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Publication numberUS3846035 A
Publication typeGrant
Publication dateNov 5, 1974
Filing dateMar 26, 1973
Priority dateMar 26, 1973
Also published asCA992781A, CA992781A1, DE2412781A1, DE2412781C2
Publication numberUS 3846035 A, US 3846035A, US-A-3846035, US3846035 A, US3846035A
InventorsDavin D
Original AssigneeBlaw Knox Const Equipment
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Reference beam grade control for asphalt pavers
US 3846035 A
Abstract
The disclosure relates to an improved type of grade control for an asphalt paver utilizing reference members positioned in leading and trailing relation to the pavement-forming screed. Control over the grade of the asphalt mat laid down by a floating screed is controlled by the combined action of the reference members moving along with the paving apparatus and sensing the average grade conditions of the base in front of the screed as well as the average grade conditions of the newly laid pavement mat. The new control provides for exceptional smoothness and uniformity of the pavement mat, and also greatly facilitates the use of mobile grade reference controls when laying extremely wide pavement mats.
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United States Patent [191 Davin 1 51 Nov. 5, 1974 [75] Inventor: Donald R. Davin, Shelbyville, 111.

[73] Assignee: Blaw-Knox Construction Equipment, Inc., Mattoon, 111.

22 Filed: Mar. 26, 1973 21 Appl. No.2 345,115

[52] [1.8. Cl. 404/84 [51] lint. Cl. E0lc 19/00 [58] Field of Search 404/83, 84; 37/DlG. 2O

[56] References Cited UNITED STATES PATENTS 2,491,275 12/1949 Millikin 404/84 2,962,979 12/1960 McCormick 404/84 X 3,259,034 7/1966 Davin 404/83 3,272,099 9/1966 Drake 404/84 3,323,427 6/1967 Schrimper 3,595,144 7/1971 Rink 404/84 1 /0 1, mm /4 26 'T 3,618,484 11/1971 Long 404/84 Primary ExaminerNile C. Byers, Jr.

Attorney, Agent, or Firm-Mandeville and Schweitzer [57] ABSTRACT The disclosure relates to an improved type of grade control for an asphalt paver utilizing reference members positioned in leading and trailing relation to the pavement-forming screed. Control over the grade of the asphalt mat laid down by a floating screed is controlled by the combined action of the reference members moving along with the paving apparatus and sensing the average grade conditions of the base in front of the screed as well as the average grade conditions of the newly laid pavement mat. The new control provides for exceptional smoothness and uniformity of the pavement mat, and also greatly facilitates the use of mobile grade reference controls when laying extremely wide pavement mats.

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\ mik REFERENCE BEAM GRADE CONTRQL FOR ASPHALT PAVERS BACKGROUND AND SUMMARY OF INVENTION In the laying of asphalt pavement roadways and the like, it is widespread practice to employ so-called floating screed paving machines. These machines include a tractor-like main frame having an engine for propulsion and for material distributing functions. Typically, there is a material receiving hopper at the front of the paver arranged to receive hot asphalt material from a truck, as the paving machine advances along the roadbed. Slat conveyors or thelike are provided to convey the material from the hopper, at the front of the machine, toward the floating screed, at the back of the machine. Immediately in front of the screed, there is typically provided a distributing auger, which receives the raw asphalt material from the slat conveyor and conveys it laterally so as to distribute the material along the front edge of the screed. As the machine advances along the prepared roadbed, the raw asphalt material flows under the screed, which levels, smooths and compacts it to provide a continuous, level pavement mat.

In a typical floating screed asphalt paver, the screed is attached to a pair of forwardly extending tow arms which engage the paver frame at their forward extremities. These tow arms are also connected to the paver frame by hydraulic or other actuators arranged to adjust the vertical position of the tow arm extremities in relation to the paver frame. By effecting proper control over the position of the tow arm forward extremities in relation to a reference plane or a reference element, substantially independent of the irregular vertical motions of the paver frame itself, it is possible to cause the floating screed to lay a pavement mat which is smooth and level in relation to the underlying base surface.

