Outside Frame Avoids Side Underride

Feb. 1, 2000
In Europe, most trucks and trailers are required to have side guards to keep pedestrians and bicyclists out from under the wheeels. However, these lightly

In Europe, most trucks and trailers are required to have side guards to keep pedestrians and bicyclists out from under the wheeels. However, these lightly constructed side guards cannot deflect an auto. Side underride is a problem.

The new Safe Liner semitrailer from Krone prevents side underride and rear underride in accidents with motorcycles and automobiles as well as pedestrians and bicyclists.

Most European semitrailers are platforms or platforms with soft-side van body (curtainsider or dropside with fitted tarpaulin body). Therefore, they have I-beam frame rails under the floor. The Krone solution is to move the longitudinal frame rails from between the wheels to the outside.

The Safe Liner outer frame is not constructed as an I-beam. It is more of a truss frame with rectangular openings to provide underbody access. Three of the openings are to compartments for storage of pallets or other cargo. The other three openings provide access to the three wheels on each side.

Krone calls its new frame concept "Plankenrahmen" (guard rail frame) because it acts as a "Leitplanke" (guard rail) on the side of the trailer. With it comes a catchy new phrase to sell the concept: "Danke, Planke!" (thanks to the planks) that guard the side of the trailer.

Fuel Savings Fully enclosing the underside of a semitrailer has other advantages, as truckers have experienced with fully skirted trailers. Splash and spray are reduced, and there is less road noise, says Dr Bernard Krone, CEO of Bernard Krone GmbH in Werlte, Germany.

Fuel consumption is reduced. According to early test track reports, the tractor-semitrailer combination would use l.4 liter (.37 gallon) less fuel in 100 kilometers (62 miles). This translates into a fuel saving of about .006 miles per gallon, or 600 gallons in a typical year of 100,000 miles traveled. Fuel savings are much more important in Europe, where fuel costs three or four times as much as in the United States.

Aerodynamics of the trailer are greatly improved because the sidewalls are completely smooth down to within 270 mm (10 1\2") of the ground. Also, the trailer is completely smooth on the underside of the belly boxes. This tends to reduce splash and spray generation. Drivers say there is much less wind buffeting of the trailer.

Crash Testing The biggest advantage, of course, is the safety improvement. Crash tests were conducted at the DEKRA Center for Accident Research in Neumunster. A VW Golf (Rabbit) was crashed into the side of the Safe Liner, approaching at a 30 degrees angle at a speed of 60 km/h (37 mph). The VW experienced serious front end damage but scarcely scratched the side frame of the trailer and only dented the pallet box cover.

A Ford Escort was crashed into the rear of the trailer at a test speed of 50 km/h (31 mph). There was extensive damage to the front of the auto, but the windshield was unbroken. Damage to the trailer was to the sheet metal skirt covering the rear underride guard.

A MAN cabover truck at 30 km/h (19 mph) was crashed into the rear of the trailer, damaging the rear skirt and rear doors of the trailer. The cab of the MAN truck was damaged but survivable for the driver.

Testing Size Regs Two of the first Safe Liner prototypes made a big splash in the European press when they were driven to Bonn to visit Chancellor Gerhard Schroder and the parliament in June 1999, while the German government was still headquartered there. Chancellor Schroder was pictured in the driver's seat and also inside the van watching films taken at the test track. It was good press and it was good politics.

One of the prototypes shown to the Chancellor and members of the Bundestag was proposed as the "trailer of the future". It was 15.65 meters (51 feet) long, about two meters (seven feet) longer than the present maximum length in Europe. To comply with the turning circle requirements, the rear axle of the three-axle trailer was self-steering.

In other words, the extra length would be the payoff and the inducement to truckers for investing in new trailers having greater safety benefit, as well as better economy and environmental impact.The proposed 51-ft trailer would have 38 pallet positions, compared to the present 34-pallet trailer, a 12% improvement.

