Method for accurately tracking relative position of aviation piston engine crankshaft TDC

Abstract

The invention discloses a method for accurately tracking the relative position of a crankshaft TDC of an aviation piston engine, the TDC-0-degree reference position of the piston engine can be accurately determined by stopping a piston twice, and any position of the crankshaft of the engine within the 360-degree range of one circle can be continuously and accurately tracked and positioned. The device is high in positioning precision, can always lock the TDC-0-degree reference position in the continuous rotation process of the crankshaft to continuously track the real-time rotation angle of the crankshaft, is high in efficiency, is objective, real and reliable in measurement result, is not influenced by subjective factors of an operator, timing pin abrasion and piston surface sediments, is suitable for any piston engine, and is suitable for popularization and application. The application range is wide.

Description

Technical Field

[0001] This invention relates to a technology in the field of aircraft maintenance, and in particular to a method for accurately tracking the relative angle of the crankshaft's top-down center (TDC) position on an spark-ignition piston engine. Specifically, it involves accurately determining the TDC position of the crankshaft on a spark-ignition piston engine, and using this as a reference to accurately show the relative angle between the crankshaft and the reference position at any rotational position. Background Technology

[0002] Piston engines are classified into spark-ignition and compression-ignition engines according to the ignition method of the air-fuel mixture in the cylinder. Spark-ignition piston engines require the spark plug to ignite the compressed air-fuel mixture in the cylinder when the piston is at an appropriate position before the compression stroke TDC (Top Dead Center). The angle between the instantaneous position of the crankshaft and the TDC position at this time is called the "pre-ignition angle". It is agreed that the instantaneous angle of the crankshaft is positive when the piston is before the compression stroke TDC and negative when the piston is after the compression stroke TDC.

[0003] The technical terms and background involved in this patent technology include: 1. Usage Environment like Figure 1 As shown, a piston engine consists of a cylinder, piston, connecting rod, crank, and related accessories. In the assembled piston engine, there is a certain correspondence between the position of the piston in the cylinder along the cylinder axis and the rotation angle of the crank.

[0004] The crank is part of the crankshaft, such as Figure 2 The crankshaft comprises components such as the crankshaft, connecting rod journals, main crankshaft journals, crankshaft end flanges, and rear crankshaft journals. The crankshaft journals, including the main and rear journals, are the load-bearing support parts of the crankshaft, and the center of rotation of the crankshaft is located on the centerline of the crankshaft journals. The connecting rod journals connect to the large end of the connecting rod, and the small end of the connecting rod connects to the piston. The connecting rod journals are offset from the centerline of the crankshaft journals by a certain distance and are connected to the crankshaft journals via the crankshaft. The connecting rod and crankshaft together convert the reciprocating motion of the piston in the cylinder into the rotational motion of the crankshaft. During crankshaft rotation, the crankshaft's center of rotation coincides with the centerline of the crankshaft. The crankshaft end flange is located at the outer end of the main crankshaft journal and is the connecting component for outputting crankshaft torque. It is used to mount loads such as propellers, and the rotation surface of the crankshaft end flange is perpendicular to the centerline of the crankshaft journal.

[0005] The cylinders involved in this patented technology all refer to the specific cylinders specified in the engine manual for determining the advance ignition position.

[0006] 2. TDC like Figure 3As shown, the piston reciprocates within the cylinder. When the connecting rod and crankshaft are collinear and the piston reaches the top of the cylinder, the piston is momentarily at a relative standstill. This position is called Top Dead Center (TDC), and is defined as TDC-0°, based on the instantaneous position of the crankshaft at this point. Subsequently, as the crankshaft rotates, the crankshaft moves away from the TDC-0° position. The angle between the instantaneous position of the crankshaft and the TDC-0° position is defined as the crankshaft rotation angle α.

[0007] Obviously, when the piston is in TDC, the crankshaft angle α = 0°.

[0008] 3. BDC like Figure 4 As shown, the piston reciprocates in the cylinder. When the connecting rod and crank are collinear and the piston moves to the bottom of the cylinder, the piston is in a relatively instantaneous state of relative stillness. The position of the piston at this time is called the bottom dead center, or BDC.

[0009] Obviously, when the piston is in BDC, the crankshaft rotation angle α = 180°.

[0010] 4. Pre-ignition angle like Figure 5 As shown, a spark-ignition piston engine requires the spark plug to ignite and generate an electric spark at a certain position when the piston is in the compression stroke but has not yet reached the TDC position. The specific value of the crankshaft angle α at this time is called the advance ignition angle.

[0011] Spark plug mounting holes are located in the cylinder head of spark-ignition piston engines. The spark plug mounting position is shown in the diagram. Figure 5 The spark plug inserts the ignition electrode into the cylinder through the mounting hole. The length of the ignition electrode extending into the cylinder is limited so that it does not contact the piston when the piston is in the TDC position.

[0012] The advance ignition angle varies among different models of piston engines, but the advance ignition angle of a specific piston engine model is fixed. This angle is determined by the engine manufacturer and marked on the engine nameplate. It is an important parameter in the operation of spark-ignition piston engines and a key parameter that needs to be strictly controlled during operation and maintenance. In the maintenance specifications of various types of aviation piston engines, engine manufacturers have made clear provisions on the numerical value and allowable tolerance of their engine's advance ignition angle.

[0013] In aviation maintenance engineering practice, it is necessary to accurately locate the engine's ignition advance angle. For various types of spark-ignition piston engines, engine manufacturers provide methods for locating the ignition advance angle position. However, these methods are essentially "dynamic / static marking methods," which involve marking dynamic and static reference lines on a rotating component of the engine that is associated with the crankshaft's rotation and on a stationary component that is not associated with the crankshaft's rotation. Typical examples include the Lycoming engine, where the scale markings on the starter gear (dynamic markings) and the reference point markings on the starter housing (static markings); and the Continental engine, where the scale markings on the timing gear (dynamic markings) and the reference line markings on the casing (static markings). These methods all rely on the operator visually observing the alignment between the scale markings and the static markings to make readings. Due to limitations in the dimensions of the components used to engrave the scale and human visual perception, the scale division cannot be made very small. Therefore, this positioning method has low accuracy and is easily affected by the operator's visual observation angle and subjective judgment, resulting in a relatively large overall positioning error, which to some extent affects the engine's performance. Statistical results from multiple positioning tests conducted by the same operator or different operators on the same engine show that positioning differences can reach 3-6°, while the positioning tolerance specified in engine maintenance technical specifications is ±1°.

