2. Background Art Pavement markers have become widely accepted as permanent installations for providing visible signals which delineate traffic lanes and control the flow of traffic on roadways in combination with, or in place of, conventional painted traffic lines. A large number of such markers employ retroreflectors which retroreflect light emanating from oncoming vehicles to provide a signal visible to the operators of such vehicles.

Retroreflective markers can be constructed in a variety of ways. One common form is a marker with an outer shell made of a high impact thermoplastic material designed to withstand forces of vehicle wheel loads, and the like. An early type of marker of a style still in use today is disclosed in Heenan, U. S. Patent No.

3,332,327. In the basic structure shown in the'327 patent, plastic retroreflector elements are first formed as part of the walls of a hollow shell, and then a layer of metal, by vacuum metalization, is deposited on the exposed faces of the retroreflector elements. Following

that step, the shell is filled, or"potted,"with a rigid epoxy-type material. The resulting structure is relatively rigid and over the years has proven to be remarkably durable in use.

In use, retroreflective markers can experience loads not only from vehicle wheels but from a variety of transient sources. While attempts have been made to increase the impact resistance of markers, these loads can and do cause marker breakage. Often a form of marker failure occurs as a result of a crack in the top of a marker that, in time, propagates to the retroreflector elements through the housing, or shell, resulting in degradation in performance of reflective characteristics.

To improve impact resistance, some markers are constructed with metal housings that offer considerably higher impact strength over markers made with the thermoplastic housings. However, these markers are typically expensive to manufacture because of the steps needed, for example, to fit the housing with a suitable retroreflector. Accordingly, it is desirable to provide a pavement marker which is specifically designed to have enhanced impact resistance in use. It is further desirable to provide such a marker which exhibits reduced incidence of failure or reflective degradation due to initial cracking of the top surface of the marker. Still further, it is desirable to provide such a marker which is readily manufacturable and cost-effective to produce.

DISCLOSURE OF INVENTION The present invention improves over the prior art by providing a retroreflective pavement marker including a housing formed of thermoplastic material having a generally planar top surface and a plurality of

side walls downwardly inclined from the top surface.

Reflector elements are fixed to at least one side wall.

At least one slot is formed in the top surface. A generally flat metal plate is provided, dimensioned and configured to be substantially coextensive with the top surface and having at least one downwardly extending barb member. The barb member is inserted into the slot preferably by ultrasonic insertion.

BRIEF DESCRIPTION OF DRAWINGS The foregoing and other novel features and advantages of the invention will be better understood upon a reading of the following detailed description taken in conjunction with the accompanying drawings wherein: FIG. 1 is a perspective view of a pavement marker constructed according to the principles of the invention; FIG. 2 is a cross-sectional view taken substantially along the line 2-2 of FIG. 1 ; FIG. 3 is an enlarged schematic cross-section illustrating the metal plate with barb member as installed on the marker housing; FIG. 4 is an exploded perspective view of a second marker embodiment constructed according to the invention; and FIG. 5 is a perspective view of a third form of marker housing which practices the invention.

BEST MODE FOR CARRYING OUT THE INVENTION Referring now to the drawings, and initially to FIG. 1, a pavement marker constructed according to the invention is designated generally by the reference numeral 10 and includes as a principal component a thermoplastic housing 12. Preferably, the housing 12 is injection molded as a unitary member from a suitable high impact plastic such as a reinforced polymer. The housing 12 is formed with a generally planar top surface 14 from which inclined side walls 16 downwardly extend. Fitted to the side walls 16, as by a suitable adhesive or ultrasonic welding, for example, are retroreflective elements 18 which may consist of cube corner retroreflectors, constructed by methods well-known in the art. In accordance with the invention, and as will be described in detail hereinafter, the housing 12 is fitted with a metal plate 20 which is dimensioned and configured to be substantially coextensive with the top surface 14 of the housing 12.

In the cross-sectional view of FIG. 2 the construction of the plate 20 can be readily seen.

Preferably the plate 20 is extruded from a suitable metal such as aluminum alloy and is integrally formed with a pair of longitudinally extending barb members 22 that project downwardly at right angles to the plate 20 and run substantially the entire width of the plate 20. The barb members 22 are generally downwardly tapering and are formed with a plurality of opposed teeth 24. Each barb member 22 is received in a downwardly tapered slot 26 formed in the housing 12 and running substantially the entire width of the housing 12. The enlarged view of FIG. 3 shows the construction of the barb members 22 and slots 26. Preferably, the slots 26 have a depth which is

slightly larger than the length of the barb members 22 such that an end 28 of each barb member 22 and bottom 30 of the associated slot 26 form a space 32 when the underside 34 of the plate 20 is in abutment with the top surface 14 of the housing 12. This allows melt flash to flow into the space 22 during barb member 22 insertion.

