CN114942186A - Towing and calibration test method and strength evaluation method for passenger car towing hook - Google Patents

Abstract

The invention provides a dragging and calibration test method and a strength evaluation method for a trailer hook of a passenger vehicle, and belongs to the field of trailer hooks. The problem of the existing tow hooks with the risk of breaking is solved. It includes wrecker drag test, soft ground drag test, enhanced bad road drag test and curved road drag test on the trailer hook. After each drag test, check the trailer hook and the test vehicle beam for cracks or breaks. , Calculate the maximum stress on the trailer hook. When the maximum stress reaches the material yield stress, the surface of the dangerous section of the trailer hook begins to undergo plastic deformation. With the further increase of the external force, the plastic deformation area on the dangerous section increases and the elastic deformation area decreases. It is mainly used for the test of passenger car tow hooks.

Description

A dragging and calibration test method and strength evaluation method of a passenger car trailer hitch

technical field

The invention belongs to the field of trailer hooks, and in particular relates to a dragging and calibration test method and a strength evaluation method of a passenger vehicle trailer hook.

Background technique

The tow hook is generally fixed to the front and rear beams of the vehicle body through a threaded connection. When the vehicle breaks down or is trapped and cannot move, external force is required on the tow hook to drag the vehicle. The strength of the tow hook needs to be large enough to ensure the smooth escape of the vehicle under the pulling of a very large external force. If the tow hook suddenly breaks during use, it may injure the surrounding people or objects, which is very dangerous. It is very important to measure the load of the trailer hitch installed on the vehicle during actual use and to ensure its safe use. It is necessary to pass some tests to verify whether there is a risk of breakage and damage of the tow hook during actual use, so as to reduce the safety risk caused by the failure of the tow hook.

SUMMARY OF THE INVENTION

In view of this, the present invention aims to provide a dragging, calibration test method and strength evaluation method for a trailer hook of a passenger vehicle, so as to solve the problem of the existing trailer hook having a fracture risk.

In order to achieve the above object, the present invention adopts the following technical solutions: a method for carrying out the dragging test of a wrecker vehicle with a trailer hook of a passenger vehicle, which comprises the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook;

Step 2: Fix the tow hook on the front beam of the test vehicle, connect the traction rope of the wrecker vehicle to the tow hook, put the test vehicle in neutral, start the winch of the wrecker to pull the test vehicle until the designated position of the wrecker vehicle, Measure the strain during the test in real time, and check whether the trailer hook and the front beam of the test vehicle are damaged;

Step 3: Fix the tow hook on the rear beam of the test vehicle, connect the traction rope of the wrecker vehicle to the tow hook, set the test vehicle in neutral, start the winch of the wrecker to pull the test vehicle, and pull it to the designated position of the wrecker vehicle , Measure the strain during the test in real time, and check whether the trailer hook and the rear beam of the test vehicle are damaged.

A method for carrying out a soft ground drag test on a tow hook of a passenger vehicle, comprising the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook;

Step 2: Park the test vehicle on soft ground, including sand pits;

Step 3: Fix the trailer hook on the front beam of the test vehicle, use another auxiliary vehicle to fix it on the trailer hook through the traction rope, put the test vehicle in neutral, drag the test vehicle for a distance of 10 meters, and measure the test process in real time medium strain, check the trailer hook and the front beam of the test vehicle for damage;

Step 4: Fix the tow hook on the rear beam of the test vehicle, use another auxiliary vehicle to fix it on the tow hook through the traction rope, put the test vehicle in neutral, drag the test vehicle for a distance of 10 meters, and measure the test in real time. Strain and inspect the trailer hitch and the rear cross member of the test vehicle for damage.

