaft has an axial hole and threaded holes at both ends, and is made of insulating material; the outer surface of the guide shaft has four annular grooves, each annular groove and the axial hole have a through hole, and the four annular grooves are respectively embedded with two limit and positioning feedback mechanisms; the limit and positioning feedback mechanism uses conductive material and is composed of a limit ring and a conductive ring; there are two ports, namely an inlet end and an outlet end, and a threaded hole is arranged on the port. The hole is used to install the pressure pipe. The port has a flange that can be connected by welding or threading. The low-pressure-loss segmented pressure differential flow metering device is connected to other pipelines by flange connection. There are four rectangular grooves on the end face of the port, three of which have screw holes for installing the shaft fixing device; the shaft fixing device consists of a welding stud and a bracket, the welding stud is threadedly connected to the guide shaft, and the bracket consists of three solid elliptical cylindrical legs and an elliptical cylindrical leg with a through hole, which forms a passage with the shaft hole in the guide shaft; the high-pressure measuring port of the differential pressure sensor is connected to the threaded hole at the inlet end through the pressure pipe, and the low-pressure measuring port is connected to the threaded hole at the outlet end through the pressure pipe; the material of the throttling body is N54 permanent magnet, the outer surface is a second-order differentiable smooth surface, and there is an annular groove on the inside of the throttling body; the outer surface of the shell has a groove for placing the control coil, and the internal channel of the shell is a structure that first contracts and then expands.

[0006] The metering section of the low-pressure-loss segmented pressure-differential flow metering device is characterized by a flow channel formed by a throttle body and a shell. When the measured fluid flows through the flow channel, a pressure drop is generated, and the flow rate is measured through the functional relationship between the pressure difference and the flow rate; the throttle body only works at the two end positions of the range limited by the limit and positioning feedback mechanism, that is, the throttle body has two working positions, namely the minimum throttle area position and the maximum throttle area position. According to the following pressure-differential flow formula, in order to ensure that there is still sufficient pressure differential under low flow conditions while reducing the pressure loss under high flow conditions, the throttle body is located at the minimum throttle area position when the flow rate is small, and the throttle body is located at the maximum throttle area position when the flow rate is large:

[0007]

[0008] Among them, C d is the flow coefficient, which is related to Re and β (indicating aperture ratio), Y1 is the expansion coefficient, which is 1 if incompressible, and S is the throttling area.

[0009] The low-pressure-loss segmented pressure-differential flow metering device is characterized by a limit and positioning feedback mechanism installed on the guide shaft. The limit and positioning feedback mechanism cooperates with the annular groove of the throttle body to ensure that the throttle body can only move within a specified range, thereby playing a limiting role on the throttle body. When realizing the positioning function of the limit and positioning feedback mechanism, the limit and positioning feedback mechanism and the throttle body jointly form a switch. Each metering section has two limit and positioning feedback mechanisms, which are connected to the controller through wires. When the throttle body contacts the limit ring of one of the limit and positioning feedback mechanisms, the limit and positioning feedback mechanism is turned on, and the controller can receive the conduction electrical signal. Therefore, the limit and positioning feedback mechanism can determine whether the throttle body is in the minimum throttling area position and the minimum throttling area.

[0010] The size of the metering section of the low-pressure-loss segmented pressure differential flow metering device can be flexibly adjusted according to the actual application. When the required range is large and the accuracy requirement is high, multiple metering sections are required to divide the range into segments; since the minimum throttling area and the maximum throttling area of ​​different metering sections may be different, the corresponding sizes of the connecting body and the shell may also be different, and the size of the annular groove in the throttling body also needs to be adjusted accordingly. The size of the shell of the metering section and the annular groove of the throttling body of the low-pressure-loss segmented pressure differential flow metering device are all related to the actual application and can be specifically configured and adjusted according to the application requirements and adjustment time.

[0011] The working principle and control method of the low-pressure-loss segmented pressure differential flow metering device are characterized as follows:

[0012] Force balance condition: The throttle body is subjected to five forces in the axial direction: magnetic force, pressure difference force and viscous friction force of the fluid on the throttle body, friction force of the shaft on the throttle body, and elastic force of the limit and positioning device on it;

[0013] The magnetic field generated by the controlled coil in space:

[0014]

[0015] Where R0 represents the coil radius, x is the distance from the field point to the center of the circle.