Also the barb members 22 are provided with upper radiused portions 36 leading to necked-down portions 38. This configuration assists in self-centering the barb members 22 in the slots 26 and also accommodate tolerance variations in the parts. The teeth 24 of the barb members 22 are, in preferred form, configured with an upper flat horizontal ledge portion 40 from which a downwardly directed angled portion 42 extends. While the teeth 24 are shown with sharp points, the teeth 24 may be radiused to better facilitate their formation by ane extrusion process. The front and back edges 44 of the plate 20 are preferably radiused (see FIGS. 1 and 2) to avoid possible damage to vehicle tires.

In accordance with the invention, the taper of the slots 26 is on the order of 9.5 degrees from vertical as shown by the symbol « in FIG. 3 although other values for-may be practiced. An imaginary line drawn through the points of the teeth 24 is at an identical angle as angle « of the slots 26. Moreover, the slots 26 are formed with vertical wall portions 46 that extend downwardly to the level of the uppermost teeth 24 when the underside 34 of the plate 20 abuts the top surface 14 of the housing 12. Further, in accordance with the invention, the plate 20 is affixed to the housing 12 preferably by ultrasonically heating the plate 20 to a temperature slightly higher than the melting point of the housing 12 polymer material then pressing the barb

members 22 into the slots 26. The walls of the slots 26 are melted and the melted polymer flows between the teeth 24, as illustrated in FIG. 3, wherein the area"A"of the slots 26 displaced by the teeth 24 flows into the void beneath each tooth 24, or area"B", for example.

Ideally, the areas"A"and"B"are approximately equal.

Thus, after the polymer cools and hardens, the plate 20 is firmly held in place on the housing 12.

FIG. 4 illustrates an exploded view of a second embodiment of a marker designated generally by the reference numeral 50. This form of marker essentially has a housing 52 with a top surface 54 which is recessed below opposed sidewalls 56 by approximately the same dimension as the thickness of plate 58. Slots 60 are provided similar to slots 26 of the marker 10 as discussed above. The plate 58 is constructed substantially the same as plate 20 discussed above. The marker 50, by its construction, offers the advantage that the barb members 62 are guided into the slots 60 during ultrasonic insertion by the sidewalls 56 and cannot slip sideways of housing 52, as can occur in the assembly of marker 10 if suitable precautions are not taken. Thus, in some respects the marker 50 is preferred for its relative ease of manufacture over the marker 10.

Yet another form of marker housing is illustrated in FIG. 5 and designated by the reference numeral 70. This housing 70 is formed with slots 72 that are formed in a top surface 74 that is not recessed as in the case of housing 52. However, the slots 72 do not run completely to sidewalls 76 and thus are shortened by comparison to slots 26 of marker 10. The shortened slots 72 accomplish the same centering or guiding effect during

ultrasonic insertion of a plate constructed like plates 20 and 58.

It can now be appreciated that a pavement marker 10 constructed according to the invention offers considerable advantages of resistance to impact loads that could cause damage to the marker over periods of use. The metal plate 20 extending across the full top surface 14 of the marker 10 serves effectively to protect the housing 12 from forming cracks that could propagate to the retroreflective elements 18, thus degrading the marker's reflective capabilities. It can also be appreciated that the marker 10 is readily constructed by conventional manufacturing techniques. The housing 12 can be formed with the slots 26 by well-known injection molding methods. Further, the plate 20 may be formed by a standard metal extrusion process. Assembly of the plate 20 to the housing 12 is conveniently accomplished by ultrasonic techniques well known in the art. The above discussed geometry of the barb members 22 and slots 26 is such that after marker 10 assembly the plate 20 is fixed to the housing 12 with considerable tensile strength that equals or surpasses the strength offered by adhesives, for example. In the preferred embodiment the plate 20 is formed with two spaced barb members 22.

However, a single barb member may be used, as well as three or more barb members to accomplish a similar construction depending on the size of the marker housing.

Also, the barb members need not run the entire width of the housing. Rather, they can be formed with the plate as cylindrical projections, for example, and received in cylindrical blind apertures in the housing.

While the present invention has been described in connection with a preferred embodiment thereof, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the true spirit and scope of the present invention.

Accordingly, it is intended by the appended claims to cover all such changes and modifications as come within the spirit and scope of the invention.