Abstract:
A horn circuit for a vehicle includes a steering wheel, a prong extending from a base, and a carbon-based contact disposed on the prong and in electrical contact with the steering wheel. A method of manufacturing a vehicular horn system includes connecting a prong to a base, connecting a steering wheel to a steering column that extends through the base, and positioning a carbon-based contact at an end of the prong to be in electrical contact with the steering wheel.

Description:
BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to components of an electrical circuit such as those used with a vehicle horn. More specifically, the invention related to an electrical contact with improved wear and operating life characteristics.  
         [0003]     2. Background Art  
         [0004]     Horns are used in all types of vehicles. A horn is particularly important in a forklift truck because of the significant dangers surrounding the use of forklift trucks. For example, many forklift trucks have structures that obscure the driver&#39;s view, making it difficult for the driver to see pedestrians in the path of the forklift truck. In addition, many forklift trucks are operated in a warehouse, where a pedestrian could walk around a blind corner and into the path of a forklift truck. In such a case, neither the pedestrian nor the forklift truck operator is able to see the other in time to prevent an accident. Additionally, forklift trucks are often used to carry heavy loads that could fall and cause severe injuries in an accident.  
         [0005]     A horn is an important safety device on a forklift truck because it enables the operator to warn people nearby to stay clear of the forklift truck. Because of the important safety aspects, the horn in a forklift truck is used much more often than a horn in a typical passenger car. In many cases, the horn on a forklift truck is used more than one million times during the life of the forklift truck.  
         [0006]     Most vehicle horns, including horns on forklift trucks, are activated by depressing the center of a steering wheel. When the center section of the steering wheel is depressed, it makes electrical contact to complete the horn circuit. The primary difficulty in completing a horn circuit is that it must be done in a way that will still enable the rotation of the steering wheel to steer the vehicle.  
         [0007]      FIG. 1  shows a steering wheel assembly  100  that includes a steering wheel  101  connected to a steering column  105 . The steering column  105  connects to the steering wheel  101  just above a base or a control assembly  107 . The steering wheel  101  includes a center section  104  that may be depressed to energize a horn circuit (not shown).  
         [0008]      FIG. 2  is an view of the underside of the steering wheel  101 . The steering wheel  101  includes a socket  204  for connecting to a steering column (e.g., column  105  in  FIG. 1 ). The steering wheel  101  also includes a conductive portion  202 . In some embodiments, the conductive portion  202  is attached to the underside of the steering wheel  101 , and in other embodiments, the conductive portion  202  may be integral to the steering wheel  101 .  
         [0009]      FIG. 3  is a cross section of a steering wheel  101  with a conductive portion  202  located on the underside of the steering wheel  101 . The steering wheel  101  is connected to a steering column  105 . A control assembly  107  is positioned below the steering wheel  101 . A conductive prong  301  extends from the control assembly  107 , and the prong  301  is coupled to the control assembly  107  (e.g., with bolt  308  or other suitable means). The prong  301  extends to be in electrical contact with the conductive portion  202  on the steering wheel  101 . As the steering wheel  101  rotates during the steering of the forklift truck (not shown), the prong  301  maintains electrical contact with the conductive portion  202 .  
         [0010]     In some embodiments, the conductive portion  202  is electrically connected to the center section  104  of the steering wheel  101 . When the center section  104  is depressed, the circuit is closed, and an electrical connection is created between the conductive portion  202  and the steering column  105 , by way of the center section  104  of the steering wheel  101 . The base of the prong  301  is electrically connected to the horn circuit, and the steering column  105  is electrically connected to ground. Thus, by depressing the center section  104  of the steering wheel  101 , the horn circuit is closed, and the horn will sound.  
         [0011]     In the embodiment shown in  FIG. 3 , the prong  301  includes a protrusion  305  at the end of the prong  301  for making electrical contact with the conductive portion  202  of the steering wheel  101 . It is noted that different shapes and geometries on the end of a prong may be used. The shape of the contact point on the prong in not important to the operation of the circuit.  
         [0012]     Wear-induced horn failure is considered a normal limitation of a horn circuit lifespan and a worn contact is often the cause. Although the prior art approach of replacing, or providing an extension for, a worn prong or brush head is effective in most cases, in certain applications even short-lived vehicular horn failure may pose an unacceptably high safety hazard.  
         [0013]     What is still needed, thus, is a horn circuit having a reduced risk of wear-induced failure.  
       SUMMARY OF INVENTION  
       [0014]     In some embodiment the invention relates to a horn circuit for a vehicle that includes a steering wheel, a prong extending from a base, and a carbon-based contact disposed at an end of the prong and in electrical contact with the steering wheel. In at least one embodiment, the invention includes a first conductive portion disposed on an underside of the steering wheel and a second conductive portion disposed on the underside of the steering wheel, wherein the carbon-based contact is in electrical contact with the first conductive portion, and the second carbon-based contact is in electrical contact with the second conductive portion.  
         [0015]     In other embodiments, the invention related to a method of manufacturing a vehicular horn system that includes connecting a prong to a base, connecting a steering wheel to a steering column that extends through the base, and positioning a carbon-based contact at an end of the prong to be in electrical contact with the steering wheel.  
