Patent Publication Number: US-2004041682-A1

Title: Battery circuit disconnect device

Description:
TECHNICAL FIELD  
       [0001] The present invention relates to a device for opening a circuit.  
       BACKGROUND OF THE INVENTION  
       [0002] Motor vehicles, such as cars, marine vessels, trucks and the like almost universally include a starter circuit and other cables that conduct high current. In many cases, such as in a starter circuit, it is impractical to protect the circuit with a fuse since a large fuse would be required to support the current needed to power the device. This size fuse would provide little or no protection during the periods of time when current is not needed to operate the device. As a result, in certain conditions, such as when wire insulation is cut or pierced, an unprotected circuit could cause electrical arcing or short circuits. This could shut down the vehicle or damage other components.  
       [0003] In addition, it may be advantageous to open a circuit in the event of a vehicle collision, short circuit, or some other event. A common solution is to use a large latching switch or contactor to disconnect selected battery circuits in the event of a post-crash short circuit. These types of devices are typically bulky and have reliability problems. The prior art includes examples of other devices. Richter, et al., German patent 4344639.6, the U.S. equivalent of which is U.S. Pat. No. 5,535,842 describes a device that slides over a battery cable and uses a pyrotechnic charge or spring force to cut a cable when initiated by an external signal. In certain applications, this device may require considerable force to cut through the cable and associated insulation. Therefore, it must be sized sufficiently large to enable enough energy to be stored to generate the required force. It also requires the cable to be repaired or replaced after an actuation. Krappel, et al., WO 97/31406, the U.S. equivalent of which is U.S. Pat. No. 6,171,121, describes a device that fires a pyrotechnic charge to dislodge a battery cable from a terminal attaching it to a battery. This device also requires the cable to be repaired or replaced after actuation. Another disadvantage is that the cable, separating mechanism, and pyrotechnic charge may not be contained during and after actuation creating risks associated with the rapidly moving ejected pieces. Totsuka, et al., Japanese patent 10-50978, the U.S. equivalent of which is U.S. Pat. No. 6,243,245 describes a forced-fusion fuse and circuit breaker that offers over-current circuit protection common to automotive fuses along with the ability to open the fuse based on input from a sensor. A disadvantage of this type of design in certain circuits is that surge current conditions can melt the fuse resulting in an unintended or nuisance opening of the circuit. Another disadvantage is in trade-offs that need to be made in sizing the fuse element to be large enough to avoid nuisance openings while being small enough to melt quickly when actuated.  
       SUMMARY OF THE INVENTION  
       [0004] The present invention overcomes the problems noted above and satisfies a need for a circuit disconnect device. The present invention provides a housing that encloses and contains a current conducting bus bar and bus bar separator mechanism. Protruding from the housing are two terminals that provide electrical connection points for the circuit to be protected. In a preferred embodiment, a connection is provided for interface to an initiator circuit.  
       [0005] The separator mechanism is capable of being actuated by a signal indicating a need to open the circuit. Events that may trigger the signal include a crash sensor detecting a vehicle crash, a crash sensor detecting a vehicle crash in combination with an occupant detector such as a load cell detecting a trapped occupant, a theft system detecting a vehicle theft condition, detection of excessive current or other electrical fault, manual activation, and other events.  
       [0006] Upon being actuated, the separator mechanism uses kinetic energy to sever the bus bar and open the circuit. The separator mechanism may comprise a pyrotechnic charge, spring, solenoid, or other energy source acting on a blade or knife-like component. The separator mechanism may also comprise a flammable gas, compressed gas, or pyrotechnic charge that is sufficiently powerful to sever the bus bar electrical conductor without the need for a blade or knife-like component. The housing of the circuit disconnect device safely contains the mechanical components and any gas pressure generated during and after actuation.  
       [0007] In order to rapidly stop the supply of current it is desirable to cut or break the electrical conductor. The use of physical force is well suited for this, and in this invention is deemed the best solution. The use of physical force is referred to herein as being based on the use of kinetic energy. This is intended to include cutting, smashing, tearing, ripping, and substantially every known manner of causing physical force to result in causing the conductor to stop conducting.  
       [0008] The current conducting bus bar is designed with appropriate materials, size, and shape such that it carries sufficient current and is not susceptible to separation due to heating caused by excessive current flow. Ideally, the bus bar will not melt or otherwise open the protected circuit through any mechanism other than that caused by the separator mechanism. The bus bar is also designed such that it loses its ability to carry current after being acted upon by the separator mechanism. In a preferred embodiment, the bus bar is a rigid or semi-rigid rectangular shaped metal bar. The bus bar design may incorporate one or more weak points relative to the remainder of its length in an area where it is impacted by the separator mechanism. This could enable the size and mass of the separator mechanism as well as the overall device to be smaller and lighter than a unit required to cut through an insulated cable. This also enables a reduced amount of pyrotechnic, flammable gas, or other material that generates kinetic energy to be used as a separating mechanism with or without the use of a blade or knife-like component.  
