In mining and construction environments, off-highway trucks are used to haul a variety of different materials such as, for example, coal, rock, ore and overburden materials (i.e. the material overlying ore/coal deposits). Such off-highway trucks generally comprise a truck chassis or frame, which supports a truck body for receiving and carrying a load.
The carrying capacity of a truck is defined by two parameters: the weight or load carrying capacity of the truck and the volumetric carrying capacity of the truck body. These two parameters must be synchronized with the density of the material to be carried by the truck to ensure that the truck is properly utilized. If not, the truck can be operating either under capacity, i.e. short in payload, or over capacity, i.e. with a heavier than desired payload.
The truck manufacturer defines the weight carrying capacity of an off-highway truck. For a given haulage application, dividing the truck weight carrying capacity by the density of the material to be carried yields the required optimal volumetric carrying capacity for the truck body in that application.
Presently, off-highway truck manufacturers provide a volumetric capacity rating for their truck bodies that is presently based on the Society of Automotive Engineers (SAE) Standard SAE J1363 (January 1985, reaffirmed November 1995) (“the SAE standard”). Unfortunately, however, this SAE standard does not provide a very accurate estimate of the actual volumetric carrying capacity of a truck body.
The SAE standard rates the volumetric capacity of a truck body both in struck and heaped volumetric capacities. The sum of its struck volume and its 2:1 heap above the struck volume/struck line is its 2:1 heaped volume. Under the SAE standard, the struck volume of large off-highway truck dump bodies is based on an assumed struck load which extends upward from the rear edge of the floor of the truck body (on open ended truck bodies) at a 1:1 slope (corresponding to a material angle of repose of 45 degrees) to the top edge of the side walls of the body. The heaped volume is based on an assumed load heap defined by the truck body sides and the line defined by the intersection of the rear struck line and the body sides and extends upwards at a 2:1 slope (corresponding to an angle of repose of 26.6 degrees).
There are major dimensional problems with the SAE 2:1 heaped volumetric rating methodology set forth in the SAE standard. First, with respect to the struck volume calculation, there are very few materials that will stand at a 1:1 slope in a static condition let alone in a dynamic condition, i.e. when the truck is moving. Second, the heaped volume calculation is based on a different slope or material angle of repose than is used in calculating the struck volume. Thus, the SAE standard essentially assumes a load that does not have a constant material angle of repose, i.e. a load wherein the angle of repose of the load material at the rear of the truck body changes from 45 degrees to 26.6 degrees above the side walls of the truck body. In the real world, each particular side of a load heap carried in a truck body nearly always has a substantially constant angle of repose. However, it should be noted, that each side of a load heap, i.e. front, back, left and right may not always have the same angle of repose.
The third major problem with the methodology of the SAE standard is that it attempts to define the load heap by a series of four flat planes, which together resemble the roof of a house. In actuality, load heaps carried in truck bodies have a configuration that is more conical in shape.
Accordingly, the methodology of the SAE standard is based on a load model that is different in several critical respects from the actual real world configuration of a load carried by a truck body. As a result, the SAE standard produces a truck body volumetric capacity rating that does not accurately reflect the actual achievable volumetric carrying capacity of a truck body. In fact, the SAE standard consistently overrates the volumetric carrying capacity of a truck body. This is recognized in certain South American countries where the practice is to “de-rate” the SAE standard volumetric capacity of a truck body to 85% of the volumetric rating produced by the SAE standard. This method, however, also provides little more than a rough estimate of the actual volumetric carrying capacity of a truck body.
Since the SAE standard substantially overrates the actual volumetric weight carrying capacity of a truck body, off-highway truck users typically are unable to achieve the full load-carrying capabilities of their truck. Moreover, attempts to match the effective volumetric carrying capacity of a truck body with the materials being hauled and the weight carrying capacity of the truck so as to achieve full payload utilization of the truck amount to little more than guesswork because of the inaccuracy of the SAE standard. Accordingly, a need exists for a method to accurately estimate the effective volumetric carrying capacity of a truck body.