CN102539160B - Jogging fatigue simulation experiment system of resonant internal combustion engine - Google Patents

Abstract

The invention relates to a jogging fatigue simulation experiment system of a resonant internal combustion engine, belonging to the technical field of fatigue strength of an internal combustion engine. The jogging fatigue simulation experiment system comprises a jogging fatigue device, an accelerometer, an electronic control component, an electric vibration exciter, a vibration exciter push rod and two inertia vibration plates; and the jogging fatigue device comprises a testing assembly, a pre-tightening bolt, a pressing head, a U-shaped connector, a base, a loading push rod and a load applying shaft. The jogging fatigue simulation experiment system of the resonant internal combustion engine, disclosed by the invention, can be used for researching a problem of jogging fatigue of a structural assembly under the action of a topical characteristic load of an internal combustion engine, and can consider contact of a plane and a plane and carry out a research on a jogging fatigue problem of the testing assembly under the action of different load characteristics and load levels by changing the size of a total load and a proportion relation of a tangent load and a normal load compared with a traditional jogging fatigue simulation experiment.

Description

A resonant internal combustion engine fretting fatigue simulation experiment system

technical field

The invention relates to a resonant internal combustion engine fretting fatigue simulation experiment system, which belongs to the technical field of internal combustion engine fatigue strength.

Background technique

Under the working state of the internal combustion engine, the contact surface of the body diaphragm and the main bearing cover is subjected to the joint action of pretightening force and alternating normal and tangential loads, which is prone to fretting damage near the contact surface and accelerates the failure of components. Studies have shown that under the same alternating external load, the effect of fretting fatigue will reduce the fatigue life of the specimen by 30% to 50%. In recent years, the research on the law of fretting fatigue damage has gradually become a research hotspot in related research fields.

Experimental research is the most important research method in the study of fretting fatigue damage. There are many ways to perform fretting fatigue experiments, and the differences mainly focus on the shape of the indenter. There are many shapes of indenters, and different indenters will lead to different stress distributions. The most commonly used indenters at this stage are bridge indenters, cylindrical indenters and spherical indenters. It is usually able to provide a fixed normal pressure and a controlled cyclic change of physical force for standard fatigue specimens. However, it is difficult for this experiment to simulate the fretting fatigue failure process under the joint action of periodic normal pressure and periodic tangential force. The dovetail structure fretting fatigue test bench developed by Ruiz of Oxford University is based on an electro-hydraulic servo fatigue test machine. The centrifugal force of the aeroengine and the force of the air on the blades are respectively simulated by biaxial non-proportional excitation, and the control of the fretting amplitude is realized by an additional high-cycle fatigue excitation. The fretting fatigue experiment of the blade structure is realized. (References Ruiz C, Boddington PHB, Chen KC. An investigation on fatigue and fretting in a dovetail joint. Exp Mech1984; 24:208-17.) At this stage, there is no research on the resonance fretting fatigue of structural parts under typical characteristic loads of internal combustion engines. Related papers and reports on the experimental system.

Contents of the invention

The purpose of the present invention is to develop a resonant internal combustion engine fretting fatigue simulation experiment system in order to fully simulate the fretting fatigue damage process under the load characteristics of the internal combustion engine.

The purpose of the present invention is achieved through the following technical solutions.

A resonant internal combustion engine fretting fatigue simulation experiment system of the present invention, the system includes a fretting fatigue device 1, an accelerometer 2, an electronic control component 3, an electric vibrator 4, a vibrator push rod 5 and two inertial vibrators plate 6; two inertial vibrating plates 6 are suspended on the track through steel wire ropes; the fretting fatigue device 1 is fixed between the two inertial vibrating plates 6 through flanges; one end of the exciter push rod 5 is fixed on the electric vibrator 4 Above; the other end of the exciter push rod 5 is fixed on an inertial vibrating plate 6; the accelerometer 2 is stuck on another inertial vibrating plate 6 by magnetic force, and its position is symmetrical with the vibrator push rod 5; the electronic control part 3 is used to control the electric vibrator 4;

Among them, the fretting fatigue device 1 includes a test piece 7, a pre-tightening bolt 8, a pressure head 9, a U-shaped connector 10, a base 11, a loading push rod 12, and a load application shaft 13; the base 11 is a cylinder as a whole ; Two symmetrical grooves are dug on the lower side of the cylinder, a trapezoidal support frame is formed between the two grooves, and the remaining parts at both ends of the cylinder are used for fixed connection with the inertial vibrating plate 6; There is a test piece mounting groove for fixing and installing the test piece 7. There is a semicircular hole on one side of the test piece 7, and a semicircular hole on one side of the indenter 9. The indenter 9 is placed on the upper surface of the test piece 7. The semicircular hole of the indenter 9 and the semicircular hole of the test piece 7 form a round hole; the test piece 7 and the indenter 9 are fixedly connected on both sides of the trapezoidal support frame through the pre-tightening bolt 8; the load application shaft 13 passes through the indenter 9 and the round hole formed by the test piece 7; the two ends of the load application shaft 13 are fixed on the two arms of the U-shaped connector 10; the U-shaped connector and the base 11 are fixedly connected by the loading push rod 12.

The electronic control unit 3 performs closed-loop control on the resonance amplitude and resonance frequency of the crankshaft bending fatigue simulation system during the test to form a closed-loop control circuit; The vibrator 4 sends out a standard sinusoidal command signal, so that the electric vibrator 4 excites the system resonance, and then the accelerometer 2 installed on the inertial vibrating plate 6 passes the measured acceleration signal through the latter part of the charge amplifier as the response of the system The signal is fed back to the servo controller, and part of it is fed back to the signal generator through the resonance tracking unit, and the counter accumulates once every cycle. The servo controller compares the amplitude and frequency of the command signal and the response signal to correct the command signal or stop the test; the control circuit also sets two units of load amplitude limit and resonance frequency limit, when the load amplitude and frequency When the change exceeds the predetermined value of the limit unit, the limit unit can stop the test to protect the test device; the counter can record the number of cyclic loading when the test is stopped, and measure the corresponding fatigue life.

The acceleration amplitude on the inertial vibrating plate 6 can be kept constant through the closed-loop control, the acceleration amplitude is the second derivative of the displacement amplitude, and there is a corresponding relationship between the displacement amplitude and the bending moment amplitude of the test, so that the test process The fatigue bending moment amplitude is kept constant. When cracks appear on the rounded corner of the crankshaft single throw test piece or the connection of the tapered sleeve becomes loose, the bending stiffness of the system decreases, and the resonance frequency decreases accordingly. The control circuit can adjust the excitation frequency to keep the system in a resonance state.

Among them, the mechanical resonance part mainly includes the test piece, indenter, fixture and loading mechanism. Among them, the structural form of the test piece and the indenter must be similar to that of the body partition and the main bearing cap. The pretightening force across the bolts between the fixture and the indenter provides a working environment similar to that of the body partition for the test piece. The loading mechanism consists of three parts: an inertial vibrating plate, an electric vibrator and a push rod. The inertial vibration plate and fixture constitute a tuning fork resonance system. By changing the length of the inertial vibration plate, the natural frequency of the tuning fork system is adjusted, and the first-order natural frequency is adjusted to be close to the load frequency of the internal combustion engine under working conditions. The electric vibrator transmits the load to the inertial vibrating plate through the push rod, and the inertial vibrating plate applies the load to the test piece and the indenter through the U-shaped push rod to realize the micro-movement of the contact surface.

The electronic control part can realize three functions: keep the load constant during the experiment, ensure that the system is always in a resonance state during the experiment, and stop the experiment in due course.

