Patent Publication Number: US-7217062-B2

Title: Control for screed heaters

Description:
This application claims priority to European Application No. 04004082.6, filed Feb. 23, 2004. 
   TECHNICAL FIELD 
   The present invention relates to paving machines having screed assemblies and, more particularly, to paving screed assemblies having screed heaters. 
   BACKGROUND 
   Paving machines are used for depositing, spreading, compacting, and smoothing paving material on a roadbed in such a manner that a uniform and drivable surface is produced. In the case of an asphalt paving machine, the paving material is typically an aggregate filled bituminous mixture that is deposited on a roadbed while hot. Once the mixture cools after being suitably compacted and smoothed, a hardened pavement surface results. 
   Paving machines use screed assemblies to smooth and compact the paving material. The screed assembly is typically drawn behind the paving machine and is adjustable to establish the thickness of the deposited layer of paving material. 
   A screed assembly typically includes a base portion and may include one or more extension portions, each of these portions having steel screed plates mounted to the screed portions in such a manner that the plates both smooth and compress the deposited paving material, leaving behind a mat of the desired thickness. The screed plates are typically heated to prevent the bituminous material from clinging to the steel plates. In modem screed assemblies, the screed plate heaters are commonly implemented in the form of resistive electrical heaters that can be optimally positioned on or near the screed plates. Screed plates may also be heated by gas or other combustible fuel heaters. 
   It is important to maintain a proper screed plate temperature. If the screed plates are either too hot or too cold, a poor finish will be obtained in the resulting pavement mat. In a simple screed having only base screed portions, each of the base screed portions typically includes both a heater and a temperature sensor. In such a system, each of the base screed plates may be individually temperature controlled according to feedback received from the associated temperature sensor. 
   However, many screed assemblies make provision for attaching extension screeds to the ends of the base screed portions. These extension screed portions must be mechanically connected to the base screed portions, and must also be connected to provide controlled power to the heating elements. It is known to merely connect the heating elements of the extension screed portions in parallel with the heating elements of the base screed. In such a configuration, the extension screed heaters are controlled in response to temperature sensors located on the base screed portion. Consequently, the extension screed portions may be either too hot or too cold to produce a desired mat finish. 
   The present invention is directed to overcoming one or more of the problem set forth above. 
   SUMMARY OF THE INVENTION 
   In one aspect of the present invention, a screed for a paving machine has at least one base screed portion having an associated heating element connected to a heating element controller. The screed also has at least one extension screed portion connectable to the base screed portion, and having a respective heating element connectable to the heating element controller. A temperature sensor is associated with each of the base and extension screed portions, and a switching device is adapted to controllably connect selected ones of the base and extension screed temperature sensors to the heating element controller. 
   In a second aspect of the present invention, a system for controlling the temperature of the screed plates of a paving machine screed includes a heating element controller, and has at least one base screed portion and at least one extension screed portion connectable to the base screed portion. Each of the base and extension screed portions has a respective heating element connectable to the heating element controller and has a respective temperature sensor positioned to be responsive to the temperature of a respective screed plate. The system includes means for connecting the at least one extension screed portion to the temperature controller and means for controlling the temperature of the base and extension screed plates in response to the connecting means. 
   In a third aspect of the present invention, a method is disclosed for selectively controlling the heating elements associated with a screed for a paving machine. The screed includes at least one base screed portion having a heating element connected to a heating element controller and one or more extension screed portions connectable to the base screed portion. Each of the extension screed portions has a respective heating element connectable to the heating element controller, a temperature sensor associated with each of the base and extension screed portions, and a switching device adapted to controllably connect selected ones of the temperature sensors to the heating element controller. The switching device includes a number of electrical connectors corresponding at least to the maximum desired number of connectable extension screed portions. The method includes the steps of connecting a desired number of the extension screed portions to selected respective ones of the switching device electrical connectors, and connecting a predetermined one of the temperature sensors to the heating element controller in response to the selected mating of the extension screed portions to the electrical connectors. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic side view of a paving machine including a screed assembly; 
       FIG. 2  is a schematic view of a portion of the screed assembly of  FIG. 1 ; and 
       FIG. 3  is a block diagram view of a portion of the screed assembly of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   A screed  10 , as depicted in the figures, is constructed as might typically be found in a commercial screed product. Screeds  10  typically include left-hand and right-hand base screed portions  18  (with reference to the screed  10  centerline) that may be independently controllable to produce a pavement surface having a desired configuration, for example, a road surface having a crowned center portion. Base screed portions  18  are often segmented, as is most clearly seen in  FIG. 2 , to provide for ready transport between job sites. In such configurations, the base screed portions  18  often include two or more sections that may be collapsed or moved inwardly toward the center of the paving machine  14  to reduce the overall screed width, and that may be moved outwardly to increase the width. In addition, one or more extension screed portions  30  may be readily attached to the outermost ends of the base screed portions  18  to provide still greater paving width capabilities. For simplicity in description, the following technical discussion generally focuses on one half, either right-hand or left-hand, of a screed assembly. However, it should be understood that the description and appended claims apply equally to the second half of such a screed assembly. Also, throughout this description, references to the base screed portions  18  are to the outermost end or extended portions of a segmented base screed, as discussed above. 
