1. Introduction The development of automotive technology largely depends on the development of experimental technology. Automotive companies with leading foreign technology have advanced testing technology and complete testing facilities, especially with an engine laboratory consisting of a considerable number of test benches. There are many engine test indicators, and engine test technology is an important part of the car test technology, and it is also the most complicated part. The indicators for measuring engine power and economy are: power, torque, speed, fuel consumption, etc. The parameters measured in the engine's routine performance test are engine power, torque, speed, fuel consumption and fuel consumption rate, fuel temperature. Lubricating oil pressure and temperature, intake pressure and temperature, exhaust gas temperature and pressure, inlet and outlet temperature of cooling water, etc.
Various parameters of the engine are measured in real time by various types of sensors. Modern high-level laboratories can measure hundreds of parameters at the same time; some parameters can be directly measured, and some parameters are calculated based on measured parameters and formulas. Modern test equipment generally provides post-processing of data, and can provide the final processing result of the required data according to user requirements, in the form of tables and curves.
This paper designs a vehicle engine thermal performance test system for the thermal performance index of automobile engine test. The system can detect the multi-point temperature, pressure and flow of the automobile engine, and can display the real-time curve of the parameters, which can be automatically Data processing and report generation, the entire test system is simple in structure, easy to operate, reliable, and high precision.
2. Test content
2.1 Cooling water flow measurement: The maximum temperature of cooling water is 150 ° C; the maximum flow rate is 10 m3 / h; pipe diameter: φ 30. Features: The pipeline space is relatively small, there is no straight pipe section before and after, and the original pipeline structure is not changed during measurement to ensure the pipeline resistance characteristics are unchanged. Measurement accuracy: ±0.5% to 2%; measurement points: 1 point.
2.2 Pressure measurement and data acquisition: medium is cooling water; maximum pressure: 2.0kgf/cm2; characteristics: sensor installation space is small, requiring pressure sensor size is small; accuracy: ±1%; measuring points: 2 points.
2.3 Temperature measurement: It is necessary to measure multiple temperatures such as cooling water, engine surface and internal environment. Temperature range: <1000°C; Accuracy: ±1°C, measuring points: <100 points.
2.4 Voltage measurement: Detect the voltage of battery, fan, etc., measuring range: 0~15VDC; measurement accuracy: ±0.1V; measuring points: 2 points.
2.5 Cooling air volume measurement: It is required to measure the air intake volume before the condenser, and measure the wind speed distribution and air volume at each point within a certain cross-sectional area (450×800) of the condenser surface; measuring point arrangement: ≤20 points . Wind speed measurement range: 15m / s (peak <50m / s), measurement accuracy: ± 2.5%
2.6 Humidity measurement: measure the humidity of the environment at the time, the measurement accuracy is ±2%. Points: 1 point.
2.7 Vehicle speed measurement: The system has online speed measurement function, measuring range: 10km/h~160km/h, points: 1 point.
3. Test System Design The test system consists of three layers: measurement and transmission layer, data acquisition and signal conversion layer, and data processing layer. The structure of the test system is shown in Figure 1.
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The measuring transmission layer is composed of various types of sensors, namely, a pressure sensor, an ultrasonic flow meter, a thermocouple, a voltage sensor, an anemometer (anemometer), and the like. Most of the above sensors can be detected by standard sensors, but the design of the cooling air volume detecting sensor of the engine is difficult. The reasons are as follows: 1) Strong electromagnetic interference, electromagnetic interference near the car engine is very strong, the author has opened the front cover of the car, started the engine, placed the electromagnetic anemometer near the car engine, in the absence of wind, due to electromagnetic interference The anemometer shows a maximum wind speed of 3 m/s. 2) High temperature environment, high temperature near the engine, so that the general electronic components can not work properly. 3) The detection position is narrow, and the thickness of the detection device cannot exceed 25 mm.
For the above reasons, the air volume detecting sensor on the market obviously cannot meet the demand, and only the design itself. According to the requirements, the design is as follows: In order to overcome the high temperature and strong electromagnetic interference inside the car, the high-temperature reflective photoelectric sensor is selected, and the detection signal is transmitted to the amplification shaping circuit through the high-temperature shielding signal line, and then sent to the CPLD, and the CPLD is programmed to realize the pair. Multiple frequency signals are detected. as shown in picture 2.
Through the wind tunnel experiment calibration, establish the relationship between wind speed, local air volume and impeller rotation frequency:
Taking a foreign model car as an example, the cooling fan of the car is turned on. The test system is tested continuously for 3 times to test the air volume of a car at different driving speeds. The unit of air volume is m3/h. The reference value is the foreign automobile company. Test values ​​under the same conditions. The specific test data is shown in Table 2. 
The data tested above is basically consistent with the results tested by the company in North America using foreign test systems.
4. The software design software system uses the famous "LABVIEW" configuration software of the United States as the development platform of computer software. The data processing layer is an application computer that transfers data (converted to RS232) on the RS485 bus to a computer, and realizes real-time data display (including trend graph display), data analysis, data saving, report generation, and printing through computer software. Printed reports are a basic function commonly required by measurement and control systems. Microsoft Excel is a powerful data processing software that is widely used. By combining with LabVIEW, the collected data is transferred to Excel, making full use of both functions. After the test is over, the tester can view the data in the Excel file for further processing.
5. Conclusion The system has been successfully applied in the laboratory of an automobile research center. The actual operation results of more than one year show that it can fully meet the needs of engine thermal parameter measurement, with high test accuracy and stable performance. Due to the use of bus structure, system expansion It is also very convenient. The author's innovation is: domestic testing of automotive engine thermal parameters mostly stays in the test of certain parameters, the research of integrated test system is in its infancy, there is no similar product, the system can test a variety of parameters at the same time, Conducive to the analysis of engine performance. In addition, it solves the detection of engine cooling air volume under high temperature and strong electromagnetic interference environment.
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