The virtual instrument is an instrument developed on the computer using a graphical programming language (G language). It combines an easy-to-use graphical development environment and a flexible and powerful programming language to provide users with an intuitive environment for data acquisition. , automated testing and instrument control and other fields have been widely used.
The use of virtual technology in the engine test system, using a general-purpose computer as a platform, makes full use of the computer's rich hardware and software resources to complete the functions of data acquisition, processing, and display of results; it overcomes the limitations of traditional instruments, and has a long development cycle. The programming efficiency is low, the program is solid and the system expansion performance is poor, and a lot of complicated data analysis and data cannot be processed.
There are shortcomings such as small storage space.
The LabVIEW-based engine fuel consumption test system makes full use of LabVIEW's powerful tools, functions, and graphical controls to achieve automatic fuel consumption measurement and real-time monitoring, as well as automatic alarms.
1 system hardware structure scheme
The system is designed and developed a transient fuel consumption test system on the original engine experimental monitoring and control bench. Its hardware structure is shown in Figure 1. The whole system is roughly composed of 3 parts: The first part is the fuel consumption sensor. Its function is to convert the engine's fuel consumption and other performance parameters to the corresponding electrical signals through the sensor. Here, the engine experimental measurement and control stand can be fully utilized to obtain the speed and torque, etc. Information; the second part is the data acquisition card, NIUSB9219 comes with signal conditioning function, the signal can be sampled, amplified, A / D conversion, and the collected data in a certain format to the host computer; the third part of the computer Processing system, its function is to achieve data processing, display and storage and alarm indication.
The system uses the National Instruments NI USB9219 data acquisition card. It is a plug-and-play, 4-channel, 6-terminal connector that can measure strain gauges, RTDs, thermocouples, load cells, and other sensor signals that require power. Data acquisition card. Each channel is individually selectable and can each acquire analog or digital signals. With 250-Vrms channel-to-channel isolation, the USB-9219 not only protects surrounding modules, chassis, and connected computer systems, but also protects other channels within the same module. In addition to improving safety, isolation between channels also eliminates problems associated with ground loops. The signal output by the fuel consumption sensor is directly input into the channel of the NI USB9219, and is analyzed and processed by the LabVIEW fuel consumption test software of the upper computer to store the data and send it to the display to output real-time display data, which provides a basis for the automobile engine state detection.
2 Fuel Consumption Test Principle
The fuel consumption rate is an important indicator for evaluating the economy of the engine. The method of determining the fuel consumption rate (referred to as the fuel consumption rate) is usually a volume method, a gravimetric method, a flow meter method, a flow meter method, and the like. This system selects the mass type fuel consumption sensor and calculates the fuel consumption per unit time of the engine by measuring the weight of fuel consumed over a period of time. The formula is: G=3.6ω/t. Where: ω is the fuel quality, unit: g; t is the measurement time, unit: s; G is the fuel consumption, unit: kg/h.
The quality fuel consumption sensor consists of a weighing device, a counting device and a control device, as shown in FIG. 2 . Weighing devices are usually scaled using bench scales with a measuring range of 10 kg and a weighing error of ±0.1-%. The weighing pan is equipped with an oil cup (1 in Fig. 2) and the fuel is added to the oil cup via the solenoid valve (4 in Fig. 2). The opening and closing of the solenoid valve is controlled by toggling the two micro limit switches (5 and 6 in Fig. 2) by the travel limiter (7 in Fig. 2) mounted on the balance block. The photoelectric sensor gives the start and end signals of fuel consumption. It is composed of two photodiodes (8 and 9 in Figure 2) mounted on a prismatic pointer, and the photodiode (8 in Figure 2) is a fixed type, photodiode ( In Fig. 2, 9) is mounted on a movable slider, the slider is moved by a rack-and-pinion mechanism, the gear shaft is connected with the drum (12 in Fig. 2), and the amount of fuel metered from the scale by rotating the drum (12 in Fig. 2) Read on the disk. At the beginning of the measurement, the light beam from the light source (10 in Fig. 2) strikes the photodiode (8 in Fig. 2). The photodiode emits a signal, which causes the counter (13 in Fig. 2) to start counting. With the consumption of fuel in the oil cup, The pointer moves. When the beam hits the photodiode (9 in Figure 2), the photodiode (9 in Figure 2) signals that the counter stops counting.