         [0016]     Other aspects and advantages of the invention will be apparent from the following description and the appended claims.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0017]      FIG. 1  shows a perspective view of a steering wheel.  
         [0018]      FIG. 2  shows a perspective view of the underside of a steering wheel.  
         [0019]      FIG. 3  shows a prior art horn circuit.  
         [0020]      FIG. 4  shows a horn circuit in accordance with one embodiment of the invention.  
         [0021]      FIG. 5  shows a carbon-based contact in accordance with one embodiment of the invention.  
         [0022]      FIG. 6  shows a horn circuit in accordance with one embodiment of the invention.  
         [0023]      FIG. 7A  shows a circuit diagram of a horn circuit in accordance with one embodiment of the invention.  
         [0024]      FIG. 7B  shows a circuit diagram of a horn circuit in accordance with another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0025]     In one embodiment, the invention comprises a wear-resistant contact for a vehicular horn circuit. In particular, embodiments of the invention use carbon-based compounds as a contact for a vehicular horn circuit. In this disclosure, the term “carbon-based” is used to mean a compresses hardened carbon based solid.  
         [0026]     In this disclosure, “connected” is used to mean joined or fastened together. It may mean that two or more things are directly connected to each other, and it may also include things that are indirectly connected. Thus, two things may be connected even when there is an intervening structure. “Electrically connected” is used to mean that electricity can flow between two things that are electrically connected. Other circuit elements may or may not be connected between items that are electrically connected, so long as electricity may flow between the electrically connected items.  
         [0027]      FIG. 4  shows a partial horn circuit  400  in accordance with one embodiment of the invention. The steering wheel  101  is connected to a steering column  105  that is used to steer the vehicle (e.g., a forklift truck). In this embodiment, the horn circuit  400  is connected through the steering wheel  101  so that depressing the center section  104  of the steering wheel  101  will close the horn circuit.  
         [0028]     The steering wheel  101  includes a conductive portion  202  located on the underside of the steering wheel  101 . Electrical contact is made between the conductive portion  202  and a prong  401  that extends from the control assembly  107  to the steering wheel  101 . A carbon-based contact  402  is positioned at the end of the prong  401  so that it makes electrical contact with the conductive portion  202  on the underside of the steering wheel  101 . Because the conductive portion  202  in this embodiment encircles the bottom of the steering wheel  101 , the carbon-based contact  402  will maintain electrical contact with the conductive portion  202 , even when the steering wheel  101  is rotated to steer the vehicle.  
         [0029]     Advantageously, the present inventors have discovered that by using a carbon-based contact, wear on the contact may be reduced. Suitably carbon-based contacts include, for example, a material such as CTI-22, typically compressed to a hardness in the 40-43 C range on the Rockwell scale.  
         [0030]     The prong  401  is connected to the control assembly  107 . It is noted that some embodiments may not include a control assembly. The prong  401  may be connected by any means known in the art. For example,  FIG. 4  shows the prong  401  coupled to the control assembly  107  by a bolt  408 . In other embodiments, the prong may be soldered, riveted, or connected by other means. A prong may be connected to any structure, generically called a “base,” that will support the prong and hold it in place.  
         [0031]     In some embodiments, the prong  401  is electrically connected in the horn circuit at the base of the prong  401 . That is, the electrical current flows through the prong  401  and the carbon-based contact  402 , when the horn circuit is closed. In other embodiments, such as the one shown in  FIG. 4 , a wire lead  411  is connected to the carbon-based contact  402 , and the wire lead  411  forms part of the horn circuit. In still other embodiments, a wire lead  411  and the prong  401  are connected essentially in parallel so that both the prong  401  and the wire lead  411  form part of the horn circuit.  
         [0032]     The partial circuit shown in  FIG. 4  includes only one conductive portion  202  and prong  401 . The horn circuit may be completed through the steering column  105 , which may be grounded to the negative terminal of the battery (not shown) in the vehicle. In such an embodiment, the electrical current flows through the prong  401 , through the carbon-based contact  402 , and into the steering wheel  101  through the conductive portion  202 . The current then flows through the center section  104  of the steering wheel  101 , when depressed, and through the steering column  105 . Note that the invention is not limited by the direction of electrical current flow. In some embodiments, the prong  401  may be electrically connected to the ground (i.e., negative terminal of the battery), and the steering column  105  is electrically connected to the positive terminal of a battery (not shown).  
         [0033]      FIG. 5  shows an enlarged view of a prong  401  and a carbon-based contact  402 , in accordance with one embodiment of the invention. The carbon-based contact  402  is positioned at the end of the prong  401 . In some embodiments, the carbon-based contact  402  is connected to an electrical lead  411  that electrically connects the carbon-based contact  402  to the horn circuit. In other embodiments, the carbon-based contact  402  is coupled to the horn circuit by the prong  401 . In some embodiments, the carbon-based contact  402  is substantially cylindrical. In other embodiments, a carbon-based contact  402  has a substantially flat upper surface for maximizing the surface area in contact with the conductive portion  202 .  
