ENGINEER FRANK DRAKE believes that as trailers evolve into multi-purpose vehicles, it is even more important that there is a standard to define the minimum requirements for critical trailer components, allowing them to be evaluated without bias.
A standard provides a way for industry to have assurance the products they specify, buy, build, and sell adhere to minimum requirements as established by unbiased professionals, he said. As capacities of trailers increase and more burden is put onto individual components, it is important that there is a standard to ensure consistent performance of the components.
“It levels the playing field so everybody is testing the same,” said Drake, director of heavy-duty product engineering for Cequent Performance Products.
With that in mind, Drake went over three key standards or informational reports in his NATM convention presentation, “Jack and Coupler Standards Made Simple.”
The first one, Society of Automotive Engineers (SAE) J2638, is an informational report dealing with fifthwheel and gooseneck trailer attachment at or below 30,000 lb Gross Trailer Weight (GTW) and of components necessary to tow these trailers. He said it likely will become a recommended practice later this year, and regulatory authorities may use this standard to formulate regulations.
The scope is to establish a minimum performance criterion for the towing interface between the tow vehicle and fifthwheel or gooseneck trailers at or below 30,000 lb GTW.
He said the test requirements included an adjustment that must be at maximum stress position and a single sample that must pass three directional dynamic tests, with 300,000 cycles in each direction and 900,000 cycles total.
For a gooseneck, the performance requirements for static test loads include: vertical, 85% of the gross trailer weight (GTW) in compression and half the GTW in tension; longitudinal, 75% of the GTW in compression and tension; transverse, 30% of the GTW right and left.
For a fifthwheel: 8000 lb plus 45% of the GTW in compression and 50% in tension; longitudinal, 110% of the GTW in compression and 75% in tension; transverse, 30% right and left.
For example, for a 20,000-lb GVW trailer with a specified vertical rating of 5000 lb, the vertical would have 17,000 lb compression and 10,000 lb tension; the longitudinal would have 15,000 lb compression and tension; and the transverse would have 6000 lb right and left.
“These are the loads the coupler has to withstand statically,” he said. “In other words, you put that load on there and the coupler has to resist it.”
For a gooseneck, the performance requirements for dynamic test loads include: vertical, a rated vertical coupler load compression plus or minus 1000 lb plus 15% of the GTW; longitudinal, plus or minus 3250 lb plus 2% of the GTW; transverse, plus or minus 1000 lb plus 4% of the GTW.
For a fifthwheel: vertical, a rated vertical coupler load of plus or minus 1200 lb plus 11% of the GTW; longitudinal, plus or minus 1000 lb plus 8% of the GTW; and transverse, plus or minus 550 lb plus 6% of the GTW.
The static performance criteria include no loss of attachment and a load that must be maintained for five seconds. The dynamic performance criteria include no loss of attachment, a load maintained throughout the test, and a test specimen that must be able to couple and uncouple after the test.
“Fatigue loads are the tough one to pass,” he said. “The static load is the strength of the components. That's relatively straightforward.”
SAE J684 is a standard that includes couplings, hitches, and safety chains used in conjunction with all types of trailers or towed vehicles whose Gross Vehicle Weight Rating (GVWR) does not exceed 10,000 lb. This includes most types of trailers normally towed by conventional passenger cars, light-duty commercial vehicles, light trucks, and multipurpose passenger vehicles. It is primarily intended for ball-and-socket type couplings and hitches.
He said a weight-distributing hitch is a mechanical device that connects the trailer to the towing vehicle and by means of leverage applied on both trailer and towing vehicle structures, when properly adjusted, distributes the imposed vertical load at the hitch and coupling connection between structures of the towing vehicle and trailer.
A weight-caring hitch is a mechanical and/or structural device that connects the trailer to the towing vehicle, and does not employ features designed to redistribute the load imposed at the hitch and coupling connection.
- Class 1: GVWR not to exceed 2000 lb.
- Class 2: GVWR over 2000 lb and not to exceed 3500 lb.
- Class 3: GVWR over 3500 lb and not to exceed 5000 lb.
