Abstract:
A power distribution module for conveying power to one or more accessories is disclosed. The power distribution module includes a constant-hot power bus; an ignition-hot power bus; and at least one output terminal for conveying power to said one or more accessories, wherein the at least one output terminal is selectively capable of providing one of ignition-hot power to said one or more accessories from the ignition-hot power bus, and constant-hot power to said one or more accessories from the constant-hot power bus.

Description:
RELATED APPLICATION 
   This disclosure claims the benefit of Provisional Patent Application No. 60/895,284, filed on Mar. 16, 2007. 

   FIELD OF THE INVENTION 
   The disclosure relates to a power distribution module and to a device for conveying power to an electrical accessory. 
   DESCRIPTION OF THE RELATED ART 
   It is known in the art that vehicles that are manufactured by an original equipment manufacturer (OEM) may not include one or more options, features, or accessories that are desired by a consumer when the vehicle is purchased by the consumer in a new or previously-owned condition. Is such situations, the consumer may resort to purchasing one or more “aftermarket” accessories, which may be permanently or removably integrated with the vehicle, that provides the function of the one or more options, features, or accessories desired by the consumer. 
   Exemplar aftermarket accessories may include video entertainment systems, navigation systems, cellular telephones, seat heating systems, computers, battery chargers, lighting systems, and the like. As in most situations, such aftermarket accessories may require power from the vehicle&#39;s on-board power source to provide the intended function of the accessory. Typically, the power for the accessory is obtained from a wiring infrastructure extending from the power source, the wires of which may be conveniently located, for example, proximate/behind a dashboard, trim panel, headliner, or the like. 
   Historically, such aftermarket accessories are typically divided into two categorizations: 1) key-on/ignition-hot accessories that require power only when the vehicle&#39;s ignition is on; and 2) key-off/constant-hot accessories that require power at all times, irrespective of the on/off state of the ignition. Because modern vehicles now have dozens, or, even hundreds of wires located, for example, proximate the dashboard area, it may be difficult to locate a dedicated key-on or key-off wire in order to “rewire” and integrate the aftermarket accessory with the vehicle. 
   Further, because copper wiring is heavy and expensive, and, because vehicle manufacturers are under continuous pressure to decrease vehicle weight while improving fuel economy, many wires are designed to specifically supply an intended electrical load without being able to accommodate the provision for larger electrical loads, as may be associated with an aftermarket accessory. Accordingly, the above factors may lead to a formidable challenge in locating an appropriate key-on/off wire so as to be able to supply the desired electrical load to the accessory. 
   In addition to the above concerns, the vehicle wiring infrastructure typically interfaces with electronic control modules (ECMs), which are a) relatively fragile, b) intolerant of electrical overloads, and c) potentially operate in conjunction with sensitive electronic switches. Accordingly, in an exemplar aftermarket installation scenario, a digital video disc (DVD) system may, for example, utilize a wire that is dedicated, in design, to a fuel injection ECM. 
   In an example, a DVD system may share a common wire and operate amicably with a fuel injection ECM even though the common wire is not intended to provide power to the DVD system. However, as an operating dynamic of the DVD system (e.g. soundtrack volume, which may be quantified in decibels) is increased by a user, the DVD system may ultimately cause failure of the ECM. One probable cause of the failure of the ECM is an increased current drain on the wire that may be attributed to a situation when soundtrack volume of the DVD system is increased from a low volume/decibel level past a second, higher volume/decibel level. Accordingly, although the DVD system may operate amicably with the fuel injection ECM when the soundtrack volume/decibel level is set to a relatively low level, the change in soundtrack volume/decibel level from the low level to a higher level may result in the failure of the ECM and subsequent stalling of the vehicle. 
   Further, if an aftermarket accessory is positively rewired according to an appropriate key-on/off operation, the correct rewiring of the accessory may ultimately prove to be unacceptably noisy due to a power sensitivity of the aftermarket accessory. As a result of these and other factors, even a seemingly simple installation of an aftermarket accessory can therefore become frustratingly difficult, unreliable, expensive, and time-consuming to trouble-shoot should a failure of the accessory and/or vehicle occur. 
