Constant voltage difference device with temperature compensation function and adjusting method thereof

Abstract

This invention relates to a constant pressure differential device and adjustment method with temperature compensation function, comprising a piston, a high-precision spring, a butterfly-shaped bimetallic thermosensitive element, a flat washer, a screw cap, and a throttling plate. The piston, high-precision spring, butterfly-shaped bimetallic thermosensitive element, flat washer, screw cap, and throttling plate are housed within a casing. The piston is located within the inner cavity of the casing, dividing the inner cavity into sub-cavities a and c. Sub-cavity a communicates with high-pressure oil P1, and sub-cavity c communicates with low-pressure oil P2. Sub-cavity b is provided on the casing. A high-precision spring is installed at the lower end of the piston, controlling the oil flow area of ​​sub-cavities a and b. A butterfly-shaped bimetallic thermosensitive element and a flat washer are installed at the lower end of the high-precision spring. A screw cap is located within the inner cavity of the casing. A throttling oil passage is provided inside the casing, and a throttling plate is installed inside the throttling oil passage. The inlet of the throttling oil passage communicates with high-pressure oil P1, and the outlet communicates with sub-cavity c. High-pressure oil P1 communicates with the inlet of an oil metering device, and low-pressure oil P2 communicates with the outlet of the oil metering device.

Description

Technical Field

[0001] This invention belongs to the field of mechanical engineering technology and relates to a constant differential pressure device with temperature compensation function and an adjustment method thereon. Background Technology

[0002] Oil metering devices are suitable for precise control of oil or gas flow in fields such as engines, petroleum, and natural gas.

[0003] Generally, oil metering devices are controlled by the size of the throttling window, and their mass flow rate equation is as follows:

[0004]

[0005] Where P1-P2 is the pressure difference before and after the window, Cd is the flow coefficient, A is the window area, and ρ is the density of the oil.

[0006] Under normal temperature conditions, the flow metering device controls the opening of the metering valve core via an electro-hydraulic servo valve, thereby accurately measuring the window area A and achieving fuel flow measurement. Traditional metering methods have the following drawbacks:

[0007] 1. The pressure difference before and after the window is difficult to guarantee precisely. Although the pressure difference can be maintained by components such as constant pressure reducing valves and overflow valves, their structure and principle are relatively complex.

[0008] 2. The density of some oils or gases (such as aviation kerosene) varies greatly with temperature, but the engine requires mass flow rate during use, which will lead to a reduction in the amount of fuel supplied to the engine at high temperatures and a decrease in power.

[0009] 3. Before the system starts, the metering window area A is zero. Because the low pressure P2 has not been fully established, it will cause a sudden increase in flow rate.

[0010] 4. If flow metering devices use temperature sensors, differential pressure sensors, etc. for data acquisition and control, there are problems such as high cost and low reliability. Summary of the Invention

[0011] To address the shortcomings of existing oil metering devices, the purpose of this invention is to provide a constant pressure differential device and adjustment method with temperature compensation function. By precisely controlling the flow rate of high-pressure oil to the return oil through the balance of spring force, high-pressure oil pressure, and low-pressure oil pressure, the pressure differential across the metering window is maintained constant. The heating and bending deformation of a butterfly-shaped bimetallic temperature-sensitive element compresses the spring, increasing the spring force and thus the pressure differential of the constant pressure differential device. This compensates for fluctuations in oil mass flow rate caused by changes in oil density under different temperature conditions. During adjustment, the compensation coefficient can be quantitatively adjusted by increasing or decreasing the number of butterfly-shaped bimetallic temperature-sensitive elements.

[0012] Compared with traditional flow metering devices, this invention has the advantages of simple structure, temperature compensation, convenient operation, high debugging efficiency, and high reliability.

[0013] The technical solution of the present invention is as follows:

[0014] A constant pressure differential device with temperature compensation function is used to adjust the inlet and outlet pressure difference of an oil metering device. It includes: a piston (1), a high-precision spring (2), a butterfly bimetallic thermosensitive sheet (3), a flat washer (4), a screw cap (5), and a throttling plate (6). The piston (1), high-precision spring (2), butterfly bimetallic thermosensitive sheet (3), flat washer (4), screw cap (5), and throttling plate (6) are placed in the housing (7) of the oil metering device.

