ANGLED PINS combined with an air-assist mechanism that has a parking brake interlock will ensure that pins engage and eliminate slider bending on trailers, Jeff Davis said in the “Trailer Suspension Issues” at the CTEA's Manufacturers' Technical Conference.
Davis, ArvinMeritor's director of sales for trailer products, said damage occurs when locking pins are not engaged, the trailer is operated, and the driver brakes.
“All sliders bend,” he said. “They just bend at different levels. We've tested every single slider available today. They'll bend at between 15 and 21 mph.
“Slider damage is typically the result of high speed impacts, and not a ‘unique’ dynamic event or fatiguing event. No existing pin mechanism or air-assist device affects pin engagement once the vehicle exceeds 4 mph. Above 4 mph, pins on all designs will not engage, resulting in a slider collision with the rear stop bar.
“In severe instances where the speed was high, you can bend a suspension. It's really basic physics. It's all associated with the slide distance and velocity of the vehicle. If the slide distance is six feet, that bogey can reach a maximum velocity of 18.15 mph (and 25.67 mph at 12 feet). In our testing, we discovered that you can build a slider that will withstand levels up to the maximum slide distance. But the net result is you destroy the trailer. And since we knew OEMs and fleets wouldn't be happy if we did that, there had to be another way. How do you prevent this from becoming a problem?”
He said ArvinMeritor had developed a theory that drivers were making mistakes, so the company wanted to understand the severity. It hired a contractor who went out to weigh stations, truck stops, and terminals in North America, taking a survey of 6473 vehicles.
ArvinMeritor discovered that 38 had pins disengaged while the vehicle was in use. (In 85% of those, the driver had released the handle in the intermediate position, so the pins were poised to hit the next hole in the rail.) The net result was .59% of the 6473 vehicles.
“It doesn't seem like much,” Davis said. “When I first looked at it, I thought, ‘This doesn't prove anything. This isn't really a very big issue.’ Then I started looking at it in-depth. The point is, if you have 1000 vehicles in the fleet and an 80% utilization rate — which actually might be low — and 65% are going to be moved today, that means 3.59% are running down road right now in that fleet without pins engaged. If that fleet runs 333 days a year, that means every trailer in the fleet at some point this year will go down the road without pins engaged. And that's a problem. There's not only damage and maintenance costs, but also safety at risk here.”
He said angled locking pins prevent slider impacts when the slider pull handle is released. The pins will engage in the first hole every time.
The handle was released in over 85% of buckling incidents. He said if the operator forgets to release the handle, angled pins alone will not prevent a slider impact.
“Combining angled pins with an air-assist mechanism that has a parking brake interlock ensures pins engage and eliminates slider bending,” he said.
He said ThermAlert, a wheel-end temperature sensor, and SimilAir, a composite spring for 22,400-lb axle ratings, are two proven ways to increase safety.
ThermAlert, a value-added option of the Meritor Tire Inflation System, alerts drivers to stop for repairs before serious damage occurs due to elevated wheel-end temperatures.
If the temperature of the wheel end approaches a critical state, the thermal screw will melt, pressurized air will vent through the hubcap tee vent, the indicator light will come on, and an audible sound will occur at the wheel end. The components that caused the high temperatures are then inspected and repaired before the trailer is returned to service.
Davis said SimilAir is a direct replacement for a steel spring and compares favorably to air ride and steel mechanical suspensions. It is paired with Meritor axle and a standard mechanical suspension from Holland, Hutch, or Reyco.
He said data from CK Marketing and Communications, which interviewed 60 fleets, indicates they had an average of 2.8 wheel-end failures per year, two wheel losses, and 1.4 trailer fires.
“What was the economic cost?” he said. “$23,000 for fires and $1300 for wheel loss. But the cost can be far greater than fixing a piece of equipment. You can end up with all kinds of liability issues.”
Proper use of components
Dana's Randy Billian said components should be used as intended.
“You can't fool steel,” he said. “There are limits to it. Keep everybody informed.”
His other tips:
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Know your customer's specifications. “A lot of times, it's helpful to call a customer and get him involved when you're dealing with setting things up.”
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Communicate your customer's needs to Dana. “Sometimes, a customer may ask you for something you don't know about, something new we're introducing in the field. So give us a call and let us get involved.”
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Use suppliers to manage product complexity. “We try to be as nimble as possible and have products available, but we also have lead times.”
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Brakes. “In the trailer market, we change linings. If you have a trailer that has only 20,000 pounds on the axle, you do not want to specify the 25,000-pound lining. You'll tend to get a noisy lining when you over-spec components.”
Speaking about vehicle integration, he said there are three widths for slider boxes: 42" for 71.5" track, 48" for 77.5" track, and 54" for 83.5" track. In body rail compatibility, he said there are three body rails: Hutch, Binkley, and TTMA.
He said that with S cam brake, there is the option of a single or double anchor pin, and a trailer style or truck style.
Spec'ing
Hendrickson's Alain Lamothe said spec'ing isn't rocket science, but it still requires a degree of care.
“A lot of end users want a trailer and they want it now,” he said, “and they want to pick whatever you've got. We need to do a better job from the sales side to let them know it doesn't work that way. You need to find out where he's going to be using it and what he really needs. Some people want it as light as possible. That may save on the suspension, but what does that really mean? Can you put more on the trailer? If you can't, maybe you should go heavier. At the end of the day, they're going to pay more for a lighter suspension and they're not going to get any benefit out of it.
“There are a lot of little things that the end user doesn't seem to get. It's all education. It's trying to work with our customers to know what they need. What they think they need and what they need are not always the same thing.
“If you can take all the components and design them together, you usually come up with a better design overall. Everything's working together, as opposed to picking this off the shelf and that off the shelf.”
He said that once a spring ride suspension is fully loaded, “it probably rides as well as air ride. The problem comes when it's not loaded. With air ride, you have a fixed ladder on the axle that does all the work. The nice thing about it is you can change the pressure. As you add load to it, the pressure goes up and the spring rate changes, so it gives you a good ride all the time.
“When we rate them, we assume the trailer's on a nice, even surface. Driving around, that doesn't happen often. So once you go into dynamic loading, it makes a big difference. You need to know what's going on, what you're going to do with that trailer.”
Spring brakes
Fuwa US's Jules Guillemette said installers and designers should always explore all the alternatives because there are several lift mechanisms available that may work for a particular installation.
“There are also different spring brake locations that can be achieved when your application allows,” he said. “Analyze your requirements, discuss it with your suppliers, and decide on the best solution.
“If your application allows, a different suspension may provide clearance to locate the spring brake behind the axle. In some cases, the spring brake can be installed in the vertical position. Always verify the brake geometry and make adjustments as required.
“Spring brakes can be installed with suspensions that use a forward lift system. There are several types of lift systems available. SSA can mount spring brakes in a number of positions. Long stroke spring brakes are not always required. Consulting your suppliers will help decide which solution will work best for you.”