A method for carrying out an enhanced rough road drag test for a tow hook of a passenger vehicle, comprising the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook;

Step 2: Park the test vehicle on a reinforced bad road, which includes disrepair pits, uneven roads, railroad tracks, Belgian roads, cobblestone roads or round raised roads;

Step 3: Fix the tow hook on the front beam of the test vehicle, and fix it on the rear end of another auxiliary vehicle with a traction rope. The test vehicle is in neutral gear. Strain during the test, check the trailer hook and the front beam of the test vehicle for damage;

Step 4: Fix the tow hook on the rear beam of the test vehicle, pull the front end of another auxiliary vehicle through the traction rope, put the test vehicle in the forward gear, and pull the auxiliary vehicle to travel 10km at a speed of 15-20km/h. Strain and inspect the trailer hitch and the rear cross member of the test vehicle for damage.

A method for towing test of a tow hook of a passenger vehicle on a curved road, which comprises the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook;

Step 2: Fix the tow hook on the front beam of the test vehicle, and fix it on the rear end of another auxiliary vehicle with a traction rope. The test vehicle is in neutral, and the auxiliary vehicle pulls the test vehicle around a radius of 20-30m at a speed of 15-20km/h. The circle is driven clockwise for 3 laps, and then counterclockwise for 3 laps to measure the strain during the test in real time, and check whether the trailer hook and the front beam of the test vehicle are damaged;

Step 3: Fix the tow hook to the rear beam of the test vehicle, and fix it to the front end of another auxiliary vehicle with a traction rope. The test vehicle is in the forward gear, and the test vehicle pulls the auxiliary vehicle around a radius of 20-30m at a speed of 15-20km/h. The circle is driven clockwise for 3 laps, and then counterclockwise for 3 laps to measure the strain during the test in real time, and check whether the trailer hook and the rear beam of the test vehicle are damaged.

A calibration device for a trailer hook of a passenger car, which includes a main body bracket and a connecting plate, the connecting plate is vertically fixed on the main body bracket, the connecting plate is provided with a threaded hole, and the threaded end of the trailer hook is connected to the connecting plate. The threaded holes on the

Further, the main body support includes two vertical plates and a bottom plate, the two vertical plates are vertically connected to the bottom plate, the connecting plate is fixedly connected between the two vertical plates by two connecting bolts, and the two vertical plates are connected to the bottom plate. Ribs are provided on the outside of the plate.

Further, the main body bracket and the connecting plate are made of cast iron.

A method for calibrating a trailer hitch of a passenger vehicle, which comprises the following steps:

Step 1: Paste the No. 1 strain gauge, No. 2 strain gauge, No. 3 strain gauge and No. 4 strain gauge on the cylindrical outer surface of the trailer near the threaded end along the circumferential direction at 90° intervals. The No. 1 strain gauge and No. 2 strain gauge The No. 3 strain gauge and the No. 4 strain gauge are symmetrically arranged;

Step 2: Calibrate the axial tension of the tow hook, screw the tow hook into the threaded hole on the connecting plate, fix the connecting plate on the calibration table with two bolts, and connect the tension gauge and the Tension machine, calculate the relationship between the axial tension F _X and the strain on the tow hook;

The calibration calculation method of strain and axial tension F _X is: F _X =K _X *(ξ ₁ +ξ ₂ ), the axial tension calibration coefficient K _X is calculated by the formula, in the formula: ξ ₁ is the measurement of the No. 1 strain gauge The strain value of ξ ₂ is the strain value measured by the No. 2 strain gauge, and the axial tension F _X is along the axial direction of the tow hook;

Step 3: Calibrate the vertical force of the tow hook, screw the tow hook into the threaded hole on the connecting plate, connect the connecting plate to the main bracket through two connecting bolts, and fix the main bracket on the calibration table, perpendicular to the tow hook Connect the tension gauge and the tension machine in turn in the direction of the direction, and calculate the relationship between the vertical force F _V and the strain on the tow hook;

The calibration calculation method of strain and vertical force F _V is: F _V =K _V *(ξ ₃ -ξ ₄ ), the vertical force calibration coefficient K _V is calculated by the formula, in the formula: ξ ₃ is the strain measured by the third strain gauge value, ξ ₄ is the strain value measured by the No. 4 strain gauge, and the direction of the vertical force F _V is perpendicular to the axis of the tow hook and parallel to the connecting line of the No. 3 and No. 4 strain gauges.

