FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to pavement constructing machines, and particularly roller compactors.

BACKGROUND

[0002] Roller compactors are used to compact a variety of substrates, from soil to asphalt. Asphalt compaction has many unique requirements that distinguish asphalt compaction from compaction of other substrates, such as soil. Most notably, in the art of asphalt compaction it is more important that the resulting paved surface be smoother than soil compaction.

Additionally, soil compactors often include a single compacting drum and are propelled by tires. If used for asphalt compaction, these tires may leave unacceptable imprints in the paved surface. Furthermore, the compacting drums of soil compactors are less constrained. In some instances, protrusions or feet are used that extend from the compaction drum of soil compactors. These feet would be generally unacceptable for compacting asphalt because the feet can cause unwanted indentations in the paved surface. The asphalt compactor is therefore distinct from a compactor intended for use on soil, but the asphalt compactor is not limited solely for use on asphalt. The asphalt compactor could be used for soil compaction or paving tasks with others materials.

[0003] In the art of asphalt paving, a paving machine often begins by depositing paving material, such as asphalt, in a layer known as a mat. When initially deposited by the paving machine, the freshly laid asphalt mat is a relatively loose mixture of gravel in a petroleum- based binder. This loose mixture tends to have a relatively low density, and significant air pockets can occur. If the mat were allowed to harden as initially deposited, the low density mat could be cracked and trampled by heavy vehicle traffic. Additionally, the air pockets are susceptible to water infiltration. The presence of water within the pockets, combined with a few freeze cycles, causes significant damage to the pavement. To address these issues, a roller compactor is often driven over the initially laid asphalt mat.

[0004] The present invention relates to an improved roller compactor.

SUMMARY

[0005] Embodiments of the present disclosure include an asphalt compactor that comprises a drum having a plurality of discrete compacting surfaces and an excitation system for vibrating the drum to generate compaction pulses. Each discrete compacting surface extends substantially from a first distal end of the drum to a second distal end of the drum across substantially a full width of the asphalt compactor.

[0006] Other embodiments of the present disclosure include an asphalt compactor that comprises a drum having a rotational axis and a plurality of discrete compacting surfaces parallel to the rotational axis. The asphalt compactor also includes an excitation system for vibrating the drum to generate compaction pulses. Each discrete compacting surface is planar.

[0007] Yet additional embodiments of the present disclosure include methods of compacting an asphalt mat. The methods include rolling a drum along the asphalt mat, the drum comprising a rotational axis and a plurality of discrete compacting surfaces parallel to the rotational axis. The method also includes vibrating the drum to generate a downward impact compaction pulse each time a bottom one of the plurality of discrete compacting surfaces faces the asphalt mat.

[0008] These and other aspects of the present disclosure will become apparent to those skilled in the art after a reading of the following description of the preferred embodiments, when considered in conjunction with the drawings. It should be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.

DESCRIPTION OF THE DRAWINGS

[0009] Having thus described the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale.

[0010] FIG. 1 shows an asphalt compactor according to embodiments of the present disclosure.

[0011] FIG. 2 shows a longitudinal cross section through a drum of the asphalt compactor.

[0012] FIGs. 3 A and 3B schematically illustrate impact pulses created by an excitation system within each drum according to one embodiment.

[0013] FIG. 4 shows a perspective view of the asphalt compactor of FIG. 1.

[0014] FIG. 5 shows a schematic profile view of a first drum for use in the asphalt compactor according to embodiments of the present disclosure as the drum rolls across a mat. [0015] FIG. 6 shows a schematic profile view of a second drum for use in the asphalt compactor according to embodiments of the present disclosure.

[0016] FIG. 7 shows a schematic of a control system according to embodiments of the present disclosure.

[0017] FIG. 8 shows a schematic profile view of a third drum for use in the asphalt compactor according to embodiments of the present disclosure.

DETAILED DESCRIPTON

[0018] Exemplary embodiments of this disclosure are described below and illustrated in the accompanying figures, in which like numerals refer to like parts throughout the several views. The embodiments described provide examples and should not be interpreted as limiting the scope of the invention. Other embodiments, and modifications and improvements of the described embodiments, will occur to those skilled in the art and all such other embodiments, modifications and improvements are within the scope of the present invention. Features from one embodiment or aspect may be combined with features from any other embodiment or aspect in any appropriate combination. For example, any individual or collective features of method aspects or embodiments may be applied to apparatus, product or component aspects or embodiments and vice versa.

