Rear door safety lock arrangement
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention relates to a locking mechanism or arrangement for locking passenger motor vehicle rear doors with locking devices preventing unauthorized unlocking of the doors from the interior of the vehicle. Such so-called child safety lock systems, which the present invention is directed at improving, are described in German Published Patent Application No. (DE-OS 3 127 732). 
     In order to make the awkward manual locking and unlocking unnecessary in the case of locking mechanisms--also known as so-called child safety locks--which each have a mechanically operable bolt on the front side of each rear door which is accessible only when the door is opened and, after it is in operation, prevents the unauthorized opening of the door from the interior side of the door, it has been comtemplated to carry out the operation from the front seats of the car and without opening the rear doors. In this case, a control unit driven by an electric motor is assigned to the locking mechanism of each door lock, said control being reversible in its rotational direction via a double pole changing switch and being connected with it and said control unit being remotely operable with respect to the locking or unlocking of the lock from a switching element that can be operated from the front seats. The locking condition of the locking