Abstract:
The security to prevent theft of a central locking system for motor vehicles is improved by arranging a switch  34, 340,  which can be switched by a coded signal, in the supply voltage lines  31  and/or  310  and/or  32  for driving an-actuating element.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to an electronic central locking system for motor vehicles and operating systems for locks or the like whose actuating elements are connected, such that they can be switched, via supply voltage lines to a controller. 
     In a known central locking system for motor vehicles, operating points which are designed as infrared receivers or else as receivers for other wire-free signals are constructed on the doors, on the trunk lid and in the vicinity of the starter switch as well as on the filler cap lock. 
     These operating points are all the same in the known central locking system. Each operating point comprises a transmitting device which includes a modulator, an amplifier and an IR diode, and a receiving device having a photo diode, an amplifier and a demodulator. Each of these operating points is connected via in each case two supply voltage lines to a controller, which essentially comprises a microcomputer and an interface circuit (DE-A 36 28 706 A1). 
     It is disadvantageous that this known central locking system is not thief-proof since the actuating elements can be changed to the “open” position by applying external voltages to the supply voltage lines. 
     SUMMARY OF THE INVENTION 
     In contrast to this, the invention is based on the object of improving a central locking system of the described type such that it is thief-proof. 
     It has been found that this object can be achieved in a simple manner by arranging a switch, which can be switched by coded signal, in the supply voltage lines for driving an actuating element. 
     According to a feature of the invention, the switch which can be switched by the coded signal is arranged in the immediate vicinity of the drive for an actuating element. 
     This means that application of an external voltage to a supply voltage line cannot operate the drive for an actuating element, since the supply voltage line is interrupted by the switch immediately upstream of the drive. The actuating element cannot be influenced until the switch in the supply voltage line has been closed by the correct coded signal. 
     The coded signals for the switches can reach said switches via signal lines which are arranged between the controller and the switches. 
     According to another feature of the invention, the coded signals can alternatively be transmitted to a switch via the supply voltage line for the drive for the actuating element. 
     It is advantageous if, according to still another feature of the invention, the drive for an actuating element, the switch and the switching electronics are combined to form a unit. An economic and simple circuit is provided by using the voltage supply for the unit both for supplying the switching electronics and for supplying the drive for the actuating element. 
     In a second exemplary embodiment, the drives for the actuating elements are driven by data signals which pass via dedicated data lines to the switches and to the switching electronics in order to drive the drives for the actuating elements. 
     According to other features of the invention, pulse modulation or amplitude modulation can be mused to apply the coded signals to the supply voltages. 
     In order to improve the security to prevent theft, the voltage supply lines and/or the signal and data lines are laid in a concealed manner. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are explained in the following text with reference to the drawings, 
     FIG. 1 shows, schematically, major elements of a known central locking system, 
     FIG. 2 shows an outline circuit diagram of a first embodiment of the invention, 
     FIG. 3 shows an outline circuit diagram of a second exemplary embodiment of the invention, 
     FIG. 4 shows a more detailed illustration of the first exemplary embodiment, and 
     FIG. 5 shows a more detailed illustration of the second exemplary embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a known electronic central locking system  1 , a plurality of identical operating points  2 ,  11 ,  12  and  13  are provided of which, for the sake of simplicity, only the operating point  2  will be explained in more detail. This includes a transmitting device  3  and a receiving device  4 . The transmitting device  3  includes a modulator  5 , an amplifier  6  as well an IR diode  7 . The receiving apparatus  4  includes a photo diode  8 , an amplifier  9  as well as a demodulator  10 . 
     Each of the operating points  2 ,  11 ,  12  and  13  is connected via lines  14  and  15  to a controller  16 , which includes a microcomputer  17  and an interface circuit  18 . 
     Actuating elements are supplied via supply voltage lines  31  and  32 , via outputs  19  and  20  as well as power stages  21  and  22 . By way of example, an actuating element  23  is used for the driver&#39;s door, an actuating element  24  for the front-passenger&#39;s door, an actuating element  25  for one rear door, an actuating element  26  for the other rear door, an actuating element  27  for a filling lock, and an actuating element  28  for a trunk. 
     A key  29 , which includes a code transmitter  30 , is provided to operate the central locking system  1 . The transmitter and the receivers for the central locking system  1  may operate by radio, or else by infrared signals. 
