Pitch angle measuring device and method for fan blades

Abstract

The present application relates to a pitch angle measurement device and method for fan blades. The device comprises a pitch measurement drive end, comprising a rolling element, a measuring rod, a compression spring, and a sensor sensing end; wherein the measuring rod, under the action of the compression spring, drives the rolling element so that the rolling element is in close contact with a pitch adjustment rocker arm; the pitch adjustment rocker arm comprises a pitch adjustment reference rocker arm and a pitch adjustment measurement rocker arm; and a pitch measurement receiving end; wherein the pitch adjustment reference rocker arm has a circular hub correction surface, and the pitch adjustment measurement rocker arm has a cam hub measurement surface.

Description

Technical Field

[0001] The present application relates to a pitch angle measurement device and a measurement method for fan blades. Background Art

[0002] The open fan engine adjusts the pitch angle of the fan blades through a variable pitch system, so that the fan blades in different working conditions can operate at the appropriate incoming flow angle, thereby improving working efficiency and reducing the engine's fuel consumption.

[0003] To measure and provide feedback on the pitch angle in real time, it is necessary to measure and collect data on the fan blade pitch angle during operation. By analyzing the relationship between the fan blade angle, blade speed, and engine power, closed-loop control of the blade angle can be achieved, thereby improving the operating efficiency of the open fan. For most propeller aircraft, because the turbine output shaft and propeller input shaft of many turboprop engines are not coaxial, existing solutions generally measure the displacement of the actuator piston using an LVDT (Linear Variable Displacement Transducer) built into the actuator. This displacement is then used to inversely calculate the propeller pitch angle.

[0004] However, for open rotor engines and some propeller aircraft, since the propeller fan input shaft and turbine output shaft are coaxial, the propeller fan pitch angle cannot be measured using the LVDT technical solution. Instead, the propeller fan pitch angle is measured by arranging a non-contact Hall sensor near the root of the blade.

[0005] However, the above-described prior art solution, due to the introduction of a reference angular displacement measurement mechanism and a displacement angle measurement mechanism, will produce rotor imbalance when the two are symmetrically arranged, and the imbalance varies with the pitch angle, making it impossible to perform direct balancing, thereby increasing the vibration of the propeller fan in the working state and affecting flight safety.

[0006] Therefore, for an open fan engine in which the turbine output shaft and the fan input shaft are coaxial, there is a need in the art for an effective pitch angle measurement device and measurement method that can reduce or avoid the generation of dynamic imbalance. Summary of the Invention

[0007] An object of the present application is to provide a pitch angle measurement device for a fan blade.

[0008] One object of the present application is to provide a measurement method.

[0009] According to the first aspect of the present application, a pitch angle measuring device for fan blades, the measuring device includes: a pitch measurement transmission end, including a rolling body, a measuring rod, a compression spring, and a sensor sensing end; wherein, the measuring rod can drive the rolling body under the action of the compression spring, so that the rolling body is close to the pitch adjustment rocker arm; the pitch adjustment rocker arm includes a pitch adjustment reference rocker arm and a pitch adjustment measuring rocker arm; and a pitch measurement receiving end; wherein, the pitch adjustment reference rocker arm has a circular hub correction surface, and the pitch adjustment measuring rocker arm has a cam hub measuring surface; when the pitch adjustment reference rocker arm is driven, the distance between the sensor sensing end and the pitch measurement receiving end is a first distance, and the first distance remains unchanged; when the pitch adjustment measurement rocker arm is driven, the rolling body drives the sensor sensing end to move, so that the distance between the pitch measurement transmission end and the pitch measurement receiving end is a second distance, and the second distance changes.

[0010] In one or more embodiments of the measuring device, the sensor sensing end and the pitch measurement receiving end constitute a Hall, eddy current, and laser sensing structure.

[0011] In one or more embodiments of the measuring device, there are multiple pitch measurement receiving ends arranged on the engine stator, and the multiple pitch measurement receiving ends are symmetrically arranged.

[0012] In one or more embodiments of the measuring device, a variation range of the measuring distance corresponding to the working profile of the cam does not exceed a measuring range of the sensor.

[0013] According to a second aspect of the present application, a measurement method is provided for measuring the pitch angle of a fan blade using the pitch angle measurement device described in the first aspect. The measurement method comprises the following steps:

[0014] Arrange the pitch adjustment rocker arm and the pitch measurement transmission end;

[0015] Performing measurements to obtain a first distance, a second distance, and a theoretical measured distance of the pitch adjustment rocker arm;

[0016] The pitch angle is obtained according to the first distance, the second distance, and the relationship between the theoretical measured distance of the pitch regulating rocker arm and the pitch angle. The relationship is as follows:

[0017] (1)

[0018] L1 is the first distance, L2 is the second distance, The theoretical measured distance of the pitch adjustment rocker arm.

[0019] In one or more embodiments of the measurement method, arranging the pitch adjustment rocker arm and the pitch measurement transmission end includes the following steps:

[0020] Select two fan blades in completely symmetrical positions, defined as a first fan blade and a second fan blade, set the pitch adjustment measurement rocker arm at the roots of the first fan blade and the second fan blade, and set the pitch adjustment reference rocker arm at the roots of the remaining fan blades;

[0021] The pitch measurement transmission end is set on the fan support hub corresponding to the first fan blade and the second fan blade, and the third fan blade and the fourth fan blade that are symmetrically distributed are selected from the remaining fan blades, and the pitch measurement transmission end is set on the fan support hub corresponding to the third fan blade and the fourth fan blade;

[0022] The circumferential phase difference between the first fan blade and the second fan blade is The circumferential phase difference between the third fan blade and the fourth fan blade is The angle between the line connecting the first fan blade and the second fan blade and the line connecting the third fan blade and the fourth fan blade is Satisfies the following formula:

[0023] (2)

[0024] In the above formula, , N is the number of fan blades, is the floor function.

[0025] In one or more embodiments of the measurement method, the sampling frequency of the pitch measurement receiving end matches the fan speed , sampling frequency The following formula is satisfied:

[0026] (3).

[0027] In one or more embodiments of the measurement method, averaging the measurement signals at various locations comprises the following steps:

[0028] Assuming different positions ( ) at the pitch measurement receiving end to measure different positions ( ) The signal at the pitch measurement receiving end is , respectively average the distance signals measured at the first fan blade, the second fan blade, the third fan blade, and the fourth fan blade:

[0029] (4)

[0030] (5)

[0031] Average the distance signals measured by the different pitch measurement receivers:

[0032] (6)

[0033] (7)

[0034] Substituting formulas (4)-(7) into formula (1), we can obtain the formula for calculating the pitch angle of the control system:

[0035] (8)

[0036] In the above formula .

[0037] In one or more embodiments of the measurement method, when a pitch measurement transmission end at a certain position fails, the pitch angle calculation formula is as follows:

[0038] When the pitch measurement transmission end at position a fails, the pitch angle calculation formula becomes:

[0039] (9);

[0040] When the pitch measurement transmission end at position b fails, the pitch angle calculation formula becomes:

[0041] (10);

[0042] When the pitch measurement transmission end at position c fails, the pitch angle calculation formula becomes:

[0043] (11);

[0044] When the pitch measurement transmission end at position d fails, the pitch angle calculation formula becomes:

[0045] (12).

[0046] In one or more embodiments of the measurement method, when a pitch measurement receiving end at a certain position fails, the pitch angle is calculated based on signals from other pitch measurement receiving ends. A total of n pitch measurement receiving ends are arranged, where the kth pitch measurement receiving end fails. The pitch angle calculation formula is:

[0047] (13);

[0048] in , k and n are both positive integers.

