Abstract:
A method and apparatus are provided for short circuit protection to a motor vehicle starter circuit. The invention includes providing a switching mechanism positioned intermediate to a DC power source and the starter. A controller manipulates the switching mechanism between an open position and a closed position, the closed position connecting the starter circuit to the DC power source and the open position disconnecting the starter circuit from the DC power source.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a system for providing short circuit protection to an electrical circuit that connects a device to a DC power source. In particular, the present invention is considered suitable for removing voltage from the circuit that connects a vehicle starter to a battery during the periods when current is not needed to power the starter.  
       BACKGROUND OF THE INVENTION  
       [0002]     Motor vehicles, such as cars, marine vessels, trucks and the like almost universally include a battery that is used for engine ignition. The battery is electrically connected to a starter that is used to crank the ignition. Typically, the starter is actuated by a solenoid relay located adjacent the starter. As a result, the conductor that carries current from the battery to the starter solenoid contains the voltage supplied by the battery. In addition, the conductor is typically sized to carry a significant amount of current needed to drive the starter.  
         [0003]     In a typical motor vehicle 12 volt electrical system, the current that goes through the starter circuit has an initial surge of 900 to 1500 amps and has a steady state current of 200 to 600 amps for about six seconds. Of all the electrical cables in a motor vehicle, the starter cable can provide the most energy at a short. It is impractical to protect the starter circuit with a fuse since a large fuse would be required to support the current needed to power the starter. This size fuse would provide little or no protection during the periods of time when current is not needed to operate the starter. As a result, in certain conditions, such as when the starter circuit wire insulation is cut or pierced, an unprotected starter circuit could cause electrical arcing or short circuits. This could shut down the vehicle or damage other components.  
         [0004]     Some existing battery protection devices are capable of shutting off power to the entire electrical system under certain conditions. Such conditions include detection of a short circuit condition, battery low voltage, or activation of a theft deterrent system. Likewise, short circuit current sensors can be used in a system to shut off current after a short condition occurs. However, these devices shut off current only after the short has already occurred.  
         [0005]     As the need for energy in motor vehicles increases with the introduction of more electrically powered components and systems, vehicle manufacturers are contemplating the introduction of higher voltage electrical architectures. Current proposals contemplate replacing 12 volt systems with a 42 volt system. The use of higher voltages increases the probability that a damaged starter cable could result in an electrical arc. The use of higher voltages also increases the amount of energy available to damage vehicle components and systems. Therefore, use of higher voltage vehicle electrical systems will need short circuit protection for the battery source.  
         [0006]     Thus far, the prior art does not adequately address preventing short circuits and electrical arcing from occurring in a starter circuit.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention overcomes the problems noted above and satisfies a need for a short circuit protection system for an electrical circuit that connects a battery to an unfused device. The invention overcomes the problems of the prior art by providing a system that removes voltage from the circuit that electrically connects a device to a DC power source, such as a battery, during periods when the device does not require power.  
         [0008]     The present invention is particularly useful to protect a starter circuit from short circuits, electrical arcing, and current leakage. In contrast to battery disconnect systems known in the prior art, this invention can remove energy from a single circuit without shutting down power to the entire electrical system. The present invention can thus be incorporated with battery protection systems and anti-theft systems known in the prior art. When used as a motor vehicle starter circuit protection system, the present invention protects the circuit while the vehicle is in operation. Other vehicle battery disconnect systems disconnect power only when conditions such as low battery voltage are detected.  
         [0009]     In accordance with the present invention, a short circuit protection system is provided to electrically protect a section of conductor that is a part of the conductive path between a DC power source, such as a battery, and a device powered by the DC power source. The system comprises two switches in the conductive path between the battery and the device. It also includes a microprocessor capable of receiving inputs indicating that the device is to be turned on and shut off and further capable of generating ouputs to open and close the two switches.  
         [0010]     In accordance with the present invention, a method is provided to remove voltage from a section of electrical conductor that is a part of the conductive path between a DC power source, such as a battery, and a device powered by the DC power source. A preferred method comprises the steps of detecting a signal indicating the device is to be shut off, opening a switch that lies in the conductive path between the device and a first end of the section of conductor to be protected, and then opening a second switch that lies in the conductive path between the battery and the other end of the section of conductor to be protected. An advantage of using this method is that the switch located between the battery and the section of conductor to be protected closes when there is no electrical load. As a result, this switch can be designed to be less rigorous than the switch located between the device and the section of conductor to be protected.  