     When the signals emitted by the code transmitter  30  arrive at a receiving device  4 , then this, via the interface circuit  18 , emits an appropriate signal to the microcomputer  17 . The interface circuit  18  adds to this signal information about which receiving device  4  received the signals. The program which is stored in the microcomputer  17  uses this information to determine information items which operate the actuating element  23  to  28 . For example, when the wire-free signals are received at the operating points  2  and  11 , all the doors and the filler cap are unlocked. When the IR signals are received at another operating point, the doors, the filler cap and the trunk lid are unlocked. When wire-free signals are received at the last operating point, close to the starter switch, only the trunk lid is unlocked. 
     FIG. 1 shows that the supply voltage lines  31  and  32  are routed directly to the actuating elements  23  to  28 . It can be seen that, under some circumstances, the actuating elements can be moved to the “open” position by applying external voltages to the supply voltage lines  31 ,  32 . 
     FIGS. 2 and 3 show, schematically, how this can be avoided according to the invention. 
     In a first exemplary embodiment according to FIG. 2, the controller  16  is connected via power supply lines  31  and  32  and via a switch  34  to the drive  33  for an actuating element. The switch  34  is furthermore connected, such that it can be switched, via a signal line  35  to the controller  16 . The drive  33  for an actuating element and the switch  34  are combined to form a unit  36 . 
     This circuit arrangement can be used to switch on the drive  33  for one of the actuating elements, via the power supply lines  31  and  32 , only if the switch  34  has previously been closed by a coded signal via the signal line  35 . This coded signal is emitted from the controller  16 . 
     FIG. 3 shows a second exemplary embodiment with a controller  160 , which is connected via a supply voltage line  310  and a supply voltage line  32  to a switch  340 . This switch  340  is located in the circuit for the drive  33  for an actuating element, and is combined with this drive  33  to form a unit  360 . The switch  340  is switched via coded signals, which are passed to the switch  340  via the supply voltage line  310 . 
     FIG. 4 shows the circuit arrangement according to FIG. 2, in detail. On a unit  38 , the drive  33  for an actuating element is directly connected to control electronics comprising a power stage  39  and a switching IC  37 . The switching electronics are connected via supply voltage lines  31  and  32  to the controller  16 . The supply voltage lines  31  and  32  also supply voltage to the drive  33 . 
     The drive  33  is driven via an appropriate data signal (unidirectional or bi-directional data interchange) via the signal line  35 . 
     According to FIG. 5, a drive  33  for an actuating element, a power stage  39  and a switching IC  370  are combined to form a unit  380 . The switching IC  370  is connected to the controller  16  via a voltage supply line  32  and via a further voltage supply lines  310 . Coded signals are passed via the voltage supply line  310  to the switching IC  370 , and cause the drive  33  to be switched. 
     The signals are applied to the supply voltage lines by, for example, amplitude modulation or pulse modulation. 
     The units  36 ,  360  and  38 ,  380  are used, according to the invention, instead of the actuating elements  23  to  28  in an electronic central locking system  1  as shown in FIG.  1 . In consequence, it is no longer possible to operate these actuating elements simply by connecting the supply voltage lines to external voltages. 
     LIST OF DESIGNATIONS USED 
       1  Electronic central locking system 
       2  Operating point 
       3  Transmitting device 
       4  Receiving device 
       5  Modulator 
       6  Amplifier 
       7  IR Diode 
       8  Photo diode 
       9  Amplifier 
       10  Demodulator 
       11  Operating point 
       12  Operating point 
       13  Operating point 
       14  Line 
       15  Line 
       16  Controller 
       160  Controller 
       17  Microcomputer 
       18  Interface circuit 
       19  Output 
       20  Output 
       21  Power stage 
       22  Power stage 
       23  Actuating element, driver&#39;s door 
       24  Actuating element, front-passenger&#39;s door 
       25  Actuating element, rear door 
       26  Actuating element, rear door 
       27  Actuating element, filler cap lock 
       28  Actuating element, trunk 
       29  Key 
       30  Coded transmitter 
       31  Supply voltage line 
       310  Supply voltage line with signal transmission 
       32  Supply voltage line 
       33  Drive for an actuating element 
       34  Switch 
       340  Switch 
       35  Signal line 
       36  Unit 
       360  Unit 
       37  Switching IC 
       370  Switching IC 
       38  Unit 
       380  Unit 
       39  Power stage