The present invention broadly relates to coupling devices for connecting a tractor with at least one trailer in a tracking position for transport of bulky or heavy loads. More specifically a fifth wheel coupling apparatus has a lubricating plate, which is securely retained against rotation by interactive surfaces and against radially outward displacement by compressive or transverse loads.
The trucking industry utilizes motorized transport vehicles for hauling freight, which vehicles or truck rigs frequently are a motorized tractor with one or more trailers in a tracking position behind it. As with most capital equipment, optimal economic benefit from the tractor and trailer is realized by maximum or continuous usage of the equipment. However, truck rig equipment requires substantial maintenance to sustain its operating condition.
Fifth wheels couple and uncouple a trailer from a tractor. Fifth wheel assemblies have a bearing plate surface and a central pocket for mating with a draft member or king pin extending from a trailer bearing plate. The king pin nests in the pocket or draft connection and is retained in the pocket to maintain the trailer in the tracking position. The tractor and trailer bearing plate surfaces react against each other during tractor and trailer coupling especially during travel along a roadway.
The bearing plate interface, or more specifically the respective bearing plate surfaces, are susceptible to abrasion from metal-to-metal contact. Rubbing contact is induced by longitudinal and transverse loads at the interface, but is further aggravated by a lateral twisting motion from cornering and rig motion as the rig traverses the road. The lateral twisting motion or pitch may induce wear from intermittent loading at diametrically opposed, bearing plate circumference positions above the fifth wheel mounting brackets. A lubricant, which has generally been a viscous grease, is usually applied between the fifth wheel and trailer bearing plate surfaces to reduce frictional wear. However, the grease layer on the fifth wheel plate surface captures particulate matter, which may act as an abrasive, causing more rapid wear and abrasion, and thus a higher repair and replacement rate of the tractor and trailer bearing plates.
As noted, maximum economic benefit of a tractor and trailer rig is derived by nearly continuous utilization of this equipment. However, continuous use of the rig requires an active maintenance program to sustain the rig in operating condition. This maintenance program includes removing the grease layer on the fifth wheel bearing surface along with the entrained grit and particulates. The frequency of maintenance in the trucking industry has not generally been adequate to minimize the effect of the abrasive materials captured between the respective tractor and trailer bearing plates, which results in lower useful life for these plates as well as more frequent repair or replacement Cleaning the fifth wheel top bearing plates of the grease and particulate matter is usually accomplished by high-pressure steam or application of organic solvents. This flushes the grease into a sewer system and discharge into a waterway, or onto the ground where it is considered an undesirable environmental element as it may leach into and contaminate an aquifer. The necessity or benefit of a lubricating barrier between the opposed bearing plates is so readily apparent that manufacturers provide automatic greasing systems and grease grooves in the tractor bearing plate in an attempt to maintain at least a minimum grease barrier at this interface. However, providing a fresh grease layer or grease addition without purging the extant contaminated grease is not adequate to provide the requisite lubrication for bearing plates.
The desire to overcome or replace the use of grease on the bearing plates has been encouraged by a requirement from the EPA and its affiliated regulatory agencies for the handling and disposal of such materials. Consequently, the trucking industry is continually seeking environmentally acceptable means to overcome wear, erosion, and abrasion between the bearing plates while continuing to provide an adequate lubricant barrier between these abrasive and frictionally engaged surfaces. The acceptable lubricant barrier must accommodate the longitudinal, transverse and pitching motions of the trailer and tractor during transport. Earlier efforts to overcome the utilization of a grease barrier or lubricant between the opposed and contacting bearing plates incorporated a liner or liner layer of low friction material positioned on the fifth wheel or trailer bearing plate to obviate the requirement for thoroughly greasing the surfaces of the bearing plates. These earlier low frictional materials between opposed bearing plates were generally soft, easily damaged or scuffed and consequently, have an inherently short useful life span. In addition, the soft material liners were susceptible to lateral or radial displacement at the bearing plate perimeter; and, they were subject to displacement by the rotational forces applied between the tractor and trailer bearing plates, as well as by a longitudinal force of the trailer during coupling.