Dr Krone maintains that the Safe Liner is not necessarily more expensive. He says his company can manufacture the outside-frame platforms and sell them at the same price as the present centerframe platforms. Another advantage is that the outside-frame platform can weigh 5% to 10% less than the present centerframe platform.Literature on the three-axle Safe Liner lists a tare weight of about 7,080 kilograms (15,600 lb) for a 13.65 m (44 1/2-ft), three-axle curtainside trailer with full skirts and three underbody belly boxes extending all the way across the trailer.

New Air Suspension Because of the full-width crossbeams that create the underbody compartments and because of the close spacing of the three axles, a new air suspension was created for the Safe Liner. Supplied by BPW to a Krone design, the suspension is 100% air sprung. That is, the air bag is directly over the axle instead of on an extended arm, so that 100% of the axle load is transferred directly to the trailer frame.

Besides an air suspension (normal for all trailers in Germany), the Safe Liner has air disc brakes with electronic actuation. Air disc brakes are becoming more standard in Europe even though they cost an additional 600 to 800 DM ($300 to $400). Presently, 25% of the trailers manufactured by Krone have air disc brakes, and that share is expected to rise to 50% in two years. The electronic actuation of the air disc brakes is new but growing steadily with the increasing sales of new truck tractors equipped with electronic braking.

The Safe Liner has accident protection against both rear underride and side underride. To put this into perspective compared to U S trailer regulations, the National Highway Traffic Safety Administration requires that trailers have a rear underride guard with a height of no more than 560 mm (22 inches). No side guards are required.

The Safe Liner, by contrast, has both a rear underride guard and full side guards. The height of the rear underride guard is 370 mm (14 1/2"), and the height of the side guards is 270 mm (10 1/2"). Test track films show that in a turn, this low side guard would push a downed bicyclist out of the way.

Fleet Testing The Safe Liner is built to withstand a force of 50 metric tonnes (110,000 lb) applied to the rear impact guard. The European Union regulations require the rear guard to resist a force of only 10 tonnes (22,000 lb) applied to the middle of the guard and 2.5 tonnes (5,500 lb) applied to either side of the rear guard.

In the U S, the NHTSA regulations require a force of 11,240 lb to be applied at the sides or middle of the guard, or a force of 22,480 lb applied at the vertical framing supports. The U S rules require energy absorption, so that the guard impact face moves forward at the rate of about 0.05" per second, and total guard displacement is about 5" forward.

The Safe Liner principle of using outside frame members to act as guard rails was the idea of a safety researcher who has spent a lifetime analyzing vehicle accidents. Dr Karl-Heinz Schimmelpfennig of the engineering firm of Schimmelpfennig and Becke in nearby Munster came up with the concept for the integral safety guard frame and worked with Krone engineers in developing a practical truck trailer with this passive safety restraint.

Since last summer, Krone has had five Safe Liners on the road undergoing fleet testing by customers. These outside frame trailers have accumulated 120,000 to 160,000 km (75,000 to 100,000 miles). Another 65 Safe Liners were built in the last half of 1999. Problems have been minimal, Dr Krone says, and fleets are accepting the new concept. Current production is at the rate of two Safe Liners per day (5% of the current production rate of 40 trailers per day). Krone plans to expand this to six per day (15% of daily production) by midyear.

The special 38-pallet trailer l5.65-meter (51 feet) that was shown to Chancellor Schroder in June received a good reception in other countries as well. Fleets in Sweden are very interested in the increased productivity. In the Netherlands, a five-truck test under government supervision will investigate whether the longer semitrailer and heavier GVW (60 metric tonnes or 132,000 lb) will actually reduce the number of trucks on the road.

Whatever the outcome of the fleet testing of this 38-pallet Safe Liner, the standard-size 34-pallet Safe Liner is already being accepted as a safer vehicle that offers more protection for other road users, including cyclists and pedestrians.

About the Author

Paul Schenck | Senior Editor