A towing, calibration test method and strength evaluation method for a passenger car tow hook

Abstract

The present application provides a kind of passenger car tow hook's towing, calibration test method and strength evaluation method, belongs to tow hook field.Solve the problem that existing tow hook exists fracture risk.It includes to tow hook is carried out to clear obstacle car tow test, soft ground tow test, intensifies bad road tow test and curved road tow test, after each tow test is ended, check whether tow hook and test vehicle crossbeam have crack or fracture, calculate the maximum stress that tow hook receives, when the maximum stress reaches material yield stress, the surface of dangerous section of tow hook begins to occur plastic deformation, with further increase of external force, plastic deformation area on dangerous section increases, and elastic deformation area reduces, it is mainly used for the test of passenger car tow hook.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of tow hooks, in particular to a towing, calibration test method and strength evaluation method for passenger car tow hooks. BACKGROUND

[0002] The tow hook is generally fixed to the front and rear cross beams of the vehicle body through threaded connection. When the vehicle is out of order or trapped and cannot move, external force needs to be applied to the tow hook to tow the vehicle. The strength of the tow hook needs to be large enough to ensure that the vehicle can be smoothly rescued under very large external force. If the tow hook suddenly breaks during use, it may harm the surrounding people or objects, which is very dangerous. It is very important to measure the load of the tow hook during actual use on the vehicle to ensure its safety. It is necessary to verify whether there is a risk of tow hook breakage during actual use through some tests to reduce the safety risk caused by the failure of the tow hook. SUMMARY

[0003] Therefore, the present application aims to provide a towing, calibration test method and strength evaluation method for passenger car tow hooks to solve the problem of breakage risk of the existing tow hooks.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical scheme: a method for towing test of a passenger car tow hook by a wrecker, which comprises the following steps:

[0005] Step 1: adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste strain gauges on the tow hook;

[0006] Step 2: fix the tow hook to the front cross beam of the test vehicle, connect the towing rope of the wrecker to the tow hook, and position the test vehicle in the neutral position. Start the winch of the wrecker to pull the test vehicle until the specified position of the wrecker. Real-time measurement of strain during the test is performed to check whether the tow hook and the front cross beam of the test vehicle are damaged.

[0007] Step 3: fix the tow hook to the rear cross beam of the test vehicle, connect the towing rope of the wrecker to the tow hook, and position the test vehicle in the neutral position. Start the winch of the wrecker to pull the test vehicle until the specified position of the wrecker. Real-time measurement of strain during the test is performed to check whether the tow hook and the rear cross beam of the test vehicle are damaged.

[0008] A method for soft ground towing test of a passenger car tow hook, which comprises the following steps:

[0009] Step 1: adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste strain gauges on the tow hook;

[0010] Step 2: Park the test vehicle on soft ground, which includes sand pit;

[0011] Step 3: Fix the tow hook to the front cross beam of the test vehicle, fix another auxiliary vehicle to the tow hook by a tow rope, park the test vehicle in neutral gear, tow the test vehicle for 10 meters, measure the strain in real time during the test, check whether the tow hook and the front cross beam of the test vehicle are damaged;

[0012] Step 4: Fix the tow hook to the rear cross beam of the test vehicle, fix another auxiliary vehicle to the tow hook by a tow rope, park the test vehicle in neutral gear, tow the test vehicle for 10 meters, measure the strain in real time during the test, check whether the tow hook and the rear cross beam of the test vehicle are damaged.

[0013] A method for conducting a bad road towing test on a tow hook of a passenger vehicle, comprising the following steps:

[0014] Step 1: Adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste strain gauges on the tow hook;

[0015] Step 2: Park the test vehicle on the bad road, which includes a pothole, an uneven road, a rail road, a Belgian road, a cobblestone road or a circular protrusion road;

[0016] Step 3: Fix the tow hook to the front cross beam of the test vehicle, fix another auxiliary vehicle to the rear end of the test vehicle by a tow rope, park the test vehicle in neutral gear, tow the test vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook and the front cross beam of the test vehicle are damaged;

[0017] Step 4: Fix the tow hook to the rear cross beam of the test vehicle, tow the front end of another auxiliary vehicle by a tow rope, park the test vehicle in forward gear, tow the auxiliary vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook and the rear cross beam of the test vehicle are damaged.