Effective control of the screed tow point adjustment may be achieved by means of suitable feeler device, for example, which is carried by one or both of the tow arms and arranged for contact with a predetermined reference surface. When the tow point becomes either higher or lower than is indicated by the reference surface, as with changing loads upon paver frame and/or irregularities in the roadbed surface, the tow point is caused to be controllably raised or lowered relative to the paver frame to maintain a constant relationship with the reference. Such an arrangement is shown in the Ackerman, et al., U.S. Pat. No. 3,236,163, for example. ln many applications, grade control of the tow point is provided at only one side of the machine. For controlling the tow point at the other side there typically may be provided a so-called slope control, which functions to maintain a constant relationship between tow points at opposite sides, either on a level basis or with a predetermined transverse slope.

in conjunction with the type of tow point control mentioned in the preceding paragraph, it is important to provide an appropriate referencefor the feeler device. In some cases, the reference maybe the edge of previously laid pavement mat, in which case a simple shoe plate or the like is arranged to be towed along the pavement surface. in other cases, it may be necessary or advantageous to position a reference wire alongside the base surface, in a position to be engaged by the sensing device, such that the screed tow arms are maintained in a constant relationship to the reference wire.

In some instances, it is undesirable or inconvenient to utilize a reference wire or a previously laid pavement surface as a grade reference. For such occasions, it has proven advantageous to utilize a mobile reference beam, which is carried along with the paver as it moves over the roadway base surface. An arrangement of this type is described and claimed in the D. R. Davin U.S. Pat. No. 3,259,034. In the arrangement of the Davin patent, an elongated beam structure is provided with a substantial plurality (e.g., ten) of independent supports, advantageously arranged on individual springs. The arrangement is such that, as the reference beam is carried along the base surface, it is supported by the combined action of the multiple, yieldable supports. The individual supports are enabled to follow the minor deviations in base contour without significantly affecting the position of the reference beam as'a whole, and the mobile reference beam thus provides a suitably accurate, averaged reference plane representing the grade to which the pavement mat is to be applied. A sensing device carried by the screed tow arms engages the reference beam near its center, to enable the tow points to be maintained in a predetermined relationship to the moving reference beam.

While the arrangement illustrated in the D. R. Davin U.S. Pat. No. 3,259,034 constituted an important advance, certain problems were encountered in using the specific apparatus of that patent with conventional paving machinery when laying extremely wide mats of paving material, as is becoming increasingly prevalent with the availability of larger and more powerful paving machines. In part, these problems derive from the fact that, in order to be suitably accurate, a moving reference beam must have substantial length, typically greater than that of the paving machine itself. When paving narrow widths, this presents no problem, as the beam may extend slightly ahead of and slightly in back of the paving machine, while being towed alongside of it by a suitable tow bracket extending laterally from the frame of the paver. However, where the floating screed and the associated material distributing augers are substantially wider than the paver frame, it becomes extremely difficult, if not impossible, to effectively tow the reference beam and to derive an accurate reference signal from a location outwardly of the lateral extremities of the screed and auger. Merely moving the reference beam forward, so as to be entirely in front of the auger and screed is not entirely satisfactory, moreover, because of practical difficulties in deriving a grade level signal reflecting the position of the tow arms in relation to the geometrical center of the reference beam.

in accordance with the invention, the utilization of a moving reference beam arrangement in connection with the laying of wide pavement mats is made feasible by the utilization of a unique combination of reference beams, one being towed ahead of the screed and auger, supported on the roadway base grade, and the other being towed behind the screed and auger, supported on the just-laid asphalt mat. To greatest advantage, the arrangement of the invention includes a system of compound levers associated with the respective leading and trailing reference beams and arranged to derive a signal which is a function of the relationship of the screed and its tow arms to the respective reference beams. ln effect, the reference beam arrangement is of greatly increased length and enables the laying of a mat of increased smoothness and accuracy in comparison to prior arrangements.

To advantage, the trailing reference beam, which is towed by the paver frame behind the auger and screed is supported by one or more wheels or in some cases by an elongated flexible slide strip. Moreover, notwithstanding that the trailing reference beam rides upon the justdaid mat, it is desirable in many cases that the trailing reference beam be supported by a large plurality of wheels arranged for independent movement, such that the trailing reference reflects an averaged reference position. In the case of either the leading or trailing reference beams, or both, it is considered preferable to utilize a rigid beam with independently yieldably movable supports. However, it is within the purview of the invention to utilize reference beam structures comprising articulated pairs of supports (e.g., see DeLeuze, French Pat. No. 1,056,865).

In its most advantageous form, the system of the invention includes leading and trailing reference beams of rigid structure, independently supported by a plurality of yieldable supports. The leading reference beam is supported by a plurality of shoes or plates, while the trailing beam is supported by a plurality of wheels. Elongated reference arms extend rearward from the leading beam and forward from the trailing beam and are pivotally connected to a screed tow arm, advantageously at a point forward of the screed itself but well behind the tow point. Thus, the reference arm pivot point is in a position to reflect deviations from the reference level of both the tow point and the screed itself.