[0019] FIG. 1 shows an asphalt compactor 10 according to one embodiment of the present disclosure. The asphalt compactor 10 is often used to compact pavement materials, such as a freshly laid asphalt mat 11. By following a paving machine and making one or more passes over the asphalt mat 11, the asphalt compactor 10 compacts the mat 11.

[0020] As shown, the asphalt compactor 10 includes a frame 16 and may include a cab 18 for an operator. Also shown, the asphalt compactor 10 of the present embodiment includes a first drum 12 and a second drum 14. According to one aspect of the present embodiment, at least one of the drums 12, 14 is configured to roll the asphalt compactor 10 along the asphalt mat 11. The rate at which the asphalt compactor 10 traverses across the asphalt mat 11 will be referred to as the transverse velocity (v) (FIG. 4) of the asphalt compactor. The asphalt compactor 10 is propelled by a drive system, such as drive system 20, which causes at least one of the drums 12, 14 to rotate about a respective rotational axis X.

[0021] FIG. 2 shows a simplified longitudinal cross section of a drum, for example drum 12, and one example of a possible drive system 20. A drive motor 22, such as, for example, a hydraulic motor or hydraulic motor combined with a gearbox, may be provided to drive the drum 12; however, it is within the scope of the present embodiment to utilize any drive system capable of driving at least one of the drums 12, 14.

[0022] In the present embodiment, the drums 12, 14 are preferably both provided with excitation systems, such as an eccentric system 30, which impart vibration to the drums 12, 14 to increase compaction efficiency. Those of ordinary skill in the art will appreciate that numerous excitation systems are known, and the scope of the present embodiment is not limited to the particular eccentric system 30 illustrated. [0023] While lesser or more complex eccentric systems may be employed within the scope of the present embodiment, for the sake of simplicity and brevity, FIG. 2, shows a relatively simple eccentric system 30 that includes a single rotatable eccentric mass 32, which may, for example, be driven by an eccentric motor 34, such as a hydraulic or electric motor, via a driving shaft 36. Those of ordinary skill in the art will appreciate that the center of mass of the eccentric mass 32 is imbalanced and does not reside on the rotational axis Y about which the eccentric mass 32 rotates. Those of ordinary skill in the art will also appreciate that, for purposes of increasing compaction efficiency, the imbalanced nature of the eccentric mass 32 of each drum 12, 14 imparts vibration to the drums as the eccentric mass rotates about rotational axis Y. Those of ordinary skill in the art will also appreciate that each revolution cycle of the eccentric mass 32 involves a downward impact compaction pulse F _D , which urges the drums 12, 14 downward to assist in compacting asphalt mat 11 as shown in FIG. 3 A. Furthermore, those of ordinary skill in the art will appreciate that each revolution cycle also involves an upward lifting force pulse F _L as shown in FIG. 3B, which urges the drums 12, 14 upward, relative to the occurrence of a downward impact compaction pulse, before the revolution cycle repeats itself.

[0024] Generally, at least three factors work together to influence the pavement surface quality created by asphalt compactors 10 of the type shown in FIG. 1. A first factor is the profile of the drums 12, 14. A second factor is the frequency at which the drums 12, 14 are vibrated. The frequency at which the drums 12, 14 are vibrated may also be referenced as the rotational velocity, or simply the velocity of the eccentric system 30 of the present embodiment (e.g. the rotational velocity of the eccentric mass 32). A third factor is the transverse velocity (v) at which the asphalt compactor 10 rolls across the mat 11. The transverse velocity may be reasonably considered as directly related to the rotational velocity of the drums 12, 14.

[0025] Whereas conventional drums used for asphalt compaction are cylindrical, the drums 12, 14 of the asphalt compactor 10 according to embodiments of the present disclosure are provided with an outer circumferential surface 40 formed with a plurality of discrete compacting surfaces 42. As best seen in FIG. 4, each discrete compacting surface 42 preferably extends substantially the full width of the drum 12 along the rotational axis X. According to an aspect of the present embodiment, the asphalt compactor 10 may have a single front drum 12 and a single rear drum 14, each extending across substantially the entire width of the asphalt compactor.