[0018] A method for conducting a bad road towing test on a tow hook of a passenger vehicle, comprising the following steps:

[0019] Step 1: Adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste strain gauges on the tow hook;

[0020] Step 2: Fix the trailer hook to the front crossbeam of the test vehicle, fix it to the rear end of another auxiliary vehicle through a traction rope, put the test vehicle in neutral position, and pull the test vehicle at a speed of 15-20 km / h to make three clockwise circles and three counterclockwise circles around a circle with a radius of 20-30 m, and measure the strain in real time to check whether the trailer hook and the front crossbeam of the test vehicle are damaged.

[0021] Step 3: Fix the trailer hook to the rear crossbeam of the test vehicle, fix it to the front end of another auxiliary vehicle through a traction rope, put the test vehicle in forward gear, and pull the auxiliary vehicle at a speed of 15-20 km / h to make three clockwise circles and three counterclockwise circles around a circle with a radius of 20-30 m, and measure the strain in real time to check whether the trailer hook and the rear crossbeam of the test vehicle are damaged.

[0022] A calibration device for a trailer hook of a passenger vehicle, comprising a main support and a connecting plate, the connecting plate being vertically fixedly connected to the main support, a threaded hole being formed in the connecting plate, and a threaded end of the trailer hook being connected to the threaded hole in the connecting plate in a matched manner.

[0023] Further, the main support comprises two vertical plates and a bottom plate, the two vertical plates being vertically connected to the bottom plate, and the connecting plate being fixedly connected between the two vertical plates through two connecting bolts, and a rib plate being arranged on the outer side of each of the two vertical plates.

[0024] Further, the main support and the connecting plate are both made of cast iron.

[0025] A calibration method for a trailer hook of a passenger vehicle, comprising the following steps:

[0026] Step 1: paste a first strain gauge, a second strain gauge, a third strain gauge and a fourth strain gauge on the cylindrical outer surface of the trailer hook at intervals of 90° in the circumferential direction near the threaded end, the first strain gauge and the second strain gauge being symmetrically arranged, and the third strain gauge and the fourth strain gauge being symmetrically arranged;

[0027] Step 2: calibrate the axial tension of the trailer hook, screw the trailer hook into the threaded hole in the connecting plate, fix the connecting plate to the calibration table through two bolts, and connect a tension meter and a tension machine in sequence along the axial direction of the trailer hook, and calculate the axial tension F X of the trailer hook in relation to the strain;

[0028] The calibration calculation method of the strain and the axial tension F X is F X = K X *(ξ1+ξ2), the axial tension calibration coefficient K X is calculated from the formula, and in the formula: ξ1 is the strain value measured by the first strain gauge, and ξ2 is the strain value measured by the second strain gauge.X along the axial direction of the trailer hook;

[0029] Step 3: calibrate the vertical force of the trailer hook, screw the trailer hook into the threaded hole on the connecting plate, connect the connecting plate with the main support through two connecting bolts, fix the main support on the calibration table, connect the tension meter and the tension machine in turn in the direction perpendicular to the trailer hook, and calculate the vertical force F of the trailer hook V and the relationship between strain;

[0030] Strain and the calibration calculation method of the vertical force F V is: F V = K V *(ξ3-ξ4), the vertical force calibration coefficient K V is calculated from the formula, in which: ξ3 is the strain value measured by the third strain gauge, ξ4 is the strain value measured by the fourth strain gauge, and the direction of the vertical force F V is perpendicular to the axis of the trailer hook and parallel to the connecting line of the third and fourth strain gauges.

[0031] A maximum stress calculation method of a passenger car trailer hook, comprising the following steps:

[0032] Step 1: tensile stress σ1 generated by the axial force F X / A, wherein F X = K X *(ξ1+ξ2), and A=πd 2 / 4, d is the diameter at the dangerous section, and the dangerous section is the first thread on the trailer hook;

[0033] Step 2: tensile stress σ2 generated by the vertical force M / W, wherein the bending moment M=F V *L=K V *(ξ3-ξ4)*L, the bending section coefficient W=πd 3 / 16, d is the diameter at the dangerous section, and L is the distance from the action point of the external force of the trailer hook to the dangerous section;

[0034] Step 3: the maximum stress σ max of the trailer hook =σ1+σ2.