[0014] In maintenance engineering practice, a positioning method using a precisely calibrated fixed-length or variable-length timing pin is also employed. This method directly stops the piston at the specified advance ignition angle using a single stop, which is quick to position. However, it has strict requirements on the length of the timing pin. As the timing pin wears down during use, the positioning accuracy will decrease. In addition, deposits on the piston surface will also have an adverse effect on the positioning accuracy of this method.

[0015] The ignition advance angle is an important parameter in the operation of spark-ignition piston engines. The magnitude of the positioning error will directly affect the engine's working performance. The dynamic and static marking method, as a traditional positioning method recommended by engine manufacturers, has caused many engine operation failures in engineering practice due to its accuracy issues, and is one of the difficulties in aviation maintenance practice. Summary of the Invention

[0016] The technical problem to be solved by the present invention is to provide a method for accurately tracking the TDC position of the crankshaft of an aero-piston engine, so as to effectively control the positioning accuracy to meet the maintenance specifications in practical operation, ensure that the positioning results are objective and accurate, and effectively avoid the adverse effects of operator subjective judgment and common factors such as wear of timing pins and deposits on piston surfaces.

[0017] In order to achieve the goal of solving the above-mentioned technical problems, the present invention adopts the following technical solution: A method for accurately tracking the TDC (Total Displacement Control) relative position of an aircraft piston engine crankshaft, namely, accurately determining the TDC position of the engine crankshaft and using it as a reference to calculate the relative angle between the engine crankshaft and the reference position in real time at any rotational position. The method defines the instantaneous position of the crankshaft corresponding to a specified cylinder when the piston is at TDC as TDC-0°, and defines the angle between the crankshaft corresponding to a specified cylinder and the TDC-0° position at any crankshaft position as the crankshaft angle. The engine crankshaft has a propeller mounted on a flange, and the propeller includes blades; the default speed ratio between the propeller and the engine crankshaft is 1:1. The method includes the following operational steps: Operation 1: Locate the compression stroke in the specified cylinder and install the stop pin in the spark plug mounting hole of the specified cylinder; The designated cylinder refers specifically to the specific cylinder used to determine the advance ignition position on this type of engine, as specified in the engine repair manual.

[0018] Operation 2: Install tilt sensors on the propeller blades; in particular, if the speed ratio between the engine crankshaft and the propeller is not equal to 1:1, the final result of this method needs to be recalculated based on the actual reduction ratio. Operation 3: Rotate the propeller in the opposite direction of the engine's normal rotation until the piston is stopped by the stop pin and can no longer rotate the propeller in the opposite direction. Read and record the inclinometer reading at this point as β. A ; Operation 4: Rotate the propeller clockwise in the normal direction of engine rotation until the piston is stopped by the stop pin and can no longer rotate the propeller clockwise. Read and record the inclinometer reading at this point as β. B ; Operation 5: β A and β B Substituting into Formula 3, we can obtain the crankshaft TDC relative rotation angle α corresponding to point B. B For α B =(β B -β A )*1 / 2; Wherein, Formula 3 is α B =180-(360-β B +β A )*1 / 2=(β B -β A )*1 / 2 Point B is the position of the connecting rod journal at the outer end of the crankshaft when the crankshaft is rotated in the forward direction until the piston is stopped; Operation 6: β A and β B Substituting into Formula 4, we can obtain that the TDC-0° reference position β0 is located at β0 = (β B +β A)*1 / 2; Wherein, Formula 4 is β0=β B -(β B -β A )*1 / 2=(β B +β A )*1 / 2 After the above steps, the system has determined the TDC-0° reference position with the horizontal plane as the reference. In this measurement, the TDC-0° position can be used as the reference to continuously track the relative rotation angle of the crankshaft with respect to the TDC-0° reference position during the rotation of the engine crankshaft. Operation 7: Substituting β into Formula 5, we can obtain the relative angle α between the crankshaft at any rotational position and the TDC-0° position: α = β - (β B +β A )*1 / 2; Where β is the output reading of the tilt sensor when the crankshaft is in any rotational position, Equation 5 is α=β-β0=β-(β B +β A )*1 / 2.

[0019] The method for accurately tracking the relative position of the crankshaft TDC of an aircraft piston engine, if the angle output by the inclinometer is β when the engine crankshaft is in any rotational position, the crankshaft rotation angle at any rotational position can be obtained as α = β - β0. Substituting Equation 4, we get α = β - β0 = β - (β B +β A )*1 / 2, which is Equation 5, where β A and β B It is a constant and is only valid during this measurement.

[0020] A method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine, more specifically, involves adding the following steps one and two before any of the following steps: Step 2, Step 3, Step 4, and Step 5. Process 1: This includes defining the coordinate system, process variables, and location points. The order of steps in the process definition is not limited. Step 1-1: Establish a reference coordinate system using the ±180° bisection method; On the crankshaft rotation plane of the engine, the crank position when the piston is at TDC is defined as TDC-0°, and the crank position when the piston is at BDC is defined as TDC-180°. According to the normal rotation direction of the engine crankshaft, the crankshaft angle is defined as positive when the piston moves from BDC to TDC, with a range of 180° to 0°; and negative when the piston moves from TDC to BDC, with a range of 0° to -180°. Based on the above definition, the 360° range of one revolution of the crankshaft is divided into two points and two segments. 0° indicates that the piston is at TDC, and 180° indicates that the piston is at BDC. The positive value range indicates that the piston is before TDC, and the negative value range indicates that the piston is after TDC. The BDC position is the step point of ±180°. At this point, the piston jumps directly from -180° to +180°, so that there is no -180° in the reference coordinate system of the ±180° bisection. Steps 1-2: Install the stop pin in the spark plug hole of the designated cylinder, with the normal rotation direction of the engine crankshaft as the positive direction, and define the position points as follows: O - Center of rotation of crankshaft and crank; A - Reverse the crankshaft to the position of the connecting rod journal at the outer end of the crankshaft when the piston is stopped; B - Rotate the crankshaft forward until the connecting rod journal at the outer end of the crank is stopped; C - Piston center position when in stop gear; Based on the above definition, according to the construction principle of piston engines and the definition of TDC-0°, OC is located on the cylinder axis. When the piston is at TDC, the connecting rod and crankshaft are collinear and located on the OC line. Therefore, TDC-0° is also located on the OC line. In actual engineering environment, after the engine is installed on the aircraft, the cylinder axis / OC line is not necessarily parallel to the horizontal plane when the aircraft is normally stopped. Steps 1-3: Define variables: α is the crankshaft rotation angle, which is the angle between the instantaneous crank position and the TDC-0° reference position; α B The crankshaft rotation angle is the connecting rod journal at the outer end of the crankshaft when it is at position B. β is the instantaneous output angle of the tilt sensor, -180°<β≤180°, and the instantaneous output angle is calculated with reference to the horizontal plane; β0 is the angle between the cylinder axis and the horizontal plane, -180° < β0 ≤ 180°; β1 is the angle between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position A, 0°≤β1<360°; the angle is positive in the direction of crankshaft rotation; β2 is the angle between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position B, 0°≤β2<360°; the angle is positive in the direction of crankshaft rotation; Step 2: Set the solution formula; During the forward and reverse rotation of the crankshaft, let the instantaneous positions of the piston center C when the piston is stopped twice by the same stop pin be C1 and C2, respectively. Obviously, the two distances OC1 = OC2. When the crankshaft is rotated in the reverse direction until the piston is stopped, the position of point A, the instantaneous position of the piston center C1, and the rotation center O of the crankshaft together form triangle △AOC1. Similarly, when the crankshaft is rotated in the forward direction until the piston is stopped, triangle △BOC2 is formed. In triangles △AOC1 and △BOC2, sides AC1 and BC2 represent the lengths of the same connecting rod, and sides OA and OB represent the lengths of the same crank, i.e., AC1 = BC2 and OA = OB. It can be seen that △AOC1 ≌ △BOC2, so the angle ∠AOC1 = ∠BOC2 = ∠AOB * 1 / 2. Different stop pin lengths or residual deposits on the piston surface can change the angle ∠AOC1 at point A and the angle ∠BOC2 at point B when the piston is stopped, but do not change the property that △AOC1≌△BOC2, nor will they change ∠AOC1=∠BOC2=∠AOB*1 / 2 and the solution deductions based on this. This is the theoretical basis for the fact that this method can effectively avoid the negative effects of stop pin wear, piston surface deposits and other factors.

