Tire-pressure Monitoring System - Heavy-duty Vehicles

Heavy-duty Vehicles

FMVSS No. 138. 2006. U.S. Dept. of Transportation, National Highway Traffic Safety Administration, FMVSS No. 138, Tire Pressure Monitoring Systems, 49 CFR, Ch. V. application only applies to vehicles under 10000 pounds for heavy duty vehicles (Classes 7 and 8, gross vehicle weight greater than 26,000 pounds), most of the above-mentioned systems don't work well, requiring the development of other systems.

The US dept. of transportation has commissioned several studies to find systems that work on the heavy duty market specifying some goals that were needed in this market. One of those studies is listed in the article "An Evaluation of Existing Tire Pressure Monitoring Systems, U.S. Dept. of Transportation, DOT HS 809 297."

Another NHTSA study below tried to define acceptance procedures for tire pressure monitoring for this vehicle class. Grygier, Paul and Samuel Daniel, Jr., National Highway Traffic Safety Administration and Richard Hoover and Timothy Van Buskirk, Transportation Research Center Inc., June 2009, Testing Of Heavy Truck Tire Pressure Monitoring Systems (TPMS) In Order To Define An Acceptance Procedure, 21st International Technical Conference on the Enhanced Safety of Vehicles, Paper No. 09-0551.

The SAE has tried to put out some best practices since defined legislation has been slow in coming as research in the article Daniel, S. 2005. Status of TPMS Rulemaking, SAE Government/Industry Meeting - May 10, 2005

The main issues sited from these an other studies are as follows:

Lack of standardization. Tires are often purchased in bulk and moved between tractors over time, so a given TPMS system can only work with compatible sensors in the tires, creating logistic problems. RF systems for these units must also work over much longer ranges, which may force repeater systems to be installed on the tractor or trailer. It is expected that battery lives on these systems should be in the five- to seven-year year range, since the cost of breaking down a tire can be so much more expensive. The Department of Transportation's maximum-loading requirements force trailer manufacturers to spread loads over multiple axles, giving rise to trailers with typically 8 to 12 tires, but as high as 96 tires on specialty haulers.

Tire casings can have typical lifetimes of ten or more years, through multiple retreading processes. This has given rise to a specialized industry that focuses solely on issues found in the trucking industry.

Central inflation systems originally claimed to eliminate the need for pressure-monitoring systems. Some major inflation systems are Meritor PSI, Hendrickson International and Vagia (used mostly in South America). However, they have not yielded a complete solution, since they do not solve all the issues (i.e., no support for the steerable axle), and they bring new issues with maintenance of the rotary couplings in the hub caps. Furthermore, inflation systems can sometimes shorten the life of tires by covering slow leaks caused by embedded objects, which drivers would otherwise remove after inspecting the problem tire.

In order for a tire-pressure sensor to be completely effective, it must have several capabilities to allow for the various maintenance personnel groups to use them.

First, each driver is required to do a pre-trip inspection, so it is beneficial if the tire-pressure monitor has an indicator that can be read without tools.

Second, it usually should have the ability to cover dual sets of tires in some fashion. It is also beneficial if the fill points can be centralized so that inflation can be accomplished easily without reaching through the small hand holes in the rims.

Third, it needs to have a wireless communication system that has an appropriate range and battery life. It is important that sensors regularly communicate an "I'm alive" condition, since having a dead sensor can be worse than having no sensor at all, if everyone thinks the monitoring is being taken care of automatically.

Fourth, these systems should have the capability to adapt to the changing of tires and trailers with minimal operator intervention. It is important to use a system having a longer range, since a repeater adds to the cost.

These requirements can be met by systems with external pressure sensors that connect to the valve stem on each tire. When tires are replaced, the sensor is simply attached to the new tire.

Although these systems can alert a driver to a hazardous blowout condition, they may not help fleets deal with slow-leaking tires, unless the driver reports them to fleet-maintenance personnel before it is too late. This has given rise in recent years to monitoring solutions that track the tire condition and send back alerts to fleet-maintenance personnel. This allows them to schedule maintenance on a slow-leaking tire on an exception basis, instead of having to check each tire manually. Many fleets today admit that tire-pressure checking is a major problem in enforcement. Most have policies in place requiring the regular check of every tire, however, the practice is not terribly effective because of the sheer scope of the issue, and the fact that it is hard to get a complete record of all tire checking.

Today the best systems employ automated data collection. Some of these use gate readers that automate the collection of tire data to a database, or to a web portal, that allows maintenance operators to see data for the entire fleet at a glance. For long-haul fleets that may not see their vehicles for long periods of time, a centralized reading system may not work, but there are emerging systems that aggregate the tire-pressure-sensor data back to the asset-tracking system so that alerts can be sent back to the main office when an issue arises. For small fleets, handheld devices exist that allow a person checking tires to simply walk around vehicles and collect data for downloading to a central database, allowing enforcement and trending to be done without errors.

Some automotive manufacturers have attempted to broaden their scope into the heavy-duty markets, a few manufacturers have focused solely on this market.