[0015] The piston (1) is installed in the inner cavity of the housing (7). The piston (1) divides the inner cavity of the housing (7) into sub-cavity a and sub-cavity c. Sub-cavity a communicates with high-pressure oil P1, and sub-cavity c communicates with low-pressure oil P2.

[0016] The housing (7) is provided with a sub-cavity b, and a high-precision spring (2) is installed at the lower end of the piston. The oil passage area of ​​the sub-cavity a and sub-cavity b is controlled by the spring force of the high-precision spring (2).

[0017] A butterfly-shaped bimetallic thermosensitive sheet (3) and a flat washer (4) are installed at the lower end of the high-precision spring (2), and a screw cap (5) is provided at the bottom of the inner cavity of the housing (7);

[0018] The housing (7) is provided with a throttling oil passage, and the throttling oil passage is provided with multiple throttling plates (6). The inlet of the throttling oil passage is connected to the high-pressure oil P1, and the outlet is connected to the sub-cavity c.

[0019] High-pressure oil P1 is connected to the inlet of the oil metering device, and low-pressure oil P2 is connected to the outlet of the oil metering device.

[0020] Furthermore, the butterfly-shaped bimetallic thermosensitive sheet (3) consists of multiple circular metal sheets with an outer diameter smaller than the inner diameter of the shell (7).

[0021] Furthermore, the butterfly-shaped bimetallic thermosensitive sheet (3) is made of a thermal bimetallic strip, the thickness of which increases with increasing temperature and decreases with decreasing temperature.

[0022] Furthermore, the flat washer (4) consists of multiple circular metal sheets, the outer diameter of which is smaller than the inner diameter of the housing (7).

[0023] Furthermore, the screw cap (5) is screwed into the bottom of the inner cavity of the housing (7), and the pre-compression distance of the high-precision spring (2) is controlled by the screwing depth.

[0024] Furthermore, the mating surfaces of the screw cap (5) and the inner cavity of the housing (7) are sealed with sealant.

[0025] Furthermore, the flat washer (4) and the butterfly bimetallic thermosensitive sheet (3) can be interchanged to adjust the temperature compensation capability of the device.

[0026] Adjustment methods for constant differential pressure devices with temperature compensation include methods to keep the actual differential pressure consistent with the design differential pressure value, methods to compensate for the design differential pressure value when the temperature changes, and methods to establish differential pressure when the metering device is in open and closed operating conditions.

[0027] (1) Methods to keep the actual pressure difference consistent with the design pressure difference value

[0028] When the constant pressure differential device is working normally, the top of the piston 1 of the constant pressure differential device is subjected to the downward force of the high-pressure oil P1 flowing through the sub-cavity a, and the bottom of the piston 1 of the constant pressure differential device is subjected to the upward spring force of the high-precision spring 2 on the piston 1 and the upward force of the low-pressure oil P2 in the sub-cavity c on the piston 1. The forces on the top and bottom of the piston 1 of the constant pressure differential device are equal. When the oil passage windows of sub-cavities a and b are open, the ratio of the spring force to the piston area is the pressure differential design value of the constant pressure differential device.

[0029] When the pressure difference between high-pressure oil P1 and low-pressure oil P2 is higher than the design value of the pressure difference, under the action of high-pressure oil P1, the piston moves downward, increasing the oil passage area of ​​sub-cavity a and sub-cavity b. Part of the high-pressure oil P1 flows into the return oil R through sub-cavity b, reducing the pressure of high-pressure oil P1, thereby reducing the pressure difference and making the actual pressure difference equal to the design value of the pressure difference.

[0030] When the pressure difference between high-pressure oil P1 and low-pressure oil P2 is lower than the design value of the pressure difference, under the combined force of low-pressure oil P2 and spring force, the piston moves upward, reducing the oil passage area of ​​sub-cavity a and sub-cavity b. The amount of high-pressure oil P1 flowing into the return oil R through sub-cavity b decreases, increasing the pressure of high-pressure oil P1, thereby reducing the pressure difference and making the actual pressure difference equal to the design value of the pressure difference.