         [0011]     In accordance with another preferred aspect of the present invention, the method includes the steps of detecting a signal indicating the device is to be turned on, closing the switch that lies in the conductive path between the battery and a first end of the section of conductor to be protected, and then closing a second switch that lies in the conductive path between the device and the second end of the section of conductor to be protected. Once these steps are completed, power is provided to the device. The method further comprises the steps of detecting a signal indicating the device is to be shut off, opening the second switch that lies in the conductive path between the device and second end of the section of conductor to be protected, and then opening the switch that lies in the conductive path between the battery and the first end of the section of conductor to be protected. As a result, power is first removed from the device then removed from the section of conductor to be protected. An advantage of using this method is that the switch located between the battery and the first end of the section of conductor to be protected always closes and opens when there is no electrical load. As a result, this switch can be designed to be less rigorous than the switch located between the device and the section of conductor to be protected.  
         [0012]     It is thus an object of the present invention to provide an improved system that removes voltage from a section of the circuit that electrically connects a battery to a device powered by the battery;  
         [0013]     It is yet another object of the present invention to enable the use of a switch in the conductive path that is less rigorous than a second switch located in the conductive path. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The invention may take physical form in certain parts and arrangement of parts, the preferred embodiment of which will be described in detail and illustrated in the accompanying drawings which form a part hereof and wherein:  
         [0015]      FIG. 1  is a circuit diagram illustrating the present invention; and  
         [0016]      FIG. 2  is a flow diagram of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Referring now to the drawings,  FIG. 1  is a circuit diagram of a short circuit protection system  10  utilized to protect an unfused starter circuit, such as a motor vehicle starter circuit. A positive terminal  12  of a battery  14  is electrically connected to a device, in this case a starter,  16  via a conductive path that includes a starter circuit  18 . The positive terminal  12  of the battery  14  is also electrically connected to other vehicle electrical loads such as lights  20   a , radio  20   b , and generator  20   c . It will be appreciated that other vehicle loads may be added such as air conditioning, etc. A starter switch  22  is located within the starter circuit  18 . The starter switch  22  is an preferably an electromechanical switch actuated by a relay (starter solenoid relay)  34 . Another switch, a battery disconnect device (BDD) switch  24 , is located within the starter circuit  18  between the starter switch  22  and the battery  14 . The BDD switch  24  is preferably an electromechanical switch actuated by a relay (BDD relay)  32 . A protected conductor  26  completes the circuit  18  and runs between battery  14  and starter  16 , with switches  22  and  24  there between. The protected conductor  26  represents a portion of the starter circuit  18  that is electrically protected by the present invention. The protected conductor  26  has a first end  28  that connects to the BDD switch  24  and a second end  30  that connects to the starter switch  22 .  
         [0018]     As to switches  22  and  24 , it will be appreciated that other types of switches such as solid state switches may also be used. It will also be appreciated that the switches may be actuated by other mechanisms such as solid state devices.  
         [0019]     The starter switch  22  and the BDD switch  24  are normally open and no power is supplied to the starter  16 . Power is provided to starter  16  when starter switch  22  and BDD switch  24  are closed. A microprocessor (BDD controller)  36  provides the logic necessary to open BDD switch  24  via a BDD switch output  38 . The BDD controller  36  also provides the logic necessary to open and close the starter switch  22  via a starter switch output  40 . It will be appreciated that the logic necessary to open and close the BDD switch  24  and the starter switch  22  can be transmitted directly from another controller such as an engine control module  42 .  
         [0020]     In the preferred embodiment, the BDD controller  36  receives input of an ignition switch  44  activation from the engine control module  42  via an input  46 . It will be appreciated that the ignition switch  44  activation signal can be transmitted directly from the ignition switch  44  to the BDD controller  36 . It will also be appreciated that the ignition switch  44  activation signal can originate from the ignition switch within the vehicle or from another device such as a remote starter (not shown). The engine control module is also capable of providing other input signals to the BDD controller. Examples of such input signals include indications of an electrical system short circuit and vehicle theft deterrent system activation. The BDD controller  36  can also use signals of this type to command the BDD switch  24  and/or the starter switch  22  to open or close.  
