A method for detecting the axis trajectory of the small end of an engine connecting rod

Abstract

The present invention belongs to the technical field of engine test, and particularly relates to a method for detecting the axis trajectory of the small end of an engine connecting rod, comprising the following steps: 1) setting a calibration point on the piston pin with interference fit at the small end of the connecting rod to be measured; 2) obtaining the position information of the calibration point on the piston pin during rotation through an axis trajectory detection module, which includes a processor and a high-speed camera. The high-speed camera obtains the position information of each frame of the calibration point with more than three consecutive frames as a cycle, and the processor obtains an axis position according to the position information of the calibration point in a single cycle, and connects the obtained axis positions in the obtained order to obtain the axis trajectory of the small end of the connecting rod. The present invention only needs to obtain the position information of the calibration point, uses the basic principle that three points determine a circle center to obtain several axis positions, and connects the axes in sequence to obtain the axis trajectory of the small end of the connecting rod, which has the advantages of being fast, accurate, intuitive, and reliable, and will not damage the connecting rod.

Description

Technical Field

[0001] The present invention belongs to the technical field of engine testing, and particularly relates to a method for detecting the axis locus of the small end of an engine connecting rod. Background Art

[0002] When the axis locus of a rotating shaft is unstable, the axis of the shaft and the center are not concentric, resulting in uncoordinated movement between the internal components of the engine power system and generating vibrations. The wear between components will also increase, which has a great impact on the power transmission of such a complex power system as an engine, significantly reducing its service life, and there are also potential safety hazards and increased noise problems. Therefore, axis locus detection is of great significance for the reliability and safety of the operation of rotating machinery.

[0003] Traditional axis locus detection is mainly achieved by means of "man-machine" dialogue. Specifically, it mainly relies on the subjective judgment combined with the vibration of the rotating shaft and the experience of technicians, and cannot depict the specific axis locus (the "axis locus" is the axis motion graph), with low accuracy. Currently, the research on the axis locus of rotating shafts at home and abroad mainly focuses on three aspects: rotor fault mechanism, axis locus extraction, and axis locus feature extraction and feature recognition. Among them, the axis locus detection method for the rotor fault mechanism is to establish a corresponding mathematical model through disciplines such as dynamics, and then obtain the axis motion information of the rotor through simulation calculation and experiments. This method is usually used to detect the fault information of fixed rotors such as motors, and does not clearly obtain the axis locus of the rotor. The axis locus extraction detection method mainly judges the motion law of the axis locus by the sound emitted when the rotating shaft rotates. Since it is affected by noise interference, extraction processing needs to be performed on the axis locus. Nevertheless, there are still large errors in this detection method. The essence of the axis locus feature extraction and feature recognition detection method is the recognition of two-dimensional images, and commonly used feature extraction methods such as Fourier descriptors are used to reflect the original axis locus as much as possible. The above three methods all obtain the axis locus through theoretical calculation or analysis, and do not truly reflect the axis locus of the rotating shaft.

[0004] In addition, there is also a method for detecting the axis locus by installing displacement sensors, but this method has many disadvantages. For example, if the displacement sensor is installed in an inlaid manner, the structure of the rotating shaft will be damaged, and if the displacement sensor is installed in a pasted manner, the displacement sensor will be thrown off by the strong centrifugal force of the rotating shaft, affecting the detection of the axis locus. Moreover, using a displacement sensor to detect the axis locus cannot directly obtain the axis locus of the rotating shaft.

[0005] Therefore, a detection method that can accurately reflect the axis locus of the rotating shaft is needed. Summary of the Invention

[0006] The present invention aims to provide a method for detecting the axis locus of the small end of an engine connecting rod to solve the problem that the existing axis locus detection method is difficult to directly reflect the axis locus of the rotating shaft.

[0007] To achieve the above object, the solution of the present invention is: a method for detecting the axis locus of the small end of an engine connecting rod, comprising the following steps:

[0008] S1. Set a calibration point on the piston pin in interference fit with the small end of the connecting rod to be measured;

[0009] S2. Obtain the position information of the calibration point during the rotation of the piston pin through the axis locus detection module. The axis locus detection module includes a processor and a high-speed camera. The high-speed camera obtains the position information of each frame of the calibration point with more than three consecutive frames as a period. The processor obtains an axis position based on the position information of the calibration point in a single period, and connects the obtained axis positions in the obtained order to obtain the axis locus of the small end of the connecting rod.