   Accordingly, there is a need in the art for an apparatus that enables an installer/end user to easily select either one or more key-on/off operating modes for one or more aftermarket accessories without the complexities or concerns associated with the rewiring of an aftermarket accessory with the vehicle&#39;s existing key-on/off wire infrastructure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The disclosure will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a circuit diagram of a power distribution module in accordance with an exemplary embodiment of the invention; 
       FIG. 2  is a circuit diagram of a power distribution module in accordance with an exemplary embodiment of the invention; and 
       FIG. 3  is a circuit diagram of a power distribution module in accordance with an exemplary embodiment of the invention. 
       FIGS. 4   a  and  4   b  are schematic depictions of a fuse placed in first and second positions respectively. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The Figures illustrate an exemplary embodiment of a power distribution module in accordance with an embodiment of the invention. Based on the foregoing, it is to be generally understood that the nomenclature used herein is simply for convenience and the terms used to describe the invention should be given the broadest meaning by one of ordinary skill in the art. 
   Referring to  FIG. 1 , a power distribution module is shown generally at  10  according to an embodiment. The module  10  may be operable from power supplied by a vehicle power source, such as, for example, a vehicle battery. A terminal that permits the module  10  to be connected to the power source is shown generally at  12 . When the module  10  is installed in a vehicle, the module  10  reduces the potential of damage to or the averse functioning of vehicle operation electronics (e.g. electronic control modules (ECMs) and the like). 
   In an embodiment, the module  10  may be powered by a single key-off/constant-hot wire, which is shown generally at  14 , extending from the power source terminal  12 . In an embodiment, the wire  14  may be, for example, approximately a 10-to-8 gauge wire. 
   In an embodiment, the positive lead of the wire  14  may be connected to a main fuse, which is shown generally at  16 . According to an embodiment, the main isolation fuse  16  may be, fore example, a 50-ampere fuse, such that an overload condition of the module  10  will result in the failure of the isolation fuse  16  to ensure that an overload caused by the module  10 , or, any accessory, A 1 -A n , attached to the module  10  does not adversely affect devices (not shown) connected to the remaining wiring infrastructure of the vehicle. 
   In an embodiment, the module  10  has a plurality of ports, which are shown generally at  18 . Each of the plurality of ports  18  are connected to a respective fuse  20 . 
   A key-off/constant-hot power bus is shown generally at  25   a  for providing power to an accessory, which is shown generally at A 1 -A n . The power bus  25   a  is disposed between the main fuse  16  and the respective fuses  20 . Accessories, A 1 -A n , that are connectable to the plurality of ports  18  include, but is not limited to, for example, video entertainment systems, navigation systems, cellular telephones, seat heating systems, computers, battery chargers, lighting systems, and the like. 
   In an embodiment, the ports  18  may include a polarized, positive-locking connector system to provide a simple and secure plug-in-type connection feature for the accessories, A 1 -A n . Polarized connectors prevent connectors from being connected improperly (which, if connected improperly, may cause electrical damage to an accessory). Although eight ports  18  are illustrated in  FIG. 1 , it will be appreciated that any number of ports  18  may be provided, as desired. In an embodiment, each port  18  may provide, for example, up to 11-amperes from the power bus  25   a , which is typically adequate for the majority of accessories, A 1 -A n ; however, it will be appreciated that the ports  18  are not limited to providing 11-amperes and that the ports  18  may provide any desirable amount of power for a particular application associated with a particular accessory, A 1 -A n . 
   To provide a) convenience, b) minimum supply impedance, c) simplified installation, and d) reduced noise, each port  18  also includes a ground lead  22  connected to ground  24  and a power lead  26  extending from a corresponding port fuse  20 . The provision of a power lead  26  and a ground lead  22  at each output  18  may a) reduce the ground impedance and b) provide a low-impedance path directly to the ground terminal  24 . In an embodiment, one or more of the ports  18  may be selected according to the position of the corresponding fuse  20 , which is explained in greater detail below. 