A method for calculating the maximum stress of a passenger car tow hook, which includes the following steps:

Step 1: The tensile stress σ ₁ =F _X /A generated by the axial force, where F _X =K _X *(ξ ₁ +ξ ₂ ), A=πd ² /4, d is the diameter at the dangerous section, and the dangerous section is The first thread on the tow hook;

Step 2: Tensile stress σ ₂ =M/W generated by vertical force, where bending moment M=F _V *L=K _V *(ξ ₃ -ξ ₄ )*L, bending section coefficient W=πd ³ /16, d is the diameter of the dangerous section, L is the distance from the point of action of the external force of the tow hook to the dangerous section;

Step 3: Maximum stress σ _max =σ ₁ +σ ₂ to the tow hitch.

A method for evaluating the strength of a passenger car tow hook, comprising the following steps:

Step 1: Carry out wrecker drag test, soft ground drag test, enhanced rough road drag test and curved road drag test on the trailer hook. After each drag test, check the trailer hook and test vehicle beam for cracks or cracks. fracture;

Step 2: Calculate the maximum stress σ _max on the tow hook. When σ _max reaches the material yield stress σ _S , the surface of the dangerous section of the tow hook begins to undergo plastic deformation. With the further increase of the external force, the plastic deformation area on the dangerous section increases. , the elastic deformation area is reduced. For a tow hook with a circular cross-section, when the maximum stress of the cross-section reaches 1.7 times σ _S and the entire dangerous cross-section undergoes plastic deformation, the cylindrical tow hook will break;

Step 3: Control the ratio of the maximum stress to the yield stress of the tow hook within the range of 1.2 to 1.4.

Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention proposes a variety of dragging test methods for the tow hook, including the dragging test of the wrecker truck, the dragging test on soft ground, the dragging test on enhanced rough roads and the In the detour drag test, various drag tests are used to check whether the tow hook and the mounting beam are damaged, so as to verify the strength of the tow hook. The calibration device and calibration method of the trailer hook are provided. The trailer hook needs to be pasted with strain gauges, the relationship between the calibration strain and the external force received, and the external force value is calculated by the strain value in the test. By calibrating the relationship between the strain of the trailer hook, the axial tension, and the force perpendicular to the trailer hook on a simple calibration bench, then the axial tension and vertical force of the external force acting on the trailer can be calculated according to the strain value under the test conditions. hook, whether plastic deformation will occur. This evaluates the strength of the tow hook and gives a control range for the ratio of maximum stress to yield stress.

Description of drawings

The accompanying drawings constituting a part of the present invention are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

Fig. 1 is a schematic diagram of the front structure of a calibration device for a trailer hook of a passenger car according to the present invention;

Fig. 2 is a side view structural schematic diagram of a calibration device for a trailer hitch of a passenger vehicle according to the present invention;

3 is a schematic top view structure diagram of a calibration device for a trailer hitch of a passenger vehicle according to the present invention;

FIG. 4 is a schematic diagram of the front structure of the main body support according to the present invention;

5 is a schematic side view of the structure of the main body support according to the present invention;

FIG. 6 is a schematic view of the front structure of the connecting plate according to the present invention;

FIG. 7 is a schematic diagram of the method for pasting strain gauges according to the present invention;

FIG. 8 is a schematic diagram of the method for calibrating the axial tension of the trailer hitch according to the present invention;

FIG. 9 is a schematic diagram of the vertical force calibration method of the tow hook according to the present invention.