[0010] The working principle and beneficial effects of this solution are as follows: This solution is applicable to an optical engine equipped with a transparent cylinder liner. The movement of the piston in the transparent cylinder liner is visible to the naked eye. The piston pin and the small end of the connecting rod are in interference fit, and there is no relative movement between the piston pin and the small end of the connecting rod during the movement.

[0011] This solution uses a high-speed camera to obtain the position information of each frame of the calibration point, and then uses the basic principle of determining the center of a circle by three points. Through calculation by the processor, several center positions are obtained. The center position is the axis position of the piston pin, that is, the axis position of the small end of the connecting rod. Connect the axis positions in the order of obtaining the axis positions, and then obtain the axis locus of the small end of the connecting rod. This solution can quickly, accurately and reliably obtain the axis locus of the measured small end of the connecting rod, avoid the large errors brought by detection methods such as "man-machine" dialogue detection, data calculation, and image generation, and can accurately reflect the true motion state of the small end of the connecting rod, so as to detect whether there is a fault in the entire mechanical structure during operation. Moreover, this solution has no impact on the measured small end of the connecting rod, belongs to non-destructive testing, and does not affect its service life.

[0012] Optionally, in step S2, the high-speed camera obtains the position information of each frame of the calibration point with three consecutive frames as a period.

[0013] In this solution, the high-speed camera obtains the position information of each frame of the calibration point with three consecutive frames as a period because when three frames are used as a period, there are three pieces of position information of the calibration point, which are sufficient for the processor to calculate and obtain an axis position. In this way, on the premise that the total number of frames captured by the high-speed camera is the same, this solution can obtain as many axis positions as possible to improve the accuracy of the axis locus.

[0014] Optionally, in step S2, the time interval for each frame is 0.1 - 0.25 s.

[0015] In this solution, through experiments, when the shooting rate of the high-speed camera is 4 - 10 frames per second, sufficient quantity of position information of the calibration points can be obtained.

[0016] Optionally, the axis trajectory detection module further includes a display screen, which is electrically connected to the processor and is used for displaying the axis trajectory of the small end of the connecting rod obtained by the processor.

[0017] In this solution, the display screen can display the axis trajectory of the small end of the connecting rod obtained by the processor, so that the tester can directly observe the axis trajectory of the small end of the connecting rod.

[0018] Optionally, the axis trajectory of the small end of the connecting rod recognized by the processor is used to obtain detection data, which includes amplitude, maximum offset and maximum offset position.

[0019] In this solution, the axis trajectory of the small end of the connecting rod recognized by the processor is compared with the standard axis trajectory of the small end of the connecting rod, and detection data such as amplitude, maximum offset and maximum offset position are calculated, so that the tester can directly and quickly judge whether there is a fault in the whole mechanical structure during operation according to the detection data.

[0020] Optionally, the calibration point is a dot formed by applying reflective paint on the piston pin.

[0021] In this solution, the calibration point is a dot formed by applying reflective paint on the piston pin. Due to the good reflective effect of the reflective paint, the calibration point is easy to be recognized in the shooting image of the high-speed camera. Moreover, the high-speed camera uses photosensitive capture and will automatically focus on the calibration point.

[0022] Optionally, the axis trajectory detection module further includes a light source, which irradiates the piston pin.

[0023] In this solution, the piston pin is irradiated by the light source to avoid the shooting image of the high-speed camera being dark and blurred. Description of the Drawings

[0024] Figure 1 is the longitudinal sectional view of a device for detecting the axis trajectory of the small end of an engine connecting rod in Embodiment 1 of the present invention;

[0025] Figure 2 is Figure 1 the left view (the fixing frame is not shown);

[0026] Figure 3 is the structural schematic diagram of the cooperation between the engine connecting rod and the piston pin in Embodiment 1 of the present invention;

[0027] Figure 4 The flowchart of a method for detecting the axis locus of the small end of an engine connecting rod in Embodiment 1 of the present invention;