   In addition, it will be appreciated that the availability of a ground lead  22  at each port  18  provides several advantages over conventional methodologies associated with providing power to prior art key-on/off accessories. As is known in the art, conventional methodologies for providing power may include, for example, a) drilling a hole through metal structure of the vehicle, b) scraping away paint, c) crimping on a ground terminal, and d) installing a ground screw. Such a conventional creation of a power system ground is subject to reliability problems, as moisture may cause corrosion of the vehicle body and degrade the makeshift ground. Conversely, in the present invention, the provision of a ground lead  22  at each port  18  results in a ready-to-use ground connection such that little or no alteration is provided to the vehicle body. 
   Referring to  FIG. 1 , an ignition control input terminal is shown generally at  28 . In operation, the ignition control input terminal  28  connects to a wire (i.e., a key-on/ignition-hot wire) in the vehicle to turn on relays, which are shown generally at  30   a ,  30   b , with a low current of, for example, about 250 milliamps to provide key-on power for a key-on power bus, which is shown generally at  25   b . This small amount of current can be supplied by most ignition-hot wires in a vehicle, without overload. The power bus  25   b  is disposed between the relays  30   a ,  30   b  and the respective fuses  20 . 
   Referring to  FIG. 1 , a polarity protection diode, which is shown generally at  32 , is connected between the ignition control input terminal  28  and the relay coil terminal(s)  34   a ,  34   b , to prevent the relay(s)  30   a ,  30   b  from actuating if the voltage polarity connected to the power source terminal  12  and ground  24  is reversed. Accordingly, the polarity protection diode  32  isolates and prevents potentially serious damage to key-on/ignition-hot accessories, A 1 -A n , that could otherwise occur. Still referring to  FIG. 1 , a diode  38  protects and isolates the module  10  against inductive transients from the relay coil(s)  34   a ,  34   b.    
   The relays  30   a ,  30   b  are inexpensive and robust. It will be appreciated, however, that the module  10  is not limited to the use of relays  30   a ,  30   b  and that other switches, such as, for example, Field Effect Transistor(s) (FET), could be used instead. In the case where less output current is required, the relay  30   a  may be deleted from the circuit diagram of the module  10 , and, in place of the relay  30   a , a jumper  40  may be installed such that a single relay  30   b  provides the switching function for key-on/ignition-hot power for the power bus  25   b.    
   Still referring to  FIG. 1 , a light emitting diode (LED)  42 , whose operating current is limited by resistor  44 , provides an illumination, I, according to the qualification of one or more specified conditions of the module  10 . For example, the LED  42  may be illuminated, I, when all of the following conditions are met: a) leads of the battery  12  and ground  24  are connected, b) the polarity of the leads of battery  12  and ground  24  are correct, c) the main fuse  16  is intact, d) the ignition control input terminal  28  is active, and e) the relay(s)  30   a ,  30   b  are functioning correctly. Accordingly, when the LED  42  is lit, the LED  42  gives the installer/end user a high degree of confidence that the module  10  is installed properly and functioning, as desired. 
   In operation, the module  10  employs a fusing scheme that permit the ports  18  to provide easy selection of key-on/ignition-hot or key-off/constant-hot power according to the power needs of a particular accessory, A 1 -A n . As seen in  FIG. 1 , each port  18  is associated with a selectable fusing configuration. In operation, the fuse  20  may be connected to a single pole double throw switch  21  to provide desired key-on/ignition-hot power from the power bus  25   b  or key-off/constant-hot power from the power bus  25   a  to a particular accessory, A 1 -A n , depending on the up/down position of the switch  21 . Alternatively, as shown in  FIGS. 4A and 4B , in an embodiment, a physical switch  21  as shown in each of  FIGS. 1-3  may be eliminated and the fuse  20  may be physically plugged in to one of two ports  23   a  ( FIG. 4A ) or  23   b  ( FIG. 4B ) to provide desired key-on/ignition-hot power from the power bus  25   b  or key-off/constant-hot power from the power bus  25   a  to a particular accessory, A 1 -A n . Whether a switch  21  is used or the approach set forth in  FIGS. 4A and 4B  is used, both techniques are electrically equivalent (although the technique set forth in  FIGS. 4A and 4B  may be more cost effective because it eliminates the need for an electrical switch  21 ). 