[0021] According to the definition of TDC-0° position, TDC-0° is located on the line OC, so ∠BOC2 is the instantaneous crankshaft rotation angle α at point B. B And it can be known that α B =∠AOB*1 / 2, which is Formula 1; Point A is the position of the connecting rod journal at the outer end of the crankshaft when the crankshaft is rotated in the reverse direction until the piston is stopped; point B is the position of the connecting rod journal at the outer end of the crankshaft when the crankshaft is rotated in the forward direction until the piston is stopped; the angle through which the crankshaft rotates from point A to point B is β2-β1. Obviously, ∠AOB=360-(β2-β1), substituting into Formula 1, we get... α B =180-(β2-β1)*1 / 2, which is Equation 2.

[0022] As shown in Formula 2, the crankshaft rotation angle α at point B can be obtained by measuring the angle through which the connecting rod journal at the outer end of the crank rotates from point A to point B. B From this position, continue forward α in the positive direction of crankshaft rotation. B The angle is the TDC-0° reference position. By using the TDC-0° position as a reference and following the two-segment reference coordinate system, continuous tracking and precise positioning of the crankshaft's instantaneous rotation angle can be achieved.

[0023] The method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine can also include the following process: Step 3: After installing the tilt sensor, the tilt sensor measures the tilt angle with the horizontal plane as a reference, and the output angle β varies within the range of ±180° with the horizontal plane as the reference. The tilt sensor can be installed on any propeller blade to measure the angle through which the blade rotates in the plane of propeller rotation; The tilt sensor can also be installed at any position within the rotation plane of the engine crankshaft end flange to measure the instantaneous rotational position of the engine crankshaft in real time within the rotation plane of the crankshaft end flange. This method assumes a propeller-to-engine crankshaft speed ratio of 1:1. For speed ratios not equal to 1:1, a secondary calculation is performed on the final result based on the actual reduction ratio. After installing a tilt sensor on the propeller, the output angle β of the tilt sensor changes with crankshaft rotation. Therefore, the change in the output angle β of the tilt sensor can reflect the change in crankshaft rotation angle α. However, due to the randomness of the tilt sensor's installation position and angle, the output angle β of the tilt sensor is not necessarily directly equal to the crankshaft rotation angle α. A functional relationship needs to be established between the two. Specifically, the tilt sensor is a tilt sensor with an accuracy of 0.1° and a range of ±180°; the tilt sensor tracks and positions the engine crankshaft in real time, and the measurement accuracy of the tilt sensor affects the final actual positioning accuracy; Step 4: Value calibration; the specific steps are as follows: Step 4-1: After performing operation 1, that is, after installing the stop pin in the spark plug mounting hole of the designated cylinder, perform operation 3; Step 4-2: Perform operation 3, that is: rotate the crankshaft in the opposite direction of the normal rotation of the engine crankshaft until the piston is stopped by the stop pin. According to the position point definition, obtain the position of point A, and record the output value of the tilt sensor at this time as β. A ; Point A is below the horizontal plane, at which point the tilt sensor outputs a negative angle, i.e., -180° < β. A <0°; Step 4-3: Perform operation 4, that is, rotate the crankshaft in the normal rotation direction of the engine crankshaft until the piston is stopped by the stop pin again. According to the position point definition, obtain the position of point B, and record the output value of the tilt sensor β at this time. B ; Point B is above the horizontal plane, at which point the tilt sensor outputs a positive angle, i.e., 0° < β. B <180°; Because the installation position and angle of the tilt sensor on the engine crankshaft or propeller are random each time, the output value β of the tilt sensor is affected when the connecting rod journal on the outer end of the crankshaft is at position A. A absolute value |β AThe value is not necessarily exactly equal to the angle β1 between the crank and the horizontal plane at this moment. Similarly, the output value β of the tilt sensor when the connecting rod journal at the outer end of the crank is at point B is not necessarily equal to the angle β1 between the crank and the horizontal plane at this moment. B It is not necessarily exactly equal to the angle β2 between the crank and the horizontal plane at that position; this angle is 360-β2. Step 5: Establish functional relationships; Step 5-1: Let β be the value of the connecting rod journal at point A on the outer end of the crank. A absolute value |β A The difference between | and β1 is θ1, which is equivalent to the tilt sensor being installed at position A1 on the rotational circumference of the connecting rod journal at the outer end of the crank. Then θ1 = ∠A1OA; let β be at position B when the connecting rod journal at the outer end of the crank is at point B. B The difference between the angles of β2 at position B and position B is θ2, then θ2 = ∠B1OB. When the connecting rod journal at the outer end of the crank rotates from position A to position B, position A1 also rotates to position B1. Obviously, ∠B1OB = ∠A1OA, then θ1 = θ2. β1 and β2 are the angles between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position A and position B, respectively. Since the tilt sensor measures the tilt angle with the horizontal plane as a reference, according to the definition of the positive direction and the angle range, -β A +θ1=β1,β B -θ2=360-β2, then β2-β1=(360-β B +θ2)-(-β A +θ1)=360-β B +β A Substituting into equation 2, we get α B =180-(β2-β1)*1 / 2=180-(360-β B +β A )*1 / 2=(β B -β A )*1 / 2, which is formula 3; The absence of θ1 or θ2 in Formula 3 indicates that the randomness of the installation position and angle of the tilt sensor does not affect the final data calculation. Step 5-2: According to the definition of the TDC-0° position, the connecting rod journal at the outer end of the crankshaft continues to rotate α in the normal direction of crankshaft rotation, starting from position B. B That is, the TDC-0° position, so TDC-0° is located at β. B -α B The position, with the horizontal plane as a reference, is clearly β0, that is, β0 = β B -α B Substituting formula 3 into the equation, we get... β0=β B -(β B -β A )*1 / 2=(β B +β A )*1 / 2, which is formula 4; Step 5-3: Since both β0 and β are referenced to the horizontal plane, β-β0 is the angle between the instantaneous crank position and the TDC-0° position, i.e., the crankshaft rotation angle α. Therefore, α = β-β0. Substituting formula 4, we get... α=β-(β B +β A )*1 / 2, which is formula 5; In Formula 5, β is the instantaneous output angle of the tilt sensor at any rotational position of the crankshaft, and is the independent variable; β A and β B These are the output values ​​of the tilt sensor when the outer end connecting rod journal of the crankshaft is at position A and position B, respectively, and are constants during this measurement period; the dependent variable is the instantaneous crankshaft rotation angle α. It can be seen that Formula 5 transforms the instantaneous output angle β of the tilt sensor at any crankshaft rotation position into the crankshaft rotation angle α at that position, thereby achieving precise tracking and positioning of the instantaneous rotation angle position of the engine crankshaft with TDC-0° as the reference. In particular, the final functional relationship formula 5 does not include the angle β0 between the cylinder axis and the horizontal plane, indicating that the attitude angle of the aircraft in the stopped state and the installation angle of the engine on the aircraft do not affect the final positioning result. Process Six: Boundary Correction; According to the definitions of positive direction and angle range, we have -180° < α ≤ 180° and -180° < β ≤ 180°, but due to the constant term β... A and β B The existence of this means that the value of α calculated according to Formula 5 may exceed the range of -180°<α≤180°, so boundary correction is required. According to the reference coordinate system established by the ±180° bisegment method, when α > 180°, it indicates that the piston has passed BDC and entered the process of moving from BDC to TDC. According to the definition of the crankshaft angle bisegment method, the crankshaft angle α should be in the range of -180° < α ≤ 0° at this time. Therefore, in this state, setting α = α - 360° can complete the correction. Similarly, when α ≤ -180°, let α = α + 360°.

