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Benefits of data acquisition for vehicles

Posted: 30 Dec 2014 ?? ?Print Version ?Bookmark and Share

Keywords:data-acquisition systems? eDAQ-lite? V8 engine? engine cranking? engine cranking?

Having worked as a test engineer at John Deere for some 35 years, I have witnessed how measurements taken on data-acquisition systems can significantly help you improve performance and reliability in vehicles from tractors to drag racers. After retiring, I brought that experience to my "encore career" in racing engineering. Data acquisition systems placed in vehicleseven when fitted in 7-second drag racerscan open your eyes to engine problems and reveal clues to improve performance.

The image below shows a eDAQ-lite data-acquisition system installed in a drag racer. The data it provides lets me improve the elapsed-time consistency, safety, and reliability of my racing vehicles. I chose the eDAQlite because can take up to 100,000 samples per second, and it's been accepted for use in the Sportsman classes of the National Hot Rod Association Championship Drag Racing Series.

Recently, I needed to make the engine of my seven-second dragsters start more easily and yet avoid the occasional "kickback." I needed to measure several engine parameters, the most important being the engine cranking speed.

To record engine speed, you typically connect the tachometer output signal from the ignition system to the data logger. That provides four pulses per crank revolution, which is generally enough resolution for most applications.

To check the mechanical condition of the engine, however, you need more detailed information. For this application, I used a speed pickup sensor connected to the flywheel. This sensor detects the passing of the teeth on the flywheel and outputs 168 pulses per crank revolution. The sampling rate was set at 200 samples per second. Figure 1 shows a comparison of these two measurement methods.

Figure 1: The overlaid traces compare pulses from a tachometer (blue) and a speed-pickup sensor (red).

The plot in figure 2 shows the engine cranking speed of the dragster's 548 cubic-inch, V8 engine over a two-second time period. The compression ratio of the engine is 15:1. While the average cranking speed is 150 rpm, it can be as high as 225 rpm during a power stroke and as low as 85 rpm during a compression stroke.

Figure 2: Pulses captured with the data-acquisition system show engine crank timing and speed.

At a 150-rpm cranking speed, the dragster's crankshaft makes 2.5 revolutions/second. For the four-cycle V8 engine, there are 10 power strokes during a 1-second period.

The plot in figure 2 lets me compare cylinder-to-cylinder variation. Any mechanical issues that affect the cylinder's "pumping" performance will change the cranking rpm. I like to periodically record the engine speed while cranking the engine and then compare the trace shape from cylinder to cylinder. It's a quick method for checking the engine's mechanical condition.

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