Vehicle Diagnostic System

Based on Vibrations

An extremely useful device can be added to all vehicles which is capable of monitoring many aspects of a vehicles operation. A warning can be provided whether a wheel becomes imbalanced, or a tire loses air pressure, or a universal joint is failing, or the engine is misfiring. Many other aspects of a vehicle are also capable of being monitored.

The device is actually quite simple. The sensor is merely a broadband vibration sensor, such as many standard devices that are based on piezoelectric crystals, solidly mounted to the frame of the vehicle. This sensor is connected to a circuit that does Fourier analysis of the complex incoming waveform patterns. Again, this is really just a standard device, often used in music software, to create sheet music. In that use, any complex input musical composition is Fourier-analyzed, which determines exactly what dominant frequencies exist in the complex input signal, and the program then has the capability of writing the sheet music for the composition. That standard software is capable of recognizing a large assortment of separate frequency components in the complex source signal.

This application does the same thing, but uses the complex vibration signals from the vibration sensor as the source. If any dominant frequencies exist in that signal, the Fourier analyzer would identify them. Fairly simple software could then give output warnings (lights or messages) for the various conditions that could cause specific vibration frequencies.

A vehicle speed sensor is also necessary for the fullest analysis of such vibrations.

This concept was invented and Engineered by October 1998. This presentation was first placed on the Internet in November 2000.

Let's say the vehicle is traveling at highway speed. The computer would know from the speed (and the pre-set wheel diameters) that the wheels were rotating at about thirteen times per second. If a significant vibration of 13 hertz appears, it would be an indication of a wheel that had become imbalanced. If a vibration of 26 hertz appeared, it could be an indication of a failing CV joint. If around 40 or 80, a universal joint could be failing. Certain higher specific frequencies could identify differential or transmission problems beginning.

If a vibration of around 30 hertz arose, it could be an indication of the beginnings of an engine cylinder that is not firing as well as the others. Certain very specific, very high frequencies are related to disk brake operation. Some of those frequencies are normally produced but some are indications that the brake system would soon need maintenance.

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There are more sophisticated uses of this vibration information. There is ALWAYS a background of miscellaneous vibrations of many frequencies present. If the signal processing system (or computer) would record and store a normal vibration signature, then several more subtle applications could be included. Much of that background vibration is created in the suspension system and is primarily due to the conditions involved in the tires contacting the road. If the background vibration would suddenly get much less, this would likely be an indication that the vehicle is 'hydroplaning' on a wet road or sliding on a icy road. There are no other indicators of such situations that exist that cost less than a whole vehicle costs!

If, instead, the low and middle frequencies of the background vibrations remain, but the high frequency background vibrations become significantly less, this is likely to indicate that one or more tires have lost some air. A tire with low pressure actually 'rides' softer, which effectively means that the high frequency component of road imperfections would be substantially reduced.

A related application would probably involve such (inexpensive) sensors at each of the vehicle's wheels. A vehicle's loading affects the natural frequency at which the springs on each wheel oscillate (called the spring rate). A vehicle with just a driver would have specific, very precise spring rates for each wheel. If a passenger gets in, the additional loading for the suspension on the passenger side wheels would slightly alter the spring rates for those wheels. If each wheel is separately monitored, a vehicle could actually 'know' IF a passenger was present, and even the approximate weight of the passenger. It could identify if the trunk was loaded with weight, which could affect vehicle handling, and offer a warning for the driver. The sensing of a passenger should be accurate enough that a passenger seat belt warning could be presented, and even a dual power safety air-bag could know the weight of the passenger, so it would automatically use a low impact air-bag velocity for a child but a full air-bag deployment for an adult.

There are an assortment of other diagnostic applications, but I suspect you should probably get the point by now. Most of these maintenance matters are not monitored in any other way, so, generally an actual failure must occur in some assembly. This method of sensing is so sensitive that it would give indication of the various maintenance considerations far before an actual breakdown could occur. This includes such things as fan belts, which have their own natural resonances, and these frequencies gradually change well prior to a belt failing. This device could indicate a fan belt that would fail weeks in the future, and no other device could give such warning.

Best of all, the vibration sensor is on the scale of a dollar and a device with a Fourier-analysis processor could certainly be mass produced for under $20, so the whole system is remarkably inexpensive! No new or exotic technology is involved, and both vibration sensors and Fourier-analyzers are now very common devices.

If there is interest in developing this invention, please contact me.

Invented, October 1998
First presented on the Internet, November 26, 2000

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Carl Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago