A wheel hub bearing unit structure fatigue test system and method

Abstract

The present invention discloses a wheel hub bearing unit structural fatigue test system and method, and relates to the field of wheel hub bearing fatigue detection. The system includes a base, a bottom tooling, a test wheel hub bearing unit, an adapter plate, a strain bridge, a loading arm, a vertical rod, an installation aid, a locking nut, an eccentric inner ring, a rolling body, an outer ring, a flexible shaft, a servo motor and a crossbeam. The test method includes load calibration, rotation frequency determination, loading test and failure determination. The wheel hub bearing structural fatigue test system provided by the present invention can better realize the accurate evaluation of the fatigue life of the wheel hub bearing structure, and eliminates the problem that the test cannot be carried out due to raceway contact fatigue failure of the test bearing. At the same time, due to the use of an electric drive loading mode, it has the good characteristics of simple and reliable structure, accurate and stable loading, convenient maintenance, and timely failure judgment.

Description

Technical Field

[0001] The invention relates to the field of wheel hub bearing fatigue detection, and in particular to a wheel hub bearing unit structure fatigue test system and method. Background Art

[0002] Hub bearing unit is a bearing used on the wheel to bear the weight of the vehicle body and transmit power. It is called hub bearing unit because the flange connected to the brake disc and wheel hub and the bearing are integrated.

[0003] Structural fatigue refers to the material failure phenomenon caused by long-term bending cycles of wheel hub bearing flange structures during application.

[0004] There are two solutions for the fatigue test of hub bearing unit structure in the prior art:

[0005] The first solution, Chinese invention patent 200420075349.3 discloses a bending fatigue testing machine for automobile wheel hub bearings. The wheel hub bearing unit is installed on the test spindle. The wheel hub bearing unit rotates during the test. The radial loading mechanism and the axial loading mechanism are connected to the two sides of the wheel hub bearing unit respectively. The radial load and the axial load are applied to the test bearing. The loading radius and the offset are consistent with the state of the test bearing installed on the actual vehicle. The bending moment of the test bearing is obtained by superimposing the loads in two directions. The loading mechanisms used in the test system are all hydraulic modes. The loading mechanisms are connected to the loading arm through a ball joint to maintain a certain loading flexibility. During the test, the wheel hub bearing unit suffers fatigue failure under the long-term action of the bending moment load. The failure is monitored by the change of vibration acceleration.

[0006] Its disadvantage is that under the bending moment condition formed by the load in two specific directions, the contact fatigue peeling of the raceway is easy to occur due to the long-term rotation of the test bearing, and the test is terminated due to contact fatigue, making it difficult to evaluate the structural fatigue life of the flange. The test bench uses a large number of ball joints, which are very likely to wear out in the dynamic operation test and affect the loading accuracy. At the same time, the use of hydraulic loading increases the complexity of hydraulic system maintenance.

[0007] The second solution, Chinese invention patent 201621028812.8 discloses a wheel hub bearing unit bending fatigue testing machine. The wheel hub bearing unit is installed on the base. The wheel hub bearing unit is fixed and does not rotate during the test. The radial loading mechanism and the axial loading mechanism are connected to the two sides of the wheel hub bearing unit respectively. The radial load and axial load are applied to the test bearing at a certain frequency. The loading radius and offset are consistent with the state of the test bearing installed on the actual vehicle. The bending moment of the test bearing is obtained by superimposing the loads in two directions. The loading mechanisms used in the test system are all hydraulic modes. The loading mechanisms are connected to the loading arm through a ball joint to maintain a certain loading flexibility. During the test, the wheel hub bearing unit suffers fatigue failure under the long-term action of the bending moment load. The failure is monitored by the change in the indication of the metal density meter connected to the bearing.