[0031] (2) Methods for compensating for differential pressure design values ​​when temperature changes

[0032] When the oil temperature increases, the oil density decreases, according to the formula... It can be seen that in order to ensure that the mass flow rate Q remains constant, the pressure difference design value P1-P2 needs to be increased. At this time, the temperature rises, the thickness of the butterfly bimetallic temperature sensor 3 increases, the compression of the high-precision spring 2 increases, the spring force increases, and the ratio of the spring force to the piston area when the oil passage windows of sub-cavity a and sub-cavity b are opened, that is, the pressure difference design value of the constant pressure difference device increases, which compensates for the decrease in oil density caused by the temperature rise and maintains the constant mass flow rate of the metering device.

[0033] When the oil temperature decreases, the oil density increases, according to the formula... It can be seen that in order to ensure that the mass flow rate Q remains constant, the differential pressure design value P1-P2 needs to be reduced. At this time, the temperature decreases, the thickness of the butterfly bimetallic temperature sensor 3 decreases, the compression of the high-precision spring 2 decreases, the spring force decreases, and the ratio of the spring force to the piston area when the oil passage windows of sub-cavity a and sub-cavity b are opened, that is, the differential pressure design value of the constant differential pressure device decreases, which compensates for the increase in oil density caused by the decrease in temperature and maintains the constant mass flow rate of the metering device.

[0034] The constant pressure differential device adjusts the temperature compensation coefficient of the butterfly bimetallic thermosensitive element by adjusting the number of butterfly bimetallic thermosensitive elements (3) and flat washers (4);

[0035] (3) Methods for establishing pressure difference in the metering device under operating conditions before and after opening.

[0036] High-pressure oil (P1) communicates with the throttling plate (6) and the sub-cavity c connected to the low-pressure oil P2. Under the conditions before and after the metering device is opened, the high-pressure oil P1 flows to the sub-cavity c of the housing (7) through the throttling plate (6) to establish the pressure of the low-pressure oil P2 in advance. This prevents the low-pressure oil P2 from being too low in pressure before or after the metering device is opened, and the pressure difference P1-P2 from being too large. This causes the piston (1) to move downward, and the oil passage window area of ​​the sub-cavity a and sub-cavity b of the housing (7) to be too large, resulting in excessive flow of high-pressure oil P1 into the return oil R through sub-cavity b. This also prevents the piston (2) from moving upward too quickly when the metering window of the metering device is opened, and the rapid change of the pressure difference P1-P2 from causing fluctuations in the metering flow.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] 1. The present invention introduces low-pressure oil into the piston chamber and maintains the pressure difference between the two chambers of the piston by overflowing and reducing the pressure of high-pressure oil. Compared with the traditional constant pressure reducing valve and overflow valve, the structure is simpler and the number of components is reduced. It has the advantages of simple structure, convenient installation and reliable performance.

[0039] 2. This invention utilizes the characteristic that the thickness of the butterfly-shaped bimetallic temperature-sensitive sheet changes with temperature, so that the design differential pressure of the constant pressure differential device changes with temperature, compensating for the reduction in mass flow rate caused by the change in oil density with temperature. Compared with existing temperature sensor and differential pressure sensor solutions, it is a purely mechanical structure, does not require a dedicated electronic controller, and has the advantages of high reliability and low cost.