[0049] The advantages of the present application include, but are not limited to, achieving effective pitch angle measurement by rationally arranging the rocker arm and pitch measurement components and processing the measurement signals while avoiding the introduction of imbalance. Specifically, the beneficial effects include, but are not limited to, one or a combination of the following:

[0050] 1. It is adaptable to a wide range of applications and can be used with different types of non-contact displacement measurement sensors, including Hall, eddy current, and laser sensors. The sensor receiving end is located at the stator end, facilitating electrical transmission. It is also adaptable to almost all types of propeller engines and open fan engines with more than four blades (the fan input shaft and turbine output shaft can be coaxial or not), and can accommodate different types of variable pitch mechanisms, including hydraulic, electric, and mechanical types. It does not introduce additional rotor imbalance during operation, reducing the risk of excessive engine vibration.

[0051] 2. Boolean operations on different sensor signals can eliminate basic vibration interference to a certain extent and improve the pitch angle measurement accuracy;

[0052] 3. The pitch measurement signal transmission end and receiving end can be designed with redundancy to improve reliability;

[0053] 4. By selecting appropriate lightweight angular displacement measurement mechanism materials, it can have the characteristics of light weight and relatively simple structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The above and other features, properties and advantages of the present application will become more apparent through the following description in conjunction with the accompanying drawings and embodiments. It should be noted that the drawings are only for illustration and are not drawn to scale, and should not be used to limit the actual scope of protection claimed in this application. Among them:

[0055] Figure 1 It is a structural schematic diagram of a pitch angle measuring device according to an embodiment.

[0056] Figure 2A as well as Figure 2B It is a structural schematic diagram of a rocker arm of a pitch angle measuring device according to one embodiment.

[0057] Figures 3A to 3C Schematic diagram of different pitch measurement signals obtained by a pitch angle measurement device according to an embodiment.

[0058] Figure 4 The figure is a schematic diagram of the layout of the rocker arm and pitch measurement components of a pitch angle measurement device according to one embodiment.

[0059] Figure 5 It is a flowchart of a pitch angle measurement method according to an embodiment.

[0060] Figure 6 Schematic diagram of a pitch angle measuring device and a blade according to an embodiment. DETAILED DESCRIPTION

[0061] The following discloses various different implementation methods or embodiments of the subject technical solution. To simplify the disclosure, specific examples of various components and arrangements are described below. Of course, these are only examples and are not intended to limit the scope of protection of this application.

[0062] In addition, it should be understood that terms such as "one embodiment," "an embodiment," and / or "some embodiments," or "one or more embodiments" refer to a feature, structure, or characteristic associated with at least one embodiment of the present application. Therefore, it should be emphasized and noted that the mention of "one embodiment," "one embodiment," "some embodiments," or "one or more embodiments" two or more times in different locations in this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics in one or more embodiments of the present application may be appropriately combined.

[0063] As attached Figure 1 As shown, the front end of an open fan engine is surrounded by a circle of multiple fan blades 1 (typically an even number, such as 4, 6, 8, 10, or 12). Each fan blade 1 is mounted on a fan support hub 2 via a fan support bearing 3. An inlet cone 6 is fixed to the fan support hub 2, which is in turn fixedly connected to the fan input shaft / turbine output shaft 9. The input end of the variable pitch mechanism 5 is typically fixed to the fan support hub 2 or the fan input shaft / turbine output shaft 9. The output end of the variable pitch mechanism 5 is connected to a pitch adjustment rocker arm 4, which is fixedly connected to the root of the fan blade 1. When the variable pitch mechanism 5 is in operation, it drives the rocker arm to rotate about the axis of the fan support bearing 3, thereby rotating the fan blades and adjusting the pitch angle. During the pitch angle adjustment process, the open fan pitch angle is measured in real time via the pitch measurement transmission terminal 7 and the pitch measurement receiving terminal 8, thereby achieving closed-loop feedback control of the pitch angle.

[0064] The following describes the principle of measuring the pitch angle of an open fan according to the solution of the embodiment.