[0028] Figure 5 The longitudinal partial sectional view of a device for detecting the axis locus of the small end of an engine connecting rod in Embodiment 2 of the present invention. Specific embodiments

[0029] The following is a further detailed description through specific embodiments:

[0030] The marks in the attached drawings of the specification include: detection platform 1, threaded blind hole 101, cylinder liner support assembly 2, first support plate 201, second support plate 202, first adjusting screw 203, L-shaped clamping plate 204, crankshaft support assembly 3, first support block 301, second support block 302, accommodation groove 303, second adjusting screw 304, third adjusting screw 305, rubber pad 306, high-speed camera 4, fixing bracket 5, processor 6, display screen 7, screw 8, connecting rod 9, small end of the connecting rod 901, big end of the connecting rod 902, piston pin 10, calibration point 11, crankshaft 12, crankshaft bearing 13, transparent cylinder liner 14, piston 15, light source 16.

[0031] Embodiment 1

[0032] This embodiment provides a device for detecting the axis locus of the small end of an engine connecting rod, as shown in Figure 1 , Figure 2 and Figure 3 . The device includes a detection platform 1 and an axis locus detection module. A support module is provided on the detection platform 1. The support module includes a cylinder liner support assembly 2 and a crankshaft support assembly 3. The cylinder liner support assembly 2 includes a first support plate 201 and a second support plate 202. Horizontally arranged first adjusting screws 203 are threadedly connected to the top ends of both the first support plate 201 and the second support plate 202. One end of the first adjusting screw 203 close to the transparent cylinder liner 14 is rotatably connected to an L-shaped clamping plate 204 through a bearing. The crankshaft support assembly 3 includes a first support block 301 and a second support block 302. Accommodation grooves 303 for placing the crankshaft bearing 13 (if the end of the crankshaft 12 lacks a bearing, an additional bearing can be sleeved on the end of the crankshaft 12 during detection) are provided at the top ends of both the first support block 301 and the second support block 302. Horizontally arranged second adjusting screws 304 and third adjusting screws 305 are threadedly connected to both the first support block 301 and the second support block 302. The opposite ends of the second adjusting screw 304 and the third adjusting screw 305 are located in the accommodation groove 303, that is, the right end of the second adjusting screw 304 and the left end of the third adjusting screw 305 are both located in the accommodation groove 303. Moreover, rubber pads 306 are bonded to the right end of the second adjusting screw 304 and the left end of the third adjusting screw 305.

[0033] The axial center locus detection module includes a high-speed camera 4, a fixing bracket 5, a processor 6 and a display screen 7. The high-speed camera 4 is installed at the top of the fixing bracket 5 through bolts. An installation through hole is provided at the bottom end of the fixing bracket 5, and a number of threaded blind holes 101 are provided on the detection platform 1. In this embodiment, the distance between two adjacent threaded blind holes 101 is 10 cm. In this embodiment, the fixing bracket 5 is fixed on the detection platform 1 by screwing a screw 8 through the installation through hole at the bottom end of the fixing bracket 5 and threadedly connecting it with the threaded blind hole 101. In addition, the high-speed camera 4 is aligned with the piston pin 10 for shooting. The high-speed camera 4 is electrically connected to the processor 6 through a data cable, and the display screen 7 is electrically connected to the processor 6 through a data cable. In this embodiment, the high-speed camera 4 selects a PCO.dimaxHS1 high-speed camera, and the processor 6 selects a 64-bit operating system to ensure that the processor 6 can smoothly run the MATLAB software.

[0034] In this embodiment, a piston pin 10 is in interference fit in the hole of the small end 901 of the connecting rod. The piston pin 10 is rotatably connected to the piston 15. The piston 15 is vertically slidably connected in the transparent cylinder liner 14. A combustion chamber is formed inside the transparent cylinder liner 14 above the piston 15. The connecting rod journal of the crankshaft 12 is rotatably connected in the hole of the big end 902 of the connecting rod. The main journal of the crankshaft 12 is rotatably connected with a crankshaft bearing 13. After the engine is started, power is transmitted to the crankshaft 12 through the piston 15 and the connecting rod 9, causing the crankshaft 12 to rotate.

