Research on the comprehensive test-bed of the hott

With the continuous development of science and technology, people put forward higher and higher requirements for vehicle ride comfort and handling stability. The parameters of automobile suspension system directly affect the ride comfort of vehicles, and springs are the core of the dynamic performance of almost all suspension systems. Because the rubber material itself has the advantages of light weight, impact resistance and easy absorption of high-frequency vibration, coupled with the improvement of rubber and metal bonding technology, the metal rubber spring formed by the combination of metal and rubber, that is, the rubber bushing, is widely used in the guiding device and support device of Automotive suspension, so it is necessary to study the influence of the stiffness of the rubber bushing on the elastic kinematics of the suspension. This kind of bushing is generally filled by one or two rigid sleeves with rubber body in the middle. When in use, the outer cylinder is fixed, and the inner cylinder deforms accordingly with the movement of the wheel. Its deformation response characteristics directly affect the kinematic and dynamic performance of the suspension

the service life of rubber elastic elements can generally reach 16 years. Due to the lack of necessary testing equipment, the stiffness and other main parameters of elastic elements cannot be tested, and the lack of relevant test data, the rubber elastic elements have to be replaced in the UN wheeling repair period (5 years), which greatly increases the maintenance cost, and some rubber elastic elements mainly rely on imports. Therefore, China Automotive Technology Research Center has successively developed a comprehensive test-bed suitable for stiffness measurement and life fatigue test of various rubber elastic components for Zhejiang Wanxiang System Co., Ltd. and Hefei axle Co., Ltd. (see Figure 1). The test-bed is mainly composed of the table body, hydraulic system, electric servo system, electric control and measurement system. Using Advantech industrial computer and acquisition card as the measurement and control center of the test-bed, it can complete the static stiffness, dynamic stiffness and fatigue life tests in the X, y and Z linear directions and the static stiffness and fatigue life tests in the rotation direction, as well as the pull-out force test of the inner cylinder of the rubber bushing, The control and test of the test process are automatically completed by the computer. The software is processed by a specific program. The control accuracy and measurement accuracy of the system can reach less than 1%. The human-computer interaction interface is friendly, and the test data is accurate and reliable, which fully meets the requirements of MSA

Figure 1 the overall structure of the automobile rubber bushing comprehensive test-bed

the overall structure of the test-bed is shown in Figure 2. The test-bed is divided into two channels: hydraulic and servo. The hydraulic channel consists of an upper fixed beam, a middle moving beam and a column to form a specimen clamping frame, which is located above the workbench, and the hydraulic cylinder and servo valve are located below the workbench. The force sensor is relatively fixed with the moving beam. The displacement sensor is a hysteresis telescopic type. The sensor body is fixed at the bottom of the hydraulic cylinder, and the magnetic ring is fixed on the hydraulic piston. The magnetic signal changes with the movement of the hydraulic cylinder to measure the displacement signal. 1 spindle and its drive system spindle (1) is composed of Panasonic exchange electromechanical (2) and pwmc pulse width speed regulation control system. The rated torque of the electromechanical system is 9.545n · m, the pulse width speed regulation range is 10 (2) 000r/min, stepless constant torque, and the high-speed accuracy is 1% The maximum power of the Electromechanical is about 1.5KW. The upper rotating channel of the main shaft (1) and electromechanical (2) is a crank connecting rod structure. The servo motor system is located under the table, the torque sensor, angle sensor and test piece tooling are located on the table, the angle sensor shaft is connected with the test piece, and the shell is connected with the torque sensor flange through the bracket, so as to measure the relative angle of the inner sleeve and the outer sleeve when the test piece is twisted. The crank eccentric wheel is engraved with scales, and each scale corresponds to an angle. The swing angle of the test piece is adjusted by adjusting the eccentricity

Figure 2 overall structure of the test bench

the maximum load of the hydraulic channel is 20KN and the stroke is ± 20mm. The maximum frequency of dynamic stiffness test is 25Hz, the amplitude is ± 2mm, and the maximum frequency of fatigue test is 5Hz. The maximum swing angle of the rotating channel is ± 18 °, and the maximum measured torque is ± 500N m. The maximum operating frequency is 3.6hz

hydraulic system

the capacity of the hydraulic pump station is 100L, the rated pressure is 21MPa, and the rated flow is 100L/min. The pump station motor adopts ABB products, Italian ATOS overflow valve and imported plunger pump, and is equipped with liquid level gauge, thermometer, oil separator, filter and other auxiliary equipment. The oil temperature and oil pressure are equipped with digital display instruments, and the oil temperature has the function of over temperature alarm and unloading protection. The oil pressure can be adjusted steplessly from 0 to 21MPa through a digital potentiometer

measurement and control system

the measurement and control scheme adopted by the test bench is: take Advantech industrial computer as the main control machine, and measure and control the test system through data acquisition card. The industrial control computer sends the action command to the hydraulic servo control card through the analog output card. The control card can reach a long-term stable cooperative relationship through PID adjustment according to the deviation between the feedback signal of the sensor and the command signal, and then output the valve signal to control the hydraulic cylinder to produce the corresponding action. The industrial computer processes the displacement and load signals collected by the data acquisition card, and obtains the force displacement characteristic curve of the specimen

when the servo motor is driven, the industrial computer controls the servo driver through the mpc-08 servo control card to make its driving motor produce corresponding rotation. At the same time, the torque and angle signals are measured, and the torque angle characteristic curve is obtained after processing

1. System hardware

the hardware composition of the system is shown in Figure 3, which can be divided into hydraulic measurement and control system and servo motor measurement and control system

Figure 3 hardware composition of computer measurement and control system

(1) hydraulic measurement and control system:

hydraulic measurement and control system is mainly composed of displacement sensor, load sensor, signal amplifier adam3016, 818L data acquisition card, hydraulic servo control card, high-speed analog output card pci1721, switching value input and output card pcld782/785 and servo valve

(2) servo motor measurement and control system:

servo motor measurement and control system is mainly composed of angular displacement sensor, torque sensor, signal amplifier adam3016, 818L data acquisition card, 32-bit four axis stepping/digital servo control card mpc-08, switch input and output card pcld782/785 and servo controller

2. System software

the system software mainly includes the following modules: system initialization module, sensor calibration and switching value detection module, channel manual debugging module, test test module, database query module and test report output module. The initialization module is mainly to load the board hardware driver, set the initial state of the board and the initial value of test parameters. The calibration module mainly completes the calibration of sensor signals and command output signals, and uses multi-point interpolation method to effectively solve the problem of signal nonlinearity. The manual debugging module is mainly to adjust the initial position or initial load of each test channel to meet the needs of different initial installation positions and loads of the test pieces. The test module is the core part of the whole measurement and control system. It converts the parameters entered by the user into a series of control instructions, calls the access module of the corresponding hardware, and drives the test device and execution device to complete the corresponding test functions. After the test, the test results can be stored in the database, and the test records can be queried in the database management module. Considering the running speed, scalability and maintainability, the system software is written in VB6.0

(1) DMA high-speed signal acquisition

generally, when the acquisition frequency is more than 100 times the signal frequency, the acquisition signal is not distorted (that is, at least 100 points per waveform of the signal). Because the loading waveform frequency of dynamic stiffness test is high (20Hz), the common software trigger acquisition method can not meet the requirements of this frequency signal acquisition at all. Therefore, the measurement and control system adopts the DMA acquisition method to continuously optimize and test to realize the manufacturing of final products. The maximum acquisition frequency can reach 40KHz. The data is read from the DMA buffer regularly through the timer control, which not only meets the requirements of high-speed signal acquisition, but also ensures the consistency of the time of each sampling point

(2) DMA high-speed waveform output

when the number of voltage points of the signal waveform driving the hydraulic servo valve is small, the hydraulic cylinder will crawl or move unevenly. Because the minimum timing period in VB6.0 environment is about 30ms, there are only more than 30 points per second at most when timing output is adopted, and the signal with frequency above 1Hz has been seriously distorted. Therefore, the system adopts pci-1721 high-speed analog output card, which supports DMA high-speed output function. The maximum output rate can reach 10MHz. When 1000 points are output per waveform, it can output 100Hz waveform signals, which is enough to meet the requirements of the test bench. The DMA output function of the card can return the number of output waveforms. With this function, the time required for the test and the remaining time can be calculated. The time error is not greater than 5S when the fatigue test of 200H is carried out

(3) command correction

due to the temperature drift of the sensor output signal, its zero point will also change after a certain number of uses. In addition, the fluctuation of the sensor supply voltage and the difference of the system oil pressure will affect the measurement and control accuracy of the measurement and control system. In order to improve the control accuracy of the system, we modify the control instructions in the software. In the dynamic stiffness test, a preload test is carried out according to the set waveform and frequency before the test, and the command is adjusted according to the measured test results, and then the formal test is carried out according to the adjusted command, which eliminates the influence of factors such as the stiffness difference of measurement system, control system and different specimens on the control accuracy, and greatly improves the control accuracy. In the fatigue test, the command waveform is adjusted in real time according to the sensor feedback signal and the signal error required by the test, so that the control accuracy of the system is less than 0.5%

conclusion

the system software is developed based on VB6.0 under Windows 2000 system, with friendly human-computer interaction interface and simple operation

after multi-point linear calibration of the sensor signal, the measurement accuracy of the system can be guaranteed to be more than 0.5%. After the command correction is adopted in the software control, the control accuracy is greatly improved. When the load range of 100kN load sensor is more than 3kn, the control error can be guaranteed to be within 0.5%

test-bed provides necessary test data for the localization of rubber components. The test-bed has good versatility, can meet the performance test of a variety of rubber elastic components, and has a broad market prospect