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Home > Nanotechnology Columns > Bourne Research > Tire Pressure Monitoring

Marlene

Abstract:
Systems which automatically monitor the pressure of your car's tires are now standard equipment in all new vehicles in the US, but don't take them for granted. You may still need to manually check the pressure of your vehicle's tires; two different approaches are in use, one of which is more accurate than the other. Find out what you need to look for and the role that MEMS sensors are playing.

January 15th, 2008

Tire Pressure Monitoring

Tire Pressure Monitoring

Systems which automatically monitor the pressure of your car's tires are now standard equipment in all new vehicles in the US, but don't take them for granted. You may still need to manually check the pressure of your vehicle's tires; two different approaches are in use, one of which is more accurate than the other. Find out what you need to look for and the role that MEMS sensors are playing.

==

Did you know that all cars now sold in the United States, starting with the 2008 models, must be equipped with an electronic tire pressure monitoring system? That sounds like a really good safety feature, right? You can just look at the instrument panel on the dashboard and see whether or not your tires need more air. So why is the American Automobile Association (AAA) warning motorists to manually check the pressure of each tire on a monthly basis?

It comes down to a matter of technology.

Two approaches are in use - one relies on MEMS sensors, the other does not. One is called the indirect method. In this case, the rate or speed sensors that are already part of a car's anti-lock braking system are used. These sensors (which are not MEMS sensors), don't actually measure or monitor the pressure of each tire. Instead, they infer - or basically guess - a tire's inflation level based on a tire's rotation and relative speed.

This approach compares all of the tires to each other, and thus can only identify a tire that's under-inflated compared to the other three. This is because a tire with lower pressure apparently rotates faster than a properly inflated tire. So, if all the tires deflate evenly, the system won't recognize that they're not inflated properly.

The indirect method was originally pushed by automakers because it was fairly easy to integrate into cars by using existing sensors, so it was also relatively inexpensive. The downside is that it's not terribly accurate.

A second approach, the direct method, does use MEMS sensors. While more complicated and costly, it's also much more accurate. In this case a MEMS pressure sensor (which is actually embedded inside each tire), continuously monitors the tire's pressure; to within one pound per square inch.

It's my understanding that the only way motorists can tell which method is being used is to look at the data that's being displayed. If the display simply warns you that a tire under-inflated then it's probably the indirect method; on the other hand, if the actual pressure for each tire is displayed, then it's the direct method.

With both systems, drivers will only get a warning light if a tire is under-inflated by more than 25 percent. This is partly why AAA issued its warning - that's really too long to wait. With the indirect method, you don't know what each tire's pressure is and won't know there's a problem until the system provides a warning.

However, with the direct method, you'll know the pressure of each tire and thus can fill them with air before that 25 percent under-inflation threshold is ever met - provided you regularly keep an eye on the display and know what the proper tire inflation level should be in the first place.

Want to know more? Listen to the Bourne Report Radio show this week for more details. Plus, you'll also hear about a new windshield for cars that uses nanomaterials to block 90% of infrared rays - this keeps your car cooler, lessens the need for air conditioning and increases fuel efficiency. I realize that a hot car isn't something that you think about during the winter, but when it comes time to fix a cracked windshield, wouldn't you like to replace it with a product like this?

This article is a transcript of the Bourne Report Podcast #77.

Want to know more? Listen to the weekly podcast: http://www.bournereport.com/tech.php

For more information about the radio show, please visit: http://www.bournereport.com

2007 Bourne Research LLC. All rights reserved.

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