[0008] The defect is that the difference between this solution and the first solution is that the bearing does not rotate, which also brings a problem. The load applied at a specific frequency can only meet the characteristics of the sine wave law, and cannot guarantee the uniform load of the structural parts, which is quite different from the actual load of the hub bearing. This solution still uses a large number of ball joints, and the wear of the joints under specific frequency loading affects the loading accuracy. The use of hydraulic loading increases the complexity of hydraulic system maintenance, and the timeliness of the failure judgment of the metal density meter used is poor. Summary of the invention

[0009] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a wheel hub bearing unit structural fatigue test system to accurately simulate the actual load bending moment of the wheel hub bearing unit and achieve accurate and stable application of the test bending moment load; abandon the use of ball joints and eliminate the problem of reduced loading accuracy caused by wear of ball joints; achieve accurate evaluation of the fatigue life of the wheel hub bearing unit structure and completely solve the problem that the test cannot be continued and the fatigue life of the structure cannot be judged due to early fatigue of the raceway; instead of hydraulic loading, an electric drive loading solution is adopted to eliminate the difficulty and complexity of hydraulic system maintenance.

[0010] The objective of the present invention is achieved through the following technical solutions: a wheel hub bearing unit structural fatigue test system, comprising a base, a bottom tooling, a test wheel hub bearing unit, an adapter plate, a strain bridge, a loading arm, a vertical rod, an installation aid, a locking nut, an eccentric inner ring, a rolling element, an outer ring, a flexible shaft, a servo motor and a crossbeam, wherein the base is placed on a horizontal ground, the bottom of the bottom tooling is fixedly mounted on the base by bolts, the test wheel hub bearing unit is placed on the bottom tooling, and the top of the bottom tooling is locked and fixed to the flange of the test wheel hub bearing unit, the outer ring of the test wheel hub bearing unit is provided with an adapter plate, the two are locked and connected by bolts, the top of the adapter plate is fixedly connected to the bottom end of the loading arm, four strain gauges are evenly distributed along the circumference of the arm of the loading arm, and the four strain gauges are mutually bridged to form the strain gauge. The strain bridge is electrically connected to an external data acquisition system, so as to collect the strain data of the loading arm in real time; the vertical rod is fixed on the base in the vertical direction, and the mounting aid is installed on the vertical rod through a guide rail, so as to move along the vertical rod in the vertical direction, and the guide rail selectively locks and fixes the mounting aid with the vertical rod; a positioning hole is provided on the mounting aid, and the arm body of the loading arm passes through the positioning hole to achieve positioning; the crossbeam is fixed on the horizontal ground, and the top of the crossbeam is suspended and fixed in the vertical direction. The servo motor is used to drive the eccentric inner ring to rotate, and the output shaft of the servo motor is connected to the input end of the flexible shaft for transmission, and the output end of the flexible shaft is sleeved with an eccentric inner ring and fixed with a locking nut, and the eccentric inner ring is connected to the outer ring through the rolling body to achieve rolling bearing contact; the outer ring is locked and fixed to the top of the loading arm by bolts.

[0011] As a further technical solution, an eccentric mass block is arranged on the outer edge of the eccentric inner ring.

[0012] As a further technical solution, a clearance fit is adopted between the mounting aid and the loading arm.

[0013] As a further technical solution, the height H3 of the adapter plate is adjusted according to the height H4 of the test hub bearing unit, and the total height H2 of the two remains constant; the height of the loading arm is constant, so that the total height H of the loading arm, the adapter plate and the test hub bearing unit is constant; the height H1 of the bottom tooling is also kept constant.

[0014] As a further technical solution, the strain gauge includes a first strain gauge, a second strain gauge, a third strain gauge and a fourth strain gauge, and adjacent strain gauges are spaced 90° apart.

[0015] A wheel hub bearing unit structure fatigue test method comprises the following steps:

[0016] 1) Load calibration: Slowly apply a radial load F to the loading arm at a height H above the bottom fixture, and detect the strain Strain of the loading arm in real time through a strain bridge to obtain the relationship function between the strain Strain and the bending moment M, where the bending moment M = F*H;

[0017] 2) Determine the rotation frequency: Start the servo motor and arrange an eccentric mass block with a mass of m on the outer edge of the eccentric inner ring. The distance between the eccentric mass block and the rotation center of the eccentric inner ring is r, that is, the rotation radius is r. During the driving rotation process, the rotation angular velocity of the eccentric mass block is ω, and the rotation frequency is f, which will generate the following centrifugal force F:

[0018] F 偏 =ω 2 r=m(2π*f) 2 r

[0019] The bending moment M generated by the eccentric mass block in the working state is:

[0020] M 偏 =F 偏 *H=m(2π*f) 2 4 H

[0021] The test loading bending moment M0 is set, and the servo motor is controlled to gradually increase the rotation frequency of the eccentric inner ring, thereby increasing the rotation frequency f of the eccentric mass block. At the same time, the strain Strain of the loading arm is measured through the strain bridge, and the actual loading bending moment M1 of the loading arm is obtained according to the relationship function between the strain Strain and the bending moment M. When the actual loading bending moment M1 is equal to the test loading bending moment M0, the rotation frequency f of the eccentric mass block no longer increases and the rotation frequency f1 at this moment is fixed;

[0022] 3) Loading test: keep the eccentric inner ring rotating at the frequency f1 obtained in step 2), monitor the actual loading bending moment M1 of the loading arm in real time through the strain bridge, and keep the actual loading bending moment M1 consistent with the test loading bending moment M0;

[0023] 4) Failure determination: When cracks appear in the test hub bearing unit, the rotation radius r of the eccentric mass block on the eccentric inner ring also increases. At this time, the servo motor is controlled to adjust the rotation frequency of the eccentric inner ring to reduce the rotation frequency of the eccentric mass block to ensure that the actual loading bending moment M1 is consistent with the test loading bending moment M0. After the reduction, the rotation frequency of the eccentric mass block is f2, and the difference between f1 and f2 is Δf. When Δf is greater than the warning value, the servo motor stops working and the test is stopped. The operator removes the test hub bearing unit for crack inspection.

[0024] As a further technical solution, the radial load F applied in step 1) is maintained on the same side and the same interface as the center of at least one of the four strain gauges, and the load calibration of the first strain gauge, the second strain gauge, the third strain gauge and the fourth strain gauge is performed in sequence.

[0025] As a further technical solution, the warning value of Δf in step 4) is ≥ 1 Hz, preferably 2 Hz.

[0026] The beneficial effects of the present invention are:

[0027] 1. A load rotation mode is used to replace the hub bearing rotation mode, which not only realizes the 360° full-scale load application on the bearing to achieve accurate simulation of the actual working conditions, but also realizes accurate evaluation of the fatigue life of the structure. The problem of being unable to continue the test due to early fatigue of the raceway and failing to judge the fatigue life of the structure will not occur;

[0028] 2. Use a non-joint loading connection mode to eliminate the problem of decreased loading accuracy caused by wear of the ball joint;

[0029] 3. It adopts an electric drive loading method, which is easy to operate and maintain;

[0030] 4. A new failure crack monitoring method is used to accurately determine the time when the wheel hub bearing unit structural fatigue occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the structure of the present invention.

[0032] Figure 2 Schematic diagram of the load calibration structure.

[0033] Figure 3 Schematic diagram of the structure of the strain bridge and strain gauge.

[0034] Figure 4 It is a schematic diagram of the installation structure of the eccentric mass block and the eccentric inner ring.

[0035] Figure 5 Schematic diagram of the force acting on the eccentric mass block.

[0036] Figure 6 This is the test monitoring curve chart.

[0037] Figure 7 It is a graph of the test cycle number and the driving rotation frequency.

[0038] Explanation of the reference numerals in the accompanying drawings: base 1, bottom tooling 2, test hub bearing unit 3, adapter plate 4, strain bridge 5, loading arm 6, vertical rod 7, mounting aid 8, locking nut 9, eccentric inner ring 10, rolling element 11, outer ring 12, flexible shaft 13, servo motor 14, crossbeam 15, strain gauge 16, guide rail 17, positioning hole 18, eccentric mass block 19, first strain gauge G1, second strain gauge G2, third strain gauge G3, fourth strain gauge G4. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to the accompanying drawings:

[0040] Example: As attached Figure 1 As shown, a wheel hub bearing unit structural fatigue test system comprises a base 1, a bottom fixture 2, a test wheel hub bearing unit 3, an adapter plate 4, a strain bridge 5, a loading arm 6, a vertical rod 7, an installation aid 8, a locking nut 9, an eccentric inner ring 10, a rolling body 11, an outer ring 12, a flexible shaft 13, a servo motor 14 and a crossbeam 15. The base 1 is placed on a horizontal ground, the bottom of the bottom fixture 2 is fixedly mounted on the base 1 by bolts, the test wheel hub bearing unit 3 is placed on the bottom fixture 2, and the top of the bottom fixture 2 is locked and fixed to the flange of the test wheel hub bearing unit 3, the outer ring of the test wheel hub bearing unit 3 is provided with an adapter plate 4, and the two are locked and connected by bolts, the top of the adapter plate 4 is fixedly connected to the bottom end of the loading arm 6, four strain gauges 16 are evenly distributed along the circumference of the arm body of the loading arm 6, the four strain gauges 16 are mutually bridged to form the strain bridge 5, and the strain bridge 5 is connected to the external data The acquisition system is electrically connected, so as to collect the strain data of the loading arm 6 in real time; the vertical rod 7 is fixed on the base 1 in the vertical direction, and the mounting aid 8 is installed on the vertical rod 7 through the guide rail 17, so as to move along the vertical rod 7 in the vertical direction, and the guide rail 17 selectively locks and fixes the mounting aid 8 and the vertical rod 7; a positioning hole 18 is provided on the mounting aid 8, and the arm body of the loading arm 6 passes through the positioning hole 18 to achieve positioning; the crossbeam 15 is fixed on the horizontal ground, and the top of the crossbeam 15 is suspended and fixed in the vertical direction. The servo motor 14 is used to drive the eccentric inner ring 10 to rotate, and the output shaft of the servo motor 14 is connected to the input end of the flexible shaft 13 for transmission. The output end of the flexible shaft 13 is sleeved with the eccentric inner ring 10 and fixed with a locking nut 9, and the eccentric inner ring 10 is connected to the outer ring 12 through the rolling body 11 to achieve rolling bearing contact; the outer ring 12 is fixed to the top of the loading arm 6 by bolts.

[0041] Preferably, an eccentric mass block 19 is arranged on the outer edge of the eccentric inner ring 10. A clearance fit is adopted between the mounting aid 8 and the loading arm 6. The height H3 of the adapter plate 4 is adjusted according to the height H4 of the test hub bearing unit 3, and the total height H2 of the two is kept constant; the height of the loading arm 6 is constant, so that the total height H of the loading arm 6, the adapter plate 4 and the test hub bearing unit 3 is constant; the height H1 of the bottom tooling 2 is also kept constant. The strain gauge 16 includes a first strain gauge G1, a second strain gauge G2, a third strain gauge G3 and a fourth strain gauge G4, and adjacent strain gauges 16 are spaced 90° apart.

[0042] refer to Figures 2 to 4 , a wheel hub bearing unit structure fatigue test method, comprising the following steps:

[0043] 1) Load calibration: At a height of H above the bottom fixture 2, slowly apply a radial load F to the loading arm 6, and the applied radial load F is kept at least on the same side and the same interface as the center of one of the four strain gauges 16, and the load calibration of the first strain gauge G1, the second strain gauge G2, the third strain gauge G3 and the fourth strain gauge G4 is performed in sequence. The strain Strain of the loading arm 6 is detected in real time by the strain bridge 5, and the relationship function between the strain Strain and the bending moment M is obtained, where the bending moment M=F*H;

[0044] 2) Determine the rotation frequency: Start the servo motor 14, and arrange an eccentric mass block 19 with a mass of m on the outer edge of the eccentric inner ring 10. The distance between the eccentric mass block 19 and the rotation center of the eccentric inner ring 10 is r, that is, the rotation radius is r. During the driving rotation process, the rotation angular velocity of the eccentric mass block 19 is ω, and the rotation frequency is f, which will generate the following centrifugal force Feccentric:

[0045] F 偏 =ω 2 r=m(2π*f) 2 r

[0046] The bending moment M generated by the eccentric mass block 19 in the working state is:

[0047] M 偏 = F bias * H = m (2π * f) 2 4 H

[0048] The test loading bending moment M0 is set, and the servo motor 14 is controlled to gradually increase the rotation frequency of the eccentric inner ring 10 so as to increase the rotation frequency f of the eccentric mass block 19. At the same time, the strain Strain of the loading arm 6 is measured by the strain bridge 5, and the actual loading bending moment M1 of the loading arm 6 is obtained according to the relationship function between the strain Strain and the bending moment M. When the actual loading bending moment M1 is equal to the test loading bending moment M0, the rotation frequency f of the eccentric mass block 19 no longer increases and the rotation frequency f1 at this moment is fixed;