       [0009] Once the device is activated, the electrical circuit remains permanently disconnected-until the activated circuit disconnect device is removed and replaced with an un-activated unit, or a component of the device is removed and replaced. For example, the bus bar can be replaced and a solenoid can be reset, a spring can be reset, and/or a pyrotechnic device can be reloaded. This would normally be done after clearing any circuit fault condition that caused activation.  
       [0010] Another embodiment of the present invention includes designing the overall electrical resistance of the bus bar conductor to a known resistance and incorporating a means to measure voltage across a length of the bus bar electrical conductor. The circuit disconnect device acts as a shunt resistor for measuring current in the protected circuit. In this embodiment, the circuit disconnect device further includes a control unit or means to communicate with an external control unit to activate the separator mechanism when the voltage differential across the bus bar electrical conductor exceeds a threshold amount. This allows the device to monitor for over-current conditions without the need for a separate current sensor. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
     [0012]FIG. 1 is a sectional view of the battery circuit disconnect device of the present invention including an interface to an initiator circuit.  
     [0013]FIG. 2 is a sectional view of the battery circuit disconnect device of the present invention that uses a pyrotechnic for severing an electrical conductor.  
     [0014]FIG. 3 is a sectional view of another embodiment of the battery circuit disconnect device of the present invention utilizing the conductor as a shunt resistor.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0015] Referring to the figures wherein like numerals refer to like elements throughout the several views, FIG. 1 illustrates a battery disconnect device  10  of the present invention. The housing  12  at least partially encloses an electrical conductor  14  having a first end  16  and a second end  18  adapted for connection in a circuit (not shown). The electrical conductor  14  comprises an electrically conductive bus bar  20  being in electrical contact with a first terminal  22  arranged at the first end  16  and being in electrical contact with a second terminal  24  arranged at the second end  18 . The electrical conductor  14  is made of suitable materials and has sufficient cross-sectional area to adequately support the electrical load being supplied. In a preferred embodiment, the electrical conductor  14  has an indentation  26  to enable a predictable severing point and to reduce the amount of force needed to sever the electrical conductor  14 . Note that an indentation is not required or more than one can be used. Also, note that the terminals  22 ,  24  are not required for the electrical conductor  14  to be adapted for connection in a circuit. For example, the electrical conductor  14  can be designed with formed terminals or it can be designed to be soldered or press fit to the protected circuit.  
     [0016] The housing  12  encloses an electrical conductor separator mechanism  28  capable of eliminating the current carrying capability of the electrical conductor  14  using kinetic energy. The separator mechanism  28  is capable of eliminating the current carrying capability of the electrical conductor  14  before rescue personnel arrive at the scene of an accident. FIG. 2 depicts the separator mechanism  28  comprising a pyrotechnic material  30  that can be ignited by a detonator  32 . The use of the pyrotechnic material in the present invention can enable the current carrying capability of the electrical conductor to be eliminated in less than 1 millisecond after receiving the signal. Alternatively, the separator mechanism  28  may comprise a spring that propels a blade, a-flammable gas initiated by a detonator, a compressed gas, a solenoid, or other mechanism using kinetic energy.  
     [0017] Referring back to FIG. 1, the separator mechanism  28  is actuated by a signal from a line  34 , which comprises one or more electrical circuits including a path to ground. Alternatively, the signal can be transmitted without the use of the line  34  using an infrared transmitter or other means. This may require additional structure within the battery disconnect device  10  to receive the signal, such as a radio frequency or infrared receiver or detector. The signal may originate from a control unit (not shown), sensor (not shown), or other source.  
     [0018]FIG. 3 illustrates another embodiment of the invention utilizing the electrical conductor  14  as a shunt resistor. In this embodiment, the battery disconnect device  10  comprises a housing  12 , an electrical conductor  14 , a separator mechanism  28 , and the line  34  going to ground. The battery disconnect device further comprises a first voltage sense line  36  attached to a first voltage sense location  38  on the electrical conductor  14  and a second voltage sense line  42  attached to a second voltage sense location  40  on the electrical conductor  14 . In this embodiment, the electrical conductor  14  between the first voltage sense location  38  and second voltage sense location  40  is designed to an appropriate known resistance value.  
     [0019] A control unit  44  measures and compares the voltages from the voltage sense lines  36 ,  42  and sends a signal to the separator mechanism  28  when a threshold voltage differential between the voltage sense lines  36 ,  42  is detected. This voltage differential corresponds to a known current. Thus, the control unit  44  signals the separator mechanism  28  to sever the electrical conductor  14  when a predetermined current is reached. Note, the control unit  44  is depicted as an integral part of the device. Alternatively, the control function can be performed by another module and signals transmitted between the other module and the battery disconnect device via the line  34 .  
     [0020] This invention has been described with reference to the preferred embodiment and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the invention. For example, one skilled in the art would realize that where a signal is detected to initiate an event, the event can also be initiated by detecting a removal of a signal, or by detecting a change to a signal.