[0040] 3. The present invention sets a throttling plate between the high-pressure oil and the low-pressure oil, so that the low pressure is established in advance, preventing excessive oil loss before or after the flow metering device is turned on or off, and also preventing excessive pressure difference fluctuations when it is turned on and off. Attached Figure Description

[0041] Figure 1 This invention relates to a constant differential pressure device with temperature compensation function;

[0042] Figure 2 This is a schematic diagram of the butterfly-shaped bimetallic temperature sensor used in this invention. Figure 1 ;

[0043] Figure 3 This is a schematic diagram of the butterfly-shaped bimetallic temperature sensor used in this invention. Figure 2 ;

[0044] Figure 4 This is a schematic diagram illustrating the connection principle between the constant differential pressure device and the flow metering device of the present invention. Detailed Implementation

[0045] To more intuitively and clearly illustrate the structural principles and working methods in the embodiments of the present invention, the following description will be based on the accompanying drawings. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0046] An embodiment of the present invention provides a constant differential pressure device with temperature compensation function. The device is installed in an oil metering device to maintain a constant pressure difference before and after the metering window and to provide temperature compensation function.

[0047] The present invention provides a constant differential pressure device with temperature compensation function, such as... Figure 1 Figure 4 As shown, it includes: 1 is a piston, 2 is a high-precision spring, 3 is a butterfly-shaped bimetallic temperature-sensitive sheet, 4 is a flat washer, 5 is a screw cap, 6 is a throttling plate, 7 is the housing of the oil metering device, 8 is the oil metering device, P1 is high-pressure oil, P2 is low-pressure oil and R is return oil, a is high-pressure oil chamber, b is return oil chamber and c is low-pressure oil chamber.

[0048] Piston 1 is installed in the inner cavity of the oil metering device housing 7. Cavities a and c at both ends of the piston are respectively connected to high-pressure oil P1 and low-pressure oil P2, which require maintaining a pressure difference. A high-precision spring 2 is installed at the lower end of the piston, and the size of the oil port from cavity a to cavity b is controlled by the spring force of the high-precision spring 2. A butterfly-shaped bimetallic temperature-sensitive sheet 3 and a flat washer 4 are installed on the lower side of the high-precision spring 2. Finally, the screw cap is screwed into the inner cavity of the oil metering device housing 7 for fixation. The high-pressure oil P1 and low-pressure oil P2 are provided with a throttling oil circuit composed of multiple throttling plates 6.

[0049] The gap between the outer diameter of piston 1 and the inner diameter of the inner cavity of oil metering device housing 7 is about 0.01mm to ensure smooth piston movement and sealing.

[0050] The outer diameters of the high-precision spring 2, the butterfly-shaped bimetallic temperature-sensitive sheet 3, and the flat washer 4 are smaller than the inner diameter of the inner cavity of the oil metering device housing 7.

[0051] The temperature compensation coefficient of the constant pressure differential device is adjusted by changing the number of butterfly bimetallic thermosensitive elements 3.

[0052] The butterfly-shaped bimetallic thermosensitive sheet 3 is a circular metal sheet made of thermo-bimetallic strip. At room temperature, it is a flat sheet, but at high temperature, it bends and deforms into a convex sheet. The amount of bending deformation increases with the temperature, converting thermal energy into mechanical energy to drive the valve sleeve to achieve automatic temperature compensation.

[0053] The throttling plate 6 can reduce its impact on the metering flow rate by setting different flow resistances. When the flow metering device 8 does not need to maintain stability at the moment of opening, a sealing plate can be installed to seal the oil circuit.

[0054] This invention provides a constant differential pressure device with temperature compensation function. By utilizing the bending and deformation of the butterfly bimetallic thermosensitive sheet 3 under temperature changes, the differential pressure device compensates for the mass flow rate of the flow metering device, thereby reducing the temperature drift of the mass flow rate.

[0055] Figure 1 This invention relates to a constant differential pressure device with temperature compensation. When the temperature is constant, the flow rate of high-pressure oil to return oil is precisely controlled by balancing the spring force, high-pressure oil pressure, and low-pressure oil pressure, thereby maintaining a constant pressure difference before and after the metering window. When the oil temperature changes, the butterfly-shaped bimetallic temperature-sensitive sheet 3 bends and deforms, increasing or decreasing the compression of the high-precision spring 2, which in turn changes the differential pressure design value of the constant differential pressure device, ensuring that the mass flow rate of the flow metering device remains stable with temperature changes.