[0016] The magnetic force generated by the magnetic field on the throttle body:

[0017]

[0018] Pressure difference force of fluid on throttling body:

[0019]

[0020] Viscous friction of fluid on throttle body:

[0021]

[0022] The combined force of the friction force of the shaft on the throttle body and the elastic force of the limit and positioning device on the throttle body:

[0023]

[0024] From Newton's second law:

[0025] ma=F m +F p +F f1 +F f2

[0026] Control method: Minimum throttle area → maximum throttle area: When the flow rate increases to a certain value, the controller receives that the throttle body is at the minimum throttle area position, and the pressure differential value input to the controller by the pressure differential sensor reaches the specified value. The controller immediately changes the current of the controlled coil, from providing a pulling force on the throttle body to offset the resistance of the fluid on the throttle body to generating a thrust, quickly pushing the position of the throttle body in the metering section to the maximum throttle area position. At this time, the controller receives the new position information of the throttle body, and the controller reduces the current of the controlled coil to a sufficient amount to maintain the throttle body in the maximum throttle area position; Maximum throttle area → minimum throttle area: When the flow rate decreases to a certain value, the controller receives that the throttle body is at the maximum throttle area position, and the pressure differential value input to the controller by the pressure differential sensor reaches the specified value. The controller immediately changes the current of the controlled coil, providing a larger pulling force on the throttle body, while offsetting the resistance of the fluid on the throttle body, pulling the throttle body to the minimum throttle area position. At this time, the controller receives the new position information of the throttle body, and the controller reduces the current of the controlled coil to a sufficient amount to maintain the throttle body in the minimum throttle area position.

[0027] The low-pressure-loss segmented pressure differential flow metering device is characterized in that multiple metering sections are cascaded. When there are n metering sections, the low-pressure-loss segmented pressure differential flow metering device has a total of n+1 working states: the throttle bodies of n metering sections are located at the minimum throttle area position, the throttle bodies of n-1 metering sections are located at the minimum throttle area position, ..., the throttle body of 0 metering section is located at the minimum throttle area position. The design process of the low-pressure-loss segmented pressure differential flow metering device with multiple metering sections cascaded is as follows:

[0028] 1) Determine the measuring range Q min →Q max And divide the range into n+1 segments: Q min →Q1, Q1→Q2, …, Q n →Q max ;

[0029] 2) Determine the maximum pressure difference P between the two ports when the low pressure loss segmented pressure differential flow metering device is working normallymax , and select the appropriate differential pressure sensor;

[0030] 3) n+1 range requires n metering sections, and the minimum throttling area of ​​each metering section is S 1min 、S 2min ,……,S nmin , the maximum throttling area is S 1max 、S 2max ,……,S nmax , the following are the constraint equations for each throttling area:

[0031]

[0032] When S 1max =S 2max =……=S nmax The minimum throttling area and the maximum throttling area of ​​each metering section can be directly obtained;

[0033] 4) Design the shell and throttle body of corresponding size for each metering section according to the maximum and minimum throttling area of ​​each metering section.

[0034] Compared with the prior art, the advantages of the present invention are:

[0035] 1) The cascaded segmented metering section achieves high pressure differential at low flow rates and low pressure differential at high flow rates, overcoming the disadvantage of the differential pressure sensor's poor accuracy at low flow rates and low pressure differentials, ensuring high-precision metering across the entire range and flow regulation requirements with low pressure loss.

[0036] 2) The throttle body is limited and positioned by the limit and positioning feedback mechanism, ensuring the normal operation of the device within the normal range. At the same time, the feedback function of the limit and positioning feedback mechanism further improves the reliability of the device;

[0037] 3) The adaptive adjustment of the controlled coil current is achieved through the feedback function of the limit and positioning feedback mechanism, ensuring that the controlled coil only requires the minimum maintenance current, which significantly reduces the current size of the controlled coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The present invention is a flow metering device for measuring fuel of aviation engines.

[0039] Figure 2 This is a cross-sectional view of the metering section for aviation engine fuel metering according to the present invention.

[0040] Figure 3 This is the first starting stage of the flow metering device for aviation engine fuel metering according to the present invention.

[0041] Figure 4This is the second starting stage of the flow metering device for aviation engine fuel metering according to the present invention.

[0042] Figure 5 The present invention is a flow metering device for measuring fuel of an aviation engine at slow speed and above.