[0065] As attached Figure 2A as well as Figure 2BAs shown, the pitch measurement component includes two parts: a pitch measurement drive end 7 and a pitch measurement receiving end 8. The pitch measurement drive end 7 further includes a rolling body 701, a measuring rod 702, a compression spring 703, a measuring bracket 704 and a sensor sensing end 705. The measuring rod 702 drives the rolling body 701 under the action of the compression spring 703, for example, the rolling body 701 is driven to the left as shown in the figure, so that the rolling body 701 is close to the pitch adjustment rocker arm 4, wherein the pitch adjustment rocker arm 4 includes two configurations, including a pitch adjustment reference rocker arm 401 and a pitch adjustment measurement rocker arm 402. As shown in the figure, compared with the pitch adjustment reference rocker arm 401, the pitch adjustment measurement rocker arm 402 has an additional cam. The cam can be manufactured integrally with the rocker arm or separately, and can be installed on the basis of the pitch adjustment reference rocker arm 401. Since the measurement is non-contact, the specific forms of the sensor sensing end 705 and the pitch measurement receiving end 8 can be designed in some embodiments using non-contact distance measurement principles such as Hall, eddy current, and laser.

[0066] Pitch adjustment reference rocker arm 401 is designed to include a correction surface with a circular hub. When pitch adjustment reference rocker arm 401 drives fan blade 1 to change its pitch angle, its outer hub is always in contact with rolling element 701. Because pitch adjustment reference rocker arm 401 uses a circular hub correction surface design, the distance L1 between sensor sensing end 705 and pitch measurement receiving end 8 remains unchanged. However, when pitch adjustment measurement rocker arm 402 drives fan blade 1 to change its pitch angle, its outer hub is always in contact with rolling element 701. Because pitch adjustment measurement rocker arm 402 uses a cam hub measurement surface design, rolling element 701, driven by the cam hub measurement surface, moves sensor sensing end 705, causing the distance L2 between sensor sensing end 705 and pitch measurement receiving end 8 to change. By comparing L1 and L2, the pitch angle of the fan rotor blade can be inversely calculated. Since the difference between L2 and L1 is used as the input for pitch measurement, this measurement method can avoid pitch measurement errors caused by axial deformation or vibration of the fan support hub 2 and the pitch adjustment rocker arm 4, compared to directly measuring the pitch using L2. Figure 3A 、 Figure 3B The L1 and L2 variation curves shown in the pitch adjustment stroke (assuming the rocker arm rotates clockwise) have many basic noise glitches on the two curves due to deformation and vibration. Indicates the theoretical measurement distance of the pitch adjustment reference rocker arm 401 (the theoretical distance between the pitch adjustment reference rocker arm 401 corresponding sensor sensing end 705 and the pitch measurement receiving end 8), which is a constant; L2, L1 and Subtracting the three curves can eliminate most of the basic noise burrs, such as Figure 3C shown.

[0067] The structural design of the cam and measuring transmission components is generally based on the open fan structure layout, pitch angle adjustment range (usually no more than ) Design the cam for pitch adjustment measuring rocker arm 402 and select the measuring sensor. Cam design and sensor selection generally require ensuring that the range of measurement distances (L1, L2) corresponding to the cam's operating profile is compatible with the sensor's effective range.

[0068] Regarding the layout of the rocker arm and pitch measurement components, the pitch measurement receiving terminal 8 is arranged on the engine stator, and is generally arranged in a completely symmetrical manner. Assuming that there are n sets of pitch measurement receiving terminals 8 ( ), then these receiving ends are arranged symmetrically on the stator, with a spacing angle of Assume n=4, such as Figure 6 As shown, the interval between the receiving ends , it can be considered to be placed at the 12 o'clock, 3 o'clock, 6 o'clock and 9 o'clock positions on the engine. If there is insufficient space, the position of the receiver can be appropriately adjusted, or the number of receivers can be reduced, but at least two sets should be guaranteed to have a redundant design.