[0035] A strength evaluation method of a passenger car trailer hook, comprising the following steps:

[0036] Step 1: perform a winch towing test, a soft ground towing test, a reinforced bad road towing test, and a curved road towing test on the trailer hook, and check whether there are cracks or fractures on the trailer hook and the test vehicle beam after each towing test;

[0037] Step 2: calculate the maximum stress σ max of the trailer hook, and when σ maxwhen the material yield stress σ S is reached, the surface of the dangerous section of the trailer hook begins to plastically deform, and as the external force further increases, the plastic deformation area on the dangerous section increases and the elastic deformation area decreases. For a circular trailer hook, when the maximum stress of the section reaches 1.7 times σ S , the entire dangerous section plastically deforms, and the cylindrical trailer hook breaks;

[0038] Step 3: Control the ratio of the maximum stress of the trailer hook to the yield stress in the range of 1.2-1.4.

[0039] Compared with the prior art, the beneficial effects of the present application are as follows: the present application proposes multiple towing tests for the trailer hook, including a wrecker towing test, a soft ground towing test, a reinforced bad road towing test, and a curved road towing test. The strength of the trailer hook is verified by checking whether the trailer hook and the mounting beam are damaged through the multiple towing tests. The present application provides a calibration device and a calibration method for the trailer hook. The strain of the trailer hook is calibrated with the relationship with the external force, and the external force value is calculated through the strain value in the test. The relationship between the strain of the trailer hook and the axial tension and the force perpendicular to the trailer hook is calibrated on a simple calibration bench, and then the axial tension and the vertical force acting on the trailer hook under the test conditions are calculated according to the strain value, and whether plastic deformation occurs is determined. The strength of the trailer hook is evaluated, and the control range of the ratio of the maximum stress to the yield stress is given. BRIEF DESCRIPTION OF DRAWINGS

[0040] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application, and do not constitute improper limitations on the present application. In the drawings:

[0041] Figure 1 FIG. 1 is a front view of a calibration device for a passenger car trailer hook according to the present application;

[0042] Figure 2 FIG. 2 is a side view of the calibration device for the passenger car trailer hook according to the present application;

[0043] Figure 3 FIG. 3 is a top view of the calibration device for the passenger car trailer hook according to the present application;

[0044] Figure 4 FIG. 4 is a front view of a main support according to the present application;

[0045] Figure 5 FIG. 5 is a side view of the main support according to the present application;

[0046] Figure 6 FIG. 6 is a front view of a connecting plate according to the present application;

[0047] Figure 7 Strain gauge sticking method for the present application;

[0048] Figure 8 Axial tension calibration method for the trailer hook of the present application;

[0049] Figure 9 Vertical force calibration method for the trailer hook of the present application.

[0050] 1-trailer hook, 2-body support, 3-connection plate, 4-connection bolt, 5-rib plate, 6-first strain gauge, 7-second strain gauge, 8-third strain gauge, 9-fourth strain gauge. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict, and the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0052] Embodiment 1: The present embodiment is a method for towing test of passenger car trailer hook by wrecker, which comprises the following steps:

[0053] Step 1: adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and stick strain gauges on the trailer hook 1;

[0054] Step 2: fix the trailer hook 1 to the front beam of the test vehicle, connect the wrecker towing rope to the trailer hook 1, and position the test vehicle to neutral gear. Start the wrecker winch to pull the test vehicle until the specified position of the wrecker, measure the strain in real time during the test, and check whether the trailer hook 1 and the front beam of the test vehicle are damaged.

[0055] Step 3: fix the trailer hook 1 to the rear beam of the test vehicle, connect the wrecker towing rope to the trailer hook 1, and position the test vehicle to neutral gear. Start the wrecker winch to pull the test vehicle until the specified position of the wrecker, measure the strain in real time during the test, and check whether the trailer hook 1 and the rear beam of the test vehicle are damaged.

[0056] Embodiment 2: The present embodiment is a method for soft ground towing test of passenger car trailer hook, which comprises the following steps:

[0057] Step 1: adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and stick strain gauges on the trailer hook 1;

[0058] Step 2: Park the test vehicle on soft ground, which includes sand pit;

[0059] Step 3: Fix the tow hook 1 to the front cross beam of the test vehicle, fix another auxiliary vehicle to the tow hook 1 through a tow rope, park the test vehicle in neutral gear, tow the test vehicle for 10 meters, measure the strain in real time during the test, and check whether the tow hook 1 and the front cross beam of the test vehicle are damaged;

[0060] Step 4: Fix the tow hook 1 to the rear cross beam of the test vehicle, fix another auxiliary vehicle to the tow hook 1 through a tow rope, park the test vehicle in neutral gear, tow the test vehicle for 10 meters, measure the strain in real time during the test, and check whether the tow hook 1 and the rear cross beam of the test vehicle are damaged.