For a better understanding of the invention andits various features and advantages, reference should be made to the following detailed description and to the accompanying drawings, with further reference to the appended claims.

DESCRIPTION OF THE DRAWING FIG. 3 is an enlarged elevational view, similar to FIG. I

2, illustrating a preferred form of yieldable support for a trailing reference beam.

FIG. 4 is a top plan view illustrating features of the trailing reference beam utilized in the apparatus of FIG. I, and showing reference beams utilized on both sides of the paving machine.

FIG. 5 is an enlarged, fragmentary elevational view illustrating details of the tow point suspension and reference signal means incorporated in the paving apparatus of FIG. 1.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, and initially to FIG. 1 thereof, the reference numeral designates generally a paver frame of a floating screed type asphalt paver. The paver per se is well known in principle and includes an engine or prime mover 11 which provides a source of tractive power and also provides power for the various material conveying and distributing functions of the machine. In the illustrated apparatus, a pair of large, pneumatic tires 12 at the back of the paver provide the necessary forward traction, with steerage and support for the front of the paver being provided by pairs of smaller wheels 13.

In front of the paver 10, there is conventionally provided a hopper 14 arranged to receive paving material, which may be aggregate, asphalt, and the like, from the tilted body of a truck (not shown). In accordance with conventional practice, the truck is brought into contact with the front of the paver, and then is pushed along by the paver, continuously discharging its contents into the hopper 14 during the progress of the paving operation, until the complete truckload is exhausted. Thereafter, the empty truck is replaced by a new, fully loaded truck, with the paving operation continuing from the hopper supply during the changeover interval.

By means of a suitable slat conveyor (not shown) the paving material is conveyed from the hopper 14 to the back of the machine and deposited in front of a controllably rotated auger 15. The auger is pitched oppositely from the center, so as to convey the conveyordischarged paving material laterally outward and distribute it more or less evenly along the full length of the auger. In this respect, it will be understood that the basic body of the paver frame 10 may have an overall width of 10 or 12 feet, for example, to accommodate its over-the-road transportation from place to place. At the same time, the paver may be and often is set up in a configuration to lay paving mats in an uninterrupted width of 20 to as much as 40 feet on occasion. In such cases, the overall width of the auger 15 is substantially equal to the full paving width.

Disposed immediately behind the auger 15 is a strikeoff and screed structure generally designated by the numeral '16, which is carried by a pair of forwardly extending tow arms 17. The screed assembly 16, like the auger 15, has a width corresponding to the desired paving width, and thus may be substantially wider than the width of the paver frame 10. The tow arms 17, are spaced so as to be closely adjacent to sides of the paver frame. Accordingly, the tow arm 17 may engage the screed assembly 16 well inboard of its lateral extremities. Intermediate portions 18 of the tow arms extend upward and over the top of the area occupied by the auger 15.

In accordance with conventional practice, the tow arms 17 may be connected to the paver frame by means of spaced tow pins 19, 20 (FIG. 5) which are freely slidable on a vertically disposed tow bar 21. An hydraulic actuator 22 is mounted at the upper end of the tow bar 21, and extends downward with its rod 23 engaging the forward portion of the tow arm 17. By appropriate control of the actuator 22, the forward extremity of the tow arm may be appropriately raised or lowered in relation to the paver frame itself to effect desired adjustments in the angular attitude of the tow arms 17 and the screed assembly 16. Similar arrangements are, of course, provided at both sides of the machine, with the respective actuators being separately controllable, however, to provide for independent manipulation of tow arm elevation on opposite sides of the machine.

In accordance with well known principles, a smooth, level mat 24 of paving material may be laid by the screed assembly 16 more or less independently of variations in the base roadbed 25 and also more or less independently of changes in the suspension of the paver frame itself resulting from changing loads in the hopper 14, for example, or movement of the wheels into or over minor discontinuities or obstructions in the roadway. This is realized in part by providing a socalled grade reference level, which is independent of the paver frame 10, and by maintaining the tow point of at least one of the arms 17, at a predetermined height in relation to that reference. The other tow arm likewise may be controlled by a similar reference means, although it is usually more common to control one of the arms from a grade reference extending longitudinally of the roadway while controlling the other tow arm by means of a so-called slope control. If the slope angle is zero, both tow arms will automatically be adjusted to maintain an equal uniform height in relation to a single grade reference. Frequently, however, a predetermined cross slope is built into the pavement surface, to facilitate drainage and/or for banking at turns. In the latter case, both tow arms can be adjusted in accordance with a single grade reference means, but the two tow arms will be maintained in an unequally spaced relation to that grade reference to provide the desired cross slope.

