First, the summary of virtual instruments
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According to the current situation of automotive engineering testing, the establishment of flexible, powerful, and low-cost automotive electrical testing systems is an urgent requirement for our current automotive testing. This testing system can be freely increased or decreased according to the requirements of each engineering test. Test system configuration, through the use of configuration system unit devices, fully use existing systemized standardized resources to improve the efficiency of integrated application of engineering test technology in an intuitive and effective way.
Now the test instruments in automotive engineering are the same as those in other projects. They also need special testing instruments. We can see the advantages of virtual instruments by comparison: (1) Some test equipments are in disrepair due to years of age, and the digital levels are compared. Low, and the product is seriously aging, some of the boards have been severely corroded and almost impossible to resume normal work. The virtual instrument can overcome the shortcomings of some previous test equipments. Through the integrity of the equipment, it can ensure the accuracy and real-time of data collection, improve the data processing function, improve the ease of operation, and update and expand the original equipment to form a Test system; (2) In the usual test system, the hardware system is to solve the input and output of the test system signal, and realize the logical relationship between the signals; the software system is the key to the operation of the whole system and the function is The signals are processed accordingly. The virtual instruments can use the same hardware system, and different functions of various measuring instruments can be realized through different design procedures. The virtual instrument's test system and the front panel display are all softwareized, that is, the software system becomes the core of the virtual instrument test system, the software can define various instruments; (3) the virtual instrument has great variability, and can be used anytime, anywhere. The advantages of the situation increase and decrease test function, improve the target design, its superiority is incomparable; and the instrument developed by the single-chip system after several years of use, because the user put forward new requirements, the original equipment can not adapt to the changing environment and was eliminated; (4) During the use of virtual instruments, the internal functions of the test system are gradually updated, and the working mode of the test system can be continuously improved at any time and place. Therefore, the more perfect the program is, the more close it is to the latest work needs; especially the development with a single chip microcomputer. The perceptual knowledge accumulated by the designers of special new products is limited to a certain scope at that time. From design to instrument, it is limited by time span and expenditure. Its reliability and stability often cause congenital deficiency and it is difficult to make up afterwards. Solve; (5) the hardware and software of the virtual instrument are accumulated for many years. Moreover, if there is any dissatisfaction in the test software, it can be easily modified to suit the needs afterwards; it is a modular integration of programming design, intuitive, and even for non-computer professional counterparts, it is easy to modify the program. From the perspective of reducing development time and reducing costs, the superiority of virtual instruments is exact. With the gradual use of virtual instruments, we will increasingly find its advantages.
Second, electric power steering system and virtual test system
Electric power steering is to add a motor as a power source based on the artificial mechanical system, and replace the hydraulic power steering with electric power. Electric power is controlled by the electrical control of the motor. In order to analyze the quality of the motor drive system and to check the working condition of the system, a system test tool must be provided to reflect the working status of the system. The virtual test system can complete the comprehensive monitoring of the electric power steering system.
The automotive electric power steering virtual test system mainly consists of the following components: electronic control unit (ECU), vehicle speed sensor and torque sensor, servo motor, speed reduction mechanism and steering column assembly, program port and computer (see Figure 1). The key ones are the electronic control unit, the signal acquisition and conditioning circuit and the computer virtual instrument, which largely determine the control effect of the electric power steering system. The specific test procedure is: when the car is in the starting or low-speed driving state, the steering wheel is turned, and the torque sensor mounted on the steering column continuously detects the torque acting on the steering column torsion bar, and inputs the signal and the vehicle speed signal simultaneously into the electronic device. The controller and the signal acquisition and conditioning circuit, the ECU processor performs arithmetic processing on the input signal to determine the magnitude and direction of the assist torque, thereby controlling the current and steering of the motor, and the motor transmits the torque to the horizontal direction of the traction front wheel through the clutch and the speed reduction mechanism. The tie rods ultimately provide the driver with an auxiliary steering force. At the same time, the torque signal T and the current signal I are signal-conditioned and then input into the LabVIEW virtual instrument control program of the computer through RS-232 serial communication mode to perform comprehensive system performance test.
The vehicle electric power steering virtual test system can be represented by Figure 2:
(1) Serial communication VI: The serial communication node generally consists of the following nodes as the communication node of the serial port.
The initialization parameters for setting the communication method using the VISA Configure Serial Port node are shown in Figure 3.
Use the VISA Read node to read the serial data node (see Figure 4).
Use the VISA Close node to shut down the resources (see Figure 5).
(2) Digital Filter VI: This device is used for filtering (see Figure 6).
This system is a frequency selective device that allows specific frequency components in the signal to pass through and greatly attenuates other frequency components. This frequency selection can filter out interference noise or perform spectrum analysis. The system uses the IIR low-pass Butterworth filter.
The system simulates the steering resistance of the car through two springs. When the steering wheel angle is gradually increased, the system changes are observed in real time, which is also the real-time characteristic of the virtual instrument.
From the experimental diagram (see Figure 7), it can be clearly seen that the torque in the electric power steering system is significantly larger when there is no power assist than when it is assisted, so that the power assist effect can be clearly observed, and the electric power steering is clearly observed. The portability of the system.
Based on the above experimental results, it can be seen that the application of the virtual instrument in the electric power steering system of the automobile is very convenient and does not require the use of more cumbersome instrument control. In the experiment, it can be seen that there is a system change before and after the assist system. Through this test system, the automation degree of the test system is greatly improved, and the error of human operation is reduced. By further system optimization, the program software of the system and other system configurations can be changed without much action. Changing the test structure can adapt to different aspects of testing needs.
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