The constant load during the experiment is realized by the acceleration closed-loop control. When the system is working, the charge generated by the accelerometer placed on the vibrating plate is amplified by the charge amplifier and converted into a standard quantized voltage signal, which is then sent to the servo controller as a response signal of the system. The command signal is given by the function generator and sent to the servo controller at the same time. Its waveform is a sine wave, the frequency is equal to the resonance frequency of the mechanical part, and the amplitude corresponds to the required experimental load. After the command and response signals enter the servo controller, the servo controller compares their amplitudes, and outputs a signal to the power amplifier, which excites the electric vibrator to push the other vibrating plate to vibrate at a certain amplitude. When some factors cause the load to change during the experiment, the loop can automatically correct this change through negative feedback, thereby keeping the load constant.

The resonance state during the experiment is realized by frequency closed-loop control. During the experiment, the stiffness of the specimen may decrease due to cracks or loose clamping, and the resonance frequency will decrease accordingly, and the original resonance state will be destroyed at this time. For this reason, a resonant frequency tracking unit is designed in the circuit, which forms a frequency automatic adjustment loop with a function generator. The command signal and the corresponding signal are input to the resonance tracking unit, after detection and amplification, they are fed back to the function generator, and the frequency of the command signal is corrected to make it equal to the current resonance frequency of the system, so as to ensure the resonance state of the system.

The test system is used to measure the micromomentum and the load on the specimen and indenter. The grating displacement sensor is used to measure the displacement micromomentum between the specimen and the contact pair of the indenter. Since the micromomentum between the contact pairs is within 100 μm during the fretting fatigue experiment, the proposed resolution is 0.1μm grating sensor. Use a force sensor to measure the load exerted by the U-shaped push rod on the specimen and the indenter.

The fretting fatigue simulation system can obtain the relationship among load, fretting moment and life. Among them, the load includes the bolt pretightening force and the periodic force of the loading mechanism. Periodic force along the contact surface can be decomposed into normal force and tangential force. By changing the angle between the loading mechanism and the contact surface, the ratio between the tangential force and the normal force can be changed.

The simulation experiment is realized through the following steps:

Through the multi-body dynamics analysis of the whole machine under multiple working conditions of the internal combustion engine, the ratio of the tangential force to the normal force under the typical working conditions of the internal combustion engine is determined, and on this basis, the angle between the loading mechanism and the contact surface in the experiment is determined;

Change the output load of the electric vibrator, measure the load exerted by the U-shaped push rod on the specimen through the force sensor, and superimpose the load and the pretightening force simulated by the fixture, so as to obtain the output load of the electric vibrator and The relationship between the cyclic loads on the specimen;

When the ratio of tangential force to normal force is constant, the output load of the electrodynamic exciter is changed, and the micromomentum of the contact pair is measured by the grating sensor, and the curve of the micromomentum changing with the output load of the electrodynamic exciter is obtained. The control of the micromomentum can be realized through this curve.

The pretightening force of the pretightening bolts, the ratio of tangential force to normal force, and the fretting amount between contact pairs are controlled, and the fretting fatigue damage experiment is carried out to obtain the relationship between each parameter and the fretting fatigue damage life.

Beneficial effect

The system can be used to study the fretting fatigue of structural parts under typical characteristic loads of internal combustion engines. Compared with traditional fretting fatigue simulation experiments, plane and plane contact can be considered, and the total load and tangential load can be changed by changing the total load and tangential load. According to the proportional relationship of load, the fretting fatigue of the specimen under different load characteristics and load levels is studied. Specific tasks that can be performed include:

Research on the law between the output load of the electrodynamic exciter and the cyclic load borne by the specimen;

Research on the control of micromomentum between contact pairs;

Research on fretting fatigue damage rule of internal combustion engine under characteristic load.

Observation and Measurement of Fretting Cracks

Description of drawings

Fig. 1 is a structural schematic diagram of a resonant internal combustion engine fretting fatigue simulation experiment system;

Figure 2 is a schematic diagram of the structure of the fretting fatigue device;

Figure 3 is a schematic diagram of the composition of electronic control components;

Among them, 1-fretting fatigue device, 2-accelerometer, 3-electronic control components, 4-electric exciter, 5-exciter push rod, 6-inertia vibration plate, 7-test piece, 8-preload bolt , 9-pressure head, 10-U connector, 11-base, 12-load push rod, 13-load application shaft.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example