1- tow hook, 2- main body bracket, 3- connecting plate, 4- connecting bolt, 5- rib plate, 6- No. 1 strain gauge, 7- No. 2 strain gauge, 8- No. 3 strain gauge, 9- No. 4 Strain gauges.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It should be noted that the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict, and the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

Embodiment 1: This embodiment is a method for carrying out the dragging test of a wrecker vehicle with a trailer hook of a passenger vehicle, which includes the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook 1;

Step 2: Fix the tow hook 1 on the front beam of the test vehicle, connect the traction rope of the wrecker vehicle to the tow hook 1, set the gear position of the test vehicle in neutral, start the winch of the wrecker to pull the test vehicle until the designation of the wrecker vehicle position, measure the strain during the test in real time, and check whether the trailer hook 1 and the front beam of the test vehicle are damaged;

Step 3: Fix the tow hook 1 to the rear beam of the test vehicle, connect the tow rope of the wrecker vehicle to the tow hook 1, set the test vehicle to neutral, start the wrecker winch to pull the test vehicle, and pull it to the side of the wrecker vehicle. Specify the position, measure the strain during the test in real time, and check whether the trailer hook 1 and the rear beam of the test vehicle are damaged.

Embodiment 2: This embodiment is a method for carrying out a soft ground drag test on a passenger car tow hook, which includes the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook 1;

Step 2: Park the test vehicle on soft ground, including sand pits;

Step 3: Fix the trailer hook 1 to the front beam of the test vehicle, use another auxiliary vehicle to fix it on the trailer hook 1 through the traction rope, the test vehicle is in neutral, drag the test vehicle for a distance of 10 meters, and measure in real time Strain during the test, check the trailer hook 1 and the front beam of the test vehicle for damage;

Step 4: Fix the trailer hook 1 to the rear beam of the test vehicle, use another auxiliary vehicle to fix it on the trailer hook 1 through the traction rope, the gear position of the test vehicle is in neutral, drag the test vehicle for a distance of 10 meters, and measure the test in real time. During the process of strain, check the trailer hook 1 and the rear beam of the test vehicle for damage.

The strength of the tow hook 1 is verified by checking whether the tow hook 1 and the mounting beam are damaged through the soft ground drag test.

Embodiment 3: This embodiment is a method for a passenger vehicle tow hook to carry out an enhanced rough road drag test, which includes the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook 1;

Step 2: Park the test vehicle on a reinforced bad road, which includes disrepair pits, uneven roads, railroad tracks, Belgian roads, cobblestone roads or round raised roads;

Step 3: Fix the tow hook 1 to the front beam of the test vehicle, and fix it to the rear end of another auxiliary vehicle through the traction rope. The gear position of the test vehicle is in neutral. Measure the strain during the test, and check whether the trailer hook 1 and the front beam of the test vehicle are damaged;

Step 4: Fix the tow hook 1 on the rear beam of the test vehicle, pull the front end of another auxiliary vehicle through the traction rope, put the test vehicle in the forward gear, pull the auxiliary vehicle to travel 10km at a speed of 15-20km/h, and measure the test process in real time medium strain, check tow hook 1 and the rear cross member of the test vehicle for damage.

The strength of the tow hook 1 is verified by strengthening the rough road drag test to check whether the tow hook 1 and the mounting beam are damaged.

Embodiment 4: This embodiment is a method for a passenger car tow hook to perform a detour drag test, which includes the following steps:

Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook 1;

Step 2: Fix the tow hook 1 to the front beam of the test vehicle, and fix it to the rear end of another auxiliary vehicle through the traction rope. The gear position of the test vehicle is in neutral, and the auxiliary vehicle pulls the test vehicle around 20-30m at a speed of 15-20km/h. The radius of the circle is driven clockwise for 3 laps, and then counterclockwise for 3 laps to measure the strain during the test in real time, and check whether the trailer hook 1 and the front beam of the test vehicle are damaged;

Step 3: Fix the tow hook 1 to the rear beam of the test vehicle, and fix it to the front end of another auxiliary vehicle through the traction rope. The test vehicle is in the forward gear, and the test vehicle pulls the auxiliary vehicle around 20-30m at a speed of 15-20km/h. The radius of the circle is driven clockwise for 3 laps, and then counterclockwise for 3 laps, and the strain during the test is measured in real time, and the trailer hook 1 and the rear beam of the test vehicle are checked for damage.