         [0021]     The BDD controller  36  controls the starter switch  22  by providing a command signal via a starter switch output  40  to an underhood bussed electrical center (UH-BEC) starter relay  48  that actuates a UH-BEC switch  50 . The UH-BEC switch  50  is located in a solenoid circuit  52  intermediate to the positive terminal  12  of the battery  14  and the starter solenoid relay  34 . When the UH-BEC switch  50  closes, power is supplied to enable the starter solenoid relay  34  to close the starter switch  22 . When the UH-BEC switch  50  opens, power is no longer supplied to the starter solenoid relay  34 . This causes the starter solenoid relay  34  to open the starter switch  22 . This approach is used to actuate the starter solenoid relay  34  because the signal output provided by a typical microprocessor does not have sufficient current to directly actuate a solenoid relay such as that found in the preferred embodiment.  
         [0022]     When the starter switch  22  and the BDD switch  24  are both closed the battery  14  supplies power to the starter  16  that then operates to start an internal combustion engine (not shown). When the starter switch  22  is open and the BDD switch  24  is closed power is not supplied to the starter  16 , but voltage is still present in the protected conductor  26 . When the BDD switch  24  is open, voltage is removed from the protected conductor  26  and the starter  16 .  
         [0023]     Referring now to  FIG. 2 , a flowchart  110  illustrates a preferred embodiment of a method to close and open the circuit connecting the starter to a DC power source such as a battery. It will be appreciated that this method can be used to add and remove voltage from a circuit connecting a DC power supply to other types of devices.  
         [0024]     A first step  112  depicts a vehicle driver actuating a vehicle ignition switch. A remote switch or some other mechanism may also be used to initiate vehicle start-up. A step  114  indicates that the vehicle engine control module receives a command signal indicating ignition switch activation and also further transmits a command signal indicating ignition switch activation. The command signal typically originates from the ignition switch or a remote starter. The function of retransmitting the signal may be omitted if all processing is performed in the same processor. The BDD controller then receives a signal indicating a command to start the vehicle  116 . In step  118  the BDD controller generates a command signal to close the BDD switch. Alternatively the engine control module or another controller can generate the signal. It should be noted that the BDD controller could be configured so that no signal is generated when a short circuit condition or a vehicle theft is detected. Step  120  indicates that the BDD switch closes. The BDD switch is located in the starter circuit between a first end of the protected conductor and the battery. In step  122  the BDD controller generates a signal to close the UH-BEC switch or the starter switch if there is no UH-BEC switch. Alternatively the engine control module or another controller can generate the signal. Step  124  indicates to close the UH-BEC switch. This step is by-passed if there is no starter relay. Step  126  indicates to close the starter switch. The starter switch is located in the starter circuit between a second end of the protected cable and the starter. At this point the starter is powered and cranks the ignition.  
         [0025]     Step  128  indicates the driver ceases to actuate the vehicle ignition switch or equivalent. Step  130  indicates that the vehicle engine control module receives a command signal indicating ignition switch activation has ceased and also further transmits a command signal indicating ignition switch activation has ceased. The command signal typically originates from the ignition switch or a remote starter. Another controller may also perform this step. The step is bypassed if the BDD controller performs the function. Step  132  indicates the BDD controller receives a signal indicating the ignition switch is no longer actuated. This step is by-passed if the ECM transmits the signals directly to the relays. In step  134  the BDD controller generates a signal to open the UH-BEC switch or to open the starter switch if there is no UH-BEC switch. Alternatively, the engine control module or another controller generates the signal. Step  136  indicates the UH-BEC switch opens. This step is by-passed if there is no UH-BEC switch. Step  138  indicates the starter switch opens. When this step is complete, power is no longer supplied to the starter and it ceases to operate. In step  140  the BDD controller generates a command signal to open the BDD switch. Alternatively, the engine control module or another controller may generate the signal. Step  142  indicates to open the BDD switch. After this occurs, voltage is removed from the protected conductor. The sequence begins again at step  112  the next time the vehicle driver actuates the ignition switch.  
         [0026]     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 signal generating, sending, or receiving is described herein, the intended purpose can also be accomplished by modifying or terminating an existing signal.