Vehicle Transmission Error Measurement System

Author(s):
Alexander Zeitlin - VI Engineering, Inc.
Yuesheng Lu - VI Engineering, Inc.

Industry:
Automotive

Products:
Dynamic Signal Analyzers, PXI/CompactPCI, LabVIEW

The Challenge:
To develop a test system to work with Laser Doppler Velocimeters for measuring the vehicle Transmission Error signal from the strong noise background generated by the non-uniformity of the motor drive rotation. The test results need to be presented on the local test computer screen and also be accessible on the company Intranet through the Web browser.

The Solution:
LabVIEW, PCI-4452 Dynamic Signal Acquisition Card, and PC-TIO-10 Counter/Timer Card are used to acquire, analyze, and present the TE signals. Advanced digital signal processing (DSP) algorithms are developed to process the signals and extract the Transmission Error harmonic components from the noise background. HTML and CGI functions in the Internet Toolkit are used to interactively publish the test results on the Web.

Abstract
A measurement system, that combines LabVIEW, digital signal processing, high performance data acquisition cards, and Laser Doppler Velocimeters, is developed to monitor the rotational transmission error of the vehicle transmission. Novel digital signal processing methods are developed to analyze the measurement data. The measurement results are accessible through the Web browser on the corporate Intranet.

Introduction
The vehicle transmission error (TE) is the rotational acceleration and deceleration of the transmission elements during the regular working cycles. The vehicle TE is usually caused by the manufacturing defects in the vehicle transmission or violation of assembly accuracy in the transmission assembly line. By measuring and analyzing the TE, it would be possible to identify the source of the problems and consequently eliminate them. A commonly used tool for measuring the TE is optical encoder. This method has the advantage of high measurement accuracy. However, it needs precise mechanical mounting in a laboratory environment. In attempting to develop a technique to measure the TE in the assembly line or even in a vehicle, Visteon engineers introduced a technique using Laser Doppler Velocimeter (LDV) to measure the TE in a non-contact fashion (Figure. 1). Two LDVs measure the rotational speeds of the in-shaft and out-shaft of the transmission. The TE is measured by applying Fourier Frequency Transform (FFT) to the difference of the two signals. In the real test condition, however, the motor drive that drives the in-shaft of the transmission rotates non-uniformly, and has a strong and widely distributed rotational noise spectrum. The weak TE signals are mostly submerged in the strong noise background. Using simple FFT method cannot measure TE signals accurately; thus more advanced signal processing methods are needed.

System Description
We chose LabVIEW as the software tool to develop the software for the test system because of its rich user interface components and powerful signal analysis functions. A PCI-4452 Dynamic Signal Acquisition Card is selected to acquire the signals. PCI-4452 provides a 16-bit analog input accuracy with simultaneous sampling at the rate of up to 200 KS/s. Its 90-dB dynamic range allows the DAQ card to pick up weak TE signals. The board’s simultaneous sampling feature and the hardware antialiasing filter can further improve the measurement accuracy. PCI-4452 acquires two channels of signals from two LDVs, which measure shaft rotational speeds from the in-shaft and out-shaft. In our software, the two input signals are separately filtered by a software digital filter (bandpass FIR filter) to further reduce unwanted low and high frequency noise signals coming from both the motor drive’s non-uniform rotation and the electromagnetic interference from the environment. The two signals are then scaled and subtracted using a special formula. Fast Fourier Transform (FFT) is performed to the subtracted signal to get the TE frequency spectrum data for the purposes of displaying and for further data processing.

In order to achieve the desired measurement accuracy of the TE signal, the software needs to eliminate the noise generated from the motor drive’s rotational non-uniformity. Since those noises are mostly random noises, they could be reduced by averaging data from multiple sampling windows. On the other hand, the synchronization of the different sampling windows is important to get a trustable TE signal. Because the motor speed varies unpredictably and the sampling windows have different lengths and phases, it is extremely difficult to do the synchronization in the time domain. Instead, we take the data and apply FFT to every sampling window, and average the multiple FFT spectrums in the frequency domain. An NI PC-TIO-10 Counter/Timer board is used to read the pulse signal from an optical speed pickup and to determine the instantaneous rotation speed of the motor drive. The speed data is then used to adjust the frequency scale for all the frequency spectrums, which are then averaged. By using this method, the noise signal on the spectrum is reduced significantly and the TE harmonics are measured with good accuracy and repeatability. The advanced harmonic detection functions in LabVIEW were used to automatically locate and calculate the frequency and magnitude of the TE harmonics. It saved us significant amount of developing time by using the advanced harmonic detection functions.

Presentation
The software has three ways of reporting and presenting the test results:
(1) Graph: The result frequency spectrum is displayed on the main screen immediately after the data collecting and analyzing are done. The user can change the base of the x-axis of the spectrum graph to Hz, pinion rotation harmonics or the gear rotation harmonics.
(2) Table: The table at the bottom of the main screen shows the mesh harmonic frequencies and magnitude up to the 12 th harmonic frequency. The software can also present the spectrum data in a tabular fashion on a separate screen if the user chooses so.
(3) Web: The test results are also published on an intranet Web site. All the test results are saved in a database on the test system computer. An HTTP server runs on the same test computer. We use Hypertext Markup Language (HTML) functions and Common Gateway Interface (CGI) functions, which are provided by Internet Toolkit to allow the user to retrieve test result dynamically. By using Web browsers, the managers and the product design engineers can browse and view the test results from their desktop computers through the company Intranet. Figure 3 shows an example of an HTML test report.

Conclusion
V I Engineering and Visteon developed a TE measurement system based on National Instruments’ LabVIEW, Internet Toolkit, and high performance data acquisition cards. We were able to develop the software for a complete and "Turn-Key" system in less than 3 months because LabVIEW provides very rich and powerful virtual instrument components and functions. The test system we developed provides the automotive manufacturers a powerful non-contact quality control tool to measure the TE on both the assembly line and in the R&D lab. The manufacturer can use this tool to find out the transmission’s manufacturing defects and assembly inaccuracies earlier, thereby reducing the manufacturing costs and enhance vehicle quality.

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