[0024] After this correction, it can be ensured that the crankshaft rotation angle α calculated according to Formula 5 conforms to -180°<α≤180°; this bisegmentation method, which divides the crankshaft rotation surface into two segments and two points by ±180°, can more intuitively show whether the instantaneous position of the crankshaft is before or after TDC, and has higher positioning accuracy, especially for the relatively static state of the piston when it is in TDC and BDC.

[0025] Limitations of this method: As shown in Process 2, different stop pin lengths or residual deposits on the piston surface do not affect the final positioning result of this method. However, different stop pin lengths or residual deposits on the piston surface can change the angle ∠AOC1 corresponding to the crank outer end connecting rod journal at point A and the angle ∠BOC2 corresponding to the crank outer end connecting rod journal at point B when the piston is stopped, which means it can change β. A and β B The size of the tilt sensor; at the same time, since the tilt sensor measures the tilt angle with the horizontal plane as a reference, as can be seen from process five, the attitude angle of the aircraft in the parked state and the engine mounting angle on the aircraft do not affect the final positioning result, but these factors can also affect β. A and β B The size of β is such that the constant β in formula 5 of this method... A and β B The time-domain validity is limited to the current installation and measurement period. Each time the tilt sensor is installed, the forward and reverse stops and value acquisition steps in process four must be performed twice.

[0026] This invention discloses a method for accurately tracking the TDC relative position of an aero-piston engine crankshaft. This method involves installing an inclination sensor on the engine crankshaft to detect the angular change of the crankshaft relative to the horizontal plane in real time. Based on this, the TDC-0° reference position of the engine crankshaft is accurately determined by rotating the engine crankshaft clockwise and counterclockwise to stop the piston at a certain position in the cylinder. Then, a mathematical calculation method is used to establish a functional relationship between the TDC-0° position and the instantaneous crankshaft rotation position. This allows for the accurate calculation of the instantaneous crankshaft rotation position based on the real-time measurements from the inclination sensor, thus achieving precise tracking of the engine crankshaft's TDC relative position. Specifically, to clearly indicate the positional relationship between the instantaneous crankshaft position and the TDC-0° reference, this invention employs a ±180° bisegment method to divide the 360° range of one crankshaft rotation into two points and two segments to establish a reference coordinate system. This enables precise and continuous tracking and positioning of the instantaneous angular position of the engine crankshaft with the TDC-0° position as the reference reference, effectively avoiding the influence of factors such as the attitude angle of the aircraft when it is stationary and the installation angle of the engine on the aircraft. The final positioning accuracy of the system depends on the measurement accuracy of the tilt sensor used. A typical low-cost general-purpose tilt sensor can achieve a positioning accuracy of 0.1°, while a high-precision sensor can achieve a positioning accuracy of 0.001°. Using a low-cost general-purpose sensor in conjunction with the algorithm of this method can fully meet the engineering practice tolerance requirement of ±1°.