[0043] Figure 6 The present invention provides a flow metering device control plan for aviation engine fuel metering. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0045] See also Figure 1 In an embodiment of the present invention, a low-pressure-loss segmented pressure-differential flow metering device comprises a pressure-differential sensor (1), a controller (2), a port (3) and two cascaded metering sections (4), wherein the metering section structure comprises: a throttle body (5), a control coil (6) and a housing (7), wherein a permanent magnet is embedded in the throttle body and can slide along a guide shaft (8) under the control of the control coil, and two limit and positioning feedback mechanisms (9) are arranged on the guide shaft in the inner cavity of the throttle body; the guide shaft has an axial hole and threaded holes at both ends, and is made of insulating material; the outer surface of the guide shaft has four annular grooves, each annular groove and the axial hole have a through hole, and the four annular grooves are respectively embedded with two limit and positioning feedback mechanisms; the limit and positioning feedback mechanism uses conductive material and is composed of a limit ring and a conductive ring; there are two ports, namely an inlet end and an outlet end, and a threaded hole is provided on the port for installing a pressure pipe, and the port There is a flange that can be connected by welding or threading, and the low-pressure-loss segmented pressure differential flow metering device is connected to other pipelines by flange connection. There are four rectangular grooves on the end face of the port, three of which have screw holes for installing an axis fixing device; the axis fixing device consists of a welding stud and a bracket, the welding stud is threadedly connected to the guide shaft, and the bracket consists of three solid elliptical cylindrical legs and an elliptical cylindrical leg with a through hole, which forms a passage with the shaft hole in the guide shaft; the high-pressure measuring port of the pressure differential sensor is connected to the threaded hole at the inlet end through a pressure pipe, and the low-pressure measuring port is connected to the threaded hole at the outlet end through a pressure pipe; the material of the throttling body is N54 permanent magnet, the outer surface is a second-order differentiable smooth surface, and there is an annular groove on the inside of the throttling body; the outer surface of the shell has a groove for placing the control coil, and the internal channel of the shell is a structure that first contracts and then expands.

[0046] See also Figure 2 The metering section of the low-pressure-loss segmented pressure-differential flow metering device is characterized in that a flow channel is formed by a throttling body and a shell. When the measured fluid flows through the flow channel, a pressure drop is generated, and the flow rate is measured by the functional relationship between the pressure difference and the flow rate; the throttling body only works at the two end positions within the range limited by the limit and positioning feedback mechanism, that is, the throttling body has two working positions, namely the minimum throttling area position and the maximum throttling area position. According to the following pressure-differential flow formula, in order to ensure that there is still sufficient pressure differential under low flow conditions while reducing the pressure loss under high flow conditions, the throttling body is located at the minimum throttling area position when the flow rate is small, and the throttling body is located at the maximum throttling area position when the flow rate is large:

[0047]

[0048] Among them, C d is the flow coefficient, which is related to Re and β (indicating aperture ratio), Y1 is the expansion coefficient, which is 1 if incompressible, and S is the throttling area.

[0049] This embodiment targets the measurement of the fluid flow of aviation kerosene with a given flow range of 200kg / h-4000kg / h. The differential pressure sensor used has a range of 5kPa. This embodiment has three operating states: starting phase 1, starting phase 2, and slow running and above. Starting phase 1 corresponds to a flow range of 200kg / h-500kg / h, starting phase 2 corresponds to a flow range of 450kg / h-1250kg / h, and slow running and above corresponds to a flow range of 1200kg / h-4000kg / h. The flow metering device operates as follows within the measurement range:

[0050] ①Starting stage is the same as Figure 3 As shown in the figure, the throttle bodies of the two metering sections are both at the minimum throttle area position; ② The starting stage is as follows Figure 4 As shown in the figure, the throttle body of the inlet metering section is at the maximum throttle area position, and the throttle body of the outlet metering section is at the minimum throttle area position; ③ Slow and above stages as shown in the figure Figure 5 As shown, the throttle bodies of the two-stage metering sections are both in the position of maximum throttling area.