The strength of the tow hook 1 is verified by checking whether the tow hook 1 and the mounting beam are damaged through the detour drag test.

Example 5: Referring to Figures 1-6, this embodiment is described, a calibration device for a trailer hitch of a passenger car, which includes a main body bracket 2 and a connecting plate 3, and the connecting plate 3 is vertically and fixedly connected to the main body bracket 2, The connecting plate 3 is provided with a threaded hole, and the threaded end of the tow hook 1 is connected with the threaded hole on the connecting plate 3 in cooperation. The trailer hook 1 and the calibration table are fixed by the calibration device.

The main body bracket 2 is made of cast iron to ensure structural strength. The main body bracket 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 Screw it into the threaded hole of the connecting plate 3, and fix the connecting plate 3 on the main body bracket 2 through two connecting bolts 4, and the main body bracket 2 is fixed on the base of the calibration table through four bolts. The outer sides of the two vertical plates are provided with rib plates 5, which can improve the rigidity of the bracket and reduce the calibration error.

The connecting plate 3 is made of cast iron to ensure structural strength. A threaded hole is processed on the connecting plate 3 , which can be matched with the threaded end of the tow hook 1 for fixing the tow hook 1 .

The connecting bolt 4 is inserted into the long round hole of the main body bracket 2 and the long round hole of the connecting plate 3 , and the other side of the connecting bolt 4 is fastened with a nut to connect the main body bracket 2 with the tow hook 1 and the connecting plate 3 together.

Example 6: Referring to Figures 1-9, this embodiment, a method for calibrating a trailer hitch of a passenger car, includes the following steps:

Step 1: Paste the No. 1 strain gauge 6, No. 2 strain gauge 7, No. 3 strain gauge 8 and No. 4 strain gauge 9 on the cylindrical outer surface near the threaded end along the circumferential direction at 90° intervals. The No. 6 strain gauge and the No. 2 strain gauge 7 are symmetrically arranged, and the No. 3 strain gauge 8 and the No. 4 strain gauge 9 are symmetrically arranged;

Step 2: Calibrate the axial tension of the trailer hook 1, screw the trailer hook 1 into the threaded hole on the connecting plate 3, and fix the connecting plate 3 on the calibration table with two bolts, along the axis direction of the trailer hook 1 Connect the tension gauge and the tension machine in turn, and calculate the relationship between the axial tension F _X and the strain on the trailer hook 1;

The calibration calculation method of strain and axial tension F _X is: F _X =K _X *(ξ ₁ +ξ ₂ ), the axial tension calibration coefficient K _X is calculated by the formula, in the formula: ξ ₁ is the No. 1 strain gauge 6 The measured strain value, ξ ₂ is the strain value measured by the No. 2 strain gauge 7, and the axial tension F _X is along the axial direction of the tow hook 1;

Step 3: Calibrate the vertical force of the trailer hook 1, screw the trailer hook 1 into the threaded hole on the connecting plate 3, connect the connecting plate 3 to the main body bracket 2 through two connecting bolts 4, and the main body bracket 2 is fixed on the calibration On the stage, connect the tension gauge and the tension machine in turn in the direction perpendicular to the trailer hook 1, and calculate the relationship between the vertical force F _V and the strain on the trailer hook;

The calibration calculation method of strain and vertical force F _V is: F _V =K _V *(ξ ₃ -ξ ₄ ), the vertical force calibration coefficient Kv is calculated by the formula, in the formula: ξ ₃ is the strain measured by the third strain gauge 8 value, ξ ₄ 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 tow hook 1, and parallel to the connecting line of the third and fourth strain gauges.