[0027] The present invention provides a method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine, the advantages of which are as follows: (1) This method can accurately determine the TDC-0° reference position of the piston engine by stopping the piston twice. The reference position is based on the horizontal plane. The positioning accuracy depends on the measurement accuracy of the tilt sensor. The low-cost measurement accuracy of 0.1° can meet the engineering requirements, and higher accuracy is available at 0.01° and 0.001°. (2) This method can continuously and accurately track and position any position within a 360° range of engine crankshaft rotation, and the final output value varies within a ±180° range; (3) The method of establishing a reference coordinate system by using the ±180° bi-segment method can more intuitively show the relative positional relationship between the instantaneous crankshaft rotation angle position and the TDC-0° reference position, especially for the relatively static state of the piston when it is in TDC and BDC, it has higher positioning accuracy. (4) This method has no requirements on the installation position and angle of the tilt sensor, and the randomness of the installation position and angle of the tilt sensor does not affect the positioning result; (5) This method has no requirements on the length of the stop pin, and stop pins of different lengths do not affect the positioning results; (6) The wear of the stop pin and the deposits on the piston surface are equivalent to the use of a stop pin of a different length, and will not affect the positioning results; (7) The attitude angle of the aircraft when it is parked and the installation angle of the engine on the aircraft do not affect the final positioning result; (8) The measurement results of this method are objective, true and reliable, effectively avoiding the influence of the operator's subjective factors, and can be applied to any piston engine, with a wide range of applications.

[0028] Prior to this method, the industry used the "dynamic and static marking method" provided by the engine manufacturer when positioning the advance ignition angle of spark-ignition piston engines. This method had low positioning accuracy and was greatly affected by the subjective factors of the operator. Alternatively, the use of fixed / variable length timing pins was susceptible to wear of the timing pins and deposits on the piston surface.

[0029] By using this method, high positioning accuracy is achieved, and the TDC-0° reference position can be locked at all times during continuous crankshaft rotation to continuously track the real-time crankshaft angle. In particular, by using the ±180° segmentation method to divide the 360° range of one crankshaft rotation into two points and two segments, the relative positional relationship between the instantaneous crankshaft angle position and the TDC-0° reference position can be displayed more intuitively. The positioning efficiency is high, and the measurement results are objective, true, and reliable. It is not affected by the operator's subjective factors, wear of the timing pin, or deposits on the piston surface. It is applicable to any piston engine and has a wide range of applications. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the connection and movement relationships of various components in the piston engine involved in the method of this invention.

[0031] Figure 2 It is a diagram showing the positional relationship between the crankshaft, connecting rod journal, crankshaft main journal, crankshaft rear journal, and shaft end flange.

[0032] Figure 3 This is a schematic diagram of the location of the top dead center (TDC) involved in the method of this invention.

[0033] Figure 4 This is a schematic diagram of the position of the bottom dead center (BDC) involved in the method of this invention.

[0034] Figure 5 This is a schematic diagram of the spark plug installation position and the position of the advance ignition angle involved in the method of the present invention.

[0035] Figure 6 This is a schematic diagram of the stop pin installation position and the defined coordinate system, process variables, and position points involved in the method of the present invention.

[0036] Figure 7 This is a schematic diagram illustrating the method for setting the solution formula according to the present invention.

[0037] Figure 8 This is a schematic diagram illustrating the method for establishing functional relationships according to the present invention.

[0038] In the diagram, 1-cylinder, 2-piston, 3-connecting rod, 4-crank, 5-connecting rod journal, 6-crankshaft main journal, 7-crankshaft end flange, 8-crankshaft rear journal, 9-spark plug, 10-stop pin. Detailed Implementation

[0039] The present patent will be further explained and described below with reference to the accompanying drawings and embodiments. However, the scope of protection of this patent is not limited to the specific implementation methods. Example 1

[0040] A method for accurately tracking the TDC (Total Displacement Control) position of an aero-piston engine crankshaft, the process of which is as follows: Process 1: Includes defining the coordinate system, process variables, and location points; Step 1-1: Establish a reference coordinate system using the ±180° bisection method; On the crankshaft rotation plane of the engine, the crank position when the piston is at TDC is defined as TDC-0°, and the crank position when the piston is at BDC is defined as TDC-180°. According to the normal rotation direction of the engine crankshaft, the crankshaft angle is defined as positive when the piston moves from BDC to TDC, with a range of 180° to 0°; and negative when the piston moves from TDC to BDC, with a range of 0° to -180°. Steps 1-2: Install the stop pin in the spark plug hole of the designated cylinder, with the normal rotation direction of the engine crankshaft as the positive direction, and define the position points as follows: O - Center of rotation of crankshaft and crank; A - Reverse the crankshaft to the position of the connecting rod journal at the outer end of the crankshaft when the piston is stopped by the stop pin; B - Rotate the crankshaft forward to the position of the connecting rod journal at the outer end of the crankshaft when the piston is stopped by the stop pin; C - Piston center position when in stop gear; Steps 1-3: Define variables: α is the crankshaft rotation angle, which is the angle between the instantaneous crank position and the TDC-0° reference position; α B The crankshaft rotation angle is the connecting rod journal at the outer end of the crankshaft when it is at position B. β is the instantaneous output angle of the tilt sensor, -180°<β≤180°, and the instantaneous output angle is calculated with reference to the horizontal plane; β0 is the angle between the cylinder axis and the horizontal plane, -180° < β0 ≤ 180°; β1 is the angle between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position A, 0°≤β1<360°; the angle is positive in the direction of crankshaft rotation; β2 is the angle between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position B, 0°≤β2<360°; the angle is positive in the direction of crankshaft rotation; Step 2: Set the solution formula; During the forward and reverse rotation of the crankshaft, let the instantaneous positions of the piston center C when the piston is stopped twice by the same stop pin be C1 and C2, respectively. Obviously, the two distances OC1 = OC2. When the crankshaft is rotated in the reverse direction until the piston is stopped, the position of the connecting rod journal at the outer end of the crank (i.e., point A), the instantaneous position of the piston center C1, and the rotation center O of the crank together form triangle △AOC1. Similarly, when the crankshaft is rotated in the forward direction until the piston is stopped, triangle △BOC2 is formed. In △AOC1 and △BOC2, AC1 and BC2 are the lengths of the same connecting rod, and OA and OB are the lengths of the same crank, i.e., AC1 = BC2 and OA = OB. It can be seen that △AOC1 ≌ △BOC2, so the angle ∠AOC1 = ∠BOC2 = ∠AOB * 1 / 2. Different stop pin lengths or residual deposits on the piston surface can alter the angles ∠AOC1 at point A and ∠BOC2 at point B when the piston is stopped, but they do not change the property that △AOC1≌△BOC2, nor do they change ∠AOC1=∠BOC2=∠AOB*1 / 2 and the calculation deductions based on this. This is the theoretical basis for this method to effectively avoid the influence of factors such as stop pin wear and piston surface deposits.

