The present disclosure is generally directed to a paving machine and, more particularly, to selective control of a tow point for a screed of a paving machine.
“Floating screed” asphalt finishing machines, or pavers, have provided an efficient and economical method of coating an old or new roadway with a compacted layer of asphalt aggregate for many years. Floating screed pavers are generally known to those skilled in the art, as reflected by the disclosure contained in U.K. Patent 1,054,151 to the Blaw-Knox Company. Such a paver typically comprises a self-propelled traction unit, or tractor, having a hopper at its front end for receiving paving material, such as asphalt aggregate, from a dump truck. A conveyor system on the machine transfers the paving material from the hopper rearwardly for distribution in front of a floating screed. Transversely arranged screw augers positioned at the rear end of the traction unit assist in moving the paving material in a lateral direction with respect to the direction of movement of the paver, so that a relatively uniform volume of paving material is distributed across the portion of the roadbed in front of the floating screed.
The screed is commonly operated so as to “float” by virtue of being connected to the forwardly moving machine by means of pivoted leveling arms or tow arms. With forward movement, the screed physically levels any paving material lying higher than a predetermined height above the roadway surface, leaving a generally uniform thickness of such material. This function is enhanced by inclining the bottom surface of the screed so that its forward edge is higher than its rear edge, thereby providing a smaller area between the screed and the roadway and a large dragging surface at the rear of the screed. The angle defined between the bottom surface of the screed and the roadway surface is called the “angle of attack.” The screed also compacts the dragged paving material in order to provide a uniform, smooth, durable pavement surface. The screed is often mounted to vibrate against the pavement material to assist in spreading and compacting the material.
The leveling arms of the screed are attached to the paver traction unit at a “tow point.” In early pavers this point was a simple fixed pin connection. As a result, the thickness of the resulting paved mat could only be controlled by means of altering the screed angle of attack. Later paver designs allowed the tow point to be moved vertically using a tow point adjuster, causing a corresponding movement in the leveling arms and screed. This arrangement accommodated changes in the grade of the road surface by automatically fine tuning the initial setting of the screed angle of attack, thereby controlling the pavement mat thickness.
The screed has numerous controls that affect the temperature of the heater, the thickness of the mat, the shape of the edges, contours, etc. In an automatic mode, sensors are used to automatically adjust the screed for some or all of these settings. However, in a manual mode, an operator can control these aspects of the screed.
When in the manual state, there is no grade or slope automation system in use. Instead, an operator manually adjusts the tow point of the screed to create the desired mat profile. In order to have precise control, the tow point adjustment moves relatively slowly. That is, movement of the tow point operates at a fixed, slow rate either up or down to give the operator fine control of the mat profile. However, when creating an obstacle, such as a speed bump, or preparing the machine for transport, the fixed, slow speed can cause delays.
With respect to paving machine controls, U.S. Publication 2014/0186115 (the '115 publication) discloses linking different controls so that, for example, a change in screed height automatically increases auger height. The '115 publication fails to address problems related to the slow tow point adjustment speed in manual operation mode.
In an aspect of the disclosure, a tow point adjustment system for a screed of an asphalt paving machine includes a first user interface that receives a selection of a high set point speed at or below a maximum tow point adjuster speed and above an operating speed. The system may also include a second user interface that sends a signal to alter a height of a tow point and a controller coupled to the first user interface and the second user interface. The controller may be configured to receive the signal from the second user interface and alter the height of the tow point at one of the operating speed or the high set point speed.
In another aspect of the disclosure, a method of adjusting a height of a tow point of a screed of an asphalt paving machine includes receiving, at a controller, a signal to alter the height of the tow point, selecting, at the controller, a speed for adjusting the height of the tow point from a plurality of predetermined speeds, and adjusting, via the controller, the height of the tow point at the selected speed.
In yet another embodiment, a method of adjusting a height of a tow point of a screed of an asphalt paving machine includes setting a high speed and a low speed for a tow point adjuster, receiving, at a controller, a signal to adjust the height of the tow point, and selecting, via the controller, one of the high speed and the low speed for the tow point adjuster. The method may conclude by setting, via the controller, the height of the tow point using the selected one of the high speed or the low speed.