[0035] This embodiment also provides a method for detecting the axial center locus of the small end of an engine connecting rod. This method uses the above-mentioned axial center locus detection device for the small end of an engine connecting rod, as Figure 4 shown. This method includes the following steps:

[0036] Step 1: Set a calibration point: A calibration point 11 is set on the piston pin 10 that is in interference fit at the small end 901 of the engine connecting rod. The calibration point 11 can be located at any point on the piston pin 10 except the axial center.

[0037] Step 2: Install the mechanical structure to be measured on the detection platform: Place the crankshaft bearing 13 of the engine into the receiving groove 303 of the first support block 301 and the second support block 302, and then rotate the second adjusting screw 304 and the third adjusting screw 305 so that the second adjusting screw 304 and the third adjusting screw 305 are tightened against the crankshaft bearing 13 to fix the engine crankshaft 12 (the connecting rod journal of the crankshaft 12 is rotatably connected to the big end 902 of the connecting rod). Then, rotate the first adjusting screw 203 so that the two L-shaped clamping plates 204 clamp and fix the transparent cylinder liner 14 from both sides of the transparent cylinder liner 14. Thus, the installation of the mechanical structure to be measured is completed.

[0038] Step 3. Position adjustment of the shaft center locus detection module: Adjust the distance between the high-speed camera 4 and the connecting rod 9 so that the transparent cylinder liner 14, the connecting rod 9, and the crankshaft 12 can all be presented in the lens of the high-speed camera 4. Among them, when adjusting the distance between the high-speed camera 4 and the connecting rod 9, remove the screw 8 at the bottom end of the fixing bracket 5 to release the fixation between the fixing bracket 5 and the detection platform 1, move the fixing bracket 5 to a suitable position so that the transparent cylinder liner 14, the connecting rod 9, and the crankshaft 12 can all be presented in the lens of the high-speed camera 4. Subsequently, align the mounting through-hole on the fixing bracket 5 with the nearby threaded blind hole 101, and finally pass the screw 8 through the mounting through-hole and thread it into the threaded blind hole 101 to fix the fixing bracket 5 on the detection platform 1 again.

[0039] Step 4. Detect the shaft center locus of the small end of the connecting rod by three-frame fixed circle: Start the engine, and the piston 15 in the transparent cylinder liner 14 reciprocates up and down. Through the transmission of the connecting rod 9, the crankshaft 12 rotates. During this process, the piston pin 10 rotates relative to the piston 15. Since the piston pin 10 is in interference fit with the small end 901 of the connecting rod, the small end 901 of the connecting rod and the piston pin 10 rotate concentrically and at the same speed. Start the shaft center locus detection module, and the high-speed camera 4 starts shooting. Set the shooting duration of the high-speed camera 4 to ten minutes. During the shooting process, the high-speed camera 4 obtains the position information of each frame of calibration point 11 with three frames as a cycle, and the interval time between each frame is 0.1 - 0.25 s. In this embodiment, the interval time between each frame is 0.1 s. The high-speed camera 4 transmits the position information of each frame of calibration point 11 to the processor 6. The processor 6 calculates an axis center position based on the position information of the calibration point 11 in a single cycle (there are three pieces of position information of the calibration point 11 in a single cycle). Specifically, the MATLAB software running on the processor 6 places the three calibration points 11 in a single cycle on the same plane, calculates the axis center position of this single cycle according to the position information of the calibration point 11 (using the basic principle that three points determine a circle center), and records this axis center position. Place the axis center positions on the same plane and connect the axis center positions of each cycle in the order obtained to get the shaft center locus of the small end 901 of the connecting rod, and this shaft center locus of the small end 901 of the connecting rod is displayed on the display screen 7. In addition, the processor 6 identifies and analyzes the obtained shaft center locus of the small end 901 of the connecting rod, compares it with the standard shaft center locus of the small end of the connecting rod, and calculates detection data such as amplitude, maximum offset, and maximum offset position. These detection data and the shaft center locus of the small end 901 of the connecting rod are displayed on the display screen 7 together for the inspectors to read, so as to judge whether there is a fault in the movement of the connecting rod 9.