In accordance with the teachings of the beforementioned Davin US. Pat. No. 3,259,034, a suitable artificial grade reference frequently may be derived from the base roadbed itself, by means of an elongated reference beam individually supported by a large plurality of independently yieldable supporting elements. The base road mat 25 may be a prepared but unpaved base, or

may even be a previously laid asphalt course, where thefinished pavement mat consists of more than one asphalt course. The present invention utilizes to a large extent some of the important principles of the beforementioned Davin patent, while at the same time providing a greatly improved mobile reference beam arrangement which is suitable for pavement configurations in which the screed and auger are of substantially greater overall width than the paver frame itself-and which, at the same time, provide for an exceptionally high degree of accuracy in the control of the level and smoothness of the resultant pavement mat.

In accordance with the invention, the paving machine is provided with dual mobile reference beams 26,

27, carried alongside and closely adjacent to the paver frame 10, with one reference beam 26 being carried in leading relationship to the auger-screed area and the second reference beam 27 being carried in trailing relationship. At least the forward beam 26, and to best advantage each of the mobile reference beams, is of highly extended length, possibly greater than the length of the paver itself. in addition, at least the leading beam 26, and advantageously both beams are supported at a multiplicity of points along its length by equally spaced, independently movable supporting elements. The arrangement is such that the reference beam is supported in a positionwhich represents an average condition of the underlying surface over an extended length. The function and operation of the forward or leading mobile reference beam 26 is in many ways similar to the mat, immediately behind the screed assembly 16. By an advantageous arrangement of reference arms or levers, reference data information from the respective beams 26, 27 is combined and made available to a sensing device 28 to effect controlled movement of the actuator 22 and thereby maintain a constant relationship between the screed assembly 16 and the respective leading and trailing reference beams 26, 27.

In the illustrated form of the apparatus, the moving reference beam 26 is in the form of a three-piece lightweight tubular beam joined at flanges 29 into a unitary assembly. The segmented construction permits disman tling for transportation, as will be understood. In its assembled form, the leading reference beam 26 may have a length on the order of 30 feet and is supported at uniformly spaced intervals by a large plurality (10 in the illustration) of yieldably mounted shoes 30 (FIG. 2). To advantage, the shoes 30, may be made of flat sheet metal, pivotally connected at 31 to a yoke bracket 32 carried at the end of a guide bolt 33. A stabilizing link 34 is pivotally connected to the yoke 32 and extends forward to a lug bracket 35, to which it is pivotally connected at 36. The bolt 33 is slidably guided in a spherical bearing 37 received in a boss 38 formed on the reference beam 26. A spring 38 extends between the spherical bearing 37 and the top of the yoke 32, and is arranged to be compressed as a function of upward movement of the shoe 30 relative to the reference beam 26.

The arrangement of the several supporting shoe assemblies for the leading reference beam is such that, when the beam is resting on the base surface 25, in its normal operating arrangement, the springs 38 of all of the shoe assemblies are partially compressed. And, although the base surface 25 may not be precisely level throughout the length of the reference beam, and may contain minor aberrations in the form of small rises or depressions, the beam itself and particularly its midpoint, will tend to maintain an averaged position above the roadway, reflecting the average condition of the surface. As will be understood, individual shoe assemblies may rise or fall relative to the beam in following anomalies in the road surface. The reference beam itself will be influenced only to a minor extent by individual movements of the shoe assemblies, but will reflect an average condition. The geometric center of the beam, in terms of the location of the supports therefor, reflects most precisely the average reference condition sought to be determined.

In the system illustrated in the Davin US. Pat. No. 3,259,034 patent, the geometric center of the beam is located near the forward extremity of one of the tow arms, and a sensing element is provided to detect the relationship between the forward portion of the tow arm and the geometric center area of the beam. In the system of the invention, however, since the leading reference beam 26 is to be located entirely forward of the auger 15, the geometric center region of an adequately long reference beam is located far ahead of even the forwardmost extremity of the tow arm 17. Thus, in accordance with one aspect of the invention, the leading reference beam 26 is provided in its effective center region with a vertically extending bracket 39 which is pivotally connected at 40 to an elongated, rearwardly extending reference arm 41. In the illustrated system, the

- reference arm 41 includes an upward extension 42 which is pivotally connected at 43 to the screed arm 17.