[0061] The strength of the tow hook 1 is verified by checking whether the tow hook 1 and the mounting cross beam are damaged in the soft ground towing test.

[0062] Embodiment 3: A method for conducting a bad road towing test on a tow hook of a passenger vehicle, comprising the following steps:

[0063] Step 1: Adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste strain gauges on the tow hook 1;

[0064] Step 2: Park the test vehicle on the bad road, which includes a pothole, an uneven road, a rail road, a Belgian road, a cobblestone road, or a circular protrusion road;

[0065] Step 3: Fix the tow hook 1 to the front cross beam of the test vehicle, fix the rear end of another auxiliary vehicle to the tow hook 1 through a tow rope, park the test vehicle in neutral gear, drive the auxiliary vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook 1 and the front cross beam of the test vehicle are damaged;

[0066] Step 4: Fix the tow hook 1 to the rear cross beam of the test vehicle, tow the front end of another auxiliary vehicle through a tow rope, park the test vehicle in forward gear, pull the auxiliary vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook 1 and the rear cross beam of the test vehicle are damaged.

[0067] The strength of the tow hook 1 is verified by checking whether the tow hook 1 and the mounting cross beam are damaged in the bad road towing test.

[0068] Embodiment 4: A method for conducting a curved road towing test on a tow hook of a passenger vehicle, comprising the following steps:

[0069] Step 1: adjust the tire pressure of the test vehicle to the full load tire pressure, load the test vehicle to the maximum design total mass, and paste strain gauges on the trailer hook 1;

[0070] Step 2: fix the trailer hook 1 to the front cross beam of the test vehicle, fix it to the rear end of another auxiliary vehicle through a towing rope, and position the test vehicle in the neutral gear. The auxiliary vehicle pulls the test vehicle to travel 3 circles clockwise and 3 circles counterclockwise around a circle with a radius of 20-30 m at a speed of 15-20 km / h, and measures the strain in real time to check whether the trailer hook 1 and the front cross beam of the test vehicle are damaged.

[0071] Step 3: fix the trailer hook 1 to the rear cross beam of the test vehicle, fix it to the front end of another auxiliary vehicle through a towing rope, and position the test vehicle in the forward gear. The test vehicle pulls the auxiliary vehicle to travel 3 circles clockwise and 3 circles counterclockwise around a circle with a radius of 20-30 m at a speed of 15-20 km / h, and measures the strain in real time to check whether the trailer hook 1 and the rear cross beam of the test vehicle are damaged.

[0072] The bending road towing test is used to check whether the trailer hook 1 and the mounting cross beam are damaged, so as to verify the strength of the trailer hook 1.

[0073] Embodiment 5: see Figures 1-6 In this embodiment, a calibration device for a towing hook of a passenger vehicle includes a main support 2 and a connecting plate 3. The connecting plate 3 is vertically fixedly connected to the main support 2. Threaded holes are formed in the connecting plate 3. A threaded end of the towing hook 1 is connected to the threaded holes in the connecting plate 3. The towing hook 1 and a calibration platform are fixed by the calibration device.

[0074] The main support 2 is made of cast iron to ensure structural strength. The main support 2 includes two vertical plates and a bottom plate. The two vertical plates are vertically connected to the bottom plate. The connecting plate 3 is fixedly connected between the two vertical plates by two connecting bolts 4. The towing hook 1 is screwed into the threaded holes in the connecting plate 3. The connecting plate 3 is fixed to the main support 2 by the two connecting bolts 4. The main support 2 is fixed to the base of the calibration platform by four bolts. Rib plates 5 are arranged on the outer sides of the two vertical plates to improve the rigidity of the support and reduce the calibration error.

[0075] The connecting plate 3 is made of cast iron to ensure structural strength. Threaded holes are formed in the connecting plate 3 to cooperate with the threaded end of the towing hook 1 for fixing the towing hook 1.

[0076] The connecting bolts 4 are inserted into the long circular holes of the main support 2 and the connecting plate 3. The connecting bolts 4 are fastened by nuts on the other side to connect the main support 2, the towing hook 1, and the connecting plate 3 together.