[0069] The rocker arm and pitch measurement drive end 7 are respectively matched with the fan blade 1 and the fan support hub 2, and are engine rotor components. Their layout generally needs to take into account the coordination with the fan blade and the balance of the rotor. Due to the inconsistency between L1 and L2 during pitch adjustment, and the inconsistency between the centers of mass of the two rocker arms, namely the pitch adjustment reference rocker arm 401 and the pitch adjustment measurement rocker arm 402, if the pitch adjustment reference rocker arm 401 and the pitch adjustment measurement rocker arm 402 are arranged symmetrically (with a circumferential difference ), will inevitably produce an unbalanced couple, which brings challenges to the balance of the engine's dynamic rotor.

[0070] To this end, in some embodiments, the following may be used: Figure 4 The arrangement of the pitch adjustment rocker arm 4 and the pitch measurement transmission end 7 is shown as follows:

[0071] Two fan blades in completely symmetrical positions are selected (points a and c in the figure), and pitch adjustment measurement rocker arms 402 are installed at the roots of the corresponding blades, and pitch adjustment reference rocker arms 401 are installed at the roots of the remaining fan blades.

[0072] The pitch measuring transmission end 7 is arranged and installed on the fan support hub 2 corresponding to positions a and c. In addition, two symmetrical positions b and d are selected and the pitch measuring transmission end 7 is installed on the corresponding fan support hub 2, that is, the pitch measuring transmission end 7 is arranged at four positions.

[0073] The following requirements apply to position points a, b, c, and d: The circumferential phase difference between position points a and c is: ; Circumferential phase difference between position points b and d ; The angle between the line connecting positions a and c and the line connecting positions c and d (Small angle, ) satisfies the following formula:

[0074] (1)

[0075] In the above formula, N is the number of blades of the open fan, is a floor function. For a 4-blade fan engine, Set as ; 6 fan blade engine, Set as ; 8 fan blades engine, Set as ; 12 fan blade engine, Set as .

[0076] The embodiment employs four sets of pitch measurement transmission ends 7 at four selected locations. This advantageously eliminates rotor unbalance couples caused by inconsistent distances between L1 and L2 during operation, reducing the risk of excessive engine vibration. Furthermore, it provides the measurement system with a redundant backup function, ensuring continuous measurement of the pitch angle in the event of a pitch measurement component failure. Because the pitch measurement components are not subject to stress, in some embodiments, lightweight materials such as plastic, aluminum alloy, or composite materials can be used, further reducing the weight of the entire measurement device.

[0077] As mentioned above, refer to Figure 5 As shown, the present application also provides a method for measuring a pitch angle, comprising the following steps:

[0078] S100. Arrange the pitch adjustment rocker arm and the pitch measurement transmission end.

[0079] For the specific layout method, please refer to the above introduction to the structural design of the pitch adjustment rocker arm and the layout position of the pitch measurement transmission end. I will not go into details here.

[0080] S200. Measure and obtain the first distance, the second distance, and the theoretical measured distance of the pitch adjustment rocker arm. As described above, the pitch angle of the fan rotor blade can be calculated by comparing L1 and L2, and L2, L1 and Subtracting the three curves can eliminate most of the basic noise glitches.

[0081] S300. Obtain the pitch angle according to the first distance, the second distance, and a relationship between a theoretically measured distance of the pitch regulating rocker arm and the pitch angle.

[0082] Specific calculation steps may include:

[0083] S301. For pitch angle calibration, in some embodiments, the blade pitch angle can be obtained according to the cam working profile function or the actual measurement calibration method. The functional relationship with L1 and L2 is as follows:

[0084] (2)

[0085] L1 is the first distance, L2 is the second distance, The theoretical measured distance of the pitch adjustment rocker arm.

[0086] Continue to refer Figure 5 As shown, the calculation step may further include: S302. Extracting and correcting the pitch measurement signal.

[0087] In some embodiments, since the rotation sensing signal is extracted, the sampling frequency of the pitch measurement receiving end 8 needs to match the open fan speed. (around the engine axis, in rpm) and the layout of the pitch measurement drive end 7, the sampling frequency (Unit: Hz) Requirements are as follows:

[0088] (3)

[0089] In the above formula The definition of is given in formula (1).

