Development Of Signal Wheel Sensor Test Bench Based On The Virtual Instrument

The crankshaft position sensor and the camshaft position sensor in the engine electronic control system belongs to the signal wheel trigger sensor, collectively referred to as signal wheel sensors, their output signals directly affect the precision of the ignition timing, injection timing and VVT control. Therefore, the quality of the crankshaft position signal and the camshaft position signals are of great significance for the effect of controlling engine, power performance, fuel economy and exhaust cleaning of engine.As output signal of the signal wheel sensor is not only related with the sensor performance, installation position, but also closely related to the machining precision of the signal wheel, in order to test the complete system of crankshaft and camshaft wheels and sensors, to test match of different signal wheels and sensors, to check whether or not the requirements of the signal wheels design to be met, a signal wheel sensor test bench was developed based on the virtual instrument technology. The main research contents were as follows:1) Designing the mechanical system of test bench. The design of the key lies in the mobile sensor fixture slider and rotary angle adjusting device of the signal wheel. A low-speed shaft (simulating camshaft) was directly driven by the driving system consisted of a frequency converter and a frequency conversion motor, and a high-speed shaft (simulating crankshaft) was driven through the transmission system consisted of the gears and toothed belt. In order to reduce friction and wear, the lubrication system composed of oil tank, electric oil pump, oil-way and bearing oil hole was used for providing lubricating oil to bearings. The installation requirements for a variety of signal wheels and sensors were met by the designed special fixture. Adjustable installation clearance between the sensor and the signal wheel, deflection angle and axial location of sensor were implemented.2) A foreground controller of the measurement and control system for the test stand was developed based on Freescale16-bit dual-core microcontrollers. An intelligent resistance attenuation network using a single-chip microcomputer and digital potentiometer was designed to avoid the acquisition card damage when magneto-electric sensor signal amplitude was too large. The magneto-electric sensor signal was transformed into standard pulse signal by a shaping circuit to compare with the original signal. The photoelectric sensor signal was transformed into electrical impulses by a standard signal generating circuit so as to produce two standard square wave signals corresponding to the edge of teeth gap of the crankshaft and camshaft signal wheel, and to judge the response of magneto-electric and hall sensor. The instructions were received by microcontrollers from the IPC through the Ethernet interface, and were sent to the frequency converter through the RS-485interface to control the frequency conversion motor operation. The speed of the low-speed shaft was calculated by the single-chip microcomputer and transmitted to IPC for real-time displaying.3) A host computer system with the IPC and a high-speed synchronous data acquisition card was constructed. The original signals of the inductive crankshaft position sensor and the hall-effect camshaft position sensor, two photoelectric sensor signals for detecting the edge of teeth, a reshaped crankshaft position signal were acquired synchronously by the IPC system. The phase relationship between crankshaft and camshaft could be determined by comparing the crankshaft original signals with camshaft original signals. The factors of influencing on the sensors output signals could be explored according to the installation clearance between the sensor and the signal wheel, installation angle of sensor, and signal voltage amplitude changes with different signal wheel speed. The characteristic of the magneto-electric crankshaft position sensor could be studied through comparing original crankshaft position signal with crankshaft position signal from photoelectric sensor. The property of the hall-effect camshaft position sensor could be investigated by comparing camshaft position signal from hall-effect sensor with camshaft position signal from photoelectric camshaft sensor.4) The measurement and control system software was developed on the Lab VIEW programming environment to control the operation of the test bench motor, and multi-channel high-speed synchronous signal acquisition and human-computer interaction were realized. By invoking the acquisition card hardware driver NI-DAQmx and DAQ Assistant, the data transmission among the hardware and settings for the acquisition card were implemented. Using of the LabVIEW ActiveX function, by calling the Microsoft ADO object, database was accessed using SQL language, and data storage rate and reading rate were improved. Appropriate control commands were sent to the foreground controller by the measurement and control system software based on the event structure, and the software had functions, such as user management, parameters setting, dynamic waveform display, parameter digital display, waveform amplitude adjustment, graphics time scale adjustment, data playback, data analysis, fault alarm display, etc.5) A lots of testing were performed under the conditions of different signal wheel, different speed, different installation location of sensor to assess and evaluate functions and working reliability for the signal wheel sensor test bench. The actual test results show that, the dynamic change process of the signal wheel sensors can be reflected from the measured data, and testing and analysis requirements for matching system with many varieties, small batch signal wheels and sensors can be satisfied, a good platform to inspect the overall performance of sensors and signal wheels is provided.