[0056] Figure 2 , 3 The butterfly-shaped bimetallic thermosensitive sheet 3 of the present invention is a circular metal sheet made of thermo-bimetallic strip. At room temperature, it is a flat sheet, but at high temperature, it is bent and deformed into a convex sheet. The amount of bending deformation increases with the increase of temperature, converting thermal energy into mechanical energy to drive the valve sleeve to realize the automatic temperature compensation function.

[0057] Figure 4 This is an oil circuit connection diagram of a constant pressure differential device with temperature compensation function and a flow metering device 8 according to the present invention. The constant pressure differential device is installed before and after the metering window of the flow metering device 8, and plays the role of maintaining a constant pressure difference between high pressure oil P1 and low pressure oil P2.

[0058] An adjustment method for a constant differential pressure device with temperature compensation function is described below:

[0059] (1) Specific methods to ensure that the actual pressure difference is consistent with the design pressure difference value

[0060] When the constant pressure differential device is working normally, the top of the piston 1 of the constant pressure differential device is subjected to the downward force of the high-pressure oil P1 flowing through the sub-cavity a, and the bottom of the piston 1 of the constant pressure differential device is subjected to the upward spring force of the high-precision spring 2 on the piston 1 and the upward force of the low-pressure oil P2 in the sub-cavity c on the piston 1. The forces on the top and bottom of the piston 1 of the constant pressure differential device are equal. When the oil passage windows of sub-cavities a and b are open, the ratio of the spring force to the piston area is the pressure differential design value of the constant pressure differential device.

[0061] When the pressure difference between high-pressure oil P1 and low-pressure oil P2 is higher than the design value of the pressure difference, under the action of high-pressure oil P1, the piston moves downward, increasing the oil passage area of ​​sub-cavity a and sub-cavity b. Part of the high-pressure oil P1 flows into the return oil R through sub-cavity b, reducing the pressure of high-pressure oil P1, thereby reducing the pressure difference and making the actual pressure difference equal to the design value of the pressure difference.

[0062] When the pressure difference between high-pressure oil P1 and low-pressure oil P2 is lower than the design value of the pressure difference, under the combined force of low-pressure oil P2 and spring force, the piston moves upward, reducing the oil passage area of ​​sub-cavity a and sub-cavity b. The amount of high-pressure oil P1 flowing into the return oil R through sub-cavity b decreases, increasing the pressure of high-pressure oil P1, thereby reducing the pressure difference and making the actual pressure difference equal to the design value of the pressure difference.

[0063] (2) Methods for compensating for differential pressure design values ​​when temperature changes

[0064] When the oil temperature increases, the oil density ρ decreases, according to the formula... It can be seen that in order to ensure that the mass flow rate Q remains constant, the pressure difference design value P1-P2 needs to be increased. At this time, the temperature rises, the thickness of the butterfly bimetallic temperature sensor 3 increases, the compression of the high-precision spring 2 increases, the spring force increases, and the ratio of the spring force to the piston area when the oil passage windows of sub-cavity a and sub-cavity b are opened, that is, the pressure difference design value of the constant pressure difference device increases, which compensates for the decrease in oil density caused by the temperature rise and maintains the constant mass flow rate of the metering device.

[0065] When the oil temperature decreases, the oil density ρ increases, according to the formula... It can be seen that in order to ensure that the mass flow rate Q remains constant, the differential pressure design value P1-P2 needs to be reduced. At this time, the temperature decreases, the thickness of the butterfly bimetallic temperature sensor 3 decreases, the compression of the high-precision spring 2 decreases, the spring force decreases, and the ratio of the spring force to the piston area when the oil passage windows of sub-cavity a and sub-cavity b are opened, that is, the differential pressure design value of the constant differential pressure device decreases, which compensates for the increase in oil density caused by the decrease in temperature and maintains the constant mass flow rate of the metering device.

[0066] The constant pressure differential device adjusts the temperature compensation coefficient of the butterfly bimetallic thermosensitive element by adjusting the number of butterfly bimetallic thermosensitive elements 3 and flat washers 4.

[0067] (3) Methods for establishing pressure difference in the metering device under operating conditions before and after opening.

