Abstract:
A circuit arrangement for supplying power to control devices in motor vehicles, having a first power supply line, a first ground line, a second power supply line and a second ground line, characterized in that the first ground line and the second ground line can be connected by a controllable switch, and in that a logic circuit closes the switch when the first ground line is faulty or interrupted.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a circuit arrangement for supplying power to control devices in motor vehicles. 
       BACKGROUND INFORMATION 
       [0002]    German patent document DE 20 2005 016 686 U1 discusses an electrical power supply to an electronic brake system of a trailer, in which an electronic brake system which is arranged in the trailer can be supplied with power via two different cables. One of the cables serves to supply power to the trailer brake lights and has a branch which leads to the electronic brake controller. The second cable has a separate cable for the electronic brake controller. If said second cable is not connected or correct power supply cannot be ensured for other reasons, electrical power is applied to the electronic control device via the first cable at least during a braking operation. 
         [0003]    German patent document DE 10 2004 008 935 A1 discusses an apparatus for redundant voltage supply for a control device in an on-board vehicle electrical system having two lines, of which the first is designed as a main connection for transferring all the power, while the second line is configured as an emergency supply line and is designed such that only relatively low power consumption is possible. The two lines are decoupled by diodes. 
         [0004]    In accordance with the Agreement Concerning The Adoption Of Uniform Technical Prescriptions For Wheeled Vehicles, §5.1.3.6 of ECE R13 allows the alternative supply of electrical power to an electronic brake system (EBS) in the trailer vehicle via a plug-type connection according to ISO standard 1185/ISO standard 12098, with this type of supply having to be restricted to the case of “failure of the electrical power supply via the plug-type connection according to ISO 7638”. 
         [0005]    In order to clarify the addressed problem,  FIG. 2  shows an electronic control device  1  with five connection pins P 1 -P 5 . The connection pin P 1  is connected to battery voltage and is wired in accordance with ISO 7638 (PIN  1  there). PIN  2  is connected to the brake light according to ISO 1185 (PIN  4  there) and is likewise supplied with supply voltage when a brake light switch (not illustrated) is operated. These two supply voltages are decoupled by diodes D 1  and D 2 . 
         [0006]    PIN P 3  is wired in accordance with ISO 7638 (PIN  2  there). PIN P 4  is connected to ground, specifically in accordance with ISO 7638 (PIN  4  there), while PIN P 5  is wired in accordance with ISO 1185 (PIN  1  there) and is likewise connected to ground. PIN P 3  is wired in accordance with ISO 7638 (PIN  2  there) and is accordingly connected to supply voltage when the ignition (IGN) is switched on. The PINs P 1  and P 4  and also P 2  and P 5  therefore each form a power supply for the electronic control device  1 , so that redundant power supply is present. The ground connections of the two redundant power supplies by ISO 7638 and ISO 1185 must not be directly connected to one another, that is to say the connection illustrated by a dashed-line circle K 1  is impermissible since otherwise an electrical load, for example a vehicle lighting system L 2 , reacts to the electronic control device  1  and therefore a brake system and also is effective when there is no fault. 
         [0007]    On account of the relatively large cross section of the ground line of the ISO 7638 plug-type connection (PIN P 4 ), a compensation current I 2  would flow in the illustrated direction, as a result of which an additional voltage drop across the ground connection of the ISO 7638 plug-type connection (PIN P 4 ) would be caused, this resulting in an increase in the ground potential, that is to say the common potential of PINs P 4  and P 5 . Depending on the magnitude of the actual supply voltage at PIN P 1 , this could lead to an undervoltage of the electronic control device  1 . If the ground line to PIN P 5  is interrupted, this being indicated by the interruption point B 1 , the current I 1  can no longer flow away via said ground line, and therefore amplifies this effect since the entire current can then flow away only as current I 3  via the ground line of PIN P 4 . 
         [0008]    L 1  denotes a brake light which is situated between PINs P 2  and P 5 . L 2  indicates a vehicle lighting system, of which the ground connection is connected to PIN P 5 . 