The calibration of the axial pulling force of the trailer hook 1 and the vertical force of the trailer hook 1 is realized by the method described in this embodiment. When calibrating, the calibration device mentioned in Embodiment 5 can be used.

Embodiment 7: Referring to Figures 1-9, the present embodiment, a method for calculating the maximum stress of a trailer hitch of a passenger car, includes the following steps:

Step 1: The tensile stress σ ₁ =F _X /A generated by the axial force, where F _X =K _X *(ξ ₁ +ξ ₂ ), A=πd ² /4, d is the diameter at the dangerous section, and the dangerous section is The first thread on the tow hook 1;

Step 2: Tensile stress σ ₂ =M/W generated by vertical force, where bending moment M=F _V *L=K _V *(ξ ₃ -ξ ₄ )*L, bending section coefficient W=πd ³ /16, d is the diameter of the dangerous section, L is the distance from the point of action of the external force of the tow hook to the dangerous section;

Step 3: The maximum stress σ _max =σ ₁ +σ ₂ experienced by the tow hook 1 .

Through this embodiment, the maximum stress on the tow hook 1 can be calculated. The axial tension calibration coefficient K _X and the vertical force calibration coefficient K _V of the tow hook 1 can be obtained by the method described in Example 6.

Example 8: Referring to Figures 1-9, the present embodiment, a method for evaluating the strength of a trailer hitch of a passenger car, includes the following steps:

Step 1: Carry out wrecker drag test, soft ground drag test, enhanced rough road drag test and curved road drag test on tow hook 1. After each drag test, check tow hook 1 and the test vehicle beam for presence or absence. cracks or breaks;

Step 2: Calculate the maximum stress σ _max of the tow hook 1. When σ _max reaches the material yield stress σ _S , the surface of the dangerous section of the tow hook 1 begins to undergo plastic deformation. With the further increase of the external force, the plastic deformation area on the dangerous section will be increases, and the elastic deformation area decreases. For the tow hook 1 with a circular cross-section, when the maximum stress of the cross-section reaches 1.7 times σ _S and the entire dangerous cross-section undergoes plastic deformation, the cylindrical tow hook 1 will break;

Step 3: In order to reduce the fracture risk of the tow hook 1, it is necessary to control the ratio of the maximum stress to the yield stress in the actual use of the tow hook 1 within the range of 1.2 to 1.4 in the design process.

The strength evaluation method of the tow hook of a passenger car is used to ensure the strength of the tow hook, avoid the breakage and damage of the tow hook, reduce the safety risk caused by the failure of the tow hook, and ensure the safety. In this embodiment, the dragging test of the wrecker vehicle, the dragging test on soft ground, the dragging test on enhanced rough roads, and the dragging test on curved roads may adopt the methods described in Embodiment 1 to Embodiment 4. The method of loading in Example 7 can be used to calculate the maximum stress on the tow hook 1 .

The embodiments of the present invention disclosed above are only used to help illustrate the present invention. The examples do not exhaust all the details, nor do they limit the invention to the specific embodiments described. Numerous modifications and variations are possible in light of the contents of this specification. The present specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention.

Claims (10)