[0049] 3) Loading test: keep the eccentric inner ring 10 rotating at the frequency f1 obtained in step 2), monitor the actual loading bending moment M1 of the loading arm 6 in real time through the strain bridge 5, and keep the actual loading bending moment M1 consistent with the test loading bending moment M0;

[0050] 4) Failure determination: When cracks appear in the test hub bearing unit 3, the rotation radius r of the eccentric mass block 19 on the eccentric inner ring 10 also increases. At this time, the servo motor 14 is controlled to adjust the rotation frequency of the eccentric inner ring 10 to reduce the rotation frequency of the eccentric mass block 19 to ensure that the actual loading bending moment M1 is consistent with the test loading bending moment M0. After the reduction, the rotation frequency of the eccentric mass block 19 is f2, and the difference between f1 and f2 is Δf. When Δf is greater than the warning value set to 2Hz, the servo motor 14 stops working and the test is stopped, and the operator removes the test hub bearing unit 3 for crack inspection.

[0051] Working process of the present invention:

[0052] Reference Figure 1 , when the servo motor 14 is not working, push the installation aid 8 upward along the vertical rod 7 until the upper end surface of the installation aid 8 is in contact with the end surface of the loading arm 6 and is lifted up by 15mm, so that the deadweight of the loading arm 6 is completely borne by the installation aid 8. At this time, the loading arm 6 is suspended, leaving enough installation space for the test sample and the tooling below. The bottom tooling 2 is fastened to the base 1 with 6 M14×1.5 bolts at the bottom, and the tightening torque of each bolt is 50N·m+90°. The test hub bearing unit 3 is fastened to the bottom tooling 2 with 5 M14×1.5 bolts, and the tightening torque of each bolt is 130N·m. The adapter plate 4 is fastened to the test hub bearing unit 3 with 3 M14×1.5 bolts, and the tightening torque is 120N·m.

[0053] Next, slowly lower the installation aid 8 along the vertical direction of the vertical rod 7, so that the lower end surface of the loading arm 6 is in contact with the upper end surface of the adapter plate 4, and use 6 M14×1.5 bolts to lock the loading arm 6 and the adapter plate 4, with a locking torque of 50N·m+90°. After completing the above work, move the installation aid 8 down a distance of 10mm along the vertical direction of the vertical rod 7, and keep the installation aid 8 from contacting the loading arm 6 to avoid affecting the loading during the test.

[0054] Reference Figure 2 , the total height of the working area of ​​the test system = H + H1 = 515mm, which is a fixed value. The total height of the working area of ​​the test system is composed of the height of the loading arm H = 450mm and the thickness of the bottom fixture 2 H1 = 65mm. H2 = 110mm is a constant value, the height of the test hub bearing unit 3 H4 = 50mm, and the design value of H3 is 60mm.

[0055] Reference Figure 2 A loading mechanism is used to slowly apply a radial load F to the loading arm 6 at a position H=450mm above the loading arm 6. The loading operation is performed at every 90° position in the circumferential direction. Figure 3 , four strain gauges 16 (G1, G2, G3, G4) are arranged below the loading arm 6. The applied radial load F is kept on the same side and the same interface as the center of at least one of the four strain gauges 16 (G1, G2, G3, G4).

[0056] During the application of radial load F, the strain gauges 16 (G1, G2, G3, G4) can sense deformation and measure and collect strain data. The load calibration of the G1, G2, G3, G4 strain gauges is performed in sequence to obtain the relationship function between strain Strain and bending moment M=F*H, as shown in the following table:

[0057]

[0058] Through linear fitting, the relationship function between the strain X and the bending moment M of the G1, G2, G3, and G4 strain gauges is obtained as follows:

[0059] Calibration function of the first strain gauge G1:

[0060] M = 0.0842X + 3.1026;

[0061] Calibration function of the second strain gauge G2:

[0062] M = 0.0891X + 5.1982;

[0063] Calibration function of the third strain gauge G3:

[0064] M = 0.0873X + 7.0711;

[0065] Calibration function of the fourth strain gauge G4:

[0066] M=0.0834X+5.0509.

[0067] The above four functional formulas are introduced into the measurement and control software and applied to the test load application in the structural fatigue test of the actual test hub bearing unit 3. Load calibration is not required for every test sample test, and calibration once a year is a better choice.