A resonant internal combustion engine fretting fatigue simulation experiment system, the system includes a fretting fatigue device 1, an accelerometer 2, an electronic control component 3, an electric vibrator 4, a vibrator push rod 5 and two inertial vibrating plates 6; Two inertial vibrating plates 6 are suspended on the track through steel wire ropes; the fretting fatigue device 1 is fixed between the two inertial vibrating plates 6 through flanges; one end of the exciter push rod 5 is fixed on the electric vibrator 4; The other end of the vibrator push rod 5 is fixed on an inertial vibrating plate 6; the accelerometer 2 is stuck on another inertial vibrating plate 6 by magnetic force, and its position is symmetrical to the vibrator push rod 5; the electronic control part 3 is used for Control the electric vibrator 4;

Among them, the fretting fatigue device 1 includes a test piece 7, a pre-tightening bolt 8, a pressure head 9, a U-shaped connector 10, a base 11, a loading push rod 12, and a load application shaft 13; the base 11 is a cylinder as a whole ; Two symmetrical grooves are dug on the lower side of the cylinder, a trapezoidal support frame is formed between the two grooves, and the remaining parts at both ends of the cylinder are used for fixed connection with the inertial vibrating plate 6; There is a test piece mounting groove for fixing and installing the test piece 7. There is a semicircular hole on one side of the test piece 7, and a semicircular hole on one side of the indenter 9. The indenter 9 is placed on the upper surface of the test piece 7. The semicircular hole of the indenter 9 and the semicircular hole of the test piece 7 form a round hole; the test piece 7 and the indenter 9 are fixedly connected on both sides of the trapezoidal support frame through the pre-tightening bolt 8; the load application shaft 13 passes through the indenter 9 and the round hole formed by the test piece 7; the two ends of the load application shaft 13 are fixed on the two arms of the U-shaped connector 10; the U-shaped connector and the base 11 are fixedly connected by the loading push rod 12.

The electronic control unit 3 performs closed-loop control on the resonance amplitude and resonance frequency of the crankshaft bending fatigue simulation system during the test to form a closed-loop control circuit; The vibrator 4 sends out a standard sinusoidal command signal, so that the electric vibrator 4 excites the system resonance, and then the accelerometer 2 installed on the inertial vibrating plate 6 passes the measured acceleration signal through the latter part of the charge amplifier as the response of the system The signal is fed back to the servo controller, and part of it is fed back to the signal generator through the resonance tracking unit, and the counter accumulates once every cycle. The servo controller compares the amplitude and frequency of the command signal and the response signal to correct the command signal or stop the test; the control circuit also sets two units of load amplitude limit and resonance frequency limit, when the load amplitude and frequency When the change exceeds the predetermined value of the limit unit, the limit unit can stop the test to protect the test device; the counter can record the number of cyclic loading when the test is stopped, and measure the corresponding fatigue life.

Through the multi-body dynamics analysis of the whole machine under multiple working conditions of the internal combustion engine, the ratio of the tangential force to the normal force under the typical working conditions of the internal combustion engine is determined, and on this basis, the angle between the loading mechanism and the contact surface in the experiment is determined as a design The basis for the bevel angles at 7 places of the fixture inlaid with the test piece. In order to make the fretting fatigue experimental system fully simulate the fretting fatigue damage process under the load characteristics of the internal combustion engine, the key dimensions of the specimen 7 and the body partition must meet the structural similarity, and the two must meet the material consistency; the indenter 9 and the main The key dimensions of the bearing cover meet the similarity of the mechanism, and the two meet the consistency of the material. After the dimensions of the indenter 9, the test piece 7, the fixture and the U-shaped push rod are determined, the inertial vibrating plate 6 is designed. Two identical inertial vibrating plates 6 are symmetrically fixed at both ends of the jig, forming a tuning fork resonance system. By changing the length of the inertial vibrating plate 6 and adjusting the natural frequency of the tuning fork system, the first-order natural frequency is adjusted to be close to the load frequency of the internal combustion engine in a working state.