[0051] See also Figure 6 Since this embodiment is directed to fuel metering for aircraft engines, it is not necessary to adjust the throttle body position in the metering section when the aircraft engine starts and enters the idle stage or above. Therefore, the stage conversion in this embodiment includes starting stage 1 → starting stage 2 → idle stage or above, and starting stage 2 → starting stage 1 when the aircraft engine fails to start. The stage conversion method of the embodiment of the present invention is as follows:

[0052] ①Starting stage 1 → Starting stage 2: When the flow rate increases to 450Kg / h, the pressure difference obtained by the pressure difference sensor reaches 4050Pa. The controller receives that both metering sections are at the minimum throttling area position, and the pressure difference value input to the controller by the pressure difference sensor is 4050Pa. The controller immediately changes the current of the controlled coil of the metering section on the inlet side, from providing a pulling force on the throttle body to offset the resistance of the fluid on the throttle body to generating a thrust, quickly pushing the position of the throttle body of the metering section on the inlet side to the maximum throttling area position. At this time, the positioning and limiting device transmits this position information to the controller, and the controller reduces the current of the controlled coil to keep the throttle body in the current position;

[0053] ②Starting stage 2 → slow speed and above: When the flow rate increases to 1200Kg / h, the pressure difference obtained by the pressure differential sensor reaches 4608Pa. The controller receives that the inlet side metering section is at the maximum throttling area position, the outlet side metering section is at the minimum flow area position, and the pressure difference value input to the controller by the pressure differential sensor is 4608Pa. The controller immediately changes the current of the controlled coil of the outlet side metering section, from providing a pulling force on the throttle body to offset the resistance of the fluid on the throttle body to generating a thrust, quickly pushing the position of the throttle body of the outlet side metering section to the maximum throttling area position. At this time, the positioning and limiting device transmits this position information to the controller, and the controller reduces the current of the controlled coil to keep the throttle body in the current position;

[0054] ③Starting stage 2 → Starting stage 1: When the flow rate decreases to 450Kg / h, the pressure difference obtained by the pressure difference sensor reaches 648Pa. The controller receives that both metering sections are in the maximum throttling area position, and the pressure difference value input to the controller by the pressure difference sensor is 648Pa. The controller immediately changes the current of the controlled coil of the metering section on the outlet side, providing a larger pulling force on the throttling body, offsetting the resistance of the fluid on the throttling body and pulling the throttling body to the minimum throttling area position. At this time, the positioning and limiting device transmits the position information to the controller, and the controller reduces the current of the controlled coil to enable the throttling body to maintain the minimum throttling body area position.

Claims

1. A low-pressure-loss segmented pressure differential flow metering device comprises a pressure differential sensor (1), a controller (2), a port (3), and one or more cascaded metering sections (4), wherein the metering section structure comprises: A throttle body (5), a control coil (6), and a housing (7) are provided. A permanent magnet is embedded in the throttle body and can slide along a guide shaft (8) under the control of the control coil. Two limit and positioning feedback mechanisms (9) are arranged on the guide shaft in the inner cavity of the throttle body. The guide shaft has an axial hole and threaded holes at both ends. The guide shaft is made of insulating material. The outer surface of the guide shaft has four annular grooves. Each annular groove and the axial hole have a through hole. The four annular grooves are respectively embedded with two limit and positioning feedback mechanisms. The limit and positioning feedback mechanisms are made of conductive material and are composed of a limit ring and a conductive ring. There are two ports, namely an inlet port and an outlet port. The port has a threaded hole for installing a pressure pipe. The port has a flange that can be connected by welding or threading. The flange connection is used to adjust the low pressure loss segmented pressure difference. The flow metering device is connected to other pipelines, and there are four rectangular grooves on the end face of the port, three of which have screw holes for installing the shaft fixing device; the shaft fixing device consists of a welded stud and a bracket, the welded stud is threadedly connected to the guide shaft, and the bracket consists of three solid elliptical cylindrical legs and an elliptical cylindrical leg with a through hole, which forms a passage with the shaft hole in the guide shaft; the high-pressure measuring port of the differential pressure sensor is connected to the threaded hole at the inlet end through a pressure pipe, and the low-pressure measuring port is connected to the threaded hole at the outlet end through a pressure pipe; the material of the throttle body is N54 permanent magnet, the outer surface is a second-order differentiable smooth surface, and there is an annular groove on the inside of the throttle body; the outer surface of the shell has a groove for accommodating the control coil, and the internal channel of the shell has a structure that first contracts and then expands; The metering section of the low-pressure-loss segmented pressure-differential flow metering device is characterized by a flow channel formed by a throttle body and a shell. When the measured fluid flows through the flow channel, a pressure drop is generated, and the flow rate is measured through the functional relationship between the pressure difference and the flow rate; the throttle body only works at the two end positions of the range limited by the limit and positioning feedback mechanism, that is, the throttle body has two working positions, namely the minimum throttle area position and the maximum throttle area position. According to the following pressure-differential flow formula, in order to ensure that there is still sufficient pressure differential under low flow conditions while reducing the pressure loss under high flow conditions, the throttle body is located at the minimum throttle area position when the flow rate is small, and the throttle body is located at the maximum throttle area position when the flow rate is large: Among them, C d is the flow coefficient, which is related to Re and β (indicating aperture ratio), Y1 is the expansion coefficient, which is 1 if incompressible, and S is the throttling area.