[0068] Reference Figure 1 After the test sample is installed, the test hub bearing unit 3, adapter plate 4, strain bridge 5 (including G1, G2, G3, G4), and loading arm 6 are all stationary and do not rotate during the entire test. The servo motor 14 is started by the measurement and control system, and the servo motor 14 transmits power to the eccentric inner ring 10 through the flexible shaft 13. Figure 4 , Figure 5 An eccentric mass block 19 with a mass of m=2000g is arranged on the outer edge of the eccentric inner ring 10. The distance between the eccentric mass block 19 and the rotation center of the eccentric inner ring 10 is r, that is, the rotation radius is r=58mm.

[0069] During the continuous test, the four strain gauges 16 (G1, G2, G3, G4) will continuously monitor the changes in the actual bending moment of the test, such as Figure 6 This is the test monitoring curve chart.

[0070] During the test, the changes in the test rotation frequency f were continuously monitored. After the test was continued for 2.35 million cycles, a downward trend in the rotation frequency was observed. When the rotation frequency dropped from the initial 27.3 Hz to 25.2 Hz, the decrease in the rotation frequency was Δf = 2.1 Hz. Figure 7 shown.

[0071] The frequency drop alarm limit set by the test system software is 2Hz. After the test bearing was tested 2.39 million times, the test system gave an alarm and stopped, judging that the test object had structural crack failure. After the test personnel inspected the test sample, they found that the test hub bearing unit 3 had two cracks at the root of the flange disc turning point.

[0072] At this point, the structural fatigue test of the test hub bearing unit 3 is completed, and it is determined that the structural fatigue life of the test hub bearing unit under the condition of bending moment M=1500 N·m is 2.39 million times.

[0073] The wheel hub bearing structure fatigue test system provided by the present invention can achieve accurate evaluation of the wheel hub bearing structure fatigue life, and eliminates the problem that the test bearing cannot be tested due to raceway contact fatigue failure. At the same time, due to the use of electric drive loading mode, it has the good characteristics of simple and reliable structure, accurate and stable loading, convenient maintenance, and timely failure judgment.

[0074] It is understandable that, for those skilled in the art, any equivalent replacement or change to the technical solution and inventive concept of the present invention should fall within the protection scope of the claims attached to the present invention.

Claims

1. A wheel hub bearing unit structural fatigue test system, characterized in that: The invention comprises a base (1), a bottom fixture (2), a test hub bearing unit (3), an adapter plate (4), a strain bridge (5), a loading arm (6), a vertical rod (7), a mounting aid (8), a locking nut (9), an eccentric inner ring (10), a rolling body (11), an outer ring (12), a flexible shaft (13), a servo motor (14) and a crossbeam (15), wherein the base (1) is placed on a horizontal ground, the bottom of the bottom fixture (2) is fixedly mounted on the base (1), and the test hub bearing unit (3) is fixedly mounted on the bottom of the bottom fixture (2). ) is placed on the bottom fixture (2), and the top of the bottom fixture (2) is locked and fixed with the flange of the test hub bearing unit (3), the outer ring of the test hub bearing unit (3) is provided with an adapter plate (4), the top of the adapter plate (4) is fixedly connected to the bottom end of the loading arm (6), four strain gauges (16) are evenly distributed along the circumference of the arm of the loading arm (6), the four strain gauges (16) are mutually bridged to form the strain bridge (5), and the strain bridge (5) is electrically connected to the external data acquisition system, so as to realize real-time The strain data of the loading arm (6) is collected; the vertical rod (7) is fixed on the base (1) in the vertical direction, and the mounting aid (8) is mounted on the vertical rod (7) through a guide rail (17), so as to move along the vertical rod (7), and the guide rail (17) selectively locks and fixes the mounting aid (8) and the vertical rod (7); a positioning hole (18) is provided on the mounting aid (8), and the arm body of the loading arm (6) passes through the positioning hole (18) to achieve positioning; the crossbeam (15) is fixed on a horizontal ground, The servo motor (14) is suspended and fixed in the vertical direction on the top of the crossbeam (15) to drive the eccentric inner ring (10) to rotate. The output shaft of the servo motor (14) is connected to the input end of the flexible shaft (13) for transmission. The output end of the flexible shaft (13) is sleeved with the eccentric inner ring (10) and fixed with a locking nut (9). The eccentric inner ring (10) is connected to the outer ring (12) through the rolling body (11) to achieve rolling bearing contact; the outer ring (12) is locked and fixed to the top of the loading arm (6).

2. The wheel hub bearing unit structural fatigue test system according to claim 1, characterized in that: An eccentric mass block (19) is arranged on the outer edge of the eccentric inner ring (10).

3. The wheel hub bearing unit structural fatigue testing system according to claim 1, characterized in that: The mounting aid (8) and the loading arm (6) are clearance-fitted.

4. The wheel hub bearing unit structure fatigue test system according to claim 1, characterized in that: The height H3 of the adapter plate (4) is adjusted according to the height H4 of the test wheel hub bearing unit (3), and the total height H2 of the two is kept constant; the height of the loading arm (6) is constant, so that the total height H of the loading arm (6), the adapter plate (4) and the test wheel hub bearing unit (3) is constant; the height H1 of the bottom tooling (2) is also kept constant.

5. The wheel hub bearing unit structural fatigue testing system according to claim 1, characterized in that: The strain gauge (16) comprises a first strain gauge (G1), a second strain gauge (G2), a third strain gauge (G3) and a fourth strain gauge (G4), and adjacent strain gauges (16) are spaced 90 degrees apart.

6. A wheel hub bearing unit structure fatigue test method, using the wheel hub bearing unit structure fatigue test system according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) Load calibration: At a height H above the bottom fixture (2), a radial load F is slowly applied to the loading arm (6), and at the same time, the strain Strain of the loading arm (6) is detected in real time through the strain bridge (5) to obtain a relationship function between the strain Strain and the bending moment M, where the bending moment M = F*H; 2) Determine the rotation frequency: start the servo motor (14), and arrange an eccentric mass block (19) with a mass of m on the outer edge of the eccentric inner ring (10). The distance between the eccentric mass block (19) and the rotation center of the eccentric inner ring (10) is r, that is, the rotation radius is r. During the driving rotation process, the rotation angular velocity of the eccentric mass block (19) is ω, and the rotation frequency is f, which will generate the following centrifugal force F: F deviation = ω 2 r = m(2π*f) 2 r The bending moment M generated by the eccentric mass block (19) in the working state is: M bias = F bias * H = m(2π*f) 2 4 H The test loading bending moment M0 is set, and the servo motor (14) is controlled to gradually increase the rotation frequency of the eccentric inner ring (10) so as to increase the rotation frequency f of the eccentric mass block (19). At the same time, the strain Strain of the loading arm (6) is measured by the strain bridge (5), and the actual loading bending moment M1 of the loading arm (6) is obtained according to the relationship function between the strain Strain and the bending moment M. When the actual loading bending moment M1 is equal to the test loading bending moment M0, the rotation frequency f of the eccentric mass block (19) no longer increases and the rotation frequency f1 at this moment is fixed; 3) Loading test: keep the eccentric inner ring (10) rotating at the frequency f1 obtained in step 2), monitor the actual loading bending moment M1 of the loading arm (6) in real time through the strain bridge (5), and keep the actual loading bending moment M1 consistent with the test loading bending moment M0; 4) Failure determination: When cracks appear in the test hub bearing unit (3), the rotation radius r of the eccentric mass block (19) on the eccentric inner ring (10) also increases. At this time, the servo motor (14) is controlled to adjust the rotation frequency of the eccentric inner ring (10) so that the rotation frequency of the eccentric mass block (19) is reduced to ensure that the actual loading moment M1 is consistent with the test loading moment M0. After the reduction, the rotation frequency of the eccentric mass block (19) is f2, and the difference between f1 and f2 is Δf. When Δf is greater than the warning value, the servo motor (14) stops working and the test is stopped. The operator removes the test hub bearing unit (3) for crack inspection.

7. The wheel hub bearing unit structure fatigue test method according to claim 6, characterized in that: The radial load F applied in step 1) is maintained on the same side and the same interface as the center of at least one strain gauge (16) among the four strain gauges (16), and the load calibration of the first strain gauge (G1), the second strain gauge (G2), the third strain gauge (G3) and the fourth strain gauge (G4) is performed in sequence.

8. The wheel hub bearing unit structure fatigue test method according to claim 6, characterized in that: The warning value of Δf in step 4) is ≥1 Hz.

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