   According to the embodiment of  FIGS. 4A and 4B , the port fuse  20  may be selectively inserted in one of two positions. For example, in a first, “up” position shown in  FIG. 4A , the fuse  20  provides for key-off/constant-hot power from the power bus  25   a , whereas, in the second, “down” position shown in  FIG. 4B , fuse  20  provides for key-on/ignition-hot power from the power bus  25   b . Accordingly, the selectable fusing configuration enables the installer or end user to quickly and easily select key-on/ignition-hot or key-off/constant-hot power delivery mode for a chosen accessory, A 1 -A n , connected at a particular port  18  without having to locate and physically connect a wire from the vehicle&#39;s existing wire infrastructure to an accessory, A 1 -A n . In an embodiment, and without limitation, the port fuse  20  may be referred to as an Automotive Type Miniature (ATM) fuse. 
   Referring now to  FIG. 2 , a power distribution module is shown generally at  100  according to an embodiment. The power distribution module  100  is substantially similar to the module  10  with the exception that that module  100  includes a current-limiting resistor  102  and LED  104  connected at each power lead  26 . 
   According to an embodiment, the LED  104  will illuminate if power is present and if the associated fuse  20  is intact. Thus, when the LED  104  is not illuminated, a non-illuminated LED  104  will serve as an indicator of a situation where power is not available such that the fuse  20  is “blown” or missing. 
   According to an embodiment, a means for inhibiting illumination of the LED  104  is also shown generally at  106 . The means  106  includes a jumper  108 , a transistor  110 , and resistors  112 ,  114 . In operation, the means  106  prevents the LED  104  from being illuminated unless an ignition control input seen at the ignition control input terminal  28  is activated (i.e., the ignition is “on”). 
   In an embodiment, if the jumper  108  is included without the transistor  110  and resistors  112 ,  114 , the LEDs  104  associated with key-off/constant-hot outputs will illuminate without regard to the status of the ignition control input terminal  28 . However, as explained above with regarding to certain aftermarket accessory installation scenarios, the resulting current drain on the vehicle&#39;s battery may be undesirable, in which case, the jumper  108  can be deleted and transistor  110  and resistors  112 ,  114  may be included. In this case, even the key-off/constant-hot LED(s)  104  will not illuminate unless the ignition control input terminal  28  is active. Accordingly, in the latter implementation without the jumper  108 , the means  106  reduces the operating current to zero when the ignition is off. 
   Referring now to  FIG. 3 , a power distribution module is shown generally at  200  according to an embodiment. The power distribution module  200  is substantially similar to the module  100  with the exception that that module  200  includes an amplifier  202  connected between the ignition control input terminal  28  and the relay coils  34   a ,  34   b . In operation, the amplifier  202  reduces drive current needed to activate the ignition control input terminal  28 . 
   In an embodiment, the amplifier  202  reduces the input current to a few milliamps, which may be supplied by virtually any desirable ignition-hot wire. In an embodiment, the amplifier  202  includes resistors  204 ,  206  and a transistor  208 . If necessary, it will be appreciated that an FET could be used in place of the transistor  208  to further reduce the drive current. 
   In an embodiment, diode  210  functions substantially similarly as diode  32  such that the diode  210  functions as a polarity-protection diode so that relays  30   a ,  30   b  will not activate if the power polarity is reversed. In an embodiment, diode  212  functions substantially similarly as diode  38  such that the diode  212  functions as an inductive transient clamp to protect transistor  208 . In an embodiment, diode  214  protects transistor  208  from reverse base-emitter breakdown if the power to the main terminals  14  and  24  is reversed. 
   The present invention has been described with reference to certain exemplary embodiments thereof. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the exemplary embodiments described above. This may be done without departing from the spirit of the invention. The exemplary embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is defined by the appended claims and their equivalents, rather than by the preceding description.