[0068] High-pressure oil P1 communicates with the sub-cavity c, which is connected to low-pressure oil P2, through the throttling plate 6. Before and after the metering device is opened, high-pressure oil P1 flows through the throttling plate 6 to the sub-cavity c of the housing 7, establishing the pressure of low-pressure oil P2 in advance. This prevents the low-pressure oil P2 from being too low or the pressure difference P1-P2 from being too large when the metering device is open or closed. This would cause piston 1 to move downward, resulting in an excessively large oil passage area between sub-cavities a and b of the housing 7, causing excessive flow of high-pressure oil P1 into the return oil R through sub-cavity b. This also prevents fluctuations in the metering flow rate caused by piston 2 moving upward too quickly when the metering window of the metering device is opened, resulting in rapid changes in the pressure difference P1-P2.

[0069] The above description is only a preferred embodiment of the present invention. Any details not covered herein are considered conventional technical means in the art. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A constant pressure differential device with temperature compensation function, used for adjusting the inlet and outlet pressure differential of an oil metering device, characterized in that, include: Piston (1), high-precision spring (2), butterfly bimetallic thermosensitive sheet (3), flat washer (4), screw cap (5), throttling plate (6), piston (1), high-precision spring (2), butterfly bimetallic thermosensitive sheet (3), flat washer (4), screw cap (5), throttling plate (6) are placed in the housing (7) of the oil metering device; The piston (1) is installed in the inner cavity of the housing (7). The piston (1) divides the inner cavity of the housing (7) into sub-cavity a and sub-cavity c. Sub-cavity a communicates with high-pressure oil P1, and sub-cavity c communicates with low-pressure oil P2. The housing (7) is provided with a sub-cavity b, and a high-precision spring (2) is installed at the lower end of the piston. The oil passage area of ​​the sub-cavity a and sub-cavity b is controlled by the spring force of the high-precision spring (2). A butterfly-shaped bimetallic thermosensitive sheet (3) and a flat washer (4) are installed at the lower end of the high-precision spring (2), and a screw cap (5) is provided at the bottom of the inner cavity of the housing (7); The housing (7) is provided with a throttling oil passage, and the throttling oil passage is provided with multiple throttling plates (6). The inlet of the throttling oil passage is connected to the high-pressure oil P1, and the outlet is connected to the sub-cavity c. High-pressure oil P1 is connected to the inlet of the oil metering device, and low-pressure oil P2 is connected to the outlet of the oil metering device.

2. The constant pressure differential device with temperature compensation function as described in claim 1, characterized in that, The butterfly-shaped bimetallic thermosensitive sheet (3) consists of multiple circular metal sheets with an outer diameter smaller than the inner diameter of the shell (7).

3. The constant differential pressure device with temperature compensation function as described in claim 2, characterized in that, The butterfly-shaped bimetallic thermosensitive sheet (3) is made of thermo-bimetallic strip, and its thickness increases with increasing temperature and decreases with decreasing temperature.

4. The constant pressure differential device with temperature compensation function as described in claim 1, characterized in that, The flat washer (4) consists of multiple circular metal sheets, the outer diameter of which is smaller than the inner diameter of the shell (7).

5. The constant differential pressure device with temperature compensation function as described in claim 1, characterized in that, The screw cap (5) is screwed into the bottom of the inner cavity of the housing (7), and the pre-compression distance of the high-precision spring (2) is controlled by the screwing depth.

6. The constant differential pressure device with temperature compensation function as described in claim 4, characterized in that, The mating surfaces of the screw cap (5) and the inner cavity of the housing (7) are sealed with sealant.

7. The constant pressure differential device with temperature compensation function as described in claim 1, characterized in that, The flat washer (4) and the butterfly bimetallic thermosensitive sheet (3) are interchangeable to adjust the temperature compensation capability of the device.

8. The adjustment method of the constant pressure differential device with temperature compensation function according to any one of claims 1-7, characterized in that, This includes methods to ensure that the actual differential pressure matches the design differential pressure value, methods to compensate for differential pressure design values ​​when temperatures change, and methods to establish differential pressure when the metering device is in open and closed operating conditions. (1) Methods to keep the actual pressure difference consistent with the design pressure difference value When the constant pressure differential device is working normally, the top of the piston 1 of the constant pressure differential device is subjected to the downward force of the high-pressure oil P1 flowing through the sub-cavity a, and the bottom of the piston 1 of the constant pressure differential device is subjected to the upward spring force of the high-precision spring 2 on the piston 1 and the upward force of the low-pressure oil P2 in the sub-cavity c on the piston 1. The forces on the top and bottom of the piston 1 of the constant pressure differential device are equal. When the oil passage windows of sub-cavities a and b are open, the ratio of the spring force to the piston area is the pressure differential design value of the constant pressure differential device. When the pressure difference between high-pressure oil P1 and low-pressure oil P2 is higher than the design value of the pressure difference, under the action of high-pressure oil P1, the piston moves downward, increasing the oil passage area of ​​sub-cavity a and sub-cavity b. Part of the high-pressure oil P1 flows into the return oil R through sub-cavity b, reducing the pressure of high-pressure oil P1, thereby reducing the pressure difference and making the actual pressure difference equal to the design value of the pressure difference. When the pressure difference between high-pressure oil P1 and low-pressure oil P2 is lower than the design value of the pressure difference, under the combined force of low-pressure oil P2 and spring force, the piston moves upward, reducing the oil passage area of ​​sub-cavity a and sub-cavity b. The amount of high-pressure oil P1 flowing into the return oil R through sub-cavity b decreases, increasing the pressure of high-pressure oil P1, thereby reducing the pressure difference and making the actual pressure difference equal to the design value of the pressure difference. (2) Methods for compensating for differential pressure design values ​​when temperature changes When the oil temperature increases, the oil density decreases, according to the formula... It can be seen that in order to ensure that the mass flow rate Q remains constant, the pressure difference design value P1-P2 needs to be increased. At this time, the temperature rises, the thickness of the butterfly bimetallic temperature sensor 3 increases, the compression of the high-precision spring 2 increases, the spring force increases, and the ratio of the spring force to the piston area when the oil passage windows of sub-cavity a and sub-cavity b are opened, that is, the pressure difference design value of the constant pressure difference device increases, which compensates for the decrease in oil density caused by the temperature rise and maintains the constant mass flow rate of the metering device. When the oil temperature decreases, the oil density increases, according to the formula... It can be seen that in order to ensure that the mass flow rate Q remains constant, the differential pressure design value P1-P2 needs to be reduced. At this time, the temperature decreases, the thickness of the butterfly bimetallic temperature sensor 3 decreases, the compression of the high-precision spring 2 decreases, the spring force decreases, and the ratio of the spring force to the piston area when the oil passage windows of sub-cavity a and sub-cavity b are opened, that is, the differential pressure design value of the constant differential pressure device decreases, which compensates for the increase in oil density caused by the decrease in temperature and maintains the constant mass flow rate of the metering device. The constant pressure differential device adjusts the temperature compensation coefficient of the butterfly bimetallic thermosensitive element by adjusting the number of butterfly bimetallic thermosensitive elements (3) and flat washers (4); (3) Methods for establishing pressure difference in the metering device under operating conditions before and after opening. High-pressure oil (P1) communicates with the throttling plate (6) and the sub-cavity c connected to the low-pressure oil P2. Under the conditions before and after the metering device is opened, the high-pressure oil P1 flows to the sub-cavity c of the housing (7) through the throttling plate (6) to establish the pressure of the low-pressure oil P2 in advance. This prevents the low-pressure oil P2 from being too low in pressure before or after the metering device is opened, and the pressure difference P1-P2 from being too large. This causes the piston (1) to move downward, and the oil passage window area of ​​the sub-cavity a and sub-cavity b of the housing (7) to be too large, resulting in excessive flow of high-pressure oil P1 into the return oil R through sub-cavity b. This also prevents the piston (1) from moving upward too quickly at the moment the metering window of the metering device is opened, and the rapid change of the pressure difference P1-P2 from causing fluctuations in the metering flow.

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