[0041] According to the definition of TDC-0° position, TDC-0° is located on the line OC, so ∠BOC2 is the instantaneous crankshaft rotation angle α at point B. B And it can be known that α B =∠AOB*1 / 2, which is Formula 1; Point A is the position of the connecting rod journal at the outer end of the crankshaft when the crankshaft is rotated in the reverse direction until the piston is stopped; Point B is the position of the connecting rod journal at the outer end of the crankshaft when the crankshaft is rotated in the forward direction until the piston is stopped. The connecting rod journal at the outer end of the crank rotates from point A to point B, turning by an angle of β2-β1. Clearly, ∠AOB = 360-(β2-β1). Substituting this into Formula 1, we get... α B =180-(β2-β1)*1 / 2, which is formula 2; Step 3: Install the tilt sensor; The tilt sensor is a general-purpose tilt sensor with an accuracy of 0.1° and a measuring range of ±180°, used to measure the tilt angle with the horizontal plane as a reference. The tilt sensor can be installed at any position within the rotation plane of the engine crankshaft end face, and the output angle β varies within the range of ±180° with the horizontal plane as the reference. On an engine with a propeller already installed, an inclination sensor can be mounted on the propeller blades, which allows the angle through which the blades rotate to be measured in the plane of propeller rotation. In this embodiment, the speed ratio between the propeller and the engine crankshaft is assumed to be 1:1. For cases where the speed ratio is not equal to 1:1, the final result of this method is recalculated based on the actual reduction ratio.

[0042] Step 4: Value calibration; the specific steps are as follows: Step 4-1: Install the stop pin in the spark plug mounting hole of the designated cylinder; Step 4-2: Rotate the crankshaft in the opposite direction of its normal rotation until the piston is stopped by the stop pin. Based on the position point definition, obtain the tilt sensor output value β when the connecting rod journal at the outer end of the crankshaft is at position A. A ; Point A is below the horizontal plane, at which point the tilt sensor outputs a negative angle, i.e., -180° < β. A <0°; Step 4-3: Rotate the crankshaft in the normal direction of engine crankshaft rotation until the piston is stopped again by the stop pin. According to the position point definition, obtain the tilt sensor output value β when the connecting rod journal at the outer end of the crankshaft is at position B. B ; Point B is above the horizontal plane, at which point the tilt sensor outputs a positive angle, i.e., 0° < β. B <180°; Because the installation position and angle of the tilt sensor are random each time it is installed, the output value β of the tilt sensor will vary when the connecting rod journal at the outer end of the crank arm is at point A. A absolute value |β A The value is not necessarily exactly equal to the angle β1 between the crank and the horizontal plane at this moment. Similarly, the output value β of the tilt sensor at point B is also not necessarily equal to the angle β1 between the crank and the horizontal plane at this moment. B It is not necessarily exactly equal to the angle β2 between the crank and the horizontal plane at that position; this angle is 360-β2. Step 5: Establish functional relationships; Step 5-1: Let β be the value of the connecting rod journal at point A on the outer end of the crank. A absolute value |β A The difference between | and β1 is θ1, which is equivalent to the tilt sensor being installed at position A1 on the crank rotation circumference. Then θ1 = ∠A1OA; assuming the connecting rod journal at the outer end of the crank is at position B, β BThe difference between the angles of β2 at position B and position B is θ2, then θ2 = ∠B1OB. When the connecting rod journal at the outer end of the crank rotates from position A to position B, position A1 also rotates to position B1. Obviously, ∠B1OB = ∠A1OA, then θ1 = θ2. β A β B β1 and β2 are the output values ​​of the tilt sensor when the connecting rod journal at the outer end of the crank is at position A and position B, respectively; β1 and β2 are the angles between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position A and position B, respectively. Since the tilt sensor measures the tilt angle with the horizontal plane as a reference, according to the definition of the positive direction and the angle range, -β A +θ1=β1,β B -θ2=360-β2, then β2-β1=(360-β B +θ2)-(-β A +θ1)=360-β B +β A Substituting into equation 2, we get α B =180-(β2-β1)*1 / 2=180-(360-β B +β A )*1 / 2=(β B -β A )*1 / 2, which is formula 3; The absence of θ1 or θ2 in Formula 3 indicates that the randomness of the installation position and angle of the tilt sensor does not affect the final data calculation. Step 5-2: According to the definition of the TDC-0° position, the connecting rod journal at the outer end of the crankshaft continues to rotate α in the normal direction of crankshaft rotation, starting from position B. B That is, the TDC-0° position, so TDC-0° is located at β. B -α B The point location, with the horizontal plane as a reference, is clearly β0, i.e., β0 = β B -α B Substituting formula 3 into the equation, we get... β0=β B -(β B -β A )*1 / 2=(β B +β A )*1 / 2, which is formula 4; Step 5-3: Both β0 and β are referenced to the horizontal plane. Clearly, β-β0 is the angle between the instantaneous crank position and the TDC-0° position, i.e., the crankshaft rotation angle α. Substituting α = β - β0 into formula 4, we get α = β - (β0) B +βA )*1 / 2, which is formula 5; In Equation 5, the independent variable is the instantaneous output angle β of the tilt sensor. A and β B As a constant term, and with the crankshaft instantaneous rotation angle α as the dependent variable, it can be seen that Formula 5 transforms the instantaneous output angle β of the tilt sensor at any rotational position of the crankshaft into the instantaneous rotation angle α of the crankshaft, thereby achieving accurate tracking and positioning of the instantaneous rotation angle position of the engine crankshaft with TDC-0° as the reference. Formula 5 does not include the angle β0 between the cylinder axis and the horizontal plane, indicating that the attitude angle of the aircraft when it is stopped and the installation angle of the engine on the aircraft do not affect the final positioning result. Process Six: Boundary Correction; According to the definition of positive direction and angle range, -180°<α≤180°, -180°<β≤180°, but due to the existence of constant terms βA and βB, the value of α calculated by formula 5 may exceed the range of this interval, so boundary correction is required. In the reference coordinate system established by the ±180° bisegment method, when α > 180°, it indicates that the piston has passed BDC and entered the process of moving from BDC to TDC. According to the definition of the crankshaft angle bisegment method, the crankshaft angle α should be in the range from -180° to 0° at this time. Therefore, in this state, setting α = α - 360° can complete the correction. Similarly, when α ≤ -180°, let α = α + 360°; After this correction, it can be ensured that the crankshaft rotation angle α calculated by Formula 5 conforms to -180°<α≤180°; this bisegmentation method, which divides the crankshaft rotation surface into two segments and two points by ±180°, can more intuitively show whether the instantaneous rotation angle position is before or after TDC, and has higher positioning accuracy, especially for the relatively stationary state of the piston when it is in TDC and BDC. Example 2

[0043] In engineering practice, the operation process should be as simple as possible while ensuring effectiveness. This patent describes a method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine. The operation steps for determining the engine TDC-0° reference position are as follows: Operation 1: Locate the compression stroke in the designated cylinder and install the stop pin in the air above the spark plug of the cylinder.