         [0009]      FIG. 3  shows the system which has been used to date to solve the problem described in conjunction with  FIG. 2 . The two ground lines to PINs P 4  and P 5  are decoupled by diodes D 5  and D 6 , and therefore the current I 2  shown in  FIG. 2  can no longer flow. 
         [0010]    However, decoupling by diodes D 5  and D 6  results in the following disadvantages:
       the internal ground potential M 1  is raised by the voltage drop across diodes D 5  and D 6 ;   the maximum continuous current is restricted since, otherwise, an excessively high power loss is produced in diodes D 5  and/or D 6 ;   the availability of the electronic control device  1  is reduced by the diode voltage of the diodes D 5  and D 6 ;   the current of the electronic control device  1  can also flow away via the brake light ground connection (ground line to PIN P 5 ) and not only, as would be correct, via PIN P 5 , that is to say the ground line according to ISO 7638.       
 
       SUMMARY OF THE INVENTION 
       [0015]    The above-described disadvantages are to be eliminated by the exemplary embodiments and/or exemplary methods of the present invention. An object of the exemplary embodiments and/or exemplary methods of the present invention is therefore to improve the circuit arrangement for power supply to control devices in motor vehicles in such a way that high currents to the control device are possible and, at the same time, guaranteed power supply to the control device is ensured even in the event of a fault. 
         [0016]    The problem is solved by the features specified herein. Advantageous refinements and developments of the exemplary embodiments and/or exemplary methods of the present invention can be gathered from the further descriptions herein. 
         [0017]    Therefore, the exemplary embodiments and/or exemplary methods of the present invention provides for conducting a first ground line directly, that is to say without decoupling diodes, and activating a second ground line via an electrical switch only when a logic circuit has identified a fault in the first ground line. 
         [0018]    Therefore, the decoupling diodes of  FIG. 3  are eliminated, and the power losses of said decoupling diodes no longer limit the maximum possible current. This also prevents the second ground line raising the potential of the first ground line and as a result reducing the available supply voltage to the control device. Nevertheless, a second ground line which is activated when there is a fault in the first ground line or the first ground line fails, provides increased security. 
         [0019]    The switch between the two ground lines electrically isolates, and therefore completely decouples, the two ground lines during fault-free operation. 
         [0020]    According to one development of the exemplary embodiments and/or exemplary methods of the present invention, the switch may be a relay. According to another exemplary embodiment, the switch can be realized by two field-effect transistors which are connected back-to-back in series and in which the reverse diodes are connected back to back. 
         [0021]    The exemplary embodiments and/or exemplary methods of the present invention will be explained in detail below with reference to an exemplary embodiment in conjunction with  FIG. 1 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows a basic circuit diagram of the circuit arrangement according to the present invention. 
           [0023]      FIG. 2  shows a basic circuit diagram for explaining the problem addressed by the present invention. 
           [0024]      FIG. 3  shows a basic circuit diagram of a circuit arrangement according to the prior art. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows an electronic controller  1  which likewise has five PINs P 1  to P 5 . The connection pin P 1  can be connected to a first line  4  to which battery voltage UB 1  is applied and is assigned in accordance with ISO 7638 in accordance with PIN  1  there. 
         [0026]    PIN P 4  can be connected to a first ground line  5  and is assigned in accordance with ISO 7638 (PIN  4  there). 
         [0027]    PIN P 3  can be connected to a line  6  and is assigned in accordance with ISO 7638 (PIN  2  there). When the ignition (IGN) of the vehicle is switched on, battery voltage is applied to the line  6 . 
         [0000]    PIN P 2  can be connected to a second power supply line  7  and is assigned battery voltage UB 2  in accordance with ISO 1185 (PIN  4  there). PIN P 5  can be connected to a second ground line  8  and assigned in accordance with ISO 1185 (PIN  1  there). 
