With the abandonment of so many spur rail lines over the past decade, grain farmers in Saskatchewan face a real problem. Delivering their product to the remaining railheads demands longer trips by truck, but the need to run some of the way on secondary roads means that load weights can’t be high enough to be efficient. Enter the Transportation Partnership Policy (TPP) of the provincial government, created in 1997 to help develop vehicles for grain and other heavy hauls that can be safely accommodated on rural roads.

One of the first products of the TPP is an oversized, heavy-load Super-B-train unit for the Saskatchewan Wheat Pool that hauls up to 56 metric tons yet nevertheless can operate even on the province’s secondary roads. The secret? Pre-programmed central tire inflation (CTI) and variable tire pressure (VTP) technology that lets the driver partially deflate the tires to create a softer “footprint” on the road surface when the load condition or vehicle speed permits it.

The Saskatchewan Wheat Pool has ordered 20 CTI-equipped Super-B-train units from Lode-King Industries in Winkler, Man., for delivery this summer. The Wheat Pool will pay $1.5 million for the new rigs, which are somewhat overlength tridem-axle units at 28 feet on the lead trailer and 44 feet for the rear unit.

It’s a hefty price, but there’s an upside.

“We’ll have a configuration with a 52-metric-ton payload in warmer weather, and 56 tons when winter weather condition status is officially in effect on the province’s roads,” explains Trenton Baisley, general manager of the commodity logistics group at the Wheat Pool. “The normal payload for our current Super-Bs is 45 tons on major highways and just 35 tons on secondaries.”

Those productivity gains will be significant, Baisley says, and the actual dollar savings will be shared 50-50 between the Wheat Pool and the jurisdictions on whose roads the trailers travel. Under the TPP, “They’ll apply those funds to road-maintenance needs,” Baisley says.

The Wheat Pool’s rigs are yet another example of how central tire inflation is being seen as more than just a funky add-on. Tires represent the second largest financial expenditure for most fleets-it’s hard not to look twice at any system designed to maximize tire life, fuel efficiency, and safety, and keep vehicles on the road generating revenue.

The technology-or variations of it-has been used with on/off-road vehicles in the forestry industry for years. Centralized tire inflation hearkens all the way back to the Second World War, when they were developed for military trucks for situations where mobility is critical. The tires can be deflated to increase traction-a feature that would have obvious benefits in vocational and other off-road pursuits today.

Some central tire inflation systems actually focus on pressure equalization, simply distributing air from one tire to another to strike a balance.

More advanced systems plumb all tires on the vehicle to a controlled air supply that automatically adjusts air pressure to a constant and proper level, even while the vehicle is moving. Toronto-based Vigia has established itself as one of the leaders in the field, marketing a CTI system to heavy-haulers and on/off-roaders for quite some time.

Among the latest to tap into the market are Meritor Automotive and Eaton Corp., the rival suppliers of drivetrain components and braking systems. Both are marketing systems to trailer original equipment manufacturers.

Eaton debuted a pressure-monitoring tool a year ago, and its new Tire Maintenance System goes a step further. It too detects under-inflated trailer tires and then automatically applies air to correct the problem. “Monitor systems are ideal for operations where the trucks return nightly, but a maintenance system is a better fit for long-haul operators,” says Gary Schultz, product manager for Eaton’s Tire Management Systems. “The [maintenance] system also will significantly reduce the potential for failed casings that result from under-pressurized tires.” Like the company’s Tire Monitor System, the Tire Maintenance System uses the Schrader-Bridgeport “Smart Valve,” which contains a remote, wireless battery-powered transmitter and replaces the wheel’s standard valve stem. The valve sensors transmit tire-pressure data via radio frequency to a receiver programmed to identify individual tires. The comparison is used to trigger solenoid valves to transfer air from the vehicle’s air supply into the under-inflated tire through rotating axle seals. The receiver can be easily set up and calibrated, says Eaton, for a wide range of pressures up to a “cold-tire” 110 psi.

Usefully, the receiver stores inflation events in memory for later retrieval and tire repair. It uses standard SAE J1587/J1708 communication protocols for programming, diagnostics (via blink codes and/or PC), and data retrieval. If tire pressure falls to less than 90% of the desired level, the warning lamp illuminates. It would happen if, for example, a leak were causing air to escape faster than the system could re-inflate the damaged tire. The light would simply stay on if pressure stayed at less than 90%, signifying a substantial leak.

Generally, however, the light should come on less frequently with the new system because it will act on its own to correct a problem. In fact, the sensors will alert the receiver and call for air if pressure falls just 3 or 4 psi below the desired level. Schultz says that an important feature of Eaton’s Tire Maintenance System is the fact that air passages to the tires are only pressurized when air is needed. He claims that continuous-pressure designs “tend to create additional maintenance work.”

Among the obvious questions about a component that borrows air from the vehicle’s braking system, two seem most likely: is it possible for tire-inflation activity to rob air needed by the truck’s brakes? And will an ordinary-spec compressor be enough for the job? Both are answered the same way. The tire-maintenance system has a fail-safe mechanism that constantly monitors brake readiness and air demand. Based on a minimum-pressure point, tires won’t get air if the brakes need it more, which means that compressor capacity need not change.

