Steering column assembly is one of the most basic components of automobile steering system. It is the key component to determine the driving safety and reliability of automobile. How to ensure that the steering column assembly meets the design performance requirements is our most concerned problem, especially the fatigue life test of the steering column assembly is an important link to ensure and improve the product quality.

Test standards and specifications

The performance requirements and test methods of automotive steering column products in China’s automotive industry standards are clearly specified in the standard “QC / t649-2000 performance requirements and test methods of automotive steering transmission shaft assembly”. The fatigue life test of automobile steering column assembly is carried out according to the standard specification.

In recent years, due to the continuous updating and improvement of the contents and requirements of fatigue life test of automobile steering column assembly by domestic and foreign automobile manufacturers, the items of fatigue life test in standards and specifications in the company’s product laboratory are also increasing. Further supplement is made on the basis of torsional fatigue life test in article 5.5 of QC / t649-2000 performance requirements and test methods of automobile steering transmission shaft assembly (the main contents are based on the requirements of automobile manufacturers and relevant technical data provided, see table for details).

Fatigue life test of automobile steering column assembly

Samples and test items

Research and Analysis on performance design requirements and fatigue life test items of steering column assembly

The above five column fatigue life tests basically represent the current domestic and foreign automobile steering column assembly fatigue life test projects. The specific items of sample test shall be determined according to the technical standards selected for the steering column assembly.

The basic principles for the selection of sample test items are as follows:

1. Generally, the first fatigue life test is selected for the test piece of automobile steering column assembly with domestic standards and specifications.

2. The second fatigue life test is selected for the test piece of automobile steering column assembly according to Japanese standards and specifications.

3. The third, fourth and fifth fatigue life tests shall be selected for the test pieces of automobile steering column assembly adopting European and American standards and specifications.

Test equipment and test methods

According to 5 test items, 6 test equipment shall be completed respectively. They are: torsional fatigue life test bench, rotary durability test bench, electric variable inclination life and vertical fatigue test bench, manual variable inclination life and vertical fatigue test bench, lateral fatigue test bench of pipe column structure and steering system life test bench

1. Torsional fatigue life test

(1) The test equipment is shown in Figure 1, which is composed of test bench and driving mechanism. Among them, the test bench: the base plate, the driving mechanism and the fixed seat are connected and fixed as a whole. The function is to provide the test piece with a fixed point at one end and a positive and negative torque at the other end; Driving mechanism: the driving mechanism is composed of motor, reducer and swing block equipped with chute. Its function is to provide positive and negative torque.

(2) Test method: first install the test piece on the test bench. A block is arranged on the top of the steering shaft, the adjustment center is installed on the driving mechanism, and the other end is fixed on the fixed seat. Then turn on the power supply and apply positive and negative torque to the test piece. After the test, remove the test piece and test it according to the standard specifications page]

2. Slewing durability test

(1) The test equipment is shown in Figure 2, which is composed of test bench, driving mechanism and load torque box. Among them, the test bench: vertical support, driving mechanism and load torque box are connected and fixed as a whole. The function is that the driving mechanism provides positive and negative ± 700 driving torque for the test piece, and the load torque box generates resistance torque at the same time; Driving mechanism: the driving mechanism is composed of motor, reducer and gear rack. The function provides a driving torque of ± 700; Load torque box: the load torque box is composed of brake wheel, brake belt, spring and nut for manually adjusting resistance torque. Its function is to generate resistance torque.

(2) Test method: first install the test piece on the test bench. The adjusting center at the top of the steering shaft of the test piece is installed on the driving mechanism, and the other end is fixed on the connecting flange of the load torque box. Then, turn on the power supply and apply the rotating torque in the positive and negative directions to the test piece. After the test, remove the test piece and test it according to the standard specifications.

3. Electric variable inclination life and vertical fatigue test

See Fig. 3 for test equipment. It is composed of test bench, electric string control system, loading system and control software. Among them, the function of the vertical support is to fix the test piece; Control the electric string system: the variable inclination and vertical motor of the test piece are driven by the power current control meter through the control line; Loading system: the cylinder and tension sensor are installed in one. The tension value is displayed in the display table; Control software: prepare test control program according to standard specifications. The main content is the test control program for controlling the electric string system and loading system.