[0077] Embodiment 6: see Figures 1-9The embodiment discloses a method for calibrating a towing hook of a passenger car, which comprises the following steps:

[0078] Step 1: paste a first strain gauge 6, a second strain gauge 7, a third strain gauge 8 and a fourth strain gauge 9 on the cylindrical outer surface of the towing hook 1 at intervals of 90 degrees in the circumferential direction near the threaded end, wherein the first strain gauge 6 and the second strain gauge 7 are symmetrically arranged, and the third strain gauge 8 and the fourth strain gauge 9 are symmetrically arranged;

[0079] Step 2: calibrate the axial tension of the towing hook 1, screw the towing hook 1 into the threaded hole on the connecting plate 3, fix the connecting plate 3 on the calibration table through two bolts, sequentially connect a tension meter and a tension machine along the axial direction of the towing hook 1, and calculate the axial tension F of the towing hook 1 X and the strain relationship;

[0080] The calibration calculation method of the strain and the axial tension F X is F X = K X *(ξ1+ξ2), wherein the axial tension calibration coefficient K X is calculated according to the formula, and in the formula, ξ1 is the strain value measured by the first strain gauge 6, ξ2 is the strain value measured by the second strain gauge 7, and the axial tension F X is in the axial direction of the towing hook 1;

[0081] Step 3: calibrate the vertical force of the towing hook 1, screw the towing hook 1 into the threaded hole on the connecting plate 3, connect the connecting plate 3 to the main support 2 through two connecting bolts 4, fix the main support 2 on the calibration table, and sequentially connect a tension meter and a tension machine in the direction perpendicular to the towing hook 1, so as to calculate the vertical force F of the towing hook V and the strain relationship;

[0082] The calibration calculation method of the strain and the vertical force F V is F V = K V *(ξ3-ξ4), wherein the vertical force calibration coefficient Kv is calculated according to the formula, and in the formula, ξ3 is the strain value measured by the third strain gauge 8, ξ4 is the strain value measured by the fourth strain gauge 9, and the direction of the vertical force F V is perpendicular to the axis of the towing hook 1 and parallel to the connecting line of the third strain gauge and the fourth strain gauge.

[0083] The axial tension of the towing hook 1 and the vertical force of the towing hook 1 are calibrated through the method.

[0084] Embodiment 7: refer to Figures 1-9 The embodiment discloses a method for calculating the maximum stress of a towing hook of a passenger car, which comprises the following steps:

[0085] Step 1: Tensile stress σ1 = F X / A, where F X = K X *(ξ1+ξ2), A = πd 2 / 4, d is the diameter at the dangerous section, which is the first thread on the trailer hook 1;

[0086] Step 2: Tensile stress σ2 = M / W, where bending moment M = F V *L = K V *(ξ3-ξ4)*L, bending section coefficient W = πd 3 / 16, d is the diameter at the dangerous section, and L is the distance from the external force acting point of the trailer hook to the dangerous section;

[0087] Step 3: The maximum stress σ max experienced by the trailer hook 1 = σ1+σ2.

[0088] The maximum stress experienced by the trailer hook 1 can be calculated through this embodiment. The axial tensile force calibration coefficient K X and the vertical force calibration coefficient K V can be obtained by the method described in Example 6.

[0089] Example 8: Referring to Figures 1-9 This embodiment describes a strength evaluation method for a passenger car trailer hook, which includes the following steps:

[0090] Step 1: Perform the wrecker towing test, soft ground towing test, reinforced bad road towing test, and curved road towing test on the trailer hook 1. After each towing test, check the trailer hook 1 and the test vehicle beam for cracks or fractures;

[0091] Step 2: Calculate the maximum stress σ max experienced by the trailer hook 1. When σ max reaches the material yield stress σ S , the surface of the dangerous section of the trailer hook 1 begins to plastically deform. As the external force increases further, the plastic deformation area on the dangerous section increases, and the elastic deformation area decreases. For a trailer hook 1 with a circular cross-section, when the maximum stress of the cross-section reaches 1.7 times σ S , the entire dangerous section plastically deforms, and the cylindrical trailer hook 1 will break;

[0092] Step 3: To reduce the risk of breaking the trailer hook 1, the ratio of the maximum stress to the yield stress during actual use of the trailer hook 1 needs to be controlled within the range of 1.2-1.4 during the design process.