1. a method for carrying out a drag test of a wrecker vehicle by a trailer hook of a passenger car, is characterized in that: it comprises the following steps: Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook (1); Step 2: Fix the tow hook (1) on the front beam of the test vehicle, connect the tow rope of the wrecker vehicle to the tow hook (1), set the gear position of the test vehicle in neutral, start the winch of the wrecker and pull the test vehicle until it is cleared. The designated position of the obstacle vehicle, the strain during the test is measured in real time, and the trailer hook (1) and the front beam of the test vehicle are checked for damage; Step 3: Fix the tow hook (1) on the rear beam of the test vehicle, connect the tow rope of the wrecker vehicle to the tow hook (1), put the test vehicle in neutral, start the winch of the wrecker to pull the test vehicle, and pull it to At the designated position of the wrecker, measure the strain during the test in real time, and check whether the trailer hook (1) and the rear beam of the test vehicle are damaged. 2. a method for carrying out a soft ground drag test by a tow hook of a passenger car, is characterized in that: it comprises the following steps: Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook (1); Step 2: Park the test vehicle on soft ground, including sand pits; Step 3: Fix the tow hook (1) on the front beam of the test vehicle, and use another auxiliary vehicle to fix it on the tow hook (1) through the traction rope. Distance, real-time measurement of the strain during the test, check the trailer hook (1) and the front beam of the test vehicle for damage; Step 4: Fix the trailer hook (1) to the rear beam of the test vehicle, use another auxiliary vehicle to fix it on the trailer hook (1) through the traction rope, the test vehicle is in neutral, and the test vehicle is dragged for a distance of 10 meters , Measure the strain during the test in real time, and check whether the trailer hook (1) and the rear beam of the test vehicle are damaged. 3. a method for carrying out an enhanced rough road drag test for a tow hook of a passenger car, is characterized in that: it comprises the following steps: Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook (1); Step 2: Park the test vehicle on a reinforced bad road, which includes disrepair pits, uneven roads, railroad tracks, Belgian roads, cobblestone roads or round raised roads; Step 3: Fix the tow hook (1) to the front beam of the test vehicle, and fix it to the rear end of another auxiliary vehicle through a traction rope. The test vehicle is in neutral, and the auxiliary vehicle pulls the test vehicle to travel 10km at a speed of 15-20km/h. , measure the strain during the test in real time, and check whether the trailer hook (1) and the front beam of the test vehicle are damaged; Step 4: Fix the tow hook (1) on the rear beam of the test vehicle, pull the front end of another auxiliary vehicle through the traction rope, put the test vehicle in the forward gear, pull the auxiliary vehicle to travel 10km at a speed of 15-20km/h, and measure in real time Strain during the test, check the trailer hook (1) and the rear cross member of the test vehicle for damage. 4. a method for carrying out a detour drag test by a tow hook of a passenger car, characterized in that: it comprises the following steps: Step 1: Adjust the tire pressure of the test vehicle to full tire pressure, the test vehicle assembly load to the maximum design total mass, and paste the strain gauge on the trailer hook (1); Step 2: Fix the tow hook (1) to the front beam of the test vehicle, and fix it to the rear end of another auxiliary vehicle through the traction rope. - The circle with a radius of 30m travels clockwise for 3 laps and then counterclockwise for 3 laps to measure the strain during the test in real time, and check whether the trailer hook (1) and the front beam of the test vehicle are damaged; Step 3: Fix the tow hook (1) to the rear beam of the test vehicle, and fix it to the front end of another auxiliary vehicle through the traction rope. The circle with a radius of -30m travels clockwise for 3 laps and then counterclockwise for 3 laps. Measure the strain during the test in real time, and check whether the trailer hook (1) and the rear beam of the test vehicle are damaged. 5. A calibration device for a trailer hitch of a passenger car, characterized in that it comprises a main body bracket (2) and a connecting plate (3), the connecting plate (3) being vertically fixedly connected to the main body bracket (2), The connecting plate (3) is provided with a threaded hole, and the threaded end of the trailer hook (1) is connected with the threaded hole on the connecting plate (3). 