[0026] As illustrated in FIG. 5, in a first embodiment, each discrete compacting surface 42 may define a plane P. Each plane P is preferably parallel with the rotational axis X of the drums 12, 14 such that a bisector B that extends normal to each plane P may pass through the rotational axis X. Each discrete compacting surface 42 is provided with width W, which is preferably uniform for each of the discrete compacting surfaces 42. The width W may vary according to the diameter of the drums 12 and 14 and the number of discrete compacting surfaces 42.

[0027] In one embodiment, the number of discrete compacting surfaces 42 is defined by the following equation:

Wherein: N is the number of discrete compacting surfaces 42. N is a whole number and is preferably even, which provides rotational symmetry to the drums 12, 14;

W is the width of each discrete compacting surface 42; and

d is the distance between two opposite discrete compacting surfaces 42 along the bisector B.

[0028] In certain embodiments, the number of compacting surfaces 42 may range from about forty and to about two-hundred, preferably, from about eighty to about one-hundred and sixty, for a drum having a diameter of about 1300 mm.

[0029] Similarly, the equation solving for the quantity of discrete compacting surfaces 42 provided above can be solved for the width W of each discrete compacting surface 42 such that:

In certain embodiments, the width W may range from about twenty and to about one-hundred millimeters, preferably from about thirty to about sixty millimeters.

[0030] Within the scope of the present embodiment, the edges 44 between each of the plurality of discrete compacting surfaces 42 may be angular as shown in FIG. 5.

Alternatively, the edge 44 may be curved as shown in FIG. 6. The edges 44 in the

embodiment of FIG. 6 may be, for example, circular segments. In one instance, the edges 44 may have a radius of curvature r _e . Use of edges 44 that are curved may help to avoid a sharp transition between each discrete compacting surface 42. Advantageously, the curved or circular segment edges 44 may limit or prevent tearing the asphalt mat 11 as the drums 12, 14 rotate. [0031] Returning to FIG. 5, when the edges 44 of the circumferential surface 40 are directly facing the asphalt mat 11 a downward impact compaction pulse may produce an indentation within the pavement. Therefore, the excitation system of the asphalt compactor is preferably controlled such that downward impact compaction pulses occur, preferably only when the plane P of a lower most discrete compacting surface 42 is directly facing (e.g. parallel) the asphalt mat 11. For example, in FIG. 5, three positions of the drum 12, 14 are shown corresponding with the occurrence of three consecutive downward impact compaction pulses timed to occur when the lower most discrete compacting surface 42 is directly facing the asphalt mat 11. At times between the three illustrated positions, an upward lifting force pulse occurs to raise the drum 12, 14 relative to the mat 11 so that when the edges 44 are directly facing the mat, the edges and drum are distanced from or only in light contact with the mat 11 to limit or prevent the occurrence of indentations in the mat.

[0032] To properly time the downward impact compaction pulses F _D , the asphalt compactor 10 may include a variety of control systems, such as, for example, a control system 50 schematically illustrated in FIG. 7. The control system 50 may include a processor 52 and software 54 that may operationally link the respective drive motor 22, used to control the rotational velocity of each drum 12, 14, with the respective eccentric system 30 of each drum to control the rotational velocity of the respective eccentric mass 32.

[0033] The rotational velocities of the drum 12 and the eccentric system 30 (i.e. the rotational velocity of the eccentric mass 32 are preferably controlled to maintain the equation:

_ ⁽ ^eccentric

^drum where N is the number of discrete compacting surfaces 42 around the circumference of the drum;

coeccentric is the rotational velocity of the eccentric shaft; and

codrum is the rotational velocity of the drum itself while being propelled.

[0034] By way of example, and not limitation, in an embodiment wherein the drum 12 has one-hundred discrete compacting surfaces 42, the eccentric system 30 may apply only a single downward impact compaction pulse to the compacting surface each time a subsequent compacting surface is rotated into contact with the mat, resulting in one-hundred downward impact compaction pulses per revolution of the drum. Then, if the drum 12 is rotating at twenty revolutions per minute, the eccentric mass 32 may be operated at two-thousand revolutions per minute to generate the appropriate number of downward impact compaction pulses per revolution of the drum.