[0093] The strength evaluation method of the towing hook of the passenger car ensures the strength of the towing hook, avoids the breakage of the towing hook, reduces the safety risk caused by the failure of the towing hook, and ensures the safety. In the present embodiment, the methods described in Embodiments 1-4 can be used for the towing test of the wrecker, the soft ground towing test, the intensive bad road towing test, and the curved road towing test. The maximum stress received by the towing hook 1 can be calculated by the method described in Embodiment 7.

[0094] The above disclosed embodiments of the present application are only used to help explain the present application. The embodiments do not describe all the details, nor limit the present application to the specific embodiments described. Many modifications and variations can be made in light of the content of the present specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application.

Claims

1. A method of evaluating the strength of a passenger vehicle tow hitch, characterized by: It comprises the following steps: Step 1: the wrecker hook (1) is subjected to a wrecker towing test, a soft ground towing test, a reinforced bad road towing test and a curved road towing test, and after each towing test, the wrecker hook (1) and the test vehicle beam are checked for cracks or breakage; Step 2: Calculate the maximum stress σ on the trailer hook (1) max When σ max reaches the material yield stress σ S , the surface of the dangerous section of the trailer hook (1) begins to plastically deform, and as the external force increases, the plastic deformation area on the dangerous section increases and the elastic deformation area decreases. For a circular trailer hook (1), when the maximum stress on the section reaches 1.7 times σ S , the entire dangerous section plastically deforms, and the cylindrical trailer hook (1) will break. Step 3: the maximum stress to yield stress ratio of the wrecker hook (1) is controlled within the range of 1.2-1.4; calculating the maximum stress σ to which the trailer coupling (1) is subjected max comprising the steps of: Step 1.1: Tensile stress σ1=F X / A, where F X =K X *(ξ1+ξ2), A=πd 2 / 4, d is the diameter at the dangerous section, which is the first thread on the trailer hook (1). Step 1.2: Tensile stress σ2 generated by vertical force σ2 = M / W, where bending moment M = F V *L = K V *(ξ3-ξ4)*L, bending section coefficient W = πd 3 / 16, d is the diameter at the dangerous section, and L is the distance from the force action point outside the trailer hook to the dangerous section. Step 1.3: Maximum stress σ experienced by the trailer hook (1) max = σ1+ σ2; The calibration device of the wrecker hook (1) comprises a main support (2) and a connecting plate (3), the connecting plate (3) is vertically fixedly connected to the main support (2), the connecting plate (3) is provided with a threaded hole, the threaded end of the wrecker hook (1) is connected to the threaded hole of the connecting plate (3) in a matched manner, the main support (2) comprises two vertical plates and a bottom plate, the two vertical plates are vertically connected to the bottom plate, the connecting plate (3) is fixedly connected between the two vertical plates through two connecting bolts (4), the outer sides of the two vertical plates are both provided with a rib plate (5), and the main support (2) and the connecting plate (3) are both made of cast iron; The calibration method comprises the following steps: Step 2.1: the wrecker hook (1) is pasted with a first strain gauge (6), a second strain gauge (7), a third strain gauge (8) and a fourth strain gauge (9) at intervals of 90° along the circumferential direction of the cylindrical outer surface close to the threaded end, the first strain gauge (6) and the second strain gauge (7) are symmetrically arranged, and the third strain gauge (8) and the fourth strain gauge (9) are symmetrically arranged; Step 2.2: The axial tension of the trailer hook (1) is calibrated, the trailer hook (1) is screwed into the threaded hole on the connecting plate (3), the connecting plate (3) is fixed on the calibration table by two bolts, the tension gauge and the tension machine are connected in turn along the axial direction of the trailer hook (1), and the axial tension F of the trailer hook (1) is calculated X Strain relationship; Strain and axial tension F X The calibration calculation method is: F X = K X *(ξ1+ξ2), the axial tension calibration coefficient K X is calculated by the formula, in which: ξ1 is the strain value measured by the first strain gauge (6), ξ2 is the strain value measured by the second strain gauge (7), and the axial tension F X is along the axial direction of the trailer hook (1). Step 2.3: calibration of the vertical force of the trailer hook (1), the trailer hook (1) is screwed into the threaded hole on the connecting plate (3), the connecting plate (3) is connected to the main support (2) through two connecting bolts (4), the main support (2) is fixed on the calibration table, the direction perpendicular to the trailer hook (1) is sequentially connected with the tension meter and the tension machine, and the vertical force F of the trailer hook is calculated V relationship between strain and stress; Strain and vertical force F V The calibration calculation method is: F V =K V *(ξ3-ξ4), the vertical force calibration coefficient K V is calculated by the formula, in which: ξ3 is the strain value measured by the third strain gauge (8), and ξ4 is the strain value measured by the fourth strain gauge (9), the direction of the vertical force F V is perpendicular to the axis of the trailer hook (1) and parallel to the connecting line of the third and fourth strain gauges.