[0044] Operation 2: By default, the propeller is directly mounted on the crankshaft end flange of the engine, and the speed ratio between the propeller and the engine crankshaft is 1:1; install an tilt sensor on any blade of the propeller so that it can measure the change of the blade's rotation angle in the plane of propeller rotation.

[0045] Operation 3: Rotate the propeller in the opposite direction of the engine's normal rotation until the piston is stopped by the stop pin and can no longer rotate the propeller in the opposite direction. Read and record the inclinometer reading as β. A =-16.35°.

[0046] Operation 4: Rotate the propeller forward as the engine normally rotates until the piston is stopped by the stop pin and can no longer rotate the propeller forward. Read and record the inclinometer reading as β. B =32.06°.

[0047] Operation 5: β A =-16.35° and β B Substituting 32.06° into Formula 3, we can obtain the crankshaft TDC relative rotation angle corresponding to point B as α. B =(β B -β A )*1 / 2=[32.06-(-16.35)] *1 / 2=24.205°.

[0048] Formula 3 is α B =180-(β2-β1)*1 / 2=180-(360-β B +β A )*1 / 2=(β B -β A )*1 / 2.

[0049] Operation 6: β A =-16.35° and β B Substituting 32.06° into Formula 4, we can obtain that the TDC-0° reference position is located at β0 = (β B +β A )*1 / 2=(32.06-16.35)] *1 / 2=7.855°.

[0050] Formula 4 is β0 = β B -(β B -β A )*1 / 2=(β B +β A )*1 / 2.

[0051] After the above steps, the system has determined the TDC-0° reference position with the horizontal plane as the reference. Thereafter, in this measurement, Formula 5 can be used to continuously track the relative rotation angle of the crankshaft with respect to the TDC-0° reference position during the rotation of the engine crankshaft.

[0052] Operation 7: Substituting β into Formula 5, we can obtain the relative angle α between the crankshaft at any rotational position and the TDC-0° position: α = β - (β B +β A)*1 / 2; Where β is the output reading of the tilt sensor when the crankshaft is in any rotational position, Equation 5 is α=β-β0=β-(β B +β A )*1 / 2.

[0053] When the connecting rod journal at the outer end of the engine crankshaft rotates back to position B, the inclinometer outputs an angle β=β. B =32.06°, according to formula 5, we can get α=β-β0=32.06-7.855=24.205°, or use α=β-(β B +β A )*1 / 2=32.06-(32.06-16.35)*1 / 2=24.205°, the value is the same as α calculated in step 5). B Totally consistent.

[0054] β as a constant term A =-16.35° and β B =32.06° is only valid during this measurement. If the tilt sensor is removed and reinstalled, the β value must be readjusted starting from step 3). A and β B To retrieve the value.

[0055] As can be seen from the above embodiments, the method proposed in this paper for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine, by rotating the engine crankshaft in both forward and reverse directions to stop the piston at a certain position in the cylinder, accurately achieves rapid positioning of the engine TDC-0° reference position and accurately tracks the relative angle of the engine crankshaft at the instantaneous position with the TDC-0° position as a reference.

Claims

1. A method for accurately tracking the TDC (Total Displacement Control) relative position of an aircraft piston engine crankshaft, namely, accurately determining the TDC position of the engine crankshaft and using it as a reference to calculate the relative angle between the engine crankshaft and the reference position at any rotational position in real time, and defining the instantaneous position of the crank corresponding to the piston of a specified cylinder when the piston is at TDC as TDC-0°, and defining the angle between the crank corresponding to the specified cylinder and the TDC-0° position when the crankshaft is at any position as the crankshaft angle; the engine crankshaft is equipped with a propeller mounted on a flange, the propeller including blades; and the default speed ratio between the propeller and the engine crankshaft is 1:1; if the speed ratio is not equal to 1:1, the final result of this method needs to be recalculated according to the actual reduction ratio; the method includes the following operation steps: Operation 1: Locate the compression stroke in the designated cylinder and install the stop pin in the upper spark plug mounting hole of the designated cylinder; Operation 2: Install tilt sensors on the propeller blades; Operation 3: Rotate the propeller in the opposite direction of the engine's normal rotation until the piston is stopped by the stop pin and can no longer rotate the propeller in the opposite direction. Read and record the inclinometer reading at this point as β. A ; Operation 4: Rotate the propeller forward as the engine normally rotates until the piston is stopped by the stop pin and can no longer rotate the propeller forward. Read and record the inclinometer reading at this point as β. B ; Operation 5: β A and β B Substituting into Formula 3, we can obtain the crankshaft TDC relative rotation angle α corresponding to point B. B For α B =(β B -β A )*1 / 2; in, Formula 3 is α B = 180 - (β2 - β1) * 1 / 2 = 180 - (360 - β B + β A ) * 1 / 2 = (β B - β A ) * 1 / 2 Point B is the position of the connecting rod journal at the outer end of the crankshaft when the crankshaft is rotated forward until the piston is stopped. Operation 6: β A and β B Substituting into Formula 4, we can obtain that the TDC-0° reference position β0 is located at β0 = (β B +β A )*1 / 2; Among them, Equation 4 is β0 = β B -(β B -β A ) * 1 / 2 = (β B +β A ) * 1 / 2 After the above steps, the system has determined the TDC-0° reference position with the horizontal plane as the reference. In this measurement, the TDC-0° position can be used as the reference to continuously track the relative rotation angle of the crankshaft with respect to the TDC-0° reference position during the rotation of the engine crankshaft. Operation 7: Substituting β into Formula 5, we can obtain the relative angle α between the crankshaft at any rotational position and the TDC-0° position: α = β - (β B +β A )*1 / 2; Where β is the output reading of the tilt sensor when the crankshaft is in any rotational position, Equation 5 is α=β-β0=β-(β B +β A )*1 / 2.

2. The method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine according to claim 1, characterized in that: If the inclinometer outputs an angle of β when the engine crankshaft is in any rotational position, the crankshaft rotation angle at any rotational position is α = β - β0. Substituting Equation 4 into Equation 5, we get Equation 5, which is α = β - β0 = β - (β B +β A )*1 / 2; where β A and β B It is a constant and is only valid during this measurement.

