Abstract:
A traffic control device includes a shell body and at least one receptacle located in the shell body. The receptacle includes a dilatant material.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Application Ser. No. 61/045,356, filed Apr. 16, 2008, herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to traffic control devices and, in one particular embodiment, to a traffic control device sensitive to the speed of a vehicle. 
     2. Description of the Current Technology 
     Conventional devices are known to help slow down the speed of traffic in selected areas. For example, conventional “speed bumps” or “rumble strips” are used in such places as school zones, parking lots, construction zones, hospital zones and similar areas where it is desired to control or reduce the speed of vehicles for the safety of pedestrians. 
     A conventional speed bump usually consists of a concrete or asphalt hump formed in the road. Drivers must slow down when driving over these speed bumps to prevent damage to their vehicle. However, even if travelling at the posted speed limit or below, these conventional speed bumps can take a toll on a vehicle&#39;s mechanical components, such as the shock absorbers and steering system. Additionally, these conventional speed bumps are very heavy and, once in place, are typically permanent fixtures on the roadway. In order to remove a conventional speed bump, the speed bump must be broken up and the roadway repaired where the speed bump used to be. Additionally, these conventional speed bumps require maintenance to repair cracks and breaks caused by heavy traffic volume. 
     Therefore, it would be advantageous to provide a traffic control device that reduces or eliminates at least some of the problems associated with conventional speed bumps. 
     SUMMARY OF THE INVENTION 
     A traffic control device of the invention comprises a shell body and at least one receptacle located in the shell body. The receptacle includes a dilatant material. 
     Another traffic control device of the invention comprises a compliant material that stiffens or hardens in response to applied pressure. The compliant material can be located in or encapsulated in another material, such as but not limited to, a flexible housing. The compliant material can be a dilatant material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the following drawing figures wherein like reference numbers identified like parts throughout. 
         FIG. 1  is a side view (not to scale) of a traffic control device of the invention in the form of a speed bump showing the interior components; 
         FIG. 2  is an end view (not to scale) of the device of  FIG. 1 ; 
         FIG. 3  shows an expansion device of the invention (not to scale) in (a) first (non-expanded) state and (b) a second (expanded) state; and 
         FIG. 4  shows the device of  FIG. 2  (not to scale) in a compressed state after contact with a vehicle. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention will be described with reference to use in a conventional speed bump configuration. However, it is to be understood that the invention is not limited to use with speed bumps but could be used in other traffic control or regulating capacities, such as but not limited to rumble strips and the like. 
     A speed-sensitive traffic control device  10  of the invention is shown in  FIGS. 1 and 2 . The device  10  includes an outer shell  12  having a top  14 , a bottom  16 , a front side  18 , a rear side  20 , and a pair of opposed ends  22 , 24 . The shell  12  may include one or more fastening holes  30  so that the device  10  can be either permanently or replaceably mounted to a roadway or other surface such as by bolts, screws, or other conventional devices. The shell  12  can be formed of any conventional material, such as but not limited to flexible or resilient materials such as polymeric materials or rubber materials. 
     The shell  12  encloses one or more housings or receivers  32  containing a compliant material, that reversibly hardens or stiffens in response to an applied pressure and goes back to its original form when the pressure is relieved, such as a dilatant material. In one embodiment, the interior of the shell  12  can be hollow and the dilatant material provided in one or more hollow spaces inside the shell  12 . However, in the embodiment shown in  FIGS. 1 and 2 , the receivers  32  are in the form of elongated, hollow, flexible tubes having closed ends. The receivers  32  can be of any desired shape but in the illustrated embodiment are shown as cylindrical tubes. The tubes may be of any material and, in one non-limiting embodiment, are formed of a flexible material, such as a polymeric or rubber material. 
     In one non-limiting embodiment, the tubes include an expansion device  40  to allow for the expansion of the dilatant material when a vehicle runs over the device  10 , as will be explained in greater detail below. This expansion device  40  can be of any configuration, such as but not limited to a conventional expansion bladder or similar device. The expansion bladder can be, for example, a conventional flexible pouch or bag in flow communication with the interior of the receiver  32 . Alternatively, the expansion bladder can be formed simply by a flexible end-portion of the receiver  32 . 