[0090] In some embodiments, the measurement signals at various positions may be averaged to more comprehensively reflect the overall pitch angle.

[0091] Assuming different positions ( ) at the pitch measurement receiving end 8 to measure different positions ( ) The signal of the pitch measurement receiving end 8 is In order to more comprehensively reflect the overall pitch angle, the distance signals measured at a, c and b, d are averaged respectively:

[0092] (4)

[0093] (5)

[0094] The distance signals measured by the receiving end 8 for different pitch measurements are averaged:

[0095] (6)

[0096] (7).

[0097] Continue to refer Figure 5 As shown, the calculation step may further include: S303. Pitch angle calculation.

[0098] Continue to refer Figure 5 , for the pitch angle calculation, substitute formula (4)-(7) into formula (2) to obtain the control system pitch angle calculation formula:

[0099] (8).

[0100] In the above formula Since the system has a redundant design, when the pitch measurement transmission end 7 or the pitch measurement receiving end 8 at a certain position fails, the pitch angle can still be measured and calculated.

[0101] When the pitch measurement transmission end 7 at position a fails, the pitch angle calculation formula becomes:

[0102] (9).

[0103] When the pitch measurement transmission end 7 at position b fails, the pitch angle calculation formula becomes:

[0104] (10).

[0105] When the pitch measurement transmission end 7 at position c fails, the pitch angle calculation formula becomes:

[0106] (11).

[0107] When the pitch measurement transmission end 7 at position d fails, the pitch angle calculation formula becomes:

[0108] (12).

[0109] When a pitch measurement receiving terminal 8 at a certain position fails, the pitch angle is calculated based on the signals from other pitch measurement receiving terminals 8. Assuming that a total of n pitch measurement receiving terminals 8 are arranged, and the kth pitch measurement receiving terminal 8 fails, the pitch angle calculation formula becomes:

[0110] (13)

[0111] in , where k and n are both positive integers.

[0112] As described above, the advantageous effects of the pitch angle measurement device and method for fan blades provided in this application include but are not limited to one or a combination of the following:

[0113] 1. It is adaptable to a wide range of applications and can be used with different types of non-contact displacement measurement sensors, including Hall, eddy current, and laser sensors. The sensor receiving end is located at the stator end, facilitating electrical transmission. It is also adaptable to almost all types of propeller engines and open fan engines with more than four blades (the fan input shaft and turbine output shaft can be coaxial or not), and can accommodate different types of variable pitch mechanisms, including hydraulic, electric, and mechanical types. It does not introduce additional rotor imbalance during operation, reducing the risk of excessive engine vibration.

[0114] 2. Boolean operations on different sensor signals can eliminate basic vibration interference to a certain extent and improve the pitch angle measurement accuracy;

[0115] 3. The pitch measurement signal transmission end and receiving end can be designed with redundancy to improve reliability;

[0116] 4. By selecting appropriate lightweight angular displacement measurement mechanism materials, it can have the characteristics of light weight and relatively simple structure.

[0117] Although the present application is disclosed above with reference to the above embodiments, they are not intended to limit the present application. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present application. Therefore, any modifications, equivalent variations, and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application shall fall within the scope of protection defined by the claims of the present application.

