Abstract:
The electrical connection system includes a power source circuit for outputting a first voltage to operate a first load circuit. The power source circuit includes a conversion circuit for converting the first voltage into a second voltage lower than the first voltage. The system includes a second load circuit operative in response to the second voltage. The system includes a protection circuit for shunting the second load circuit with a threshold voltage between the first voltage and second voltage. The threshold voltage has identical influence on the second load circuit relative to the first voltage.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electrical connection system for a vehicle which includes a high-voltage battery supplying higher voltage than that required for driving vehicle load in the vehicle. This system converts electrical power from a high-voltage battery and supplies it to handle the vehicle power load. 
     In recent years, a development is pursued to enhance fuel economy. According to this development, high-voltage power source of 42V is connected to a motor generator. This power source drives various vehicle loads mounted in an automobile. 
     This high-voltage power source is mounted in an in-car multiplex communication system. This system includes a signal line wired in the vehicle and a power source line. In this system, each ECU (Electrical Control Unit) controls the vehicle load provided in each portion of the vehicle. Each ECU requires a low-voltage power source as low as 5V. 
     As disclosed in Japanese Patent Application Laid-open No.H10-84626, when high-voltage from the high-voltage power source is converted into low-voltage in this system, the high-voltage is collectively converted using a DC/DC converter in a junction box, and electricality is distributed to each ECUs. 
     SUMMARY OF THE INVENTION 
     In the electricity distributing method, however, when failure of ECU or the like causes for short-circuit between a low-voltage circuit which is activated by low voltage and a high-voltage circuit which transmits high voltage, high voltage is applied to every low-voltage circuit including a plurality of ECUs. With this application of voltage, normally activating ECUs or output side of the DC/DC converter in the junction box are brought into overvoltage state. 
     Even when a fuse is inserted into the junction box and a low-voltage electrical wire between ECUs, high voltage is adversely applied to the low-voltage circuit unless current which blows out the fuse flows. 
     According to the conventional system, if a failure is caused in a single ECU out of a plurality of ECUs connected to each other, there is an adverse possibility that this failure interfere with all the low-voltage circuits. 
     The present invention designs an electrical connection system for a vehicle. With this system, even if a failure is caused in a single vehicle load out of a plurality of vehicle loads handling different voltage, other vehicle loads can reliably be protected. 
     The first aspect of the invention is directed to an electrical connection system for a vehicle. The system includes: a voltage converter including an input terminal connected to a first power supply line to supply a first voltage for converting the first voltage into a second voltage to be output to first vehicle-mounted loads through a second power supply line. The system includes a first voltage supplier branched from the first power supply line for supplying the first voltage to each of second vehicle-mounted loads. The system includes fuses provided respectively to the second vehicle-mounted loads between the voltage converter and each of the second vehicle-mounted loads on the second power supply line; 
     a switch provided between the voltage converter and the fuses, with a terminal connected to the second power supply line, and with another terminal connected to a ground terminal. The system includes a voltage detector provided between the voltage converter and the fuses for detecting a voltage to be supplied to the second power supply line. The system includes an overvoltage protector configured to turn on the switch to connect the second power supply line to the ground terminal, when the overvoltage protector decides an overvoltage to occur on the second power supply line due to occurring a short circuit between the first power supply line and the second power supply line at a vehicle-mounted, load, based on a voltage to be detected by the voltage detector. 
     Preferably, the second vehicle-mounted loads include electrical control units (ECU) for controlling vehicle-mounted electrical components. 
     Preferably, the fuses are adapted for the first voltage. 
     The second aspect of the invention is directed to an electrical connection system. The system includes a power source circuit for outputting a first voltage to operate a first load circuit. The power source circuit includes a conversion circuit for converting the first voltage into a second voltage lower than the first voltage. The system includes a second load circuit operative in response to the second voltage. The system includes a protection circuit for shunting the current from the second load circuit when a threshold voltage in the second load circuit exceeds a maximum rated voltage of the second load circuit that is between the first voltage and second voltage. The threshold voltage affects the second load circuit in substantially the same way as when the first voltage is applied to the second load circuit. 
     Preferably, the protection circuit includes a switch connected to the second load circuit. 