[0040] Step Five, End of Detection: Turn off the shaft center locus detection module, release the fixation of the L-shaped clamping plate 204 on the transparent cylinder liner 14, release the fixation of the second adjusting screw 304 and the third adjusting screw 305 on the crankshaft bearing 13, and remove the mechanical structure from the detection platform 1.

[0041] In this embodiment, considering that there will be errors in directly photographing the motion locus by the high-speed camera 4, the three-frame fixed circle principle is utilized. The shaft center position is calculated through the position information of the calibration point 11, and those tiny motion deviations can also be clearly calculated, so as to truly reflect the actual shaft center locus of the small end 901 of the connecting rod, changing the previous unrealistic and error-prone detection methods such as simulating, analyzing, and guessing the shaft center locus, and avoiding detection errors. Therefore, this embodiment has small errors, rapid detection, and reliable results. Moreover, this embodiment does not require any modification to the mechanical structure, nor complex simulation calculations, and will not cause any damage to the mechanical structure, and can obtain the true shaft center locus of the small end 901 of the connecting rod. This method can help domestic engine manufacturers conduct rapid, effective, and reliable quality inspections on products.

[0042] Embodiment Two

[0043] The difference between this embodiment and Embodiment One lies in: As shown in Figure 5 , the calibration point 11 in this embodiment is a dot formed by applying reflective paint on the piston pin 10, and the shaft center locus detection module further includes a light source 16. The light source 16 is fixedly installed on the fixing frame 5, and after the light source 16 is turned on, the light irradiates on the piston pin 10.

[0044] In the method of this embodiment, in Step Four, after the shaft center locus detection module is started, the light source 16 is turned on, the light irradiates on the piston pin 10, the calibration point 11 reflects strongly, and the high-speed camera 4 uses photosensitive capture and automatically focuses on the calibration point 11, so as to take a clear picture and facilitate accurately obtaining the position information of the calibration point 11.

[0045] The above are only examples of the present invention, and the invention is not limited to the fields involved in these examples. Common knowledge such as the specific structures and characteristics known in the art is not described in detail herein. Those of ordinary skill in the art know all the common general technical knowledge in the technical field to which the invention pertains before the filing date or the priority date, are able to learn all the existing technologies in this field, and have the ability to apply the conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application, complete and implement this solution in combination with their own abilities. Some typical well-known structures or well-known methods should not become obstacles for those of ordinary skill in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can also be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the present invention. The protection scope claimed in this application should be based on the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to interpret the content of the claims.

Claims

1. A method for detecting the axis locus of the small end of an engine connecting rod, characterized in that: Including the following steps: S1. Set a calibration point on the piston pin with an interference fit at the small end of the connecting rod to be measured; S2. Obtain the position information of the calibration point on the piston pin during rotation through the axis orbit detection module. The axis orbit detection module includes a processor and a high-speed camera. The high-speed camera obtains the position information of each frame of the calibration point with more than three consecutive frames as a cycle, and the time interval between each frame is 0.1 - 0.25 s. The processor obtains an axis position based on the position information of the calibration point in a single cycle, and connects the obtained axis positions in the obtained order to obtain the axis orbit of the small end of the connecting rod.

2. The method for detecting the axis locus of the small end of the engine connecting rod according to claim 1, characterized in that: In step S2, the high-speed camera obtains the position information of each frame of the calibration point with three consecutive frames as a cycle.

3. The method for detecting the axis locus of the small end of the engine connecting rod according to claim 1, wherein: The axis orbit detection module further includes a display screen, which is electrically connected to the processor, and the display screen is used to display the axis orbit of the small end of the connecting rod obtained by the processor.

4. The method for detecting the axis locus of the small end of the engine connecting rod according to claim 1, characterized in that: The processor identifies the axis orbit of the small end of the connecting rod to obtain detection data, and the detection data includes amplitude, maximum offset, and maximum offset position.

5. The method for detecting the axis locus of the small end of an engine connecting rod according to claim 1, characterized in that: The calibration point is a dot formed by applying reflective paint on the piston pin.

6. The method for detecting the axis locus of the small end of the engine connecting rod according to claim 1 or 5, characterized in that: The axis orbit detection module further includes a light source that irradiates the piston pin.

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