6 . The device for calibrating a trailer hitch for a passenger vehicle according to claim 5 , wherein the main body bracket ( 2 ) comprises two vertical plates and a bottom plate, and the two vertical plates are vertically connected to the bottom plate. 7 . The connecting plate (3) is fixedly connected between two vertical plates by two connecting bolts (4), and rib plates (5) are provided on the outside of the two vertical plates. 7 . The device for calibrating a trailer hitch of a passenger vehicle according to claim 5 , wherein the main body bracket ( 2 ) and the connecting plate ( 3 ) are made of cast iron. 8 . 8. A calibration method for a trailer hitch of a passenger vehicle, characterized in that: it comprises the following steps: Step 1: Attach the No. 1 strain gauge (6), No. 2 strain gauge (7), No. 3 strain gauge (8) and No. 4 strain gauge to the cylindrical outer surface near the threaded end at 90° intervals in the circumferential direction. No. 1 strain gauge (9), the No. 1 strain gauge (6) and No. 2 strain gauge (7) are symmetrically arranged, and the No. 3 strain gauge (8) and No. 4 strain gauge (9) are symmetrically arranged; Step 2: To calibrate the axial tension of the tow hook (1), screw the tow hook (1) into the threaded hole on the connecting plate (3), and fix the connecting plate (3) on the calibration table with two bolts , connect the tension gauge and the tension machine in turn along the axis direction of the trailer hook (1), and calculate the relationship between the axial tension force F _X and the strain of the trailer hook (1); The calibration calculation method of strain and axial tension F _X is: F _X =K _X *(ξ ₁ +ξ ₂ ), the axial tension calibration coefficient K _X is calculated by the formula, in the formula: ξ ₁ is the No. 1 strain gauge ( 6) The measured strain value, ξ ₂ is the strain value measured by the No. 2 strain gauge (7), and the axial tension F _X is along the axial direction of the tow hook (1); Step 3: Calibrate the vertical force of the tow hook (1), screw the tow hook (1) into the threaded hole on the connecting plate (3), and connect the connecting plate (3) to the main body through two connecting bolts (4). The bracket (2) is connected, the main bracket (2) is fixed on the calibration table, and the tension gauge and the tension machine are connected in turn in the direction perpendicular to the trailer hook (1), and the relationship between the vertical force F _V and the strain on the trailer hook is calculated. ; The calibration calculation method of strain and vertical force F _V is: F _V =K _V *(ξ ₃ -ξ ₄ ), the vertical force calibration coefficient K _V is calculated by the formula, in the formula: ξ ₃ is the third strain gauge (8) The measured strain value, ξ ₄ is the strain value measured by the No. 4 strain gauge (9). The direction of the vertical force F _V is perpendicular to the axis of the tow hook (1) and parallel to the connecting line of the No. 3 and No. 4 strain gauges. 9. A maximum stress calculation method of the method for calibrating a trailer coupler of a passenger vehicle as claimed in claim 8, characterized in that: it comprises the following steps: Step 1: The tensile stress σ ₁ =F _X /A generated by the axial force, where F _X =K _X *(ξ ₁ +ξ ₂ ), A=πd ² /4, d is the diameter at the dangerous section, and the dangerous section is The first thread on the tow hook (1); Step 2: Tensile stress σ ₂ =M/W generated by vertical force, where bending moment M=F _V *L=K _V *(ξ ₃ -ξ ₄ )*L, bending section coefficient W=πd ³ /16, d is the diameter of the dangerous section, L is the distance from the point of action of the external force of the tow hook to the dangerous section; Step 3: The maximum stress σ _max =σ ₁ +σ ₂ experienced by the tow hook ( 1 ). 10. A method for evaluating the strength of a passenger car tow hook, characterized in that: it comprises the following steps: Step 1: Carry out the wrecker drag test, soft ground drag test, enhanced rough road drag test and curved road drag test on the tow hook (1). Check the tow hook (1) and the test after each drag test. Whether the vehicle beam is cracked or broken; Step 2: Calculate the maximum stress σ _max of the tow hook (1), when σ _max reaches the material yield stress σ _S , the surface of the dangerous section of the tow hook (1) begins to plastically deform. The upper plastic deformation area increases and the elastic deformation area decreases. For the tow hook (1) with a circular cross-section, when the maximum stress of the cross-section reaches 1.7 times σ _S and plastic deformation occurs in the entire dangerous cross-section, the cylindrical tow hook (1) ) will break; Step 3: The ratio of the maximum stress to the yield stress of the tow hook (1) is controlled within the range of 1.2 to 1.4.

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