     Preferably, the protection circuit includes a controller for comparing the second load circuit with the threshold voltage to output a signal for closing the switch. 
     Preferably, the first and second load circuits include an electrical component connected thereto, for activating by the second voltage to control the first voltage. 
     Preferably, the second load circuit includes an overcurrent device connected to the electrical component. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
     FIG. 1 is a circuit diagram showing a structure of an electrical connection system for a vehicle to which the present invention is applied; 
     FIG. 2 is a circuit diagram showing a structure of a junction box in FIG. 1; 
     FIG. 3 is an illustrative view of flow of current when short-circuit is generated in ECU in FIG. 2; 
     FIG. 4 is a timing chart showing a relation of voltage of a low-voltage circuit, operation of a controller and current flowing through a switch when a high-voltage power supply line and a low-voltage power source line are short circuited; and 
     FIG. 5 is an illustrative view of a structure of a trunk line which connects junction boxes or the like. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be explained with reference to the drawings below. 
     The invention is applied to an electrical connection system in a vehicle having a structure shown in FIG. 1 for example. 
     The electrical connection system for a vehicle includes motor generator  1 . The system includes high-voltage battery  2  connected to generator  1  through high-voltage power supply line  11 . The system includes a plurality of vehicle controllers  3  connected to battery  2  through high-voltage trunk lines  12 . In this system, high voltage generated in generator  1  is charged into battery  2 . Battery  2  supplies the charged high voltage to plurality of control systems  3  ( 3 A,  3 B and  3 C) through trunk lines  12 . 
     As shown in FIG. 5, trunk line  12  includes coating layer  101 , and reinforcing layer  102  is disposed inside coating layer  101 . Short-circuit detecting layer  104  is disposed inside reinforcing layer  102  through sheath  103 . Various electrical lines are disposed inside detecting layer  104 . The various electrical lines are power source lines  107  connected to an output end of battery  2 , e.g., multiple signal lines  108  and drain lines  109  such as twist lines for signal from operation switches. 
     As shown in FIG. 1, each control system  3  includes junction box (J/B)  21  connected to trunk line  12 . System  3  includes a plurality of ECUs (electrical control unit)  24  connected to junction box  21  through high-voltage power supply line  22  and low-voltage power source line  23 . High voltage 42V is supplied to system  3 . System  3  drives ECUs  24  with low voltage of 5V as vehicle load to be driven. 
     Low voltage is supplied to each ECU  24  from DC/DC converter  31  through low-voltage fuse  34  to activate the ECU. ECU  24  sends and receives information to and from another ECU  24 , and controls another vehicle mounted electrical component. 
     As shown in FIG. 2, junction box  21  includes converter  31  which is connected to trunk line  12  and to which high voltage is supplied. Junction box  21  includes an overvoltage protection circuit  33  connected to converter  31  through low-voltage power source line  32 . Junction box  21  includes low-voltage fuse  34  connected to circuit  33  through line  32 . Junction box  21  includes high-voltage fuse  36  connected to an input terminal of converter  31  through high-voltage power supply line  35 . 
     High voltage is supplied to converter  31  through trunk line  12 . Converter  31  converts the high voltage into low voltage to be supplied to protecting circuit  33  through low-voltage power source line  32 . Converter  31  converts high voltage of 42V for example into low voltage of 5V which is driving voltage of ECU  24 , to be supplied to protecting circuit  33 . 
     Protecting circuit  33  includes controller  41  connected to low-voltage power source line  32  between converter  31  and fuse  34 . Protecting circuit  33  includes switching element connected to line  32 , i.e., switch  42 , e.g., a transistor. Switch  42  is disposed closer to fuse  34  than controller  41 , i.e., between controller  41  and the fuse  34 . 
     Protecting circuit  33  monitors voltage of the low-voltage circuit which is output side of converter  31 , using a comparator. If controller  41  detects that overvoltage which is higher than a preset predetermined voltage value such as a maximum rated voltage of a low-voltage load  24  (threshold voltage) is generated, controller  41  generates a control signal to be supplied to switch  42 . This control signal turns on switch  42 . A terminal of switch  42  is connected to low-voltage power source line  32 . The other terminal of switch  42  is connected to grounding terminal  51 . 
     High voltage is supplied to junction box  21  through trunk line  12 . High voltage is supplied to ECU  24  through high-voltage fuse  36  and high-voltage power supply line  22 . High voltage is converted into low voltage by converter  31 . The low-voltage is supplied to ECU  24  through line  32 , protecting circuit  33  and fuse  34 . With this, each ECU  24  is activated by the low voltage. ECU  24  drives another vehicle load circuit (not shown) with high voltage. 
     In the above system, 42V may be converted into 7V by converter  31 , the 7V may be converted into 5V by a series regulator in ECU  24  as driving voltage of ECU  24 . 
     In this system, failure is caused in one of the plurality of ECUs  24 , and high-voltage power supply line  22  and low-voltage power source line  23  are short circuited at portion S. As shown with time T1 in FIGS. 3 and 4, this short-circuit applies high voltage (42V) to low-voltage power source line  23  and low-voltage fuse  34  from high-voltage power supply line  22  (A 1  in FIG.  4 ). Then, if controller  41  detects the overvoltage (42V) of line  32 , controller  41  supplies a control signal to switch  42  to turn ON switch  42 . 
     With this, low-voltage power source line  23  and grounding terminal  51  are connected to each other. Next, the great current flows into low-voltage power source line  23  due to the short-circuit. The current is shunted into grounding terminal  51  through fuse  34  and switch  42  as shown in FIG. 3 (C 1  in FIG.  4 ). Then, the current flows through switch  42  up to time T2, and blows out fuse  34  at time T3. At that time, fuse  34  on the first ECU is blown out by the great current, but since great current does not flow through the second ECU  24  different than the first ECU  24 , the fuse  34  on the second ECU  24  is not blown out. 
     Here, in the case of a known fuse of 14V exceeding low voltage (5V) as fuse  34 , strong scattering in the fuse is caused by high voltage (42V) and the insulative resistance of the fuse  34  fails. Thus, the high-voltage fuse (42V) is used for short-circuiting circuits with currents including voltages between the high voltage (42V) and low voltage (5V). 
     At time T3, fuse  34  is blown out. Controller  41  again detects that voltage of line  32  is low voltage (5V) (A 1  in FIG.  4 ). At that time, controller  41  stops supply of a control signal to switch  42  to turn OFF switch  42 . 
     With this, according to the electrical connection system, even if failure is caused in one of plurality of ECUs  24  and short circuit is caused between high-voltage power supply line  22  and low-voltage power source line  23 , supply of great current to other ECUs  24  through lines  32  and  22  is prevented. 
     Even if the high-voltage circuit and the low-voltage circuit are short circuited by inside failure, the overvoltage is detected by controller  41  connected to the low-voltage circuit to turn ON switch  42 . With this, great current can be shunted into grounding terminal  51  from the low-voltage circuit. The shunt allows fuse  34  of the low-voltage circuit to be blown out. 
     As shown in FIG. 1, plurality of ECUs  24  are activated using low voltage converted by single converter  31 . In this case, if failure is caused in one of ECUs  24  and short circuit is caused between high-voltage power supply line  22  and low-voltage power source line  23 , low-voltage power source line  32  is brought into overvoltage state. At that time, switch  42  is turned ON by controller  41 , and failed ECU  24  and grounding terminal  51  can be connected to each other. 
     Fuse  34  connected to failed ECU  24 , and influence on other normally actuating ECUs  24  can be avoided. 
     Since only a fuse of failed ECU  24  can reliably be blown out, stopped state of all low-voltage circuits on the output side of converter  31  can be avoided, and the low-voltage system can reliably be protected. 
     When a vehicle mounted electrical component is controlled by ECUs  24 , even if one of ECUs  24  is failed and short circuit is generated between high-voltage power supply line  22  and low-voltage power source line  23 , great current is not supplied to other ECUs  24  to cause failure, and other vehicle mounted electrical components controlled by other ECUs  24  can normally be operated. 
     The electrical connection system in a vehicle has been explained based on ECUs as vehicle loads constituting low-voltage circuits, but the present invention is not limited to this, and the invention can be applied to a vehicle load which is operated by other low voltage of course. 
     The entire contents of Japanese Patent Applications P2001-239438 (filed Aug. 7, 2001) are incorporated herein by reference. 
     Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims.