CONTROL GP-TRANSMISSION 1068984 - Caterpillar

Changes in Forward speed of the Paver
The density of material in the strike-off zone provided by the compacting action of the screed varies as the machine forward speed varies. The given number of blows (impacts) delivered to a given area or quantity of material is dependent on the speed at which the screed strikes off and passes over the mix.When the paver slows, there is more compaction and the screed rises. When the paver speeds up, there is less compaction and the screed lowers.To meet varying desired production rates and different pavement thicknesses and widths, a paver must be capable of operating at different speeds. However, UNCONTROLLED speed variations must be avoided to obtain optimum performance of the floating screed.Changes in Screw Action
As the distributing screw operates to move the paving material from the center portion to the outer edges of the screed, the material exerts force on the deflector plate through the material. Remember, these forces change with the level of material in the screw chamber. Because variations affect pressures applied against the screed and material density, the screw should be operated with as few interruptions as possible to insure optimum stability and a smooth mat.Screed Compacting Process
In addition to the strike-off and leveling function, the screed also compacts the paving material in the strike off zone and under the screed plate. Along with paving speed and material quantities, the weight of the screed and the amount and type of compacting energy generated at the screed affect compaction.The key elements to remember in considering compaction during strike-off and leveling is that the material should be compacted uniformly, in the direction of the paving and also across the mat. Uniform compaction is important for two reasons:1. To achieve optimum leveling with the floating screed.2. To make sure that the subsequent rolling will not cause permanent distortion of the mat surface.Uniform mix consolidation combined with precise control of paving speed and material distribution results in a smooth and uniformly-compact pavement.Automatic Control Systems
There are various kinds of automatic control systems. When using an automatic control system, the screed follows a path parallel to an external profile grade reference. A desired transverse slope is established regardless of disturbances from the tow points or the screed itself. In these systems, the grade is controlled by a grade sensor. The sensor takes sensings from a leveler or other grade reference.Transverse slope is controlled with gravity-oriented sensings taken from a beam transversely connecting the two leveling arms.The floating screed tends to follow the path of the tow points. The automatic leveling control systems make the screed movement independent of undesirable vertical motions of the tractor as it moves over the surface to be paved. The automatic controls adjust the tow points so the screed, and therefore the pavement surface, traces a path parallel to grade and slope references instead of the vertical motions of the tractor.Sensor Location
Location of grade and slope sensors is an important consideration in obtaining automatic leveling systems.Before selecting the sensor