Other probable questions involve the in-tire sensor/valve/transmitter. Its aftermarket list price is about $75, and if you’re replacing one you’ll have to introduce it to the receiver. That requires a special tool (about $120) to re-align the sensor with the receiver. It’s actually a simple battery-powered “wand” about 18 inches long with an exciter coil on its head. You simply have to place it close to the valve. The receiver “learns” the individual tire’s correct pressure, assuming it’s been inflated to that level, and one of its blink-code lights illuminates for five seconds to confirm that it’s receiving information.

The other new player in the CTI market is Meritor, which in January announced a collaborative deal to market and distribute a product made by Pressure Systems International Inc.

The PSI system uses compressed air from the trailer air lines to inflate any tire that falls below a pre-set pressure while the trailer is moving.

The system connects all tires of a trailer to the existing trailer air supply. Axles provide air through a rotary union assembly at the spindle end that distributes air, as needed, to the tires. As air pressure decreases from the tire manufacturer’s recommended level, the system automatically routes air supply to a control box and then into the axle.

The air is then distributed to each tire, helping to extend tire life and allowing for more even wear and maximized recap potential.

Meritor started distributing the product to trailer original equipment manufacturers in March.

The Wheat Pool’s B-trains are fitted after delivery with the Redline-Eltek tire-pressure control system provided by TPC International of Edmonton. “That system is instrumental to the whole idea of reducing wear and tear on the roadway and allowing us to run at these proposed weights,” Trenton Baisley emphasizes. It allows for a larger footprint on the secondary roads or when the vehicle is running empty, he says, spreading the weight over a larger area of the road.

And most importantly, it’s a softer footprint that “embraces” the road surface rather than attacking it as a firm, fully inflated tire would.

“This installation for the Wheat Pool is an off-the-shelf product that we’ve been manufacturing and marketing for about eight years,” says Brian Spreen, president of TPC International. “We sold quite a few for forestry-related applications during that time.”

The Redline-Eltek system integrates with the vehicle’s existing air supply that feeds the air brakes, and basically consists of five component assemblies: an in-cab computer that lets the driver change pressures and warns of any problems; air priority valves that protect air-brake system integrity; control air valves; air lines to and from the control valves; and axle-end rotary-union hardware to transmit air into and out of the rotating tires.

“The driver selects the appropriate setting from the four buttons on his dashboard module-highway/loaded, highway/unloaded, off-highway/loaded, and off-highway/unloaded-and that sends a signal to open either the ‘inflate’ or ‘deflate’ control valve,” Spreen explains. “Air from the wet tank is then drawn into the tire-pressure control system to inflate the tires; if partial deflation is chosen, that air is exhausted through the deflate valves.”

For the purposes of the Wheat Pool applications, travel on secondary roads will equate to the “off-highway” control setting.

“The system also monitors vehicle speed, since there are maximum limits for the off-highway settings,” Spreen says. “And there are safety features: if the driver forgets to select pressure ‘up’ when he gets onto a primary highway, for example, the system will automatically do that once he exceeds a certain speed.”

Asked if running on partially deflated tires might have a harmful effect on tire life-notwithstanding benefits to the road surface-Spreen explains that there’s no problem at all as long as the appropriate vehicle condition (unloaded, and/or modest speed) is in effect.

“It’s all based on tire deflection: the change in tire cross-section height from its freestanding status at full inflation to the loaded height,” he says.

“You can use half the tire pressure on an empty vehicle that you’d use on a loaded one and not hurt the tire, because you’re still operating with the proper deflection range for the tire. The same effect applies if you reduce speed.”

The specific inflation settings for the Wheat Pool rigs are as follows (read the set points as highway-loaded/highway unloaded/secondary-highway-loaded/ secondary-highway-unloaded): steer-axles: 100 psi at all times; drive axles: 100/45/65/30; trailer axles: 85/40/60/30. Max speeds for primary highways are the posted speed limit; for secondary highways it’s 80 km/h, loaded or unloaded.

“These vehicles will mean a lot for our customers,” Trenton Baisley observes, “and in the near future they’ll become even more sophisticated: we’re planning on incorporating a GPS-based communications system that could precisely determine vehicle location and ensure that the proper tire-inflation level is set.

“This system could also provide a data file to the department of highways that would confirm weights, speeds, tire pressures, and routing, so enforcement could adequately be administered.” It’s no surprise, then, that the Wheat Pool’s trailers have drawn a lot of interest from other jurisdictions, and will be on display at the Sixth World Congress on Intelligent Transportation Systems in Toronto this coming November.

Eaton’s Schultz sees the day coming soon when the inflation system’s computer will automatically alert the fleet manager to a tire problem, so he can instruct the driver where to have it repaired. “Tire repairs,” he says, “can thus become pit stops.” ___

FOR MORE INFO

* TPC International, Edmonton, 888/338-3587; www.tirepressurecontrol.com * Meritor Automotive Heavy Vehicle Systems, Troy, Mich., 800/535-5560; www.meritorauto.com * Pressure Systems International, San Antonio, Tex., 800/375-6464 * Eaton Corp. Truck Components, Kalamazoo, Mich., 800/826-4357; www.roadranger.com * Vigia, Toronto, 888/438-8444. u TMS-Bandag, Muscatine, Iowa, 800/548-9721, www.bandag.com