Desirably, the pivot point 43 connecting the reference arm 41 to screed tow arm is located rearward of the tow bracket 21 and at the same time well forward of the screed assembly 16. A point approximately midway between these areas is advantageous, inasmuch as vertical movement relative to the desired reference of either the screed assembly I6 or its tow point will be reflected in vertical movement of the pivot point 43 and a corresponding vertical movement of the reference arm 41.

The reference beam 26 is carried along with the paver frame by means of a forward tow linkage 44, by which the beam is attached to the front of the paver. An articulated stabilizing linkage 45 connects the back of the reference beam 26 to a portion 46 of the paver frame (FIG. 5) to provide lateral stability.

The trailing reference beam 27 typically may be somewhat shorter in length than the leading beam 26. For example, a beam length of feet for the trailing beam may be suitable, while a 30 foot length on the leading beam would be preferable. In the illustrated arrangement, the trailing beam is constructed in two sections, bolted together at a center flange 47. To greatest advantage, the trailing reference beam 27 is supported by a large plurality of uniformly spaced sets of elements, there being eight such sets in the specific illustration. Under some conditions, a single support element might suffice for the rear reference, but a plurality is required and/or desired in most instances. Wheels are used rather than flat shoe plates, as in the case of the leading reference beam, because the newly laid asphalt mat 24 is still in a soft condition when traversed. by the reference beam andcould be scraped or marred by individual sliding shoes. Most advantageously, the wheels 48 are arranged in pairs for increased flotation on the soft mat surface, and also to impart stability to the beam to facilitate its handling when detached from the paver.

Notwithstanding that the newly laid pavement mat 24 may have a high degree of smoothness and levelness, it is advantageous in most cases that the plurality of wheel pairs 48 for the trailing reference beam be independently supported, so that the position of the beam reflects an average position of the multiplicity of wheel pairs. To this end, the wheel pairs may be supported much in the same manner as the shoes 36 of leading reference beam. Thus, an axle 49 connecting the two wheels of a pair is journalled in a yoke bracket 50 carried at the end of a guide bolt 51 slidably received in a spherical bearing 52. A coil spring 53 urges the yoke bracket 50 downward. A stabilizing linkage 54 extends forward from the bracket and is pivotally connected to a fixed lug 55 extending downward from the bottom of the beam 27. The arrangement is such as to freely accommodate individual, yieldably resisted vertical movement of the wheel pairs relative to the rigid beam.

In some cases, it may be appropriate to provide the trailing beam with non-rotating supports, like those of slide strip is suitably secured at its front end to the reference beam or to the paver itself, so as to be towed along with the beam. The strip readily flexes to accommodate the desired independent movement of the beam supports.

The trailing beam advantageously is towed from the screed assembly 16, by means of a pivoted tow link 56 (FIG. 4) extending rearward from a bracket 57 suitably attached to the screed. For lateral stabilization of the back of the trailing beam 27, there is provided a diagonal stabilizing linkage consisting of a tie rod 58 secured to the beam by a clamp 59 and extending forwardly to a connection point at the opposite side of the machine. In the arrangement shown in FIG. 4 of the drawings, the equipment is set up to employ reference beam systems on both sides of the paving machine. In that case, the stabilizing bar 58 for the reference beam 27 may be secured by a clamp 60 to the forward portion of the opposite side trailing reference beam 270. Likewise, the beam 27a will be stabilized by a tie bar 58a secured by clamps 59a and 60a. Where only a single trailing reference beam is utilized, the stabilizing bar 58 can be connected more directly to the screed assembly 16.

In the effective center region of the beam 27, in terms of the location of the uniformly spaced supports, there is provided a vertically disposed extension bracket 61 which pivotally engages at 62 the trailing end of a reference armstructure 63. The reference arm structure 63 desirably is constructed in the form of a truss arranged to support an elongated, forwardly extending reference arm element 64. The specific configuration of the truss 63 is unimportant, apart from the fact that it must be consistent with its passing over the top of the screed and auger structures at the back of the paver.

In the illustrated arrangement, the reference arm 64 is attached by the pivot pin 43 to the forward reference arm 41 and to the screed tow arm 17. Within the purview of this invention, the forward and rearward reference arms 41, 64 could be separately pivoted to the tow arms 17, or they could be pivotally connected together and pivoted to the tow arm 17 at a different axis. However, a common pivot point at the pin 43 is simple and advantageous.