Claims

1. A measurement method, characterized in that: A measuring device is used to measure the pitch angle of a fan blade, the measuring device comprising: a pitch measurement transmission end, comprising a rolling body, a measuring rod, a compression spring, and a sensor sensing end; wherein, the measuring rod can drive the rolling body under the action of the compression spring, so that the rolling body is close to the pitch adjustment rocker arm; the pitch adjustment rocker arm comprises a pitch adjustment reference rocker arm and a pitch adjustment measuring rocker arm; and a pitch measurement receiving end; wherein, the pitch adjustment reference rocker arm has a circular hub correction surface, and the pitch adjustment measuring rocker arm has a cam hub measurement surface; when the pitch adjustment reference rocker arm is driven, the distance between the sensor sensing end and the pitch measurement receiving end is a first distance, and the first distance remains unchanged; when the pitch adjustment measuring rocker arm is driven, the rolling body drives the sensor sensing end to move, so that the distance between the pitch measurement transmission end and the pitch measurement receiving end is a second distance, and the second distance changes; The measuring method comprises the following steps: Arrange the pitch adjustment rocker arm and the pitch measurement transmission end; Performing measurements to obtain a first distance, a second distance, and a theoretical measured distance of the pitch adjustment rocker arm; The pitch angle is obtained according to the first distance, the second distance, and the relationship between the theoretical measured distance of the pitch regulating rocker arm and the pitch angle. The relationship is as follows: （1） L1 is the first distance, L2 is the second distance, The theoretical measured distance of the pitch adjustment rocker arm.

2. The measuring method according to claim 1, wherein Arranging the pitch adjustment rocker arm and the pitch measurement transmission end includes the following steps: Select two fan blades in completely symmetrical positions, defined as a first fan blade and a second fan blade, set the pitch adjustment measurement rocker arm at the roots of the first fan blade and the second fan blade, and set the pitch adjustment reference rocker arm at the roots of the remaining fan blades; The pitch measurement transmission end is set on the fan support hub corresponding to the first fan blade and the second fan blade, and the third fan blade and the fourth fan blade that are symmetrically distributed are selected from the remaining fan blades, and the pitch measurement transmission end is set on the fan support hub corresponding to the third fan blade and the fourth fan blade; The circumferential phase difference between the first fan blade and the second fan blade is The circumferential phase difference between the third fan blade and the fourth fan blade is The angle between the line connecting the first fan blade and the second fan blade and the line connecting the third fan blade and the fourth fan blade is Satisfies the following formula: （2） In the above formula, , N is the number of fan blades, is the floor function.

3. The measuring method according to claim 2, wherein: The sampling frequency of the pitch measurement receiver matches the fan speed , sampling frequency The following formula is satisfied: （3）。 4. The measuring method according to claim 3, wherein: Averaging the measurement signals at each position includes the following steps: Assuming different positions ( ) at the pitch measurement receiving end to measure different positions ( ) The signal at the pitch measurement receiving end is , respectively average the distance signals measured at the first fan blade, the second fan blade, the third fan blade, and the fourth fan blade: （4） （5） Average the distance signals measured by the different pitch measurement receivers: （6） （7） Substituting formulas (4)-(7) into formula (1), we can obtain the formula for calculating the pitch angle of the control system: （8） In the above formula .

5. The measuring method according to claim 4, wherein: When the pitch measurement transmission end at a certain position fails, the pitch angle calculation formula is as follows: When the pitch measurement transmission end at position a fails, the pitch angle calculation formula becomes: （9）； When the pitch measurement transmission end at position b fails, the pitch angle calculation formula becomes: （10）； When the pitch measurement transmission end at position c fails, the pitch angle calculation formula becomes: （11）； When the pitch measurement transmission end at position d fails, the pitch angle calculation formula becomes: （12）。 6. The measuring method according to claim 4, wherein: When a pitch measurement receiving end at a certain position fails, the pitch angle is calculated based on the signals of other pitch measurement receiving ends. A total of n pitch measurement receiving ends are arranged, among which the kth pitch measurement receiving end fails. The pitch angle calculation formula is: （13）； in , k and n are both positive integers.

7. The measuring method according to claim 1, wherein: The sensor sensing end and the pitch measurement receiving end constitute a Hall, eddy current and laser sensing structure.

8. The measuring method according to claim 1, wherein: There are multiple pitch measurement receiving ends, which are arranged on the engine stator, and the multiple pitch measurement receiving ends are symmetrically arranged.

9. The measuring method according to claim 1, wherein: The variation range of the measuring distance corresponding to the working contour line of the cam does not exceed the measuring range of the sensor.

Images