- Class 4: GVWR over 5000 lb and not to exceed 10,000 lb.
- Class 5: not currently defined by SAE.
He said couplings must be permanently marked with: SAE classification and trailer GVWR; the intended ball diameter; the style or model number; and the manufacturer's ID.
The balls must be permanently marked with: the intended ball diameter and the SAE classification and trailer GVWR.
The coupling attachment must safely withstand the following static test loads: 1½ times the maximum trailer GVWR in longitudinal tension and compression; half the maximum trailer GVWR in transverse thrust; half the maximum trailer GVWR in vertical tension and compression.
“These are not pullout loads,” he said. “It's how good the attachment has to be behind the coupling device. Usually, that's not an issue.”
With the safety chain installation, two are required, one on each side, with minimal slack. They must be crossed under the tongue and cannot be secured with the same fastener as the ball.
“I don't know how you would do that anyway,” Drake said, “but that's what the standard says.”
Each individual safety chain (two are required) and attachment must meet these minimum breaking forces: 2000 lb for Class 1, 3500 lb for Class 2, 5000 lb for Class 3 and equal to GVWR for Class 4.
Hitches must be permanently marked with: the maximum trailer GVWR to be drawn; the intended ball diameter; style or model number; manufacturer's ID; and maximum vertical tongue weight allowed.
In the minimum strength test for hitches, the forces must be applied in any sequence as follows: apply the specified downward vertical force concurrently with the specified compressive longitudinal force or spring bar moment; apply the specified tensile or compressive longitudinal force concurrently with the specified downward vertical force; apply the specified transverse force; for hitches with weight-distributing capability, apply the specified spring bar or leveling moment (leveling force couple) concurrently with the specified downward vertical force.
All forces are to be applied among an axis that intersects the center of the ball. All forces are to be applied with an onset rate of not more than 0.667 kN/s (150 lb/s) and maintained at the maximum specified force level for at least five seconds.
This is a standard designed by the American Society of Agricultural & Biological Engineers (ASABE) to define terms, establish test procedures, and create minimum performance requirements for telescopic mechanical screw-type jacks.
It applies to telescopic mechanical-screw type implement-mounted jacks. These jacks are used specifically for supporting hitch points of towed implements during storage, lifting and lowering of implement tongues to facilitate attaching to or disconnecting from a tractor, and leveling of machinery for stationary use.
Drake gave these key definitions:
- Static compressive load: Vertical force used to support the intended application under static conditions.
- Dynamic compressive load: Vertical force used to lift the intended application measured during cranking (dynamic) circumstances.
- Side load (fore-aft): Force applied in a direction generally aligning with the towing direction of the towed implement.
- Side load (lateral): Force applied at right angles to the general towing direction of the towed implement.
- Jack cycle: Consists of extending the jack through 65% of the jack screw travel and then retracting the jack back to its original length.
- Crank effort: During the jack cycle, the crank effort shall not exceed 225 N (50 lb) while the jack is loaded to its rated dynamic compressive load capacity.
- Over travel: The jack shall be fitted with sufficient means to withstand the applied force (1½ times) that is required to lift the Dynamic Compressive Load when attempting to extend or retract beyond the intended screw travel.
- Service life: The service life (often referred to as cycle life) for the jack shall be greater than 250 jack cycles.
- Rated static compressive load capacity: Often referred to as static capacity, it shall not exceed one-half that of the static compressive load sufficient to cause catastrophic failure.
- Rated dynamic compressive load capacity: Often referred to as lift capacity, it shall not exceed the largest dynamic compressive load that the jack will repeatedly lift and meet all requirements of the standard.
- Rated static side load capacity: It shall not exceed one-half that of the static side load sufficient to cause catastrophic failure.
- Corrosion protection: The jack must not experience a functional failure after a 48-hour salt spray exposure per ASTM B-117. “It doesn't mean that it looks nice,” he said. “It means it has to work. It gives you a clue on how well the jack is sealed off, how the grease is, and what the quality of the parts is.”