     In the illustrated embodiment, the expansion device  40  is shown as a piston device having a piston  42  movable in the tube and connected to a spring  44  or similar biasing member. Under normal conditions, the spring  44  biases the piston  42  to a first position in  FIG. 3(   a ). When the shell  12  is compressed (such as when a vehicle runs over the device  10 ), the tubes are also compressed and the pressure of the dilatant material in the tubes pushes against the piston  42  and compresses the spring  44 , as shown in  FIG. 3(   b ) and as described in detail below. In one non-limiting embodiment, the receivers  32  can include a flow restriction device  50  to enhance the function of the dilatant material. For example,  FIGS. 3(   a ) and  3 ( b ) illustrate the flow restriction device  50  in the form of baffles within the tubes. Of course, other types of flow restrictors could be used. For example, a porous material (such as a porous foam) could be placed within the tubes to restrict the movement of the dilatant material. 
     Dilatant material is also sometimes referred to as a shear thickening fluid or a non-newtonian fluid. That is, below a critical shear rate the material acts like a fluid but above a critical shear rate the material acts like a solid. A dilatant material is typically a material in which the viscosity increases with the rate of shear. Examples of such dilatant materials include the fluid used in the torque converters of some conventional all wheel drive vehicles. Other dilatant materials are formed by dissolving particulate matter in a carrier fluid. One example is formed by placing silica particles in a fluid, such as polyethylene glycol. At high shear rates, the hydrodynamic forces overcome the repulsive interparticle forces and silica hydroclusters form which increase the viscosity of the fluid. The shear rate at which the viscosity increases and the rate of viscosity increase can be controlled by adjusting the amount of colloidal silica particles in the fluid. Other known dilatant materials include dissolving one or more water soluble polymers (such as KLUCEL® polymers commercially available from Hercules Incorporated) in an aqueous solution. In another non-limiting embodiment, an impact hardening foam (such as manufactured by d30) can be used with the dilatant material. 
     Operation of the traffic control device  10  will now be described. 
     The device  10  can be either permanently or temporarily mounted at a desired location, such as in a street or roadway. The dilatant material in the tubes can be selected based on a desired shear rate (which can correspond to a predetermined vehicle speed). When a vehicle rolls over the device  10  below the predetermined speed (i.e. below the critical shear rate of the dilatant material), the dilatant material remains in fluid form and the weight of the vehicle compresses the shell  12  and the tubes, thus pushing the dilatant material (fluid) against the piston  42  and moving the piston  42  from the position shown in  FIG. 3(   a ) to the position shown in  FIG. 3(   b ). The shell  12  and tubes are compressed as shown in  FIG. 4 . When the vehicle has passed over the device  10 , the shell  12  returns to its initial shape and the spring  44  pushes against the piston  42  to push the dilatant material back into the tubes (which also return to their original shape). Thus, below the critical shear rate, little impact is felt by the driver and little stress placed on the mechanical components of the vehicle. Therefore, if the vehicle is traveling under the selected speed limit (and providing a shear rate less than the critical shear rate), the vehicle will not suffer the hard and jolting impact as would occur with a conventional speed bump. 
     However, in the event a vehicle impacts the control device  10  at a speed above the predetermined speed (that is, providing a shear rate above the critical shear rate), the viscosity of the dilatant material increases (i.e. the dilatant material acts as a solid) and the control device  10  substantially retains the speed bump shape shown in  FIGS. 1 and 2 . The control device  10  in this scenario acts similarly to a conventional speed bump and the driver of the vehicle exceeding the selected speed limit will experience a bump or jolt as would be felt with a conventional speed bump. 
     It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. For example, in one embodiment the shell  12  can be eliminated and just one or more of the receivers  32  containing the dilatant material used as the traffic control device. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.