2. A low pressure loss segmented pressure differential flow metering device as claimed in claim 1, characterized in that The limit and positioning feedback mechanism installed on the guide shaft cooperates with the annular groove of the throttle body to ensure that the throttle body can only move within the specified range, thereby playing a limiting role on the throttle body. When realizing the positioning function of the limit and positioning feedback mechanism, the limit and positioning feedback mechanism and the throttle body jointly form a switch. Each metering section has two limit and positioning feedback mechanisms, which are connected to the controller through wires. When the throttle body contacts the limit ring of one of the limit and positioning feedback mechanisms, the limit and positioning feedback mechanism is turned on, and the controller can receive the conduction electrical signal. Therefore, the limit and positioning feedback mechanism can determine whether the throttle body is at the minimum throttling area position and the minimum throttling area.

3. A low pressure loss segmented pressure differential flow metering device as claimed in claim 1, characterized in that The magnetic field generated by the control coil generates a magnetic force on the throttle body, so that the throttle body overcomes the resistance generated by the fluid and maintains the original working position or changes the working position. The specific control method is as follows: Minimum throttle area → maximum throttle area: When the flow rate increases to a certain value, the controller receives the information that the throttle body is at the minimum throttle area position, and the differential pressure value input to the controller by the differential pressure sensor reaches the specified value. The controller immediately changes the current of the controlled coil, from providing a pulling force on the throttle body to offset the resistance of the fluid on the throttle body to generating a thrust, quickly pushing the position of the throttle body in the metering section to the maximum throttle area position. At this time, the controller receives the new position information of the throttle body and reduces the current of the controlled coil to a level sufficient to maintain the throttle body at the maximum throttle area position. Maximum throttling area → minimum throttling area: When the flow rate decreases to a certain value, the controller receives that the throttling body is at the maximum throttling area position, and the pressure difference value input to the controller by the pressure difference sensor reaches the specified value. The controller immediately changes the current of the controlled coil, provides a larger pulling force to the throttling body, and offsets the resistance of the fluid on the throttling body while pulling the throttling body to the minimum throttling area position. At this time, the controller receives the new position information of the throttling body, and the controller reduces the current of the controlled coil to be sufficient to maintain the throttling body at the minimum throttling body area position.

4. A low pressure loss segmented pressure differential flow metering device as claimed in claim 1, characterized in that When multiple metering sections are cascaded and there are n metering sections, the low-pressure-loss segmented pressure differential flow metering device has n+1 working states: the throttle bodies of n metering sections are located at the minimum throttle area position, the throttle bodies of n-1 metering sections are located at the minimum throttle area position, ..., the throttle body of 0 metering section is located at the minimum throttle area position. The design process of the low-pressure-loss segmented pressure differential flow metering device with multiple metering sections cascaded is as follows: 1) Determine the measuring range Q min →Q max And divide the range into n+1 segments: Q min →Q1, Q1→Q2, …, Q n →Q max ; 2) Determine the maximum pressure difference P between the two ports when the low pressure loss segmented pressure differential flow metering device is working normally max , and select the appropriate differential pressure sensor; 3) n+1 range requires n metering sections, and the minimum throttling area of ​​each metering section is S 1min 、S 2min ,……,S nmin , the maximum throttling area is S 1max 、S 2max ,……,S nmax , the following are the constraint equations for each throttling area: When S 1max =S 2max =……=S nmax The minimum throttling area and the maximum throttling area of ​​each metering section can be directly obtained; 4) Design the shell and throttle body of corresponding size for each metering section according to the maximum and minimum throttling area of ​​each metering section.

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