(2) Test method first install the test piece on the test bench. The steering wheel of the test piece is connected with the cylinder through a relay piece. Then, turn on the computer, call out the control program and start the test. After the test, remove the test piece and conduct post test inspection on the test piece according to the standard specifications.

4. Manual variable inclination life and vertical fatigue test

(1) See Fig. 4 and Fig. 5 for test equipment. It consists of test bench, telescopic mechanism, inclination mechanism, locking mechanism, loading mechanism and control software. The test bench is composed of a wall stand and a test piece top seat. The function is to provide attachment support and fixation for the test piece; Telescopic mechanism: the cylinder piston rod is fixed with the push rod. Push the test piece sleeve to expand and retract; Inclination mechanism: the cylinder is fixed on the telescopic mechanism. Push the pipe string vertically up and down; Locking mechanism: the stepping motor gear pushes the rack, and the rack drives the crank to lock and open the handle of the test piece; Loading mechanism: the cylinder piston rod is connected with the steering wheel of the test piece. Apply a downward force. A tension sensor is installed at the lower end of the cylinder, and the tension value is displayed by the display; Control software: prepare test control program software according to standard specifications. The main content is to program control the telescopic mechanism, inclination mechanism, locking mechanism and loading mechanism according to the sequence and residence time required by the standard.

(2) Test method: first install the test piece on the test bench, and the steering wheel and cylinder of the test piece are connected together through the connecting piece. See Figures 4 and 5. Then, turn on the computer, call out the control program and start the test. After the test, remove the test piece and conduct post test inspection on the test piece according to the standard specifications.

5. Lateral fatigue test of pipe string structure

(1) See Fig. 6 for test equipment. It is composed of test bench and lateral force mechanism. The test bench is composed of wall stand and box base. Its function is to provide attachment support and fixation for lateral force mechanism and test piece; Lateral force mechanism: the cylinder double piston rod is fixed on the wall stand, the base plate is fixed on the cylinder block, and the force sensor is fixed on the base plate. The force value is displayed by the display.

(2) test method: first, the test piece is installed on the wall vertical frame, and the building blocks are placed on the top of the steering shaft of the test piece, then the test piece is adjusted, and the blocks are placed in the middle position of the two force sensors, and then the power supply and the gas source are connected. The computer controls the solenoid valve with 8 /min interrupts, and the lateral force mechanism exerts 345 + 17.25N directional force on the test piece. Finally, set the computer count to reach 15000 automatic alarms. After the test, remove the test piece for post test inspection according to the standard specifications.

6. Steering system life test

(1) See Fig. 7 for partial test equipment. It is composed of test bench, driving mechanism, load mechanism and control software. The test bench is composed of wall stand and box base. Its function is to provide attachment support and fixation for driving mechanism, load mechanism and test piece; Driving mechanism: the driving mechanism is composed of stepping motor and worm reducer; Load mechanism: the load mechanism is composed of magnetic particle brake and torque sensor; Control software: prepare test control program according to standard specifications. The main content is to control the procedure according to the sequence and residence time required by the standard. Set the speed of the stepping motor and the rotation angle in the positive and negative directions as variables, and the cycle times of the program will be recorded and displayed automatically. Set the number of durable cycles and alarm automatically when the set value is reached.

(2) Test method: first install the test piece on the wall stand; Then turn on the computer and select the automatic control program. Parameter setting: clockwise 1.5 γ, Counterclockwise 3 γ, Then clockwise 1.5 γ, Identified as a cycle. Automatically count 60000 times and alarm automatically. Finally, press OK to start the test; Next, set the load: the current loading value of the magnetic particle brake can be observed from the display, manually adjust the control power supply of the magnetic particle brake, increase (reduce) the resistance torque load by increasing (reducing) the current, and adjust it to 41 ± 5nm. After the test, the alarm will be given automatically, and the test piece will be removed for post test detection according to the standard specifications.

Conclusion

This paper introduces the fatigue life test items of our company, as well as the equipment and test methods of each test. These test items basically represent the current fatigue life test items of automobile steering column assembly at home and abroad. The purpose is to communicate with peers and jointly improve the test level of domestic auto parts.

Responsible editor: GT

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