These and other aspects and features will be more readily understood when reading the following detailed description when taken in conjunction with the accompanying drawings.
Referring to
In manual operation, the tow point adjuster 106 may be controlled by an operator. As discussed above, it may be desirable for the tow point adjuster 106 to move fairly slowly so that the operator can make fine adjustments as the asphalt mat is laid down. However, when making an obstacle, such as a speed bump, or when moving the screed 102 into a transport position, the slow pace of movement of the tow point adjuster 106 may be a nuisance or even a hindrance. In an embodiment, the user interfaces 108, 110 may include additional controls that allow various settings related to speed control of the tow point adjuster 106.
One element of a tow point adjuster speed control is illustrated in
A selector 128 allows setting either the low set point speed 134 or the high set point speed 136 by successively pressing the selector 128. Once either set point 134 or 136 is selected, an increase button 130 and a decrease button 132 may be used to move the selected set point to the desired setting. The low set point speed 134 may set at or above the minimum speed 124. The high set point speed 136 may be set at or below the maximum speed 126 and above the low set point speed 134. In operation, the user interface described below with respect to
A proportional control 150 is illustrated in
Another control 160 for moving the tow point adjuster 106 is shown in
A block diagram of a controller 112 is depicted in
Also connected to the data bus 204 may be input devices coupled to external sensors and user interfaces. A first input 206 may be coupled to a first user interface element 120. Another input 208 may be coupled to a speed selector switch 142 allowing selection between fast and slow speeds, while additional inputs 210 and 212 may be coupled to up button 144 and down button 146, respectively.
In embodiments so equipped, another input 214 may be coupled to a proportional input device such as proportional control 150. In an embodiment, the input 214 may have an analog input capable of processing either a current signal or an analog voltage signal. In an embodiment, all user interface elements may be coupled to the controller via a single user interface device, such as a touch screen display (not depicted).
An output 216 may drive the tow point adjuster 106. In various embodiments, the output 216 may control a hydraulic valve or an electric motor drive.
The memory 202 may contain programs and settings that cause the processor 200 to perform various functions. The memory 202 may include an operating system 218 supporting core functions of the controller 112 as well as utilities 220 that may include calibration and diagnostic functions. Speed settings 222 may include data related to minimum and maximum tow point adjuster speeds, low and high set point speeds, and transfer functions such as those discussed above with respect to
In general, the present disclosure can find industrial applicability in a number of different settings. For example, the present disclosure may be employed in both wheel and track-based asphalt paving machines. Such machines may be used in a variety of applications, such as, but not limited to those used in the construction industry.
A flowchart of a method 300 of adjusting a height of a tow point 114 of a screed 102 of an asphalt paving machine 100 is illustrated at
In one embodiment, the method 300 may continue at block 304 where a speed for the tow point adjuster 106 is selected using a switch 142. At block 306, either button 144 or button 146 may be selected to raise or lower the tow point 114 at the speed selected at block 304.
In another embodiment, the method 300 may follow from block 302, if used, to block 308 to implement speed control based on selection of an up button 162 or down button 164 as illustrated in
In yet another embodiment of method 300, execution follows block 302, if used, at block 310 so that the tow point adjuster 106 is moved at a speed proportional to a distance of a lever or slider 154 from a neutral position 156. That is, the farther the slider 154 is moved away from the neutral position, the faster the tow point 114 is moved by the tow point adjuster 106. The speed may cap at either the high set point speed 168 or at the maximum possible speed, based on a configuration of the machine 100.
The ability to change the speed of the tow point adjuster 106 benefits owners and operators of paving machines for several reasons. Paving operations may be completed more quickly for paving operations such as formation of speed bumps. Similarly, preparing the paving machine 100 for transport may be accomplished more quickly, saving time and money. Operators benefit from the ability to change the tow point adjuster speed simply because an operator is simply able to reduce the time spent waiting for these operations to complete.
While the above discussion has been directed to a particular type of vehicle, the techniques described above have application to many other machines.
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