Install the designed and manufactured mechanical resonance system on the experimental bench.

The electronic control part is used to control the output load and frequency of the electric vibrator 4 .

Change the output load of the electric vibrator 4, measure the load applied by the U-shaped push rod on the test piece 7 and the indenter 9 through the force sensor, and superimpose the load and the pretightening force simulated by the fixture, so as to obtain the electric exciter. The relationship between the output load of the vibrator 4 and the cyclic load borne by the test piece 7 and the indenter 9.

When the ratio of the tangential force to the normal force is constant, change the output load of the electrodynamic exciter 4, measure the micromomentum of the contact pair between the test piece 7 and the indenter 9 through the grating sensor, and obtain the micromomentum with the electric vibration The device 4 outputs the curve of load change. The control of the micromomentum can be realized through this curve.

The parameters such as the pretightening force of the pretightening bolt 8, the ratio of tangential force to normal force, and the fretting amount between the contact pairs are controlled, and the fretting fatigue damage experiment is carried out to obtain the relationship between each parameter and the fretting fatigue damage life.

Claims (1)

1. A resonant internal combustion engine fretting fatigue simulation experiment system, characterized in that: the system includes a fretting fatigue device (1), an accelerometer (2), an electronic control component (3), an electric vibrator (4), Vibrator push rod (5) and two inertial vibration plates (6); the two inertial vibration plates (6) are suspended on the track by wire ropes; the fretting fatigue device (1) is fixed on the two inertial vibration plates by flanges (6); one end of the exciter push rod (5) is fixed on the electric vibrator (4); the other end of the exciter push rod (5) is fixed on an inertial vibrating plate (6); the acceleration The gauge (2) is magnetically attached to another inertial vibrating plate (6), and its position is symmetrical to the push rod (5) of the vibrator; the electronic control part (3) is used to control the electric vibrator (4); The fretting fatigue device (1) includes the test piece (7), the pre-tightening bolt (8), the indenter (9), the U-shaped connector (10), the base (11), the loading push rod (12) and the load application The shaft (13); the base (11) is a cylinder as a whole; there are two symmetrical grooves on the lower side of the cylinder, a trapezoidal support frame is formed between the two grooves, and the remaining parts at both ends of the cylinder are used for It is fixedly connected with the inertial vibrating plate (6); there is a test piece installation groove on both sides of the trapezoidal support frame, which is used to fix and install the test piece (7), and there is a semicircular hole on one side of the test piece (7). There is a semicircular hole on one side of (9), and the indenter (9) is placed on the upper surface of the test piece (7), and the semicircular hole of the indenter (9) and the semicircular hole of the test piece (7) just form a circular hole; The test piece (7) and the indenter (9) are fixedly connected on both sides of the trapezoidal support frame through pre-tightening bolts (8); the load application axis (13) passes through the circle formed by the indenter (9) and the test piece (7). hole; there are two U-shaped connectors (10), and the two U-shaped connectors (10) are symmetrically fixed in two grooves, wherein the two arms of the U-shaped connector (10) respectively fix the load applying shaft (13) Two U-shaped connectors (10) are respectively fixedly connected to the base (11) through the loading push rod (12) at the two ends; The signal generator in the electronic control unit (3) inputs the signal to the servo controller, and the servo controller sends a standard sinusoidal instruction signal to the electric vibrator (4) through the power amplifier, so that the electric vibrator (4) excites system resonance, and then the accelerometer (2) installed on the inertial vibrating plate (6) feeds the measured acceleration signal back to the servo controller as a response signal of the system through the charge amplifier, and feeds back the signal to the servo controller through the resonance tracking unit Generator, the counter accumulates once every cycle; the servo controller compares the amplitude and frequency of the command signal and the response signal to correct the command signal or stop the test; the electronic control part (3) also sets the load amplitude limit harmony The vibration frequency limits two units. When the change of load amplitude and frequency exceeds the predetermined value of the limit unit, the limit unit can stop the test to protect the test device; the counter can record the number of cyclic loading when the test is stopped, and measure the corresponding fatigue life .

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