[0035] The control system 50 may operate such that if the asphalt compactor 10 were propelled at a different rotational velocity (codrum), the control system may signal the eccentric system 30 to adjust its rotational velocity (co _eC centric) to maintain the ratio above, so that the drive system 20 and the excitation system remain synchronized. As seen in FIG. 7, the control system 50 may receive an operator input signal 55 corresponding to a desired rotational velocity (codmm)- Further, upon initial activation, the rotational velocity (codrum) may be expected to ramp up gradually from zero toward the desired operational traverse velocity of the asphalt compactor 10. The control system 50 may signal the eccentric system 30 to similarly and proportionately ramp up the rotational velocity of the eccentric shaft 32 as well for each drum 12, 14. [0036] The control system 50 may also include a plurality of position sensors 56 to determine or monitor the positions of the drums 12, 14, via the drive system 20, and the positions of the eccentric masses 32. These position sensors 56, according to aspects of the present embodiment, may then directly or indirectly help ensure that the timing of the eccentric system 30 is such that one of the discrete compacting surfaces 42 is substantially directly facing (e.g. parallel) the asphalt mat 11 with each downward impact compaction pulse and so that the edges 44 are directly facing the mat during the upward lifting force pulse of each revolution of the eccentric mass 32. The type of position sensor 56 that is used is not particularly limited, but may include electrical sensors or encoders, optical sensors, magnetic sensors, etc. Therefore, the control system 50 may synchronize the relative drum position and the vibration thereof.

[0037] Advantageously, drums 12, 14 according to the present disclosure allow for a greater linear distance D (FIG. 5) between downward impact compaction pulses compared to a conventional cylindrical drum. Therefore, use of nine or fewer downward impacts per foot is possible. By allowing an increase in the distance D between downward impacts, the asphalt compactor 10 may travel at a greater transverse velocity (v) without having to increase the rotational velocity of the eccentric system 30. Increasing the transverse velocity of the asphalt compactor 10 allows the operator to compact a greater amount of the mat 11 in the same amount of time. By increasing the transverse velocity (v) of the asphalt compactor 10, and thereby increasing the area of asphalt mat 11 that it can compact in a given time, a crew may reduce costs by operating fewer machines to complete the same job in the same time.

[0038] Turning now to FIG. 8 a drum 112 according to another embodiment is illustrated in profile. As shown, each discrete compacting surface 42 is curved instead of planar as seen in FIG. 5. Aspects of the embodiment of FIG. 5 may similarly apply to the drum 112 of the present embodiment. By way of example, and not limitation, each discrete compacting surface 42 may extend from a first distal end of the drum 112 to a second distal end of the drum along substantially the entire width of the asphalt compactor. The profile of the drum 112 along the rotational axis X may be constant such that each discrete compacting surface 42 is parallel with the rotational axis X.

[0039] FIG. 8 also shows a drum 12 according to aspects of the embodiment of FIG. 5 in phantom lines, which is also inscribed within a traditional cylindrical drum of radius r, also shown in phantom lines. In one embodiment, the curved discrete compacting surfaces 42 of the drum 112 are circular segments when view in profile with a radius of curvature R, which is greater than the radius r of the corresponding cylindrical drum. In one embodiment R is greater than or equal to about 1. lr. In other embodiments, R is greater than or equal to about 1.5r, greater than or equal to about 2r, or greater than or equal to about lOr. One of ordinary skill in the art will appreciate that the upper limit of these functions is substantially infinite because as R approaches infinity the shape of the curved discrete compacting surface 42 would approach the planes P of the drum 12. In one embodiment, the profile of the drum 112 is a Reuleaux polygon. One of ordinary skill in the art will also appreciate that the curved discrete compacting surfaces 42 of drum 112 are not necessarily limited to circular segments, but may also represent portions of other curved shapes, including but not limited to ovals and ellipses.

[0040] Although the above disclosure has been presented in the context of exemplary embodiments, it is to be understood that modifications and variations may be utilized without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the appended claims and their equivalents.