3. The method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine according to claim 1, characterized in that... Add the following process one and process two before any of the following steps: Operation 2, Operation 3, Operation 4, and Operation 5: Process 1: This includes defining the coordinate system, process variables, and location points. The order of steps in the process definition is not limited. Step 1-1: Establish a reference coordinate system using the ±180° bisection method; On the crankshaft rotation plane of the engine, the crank position when the piston is at TDC is defined as TDC-0°, and the crank position when the piston is at BDC is defined as TDC-180°. According to the normal rotation direction of the engine crankshaft, the crankshaft angle is defined as positive when the piston moves from BDC to TDC, with a range of 180° to 0°; and negative when the piston moves from TDC to BDC, with a range of 0° to -180°. Steps 1-2: After performing operation 1, i.e., after installing the stop pin in the spark plug hole of the designated cylinder, define the position points as follows, taking the normal rotation direction of the engine crankshaft as the positive direction: O - Center of rotation of crankshaft and crank; A - Reverse the crankshaft to the position of the connecting rod journal at the outer end of the crankshaft when the piston is stopped; B - Rotate the crankshaft forward to the position of the connecting rod journal at the outer end of the crankshaft when the piston is stopped; C - Piston center position when in stop gear; Steps 1-3: Define variables: α is the crankshaft rotation angle, which is the angle between the instantaneous crank position and the TDC-0° reference position; α B The crankshaft rotation angle is the connecting rod journal at the outer end of the crankshaft when it is at position B. β is the instantaneous output angle of the tilt sensor, -180°<β≤180°, and the instantaneous output angle is calculated with reference to the horizontal plane; β0 is the angle between the cylinder axis and the horizontal plane, -180° < β0 ≤ 180°; β1 is the angle between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at point A, 0°≤β1<360°; the angle is positive in the direction of crankshaft rotation; β2 is the angle between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position B, 0°≤β2<360°; the angle is positive in the direction of crankshaft rotation; Step 2: Set the solution formula; Set the instantaneous crankshaft rotation angle at point B to α. B , thus obtaining α B =∠AOB*1 / 2, which is Formula 1; α B =180-(β2-β1)*1 / 2, which is Equation 2.

4. The method for accurately tracking the relative position of the crankshaft TDC of an aircraft piston engine according to any one of claims 1-3, characterized in that: Add the following process: Step 3: After installing the tilt sensor, the tilt sensor measures the tilt angle with the horizontal plane as a reference, and the output angle β varies within the range of ±180° with the horizontal plane as the reference. Step 4: Value calibration; the specific steps are as follows: Step 4-1: After performing operation 1, that is, after installing the stop pin in the spark plug mounting hole of the designated cylinder, perform operation 3; Step 4-2: Perform operation 3, that is: rotate the crankshaft in the opposite direction of the normal rotation of the engine crankshaft until the piston is stopped by the stop pin. According to the position point definition, obtain the position of point A, and record the output value of the tilt sensor at this time as β. A ; Point A is below the horizontal plane, at which point the tilt sensor outputs a negative angle, i.e., -180° < β. A <0°; Step 4-3: Perform operation 4, that is, rotate the crankshaft in the normal rotation direction of the engine crankshaft until the piston is stopped by the stop pin again. According to the position point definition, obtain the position of point B, and record the output value of the tilt sensor β at this time. B ; Point B is above the horizontal plane. At this point, the angle output by the tilt sensor is positive, i.e., 0° < β. B <180°; Step 5: Establish functional relationships; Step 5-1: Assume that when the connecting rod journal at the outer end of the crank is at position A, β A absolute value |β A The difference between | and β1 is θ1, which is equivalent to position A1 of the circumference of the connecting rod journal at the outer end of the crank where the tilt sensor is installed. Then θ1 = ∠A1OA; let β be at position B when the connecting rod journal at the outer end of the crank is at point B. B The difference between the angles of β2 at position B and position B is θ2, then θ2 = ∠B1OB. When the connecting rod journal at the outer end of the crank rotates from position A to position B, position A1 also rotates to position B1. Obviously, ∠B1OB = ∠A1OA, then θ1 = θ2; β1 and β2 are the angles between the crank and the horizontal plane when the connecting rod journal at the outer end of the crank is at position A and position B, respectively. Since the tilt sensor measures the tilt angle with the horizontal plane as a reference, according to the definition of the positive direction and the angle range, -β A +θ1=β1,β B -θ2=360-β2, then β2-β1=(360-β B +θ2)-(-β A +θ1)=360-β B +β A Substituting into equation 2, we get α B = 180 - (β2 - β1) * 1 / 2 = 180 - (360 - β B + β A ) * 1 / 2 = (β B - β A ) * 1 / 2, that is, Formula 3; Step 5-2: According to the definition of the TDC-0° position, starting from point B, continue rotating the crankshaft in the normal direction of rotation by α. B That is, the TDC-0° position, so TDC-0° is located at β. B -α B Position, i.e., β0 = β B -α B Substituting formula 3 into the equation, we get... β0 = β B -(β B -β A ) * 1 / 2 = (β B +β A ) * 1 / 2, that is, Equation 4; Step 5-3: Define β as the instantaneous output angle of the tilt sensor when the crankshaft is at any rotational position. Then β-β0 is the angle between the instantaneous position of the crank and the TDC-0° position, which is the crankshaft rotation angle α. Therefore, α = β-β0. Substituting Equation 4, we can obtain... α = β - β0 = β - (β B + β A ) * 1 / 2, that is, formula 5; Process Six: Boundary Correction; According to the reference coordinate system established by the ±180° bisegment method, when α>180°, it indicates that the piston has passed BDC and entered the process of moving from BDC to TDC. According to the definition of the crankshaft angle bisegment method, the crankshaft angle α should be in the range from -180° to 0° at this time. Therefore, in this state, setting α=α-360° can complete the correction. When α ≤ -180°, let α = α + 360°.

5. The method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine according to claim 1, characterized in that: The tilt sensor is installed at any position within the rotation plane of the engine crankshaft end flange, and measures the instantaneous rotational position of the engine crankshaft in real time within the rotation plane of the crankshaft end flange.

6. The method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine according to claim 1, characterized in that: The tilt sensor is installed on any propeller blade and measures the angle through which the blade rotates in the plane of propeller rotation.

7. The method for accurately tracking the relative position of the crankshaft TDC of an aero-piston engine according to claim 1, characterized in that: The designated cylinder refers to the specific cylinder used to determine the advance ignition position on this type of engine, as specified in the engine repair manual.

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