   Referring generally to the Figures, a screed  10  for a paving machine  14  is shown. The screed  10  has at least one base screed portion  18  having an associated heating element  22  connected to a heating element controller  26 . The screed  10  may also have at least one extension screed portion  30  connectable to the base screed portion  18  and having a respective heating element  34  connectable to the heating element controller  26  through a switching device  42 . A temperature sensor  38  is associated with each of the base and extension screed portions  18 ,  30 , and the switching device  42  is adapted to controllably connect selected ones of the base and extension screed temperature sensors  38  to the heating element controller  26 . In a preferred embodiment, the heating elements  22 ,  34  are resistive electrical heating elements, but may also be fuel fired burner elements. 
   In the case of a segmented screed  10  as previously discussed, the base screed portion  18  of interest is the outermost portion of the segmented base screed. In this configuration, the innermost portions of the base screed may also include respective heating elements  24  and temperature sensors  40  connected to the heating element controller  26  in a conventional feedback arrangement in which respective heating elements  24  respond directly to respective associated temperature sensors  40 . Where this configuration is used, any portions of the base screed that employ such direct static temperature control in which the associated temperature sensors  40  are not connectable to the switching device  42  are likewise not subject to control in accordance with the present invention. 
   The switching device  42  includes a number of electrical connectors  46 ,  50  corresponding at least to the maximum desired number of connectable extension screed portions  30 . Each of the extension screed portions  30  may also include a respective electrical connector  48 ,  52  suitable for plugging in to or mating with the switching device electrical connectors  46 ,  50 . Mating the extension screed portion electrical connectors  48 ,  52  with selected ones of the switching device electrical connectors  46 ,  50  determines which of the temperature sensors  38  are actually connected to the heating element controller  26 . 
   A predetermined one of the switching device electrical connectors  46  is connected to the relay  54 , and each of the extension screed portion electrical connectors  48 ,  52  includes a mechanism  58  sufficient to actuate the relay  54  in response to connecting an extension screed portion electrical connector  48 ,  52  to the predetermined switching device electrical connector  46 . In particular, the relay activation mechanism  58  may be an internal connection within the extension screed portion electrical connectors  48 ,  52  that, when connected to the predetermined one of the switching device electrical connectors  46  that is associated with the relay  54 , closes a circuit to provide electrical power to switch the relay  54 . As a consequence, plugging an extension screed portion electrical connector  48 ,  52  into the predetermined one of the switching device electrical connectors  46  causes the relay  54  to select an appropriate temperature sensor  38  that will be connected to the heating element controller  26 . 
   In another embodiment, each of the temperature sensors  38  may be connected to the heating element controller  26  in response to plugging the extension screed portion electrical connectors  48 ,  52  into the switching device electrical connectors  46 ,  50 . In this embodiment, none of the switching device electrical connectors  46 ,  50  are associated with a relay. Instead, the temperature sensor  38  associated with each extension screed portion  30  that is plugged in is connected to the heating element controller  26 . All of the temperature signals received by the heating element controller  26  from the extension screed portions  30  and the base screed portion  18  are averaged by the heating element controller  26 , and the heating elements  34  are controlled in response to this determined average value. However, this simplified embodiment does not optimize the amount of heat provided to each of the base and extension screed portions  18 ,  30 . 
   INDUSTRIAL APPLICABILITY 
   In a typical paving operation, a screed assembly  10  associated with a paving machine  14  must be properly configured prior to beginning paving activity. Where present, the left-hand and right-hand segments of the base screed portions  18  are extended in opposite directions from the machine  14 . An appropriate number of extension screed portions  30  are then mechanically attached one to another and to the ends of the base screed portions  18  to provide a desired working width of the overall screed  10 . A typical configuration might include two extension screed portions  30  connected sequentially to each of the left and right-hand sides of the screed  10 . However, some applications will not require any extension screed portions  30  while others might require only one or more than two. 
   With the extension screed portions  30  mechanically attached to the base screed portions  18 , an electrical connector  48 ,  52  on each of the extension screed portions  30  is selectively mated with an electrical connector  46 ,  50  associated with the switching device  42 . As mentioned above, each of the right-hand and left-hand halves of the screed  10  is configured identically, and a switching device  42  may be found on each screed half or a single switching device  42  may be configured to accept connections from both screed halves. In either case, the switching devices  42  will connect to the heating element controller  26 . 
   The particular one of the switching device electrical connectors  46 ,  50  into which an extension screed portion electrical connector  48 ,  52  is inserted will determine which of the temperature sensors  38  will control the electrical current supplied from the heating element controller  26  to particular ones of the heating elements  22 ,  34 . For example, in the case where no extension screed portions  30  are used, the relay  54  in the switching device  42  will be in the normally closed position. Therefore, the base temperature sensor  38  will be connected through the relay  54  to the heating element controller  26 . 
   In the case where one extension screed portion  30  is to be used in association with a base screed portion  18 , the operator may choose to connect the extension screed portion  30  to any of the switching device electrical connectors  46 ,  50 . In the event that the extension screed portion  30  is connected to the switching device electrical connector  50  that is not connected to the relay  54 , the relay activation mechanism  58  will not actuate the relay  54  and the base temperature sensor  38  will control the temperature of both the respective base screed portion  18  and the connected extension screed portion  30 . This is because the extension screed portion temperature sensor  38  remains isolated from the heating element controller  26 . 
   However, if the extension screed portion  30  is instead connected to the switching device electrical connector  46  connected to the relay  54 , the relay activation mechanism  58  will cause the relay  54  to switch, resulting in the extension screed temperature sensor  38  being connected to the heating element controller  26  and the base temperature sensor  38  being disconnected from the controller  26 . In this case, feedback from the extension screed portion temperature sensor  38  will control the amount of heat delivered to both the base and extension screed portions  18 ,  30 . The operator will decide which of these configurations to use depending on whether the extension screed portion  30  is operating too hot or too cold, determined according to the mat finish that the operator observes as paving proceeds. 
   In like manner, if two or more extension screed portions  30  are to be used on a side of the screed  10  in a given instance, the operator is free to select whether the inner or outer ones of the extension screed portions  30  are to control the amount of heat delivered to each of the base and extension screed portions  18 ,  30 . Again, selecting which of the switching device electrical connectors  46 ,  50  into which to plug a selected one of the inner and outer extension screed portions  30  will determine whether the inner or the outer extension screed temperature sensor  38  is connected to the heating element controller  26  and, consequently, will determine which of the inner and outer-most extension screed portions  30  controls the amount of heat to be delivered to the base and extension screed portions  18 ,  30 . 
   In this way, by merely selecting appropriate mating connections between the extension screed electrical connectors  48 ,  52  and the switching device electrical connectors  46 ,  50 , the paving machine operator can exercise control over the amount of heat delivered to the various screed portions  18 ,  30 . Consequently, the quality of the pavement mat produced may be enhanced. 
   Although the invention has been described with reference to a preferred embodiment, it is clear in light of the overall disclosure that one skilled in the relevant arts may readily recognize or conceive modifications, variations, and alternative constructions not specifically addressed in detail above. For example, one could readily replace the specially configured connectors described above with a suitable mechanical switch, such as a toggle switch, to accomplish the selection of temperature sensors to be connected to the heating element controller. Likewise, the selection could be controlled through the use of electronic logic and control circuitry without using mechanical switching devices. These and other adaptations are intended to be covered by the appended claims. 
   Other aspects, objects, and advantages of this invention may also be obtained from a study of the drawings, the disclosure, and the appended claims.