As is reflected in FIGS. 1 and 5, the rearward reference arm 64 extends forwardly well beyond the pivot pin 43, to a region located approximately over the center of the forward reference arm 41. The sensing device 28, typically in the form of a potentiometer actuated by a feeler element 65, is secured to the upper reference arm 64, by means of a clamping bracket 66. The bracket 66 may be secured in any of several positions along the length of reference arm 64, so as to be properly positioned with respect to the forward reference arm 41. In addition, the sensing device 28 has a vertically extendable support 67 adjustably secured in the clamp 66. As reflected in FIG. 5, the sensing device 28 may be vertically adjusted in the clamp 66 to a position in which the feeler element bears upon the center region of the forward reference arm 41. When properly adjusted, the feeler element 65 will be approximately midway between its upper and lower extreme positions when the proper space relationship exists between the respective reference arms 41, 64. Any change in the spacing between these arms, in the region of the sensor 28, will cause a displacement of the feeler 65, either upward or downward. In accordance with principles which are well known and need not be repeated here, movement of the potentiometer feeler element 65 away from its neutral position can be utilized to effect energization of the actuator 22 in a direction that will tend to restore the feeler to its neutral position by appropriate upward or downward movement of the tow arm 17, as may be necessary.

In typical operation, the reference arms 41, 64 are arranged to be more or less horizontal and parallel when the respective leading and trailing reference beams are in a desired, predetermined relationship and the tow arms 17 are properly positioned. To this end, the vertical supports 39, 61 may be provided with a plurality of openings or other adjustment facilities for establishing a desired level for the pivot points 40, 62 of the respective reference arms.

When the system is in operation, the paver frame advances forwardly (to the left in FIG. 1) carrying with it the reference beams 26, 27, the former riding on the roadway base surface and the latter riding on the just laid pavement mat. Assuming, for example, that the level of the paver frame 10 were to drop, relative to the reference, as by reason of an increased load in the hopper and/or one or more of the wheels moving into a minor depression in the roadway, the forward extremity of the tow arm 17, being attached to the paver frame through the hydraulic actuator 22, would be correspondingly lowered relative to the reference beams 26, 27. This would in turn cause a lowering of the pivot point 43 and a resulting relative closing of the distance between the reference arms 41, 64 in the region of the sensor 28. Immediately, the actuator 22 would be energized to raise the forward end of the tow arm 17 suffiv ciently to re-establish proper spacing between the reference arms. As a result, the orientation of the tow arms 17 to the roadway base surface 25 and to the pavement surface 24 is retained substantially constant, notwithstanding vertical deviations of the paver frame itself.

As will be appreciated, the screed assembly 16 is supported by flotation on the viscous asphalt paving material as the paver is advanced on the roadway. The viscosity and other characteristic nature of this material ideally should be constant at all times. As a practical matter, however, the consistency of the mixture may vary from truckload to truck load, and the viscosity characteristic of even the same mixture may vary somewhat as a function of temperature, for example. Accordingly, assuming the paving frame 10 itself is traveling a perfectly level course, there may be some tendency for the screed assembly 16 to deviate upward or downward in some measure from the desired paving level. When this occurs, it is reflected in upward or downward movement of the pivot point 43 and a corresponding change in the relationship of the reference arms 41, 64. For example, if the screed assembly would tend to sink into the mat, as a result of a lowering of the material viscosity, a reduction in forward speed, or like circumstance, the pivot point 43 would be correspondingly lowered, and the distance between the reference arms and the region of the sensor 28 would be correspondingly reduced. The potentiometer feeler 65 would be displaced from its neutral position, energizing the actuator 22 and raising the forward extremity of the tow bar 17 to re-establish the proper spacing. In this respect, raising of the forward end of the tow bar would increase the angle of incidence of the screed bottom plate 68 with respect to the pavement mat, tending to cause the screed assembly 16 to seek a higher level and thereby re-establish the desired level of the pavement surface.

The dual reference beam system of the invention results in an exceptionally high degree of accuracy and smoothness in the laying of an asphalt paving mat, because the level of the screed .plate is controlled as a combined function of the roadway base surface 25 and the just-laid pavement surface 24. Moreover, the extreme overall length of the dual reference beam system provides for exceptional overall responsiveness of the control to deviations from a desired level surface.

In addition to the foregoing advantages, the system of the invention provides a rather simplified and wholly practical arrangement for utilizing a mobile reference means in conjunction with heavy duty asphalt pavers having the capacity to lay a pavement mat of far greater width than that of the paver frame itself. This is of particular importance in view of current trends toward the paving of 30 and 40 foot mat widths in a single pass with the paving machine.

In a most advantageous form of the invention it is provided that the trailing reference beam, although riding on an essentially smooth and level, just-laid pavement surface, is supported by a large plurality of elements, preferably wheels, each being independently supported. in this respect, notwithstanding the essentially smooth, flat characteristic of the newly laid pavement surface, wheels can, in continued operation, become rather irregular through non-uniform pickup of adherent asphalt material. By reason of the multiple, independent support of the plurality of wheels, the trailing reference beam can be supported in an appropriately averaged position notwithstanding a degree of out-of-roundness of the individual wheels during normal operations.

It should be understood, of course, that the specific form of the invention herein illustrated and described is intended to be representative only, as certain changes may be made therein without departing from the clear teachings of the disclosure. Accordingly, reference should be made to the appended claims in determining the full scope of the invention.

I claim:

1. A dual reference beam grade control system for i use in combination with an asphalt paver of the type having a transversely disposed material distributing auger, a floating screed positioned behind the auger, tow

' arms extending forwardly from the screed and connected to the paver frame, and tow arm suspension means for vertically adjusting the tow point connections of said tow arms to effect changes in the attitude angle of the screed, said grade control system comprismg a. a beam-like first reference member towed by the paver frame and extending longitudinally along one side thereof,

b. said first reference member being disposed entirely forward of the auger,

c. a plurality of independently movable supports for said first reference member spaced along its length and supporting said reference member at an averaged position above a base grade surface,

d. a first reference arm pivotally connected to the first reference member in its central region and extending rearwardly toward and being pivotally connected to one tow arm,

e. a second reference member towed by the paver frame and being disposed entirely behind the screed,

f. support means for supporting said second reference member above an asphalt mat grade surface,

g. a second reference arm connected to the second reference member and extending forwardly toward and being pivotally connected to said one tow arm and/or said first reference arm, and

h. tow arm height reference control means associated with each of said reference arms and operatively associated with said tow arm suspension means for raising and lowering the tow point of said one tow arm relative to the paver frame in response to relative movements of one or both of said reference arms in relation to said one tow arm.

2. The grade control system of claim 1, further characterized by a. said reference control means including means engaging both of said reference arms and operative to detect relative movement therebetween.

3. The grade control system of claim 2, further characterized by a. said control means including a sensing potentiometer or the like carried by one of said reference arms and engageable with the other to detect rela tive movement.

4. The grade control system of claim 1, further characterized by a. said reference arms being pivotally connected to said one tow arm,

b. one of said reference arms having a portion extending longitudinally for a substantial distance beyond its pivot axis in the direction of the other reference arm, and

c. said reference control means being operatively associated between the extending portion of said one reference arm and a portion of said other reference arm.

5. The grade control system of claim 4, further characterized by a. said second reference arm having a portion extending longitudinally forward of said axis.

6. The grade control system of claim 5, further characterized by a. said reference arms being connected to said one tow arm along a common pivot axis.

7. The grade control system of claim 6, further characterized by a. said pivot axis being located on said one tow arm between the tow point and the screed and closer to the screed than the tow point.

8. The grade control system of claim 1, further char- 10. The grade control system of claim 9, further characterized by a. the support elements for said second reference member comprising wheels. 11. The grade control system of claim 10, further characterized by a. each of said support elements comprising a pair of axially spaced wheels, positioned on opposite sides of the reference member. 12. The grade control system of claim 10, further characterized by a. the support elements for the first reference beam comprising bearing plates slidably engageable with the base reference. 13. The grade control system of claim 9, further characterized by a. flexible slide strip means interposed between the asphalt mat surface and each of the support elements for the second reference member.

14. The grade control system of claim 1, further characterized by a. said first reference member being towed from the paver frame from a point substantially forward of the back end of the member,

b. stabilizing linkage means being connected between the paver frame and the back portion of the first reference member,

c. the second reference member being towed from the paver frame from a point in the forward region of the reference member, and

d. stabilizing linkage means being connected to the back portion of the second reference member and extending diagonally forwardly and toward the opposite side of the back portion of the paver frame.

15. The grade control system of claim 14, further characterized by a. the combination comprising dual reference member grade control systems at each side of the paver frame for separately controlling the tow point positions of the respective tow arms, and

b. the diagonally disposed stabilizing linkage means extending from the back portion of one of the second reference members to the forward portion of the other thereof.