2. The method of evaluating the strength of a tow hitch of a passenger vehicle according to claim 1, characterized in that: The wrecker towing test on the wrecker hook (1) comprises the following steps: Step 1: adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste the strain gauges on the wrecker hook (1); Step 2: fix the wrecker hook (1) to the front beam of the test vehicle, connect the towing rope of the wrecker to the wrecker hook (1), and set the gear of the test vehicle to neutral, then start the winch of the wrecker to pull the test vehicle until the specified position of the wrecker, measure the strain in real time during the test, and check whether the wrecker hook (1) and the front beam of the test vehicle are damaged; Step 3: fix the wrecker hook (1) to the rear beam of the test vehicle, connect the towing rope of the wrecker to the wrecker hook (1), set the gear of the test vehicle to neutral, and start the winch of the wrecker to pull the test vehicle until the specified position of the wrecker, measure the strain in real time during the test, and check whether the wrecker hook (1) and the rear beam of the test vehicle are damaged.

3. The method of claim 1, wherein: The soft ground towing test on the wrecker hook (1) comprises the following steps: Step 1: adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste the strain gauges on the wrecker hook (1); Step 2: park the test vehicle on the soft ground, and the soft ground comprises a sand pit; Step 3: fix the wrecker hook (1) to the front beam of the test vehicle, fix another auxiliary vehicle to the wrecker hook (1) through the towing rope, set the gear of the test vehicle to neutral, and then pull the test vehicle for a distance of 10 meters, measure the strain in real time during the test, and check whether the wrecker hook (1) and the front beam of the test vehicle are damaged; Step 4: Fix the tow hook (1) to the rear cross beam of the test vehicle, fix another auxiliary vehicle to the tow hook (1) through the towing rope, put the test vehicle in the neutral gear, tow the test vehicle for 10 meters, and measure the strain in real time during the test to check whether the tow hook (1) and the rear cross beam of the test vehicle are damaged.

4. The method of claim 1, wherein: The strengthening bad road towing test of the tow hook (1) includes the following steps: Step 1: Adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste strain gauges on the tow hook (1); Step 2: Park the test vehicle on the strengthening bad road, which includes the damaged road, uneven road, rail road, Belgium road, cobblestone road or circular protrusion road; Step 3: Fix the tow hook (1) to the front cross beam of the test vehicle, fix the other auxiliary vehicle to the rear end through the towing rope, put the test vehicle in the neutral gear, and drive the test vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook (1) and the front cross beam of the test vehicle are damaged; Step 4: Fix the tow hook (1) to the rear cross beam of the test vehicle, pull the other auxiliary vehicle through the towing rope, put the test vehicle in the forward gear, and pull the auxiliary vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook (1) and the rear cross beam of the test vehicle are damaged.

5. The method of evaluating the strength of a tow hitch of a passenger vehicle according to claim 1, characterized in that: The bending road towing test of the tow hook (1) includes the following steps: Step 1: Adjust the tire pressure of the test vehicle to the full load tire pressure, assemble the load of the test vehicle to the maximum design total mass, and paste strain gauges on the tow hook (1); Step 2: Fix the tow hook (1) to the front cross beam of the test vehicle, fix the other auxiliary vehicle to the rear end through the towing rope, put the test vehicle in the neutral gear, and drive the test vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook (1) and the front cross beam of the test vehicle are damaged; Step 3: Fix the tow hook (1) to the rear cross beam of the test vehicle, fix the other auxiliary vehicle to the front end through the towing rope, put the test vehicle in the forward gear, and pull the auxiliary vehicle at a speed of 15-20 km / h for 10 km, measure the strain in real time during the test, and check whether the tow hook (1) and the rear cross beam of the test vehicle are damaged.

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