Land vehicles – Wheeled – Running gear
Patent
1993-04-23
1995-12-19
Tyson, Karin L.
Land vehicles
Wheeled
Running gear
298 22R, 296182, 280688, 180 2408, B62D 2100, B62D 6100
Patent
active
054762855
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to suspension systems and configurations for the main structural components of very large trucks of the type used in mining operations.
BACKGROUND OF THE INVENTION
There is much commonality between currently available large mining trucks made by different manufacturers and the following observations are generally applicable regardless of the truck manufacturer:
The empty vehicle weight is a high proportion of the maximum gross vehicle weight. Typically the ratio of payload to empty vehicle weight is only about 1.4:1. This means that much of the cost of operating such trucks is related to moving the empty vehicle weight rather than the payload.
The total width of the four rear tires is large compared to the total width of the truck. Typically 65% of the total width of a truck is taken up by the four rear tires. With present designs of truck this leads to a very narrow main frame for the truck and very high bending loads on the rear axle and rear wheel support systems. The narrow main frame causes shortage of space for maintenance of some components, high stress changes during cornering maneuvers, the need for vertically stiff rear suspension springs and design restrictions on the body. The net effect is high weight and cost for the main frame, the rear axle, the rear wheel support assemblies and the body.
The travel of the rear suspension system of a fully loaded truck is very limited compared to the scale of the truck. Typically the maximum travel in the compression direction of the rear axle relative to the main frame is only of the order of 50 mm when loaded. This limited travel is a result of the need to achieve adequate roll stiflenets from the two narrowly spaced rear spring units.
The main frames of these trucks are complex welded steel structures that are heavy (e.g. 16.5 tons for the main frame of a truck with a payload rating of 172 tons), expensive to design, develop and manufacture, and prone to fatigue cracking.
The main load carrying member (the body) of the trucks is a very strong and generally stiff member. This strength and stiffness is a consequence of the need for the body to withstand the shock loads applied during loading of large rocks by large excavators.
The body is generally supported from the main frame of the truck at numerous points. For example at the rear pivot points, at two, four, six or eight points along the underside of the body and in some trucks also at forward extensions of the body which contact the main frame at points which are close to being above the line of the front wheels. This system of supporting the stiff body causes high variation of stress levels in the main frame of the truck and the body as the truck traverses over uneven ground. This feature causes fatigue problems, high design and fabricating costs and the need for considerable expenditure to limit the unevenness of the ground on which the trucks travel.
The body is tipped (hoisted) by hydraulic cylinders which react against the main frame of the truck at points near to midway between the front and rear wheels. This causes very large bending loads to be applied to the main frame of the truck and requires that the main frame be very massive at the mid sections. It can also cause large stress changes in the body.
The dual rear tires are rotationally locked together. During short radius turning maneuvers (frequent occurrences in typical mining operations), this causes severe scrubbing type wear of the tires due to the differential travel distance effect. Relative scrubbing between the two tires of a dual set is considered to contribute significantly to total wear of rear tires on large mining trucks.
The combination of four wide tires on a solid beam axle type rear axle causes large variations in individual tire loads as the trucks traverse uneven ground conditions. This arrangement also means that it is necessary to take considerable care in matching tire outside diameters and inflation pressures to minimise the unevenness in tire loads on level ground con
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Derwent Abstract Accession No. B7994/D09.
Patent Abstracts of Japan, M-72, p. 132, JP,A,56-34574.
BHP Australia Coal PTY Ltd A.C.N.
Tyson Karin L.
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