16. A reference beam grade control system for use in combination with an asphalt paver of the type having a transversely disposed floating screed towed behind a paver frame and screed control means for maintaining a predetermined relationship of the screed to a reference, which comprises a. a plurality of about six or more supporting wheels,

b. an elongated reference control member supported by said plurality of wheels in an averaged position in relation to a surface,

c. resilient means mounting said wheels in a longitudinally aligned relationship along said reference control member for independent vertical movement in relation to said reference control member,

d. means for towing said reference control member directly behind a portion of said screed, whereby all of the said wheels engage the finished asphalt mat laid by said screed, and

e. means for actuating the screed control means in response to predetermined relative vertical moveb. said screed control means being actuated by movements of said reference arm.

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4140420 *Mar 16, 1978Feb 20, 1979Cmi CorporationPortable grade averaging apparatus
US4213719 *Sep 28, 1978Jul 22, 1980Cmi CorporationGrade averaging apparatus
US4270801 *Aug 14, 1979Jun 2, 1981Cmi CorporationSteering and cutter drum positioning in a paved roadway planing machine
US4580923 *Aug 15, 1984Apr 8, 1986Ingersoll-Rand CompanyActuating means for a servo valve
US5201603 *May 17, 1991Apr 13, 1993Caterpillar Paving Products Inc.Tow point for an asphalt paver
US5344254 *Apr 14, 1993Sep 6, 1994Blaw-Knox Construction Equipment CorporationPivoting screed edger
US5362177 *Feb 16, 1993Nov 8, 1994Blaw-Knox Construction Equipment CorporationPaving method and apparatus with fresh mat profiler
US5549412 *May 24, 1995Aug 27, 1996Blaw-Knox Construction Equipment CorporationPosition referencing, measuring and paving method and apparatus for a profiler and paver
US5599134 *Sep 15, 1995Feb 4, 1997Cedarapids, Inc.Asphalt paver with compaction compensating system
US5702201 *Jul 11, 1996Dec 30, 1997Cedarapids, Inc.Method for compensating differential compaction in an asphalt paving mat
US5752783 *Feb 20, 1996May 19, 1998Blaw-Knox Construction Equipment CorporationPaver with radar screed control
WO1992020870A1 *Apr 15, 1992Nov 26, 1992Caterpillar Paving Products Inc.Tow point for an asphalt paver
Classifications
U.S. Classification404/84.1
International ClassificationE01C19/45, E01C19/48, E01C19/00
Cooperative ClassificationE01C19/4873
European ClassificationE01C19/48D3
Legal Events
DateCodeEventDescription
Sep 23, 1993ASAssignment
Owner name: BLAW-KNOX CONSTRUCTION EQUIPMENT CORPORATION, ILLI
Free format text: CORRECTIV;ASSIGNOR:WHITE CONSOLIDATED INDUSTRIES, INC.;REEL/FRAME:006682/0585
Effective date: 19930528
Jul 13, 1987AS02Assignment of assignor's interest
Owner name: BLAW-KNOX CONSTRUCTION CORPORATION, EAST ROUTE 16,
Owner name: WHITE CONSOLIDATED INDUSTRIES, INC., A DE CORP.
Effective date: 19870618
Jul 13, 1987ASAssignment
Owner name: BLAW-KNOX CONSTRUCTION CORPORATION, EAST ROUTE 16,
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:WHITE CONSOLIDATED INDUSTRIES, INC., A DE CORP.;REEL/FRAME:004740/0980
Effective date: 19870618
Owner name: BLAW-KNOX CONSTRUCTION CORPORATION,ILLINOIS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WHITE CONSOLIDATED INDUSTRIES, INC., A DE CORP.;REEL/FRAME:4740/980
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:WHITE CONSOLIDATED INDUSTRIES, INC., A DE CORP.;REEL/FRAME:004740/0980
Aug 24, 1981ASAssignment
Owner name: BLAW-KNOX COMPANY
Free format text: MERGER;ASSIGNORS:AETNA-STANDARD ENGINEERING COMPANY;BLAW-KNOX CONSTRUCTION EQUIPMENT, INC.,;BLAW-KNOX EQUIPMENT, INC.;AND OTHERS;REEL/FRAME:003926/0382
Effective date: 19781221
Aug 24, 1981AS03Merger
Owner name: AETNA-STANDARD ENGINEERING COMPANY
Owner name: B
Effective date: 19781221
Owner name: BLAW-KNOX COMPANY
Owner name: BLAW-KNOX CONSTRUCTION EQUIPMENT, INC.,