         [0028]    Electrical loads, for example a vehicle lighting system L 1 , which are disconnected from the control device  1  are connected to the second ground line  8 . A brake light L 2  is situated between the second power supply line  7  and the second ground line  8  and is switched on and off by a switch S 2 . 
         [0029]    As already described in connection with  FIGS. 2 and 3 , the two power supply lines  4  and  7  are decoupled by the diodes D 1  and D 2  and connected to the output stage  3  which is controlled by a microcontroller  2 . The line  6  is connected to a control input  13  of the microcontroller  2  via the PIN P 3  and a diode D 4 . The microcontroller  2  and the output stage  3  are each directly connected to the first ground line  5  via the PIN P 4  and therefore are at the ground potential M 1 . 
         [0030]    The second power supply line  7  is connected to the control input  13  of the microcontroller  2  via a diode D 3 , and therefore this control input is supplied with battery voltage both when the ignition is switched on, via the line  6 , and also when the brake light L 2  is switched on by the switch S 2 , via the line  7 . 
         [0031]    The first ground line  5  and the second ground line  8  can be connected by a switch S 1 . This switch S 1  can be controlled by a logic circuit  9 , with a first input  10  of the logic circuit  9  being connected to the second power supply line  7 , a second input  11  of the logic circuit  9  being connected to the first ground line  5 , and a third input  12  of the logic circuit  9  being connected to the second ground line  8 . 
         [0032]    During normal fault-free operation, power is supplied to the control device  1  via the lines  4 ,  5  and  6 . In particular, the current I 3  can flow away only via the first ground line  5 . Even when the brake is operated and therefore the brake light L 2  is switched on, the current consumed by the electronic control device  1  flows away solely via the first ground line  5 , whereas the current required by the brake light L 2  (switch S 2 ) flows via the lines  7  and  8 , but this not influencing the current for the control device  1 . In particular, potential shifts on the second ground line  8  do not have any influence on the power supply to the control device  1 . 
         [0033]    In the event of a fault, in which the first ground line  5  is faulty and, in particular, is interrupted, the logic circuit  9  identifies this state and switches on the switch S 1 , as a result of which the two ground lines  5  and  8  are internally connected, and therefore the current consumed by the control device  1  can then flow away via the ground line  8  (cf. arrow I 1 ). 
         [0034]    In the normal case, the microcontroller  2  is supplied with power via the line  6  and PIN P 3  when the ignition of the vehicle is switched on. When the brake is operated and therefore the brake light L 2  is switched on, the second supply voltage line  7  also conducts battery voltage which reaches the microcontroller  2  via the diode D 3  and reaches the output stage  3  via the diode D 2 . The two possible supply voltages on the lines  4  and  7  for the output stage  3  are decoupled by the diodes D 1  and D 2 , whereas the two possible supply voltages for the microcontroller  2  on the lines  6  and  7  are decoupled by the diodes D 4  and D 3 . A control input of the microcontroller  2  is not illustrated for reasons of clarity. 
         [0035]    In principle, the logic circuit  9  identifies whether the first ground line  5  is faulty or interrupted. As soon as the brake is operated, and therefore a voltage is applied to the second power supply line  7 , the logic circuit  9  can check the two voltages firstly between the lines  7  and  5  and secondly between the lines  7  and  8 . If the ground line  5  is interrupted, the potential of said ground line increases across the internal resistor of the output stage  3 , and therefore the voltage difference between the lines  4  and  5  falls below a threshold value, whereas the voltage difference between the lines  7  and  8  should correspond to the voltage difference of the on-board voltage. If the logic circuit identifies this state, the switch S 1  is switched through, and therefore the second ground line  8  is also active for the control device  1 . 
         [0036]    This state is maintained (latched) by the logic circuit  9  until the brake light L 2  is switched off again, that is to say the voltage on the line  7  drops. This prevents the switch S 1  from being switched through too often, this being possible, for example, on account of a wobbly contact at PIN P 4  or the first ground line  5 .