         [0034]      FIG. 6  shows an embodiment of a partial horn circuit  600  in accordance with another embodiment of the invention. The steering wheel  101  includes a first conductive portion  202  and a second conductive portion  602 . As with the embodiment shown in  FIG. 4 , the circuit  600  includes a prong  401  with a carbon-based contact  402  that is in electrical contact with the first conductive portion  202  on the underside of the steering wheel  101 . The carbon based-contact  402  may include an electrical lead  411  that connects the carbon-based contact  402  to the remainder of the horn circuit  600 .  
         [0035]     The circuit also includes a second prong  604  that is coupled to the control assembly  107 . The second prong  604  includes a second carbon-based contact  603  that is in electrical contact with the second conductive portion  602  on the underside of the steering wheel  101 . Again, because the second conductive portion  602  is circular, the second carbon-based contact  603  remains in electrical contact with the second conductive portion  602  even when the steering wheel  101  is rotated.  
         [0036]     In the embodiment shown in  FIG. 6 , the steering column  105  need not be grounded. The steering wheel  101  includes two conductive portions  202 ,  602  that are in electrical contact with two carbon-based contacts  402 ,  603  and prongs  401 ,  604 , respectively. The positive connection may be made through one of the prong-contact-ring connections, and the negative (or ground) connection may be made through the other.  
         [0037]      FIG. 7A  shows a circuit diagram for one embodiment of a horn circuit  700  in accordance with the invention. A horn  704  is electrically connected to a battery  702  that supplies electrical power to the horn  704 . The horn  704  is also electrically connected to a switch  712  that enables activation of the horn  704 . The switch  712  may be the center section of a steering wheel that will complete the circuit  700  when it is depressed.  
         [0038]     A prong  708  is shown between the horn  704  and the switch  712 . In some embodiments, the prong  708  is electrically connected to both the horn  704  and the switch  712 . A carbon-based contact  710  is shown as a node between the prong  708  and the switch  712 . As described above, in some embodiments, a carbon-based contact is positioned at the end of the prong and is in electrical contact with a conductive portion on the steering wheel. The conductive portion is electrically connected to the switch  714  in the center section of the steering wheel (e.g.,  104  in  FIG. 4 ).  
         [0039]     Some embodiments, such as the one shown in  FIG. 7A , include a wire lead  706  that is electrically connected between the horn  704  and the carbon-based contact  710 . Those having ordinary skill in the art will realize that a wire lead  706  may be used with a non-conductive prong (a non-conductive prong would not appear on a circuit diagram). Alternatively, as shown in  FIG. 7A , the wire lead  706  and a conductive prong  708  may be electrically connected in parallel.  
         [0040]     The section designated at  714  represents a steering column that is electrically connected between the switch  712  and the chassis ground  716 . The chassis ground  716  is electrically connected to the negative terminal of the battery  702  to complete the circuit  700 .  
         [0041]      FIG. 7B  shows another embodiment of a horn circuit  750  in accordance with the invention. A battery  702  is electrically connected to a horn  704 , and the horn is electrically connected to a switch  712  by a prong  758  and/or a wire lead  756 . A carbon-based contact  760  is electrically connected to the prong  758  and the wire lead  756 , and the carbon-based contact  760  is in electrical contact with a conductive portion on the steering wheel (not shown). The conductive portion is electrically connected to the switch  712 . The circuit  750  does not include a steering column, as in  FIG. 7A . In  FIG. 7B , a a second carbon-based contact  770  is in electrical contact with a second conductive portion (not shown). A second prong  772  and/or a second wire lead  771  are electrically connected to the chassis ground  716 , which may be electrically connected to the negative terminal of the battery  702 .  
         [0042]     As with the embodiment shown in  FIG. 7A , the wire leads  756 ,  771  may be used in parallel with the prongs  758 ,  772 , or they may be used independently of the prongs  758 ,  772 . Additionally, some embodiments may not include wire leads  756 ,  771 .  
         [0043]     A carbon-based contact may comprise any carbon-based compound or carbon graphite compound known in the art. In one embodiment, the carbon based contact may comprise a CTI-22 type carbon compound, available from Morgan AM&amp;T (St. Marys, Pa.). Additionally, a carbon-based contact in accordance is not limited to a cylindrical shape. For example, a carbon-based contact may comprise a brush as known in the art. Other shapes are possible.  
         [0044]     Embodiments of the invention may present one or more of the following advantages. A carbon-based contact may enable a larger surface area to be in contact with a conductive portion on a steering wheel. The larger surface area will enable better electrical contact. Additionally, the larger surface area will decrease the tendency of the contact to gall, gauge, or score the steering wheel or conductive portion, thereby increasing the operating life of the horn circuit. Further, while the embodiment described refer to certain geometries for various components, those having ordinary skill in the art will appreciate that other geometries may be used without departing from the scope of the invention.  
         [0045]     Advantageously, a carbon-based contact will not wear as easily as other materials, thus increasing the life of a horn circuit. The carbon-based contact may also provide a lower coefficient of friction with a steering wheel or a conductive portion. This will decrease the tendency of the contact to wear from the friction with the steering wheel or conductive portion.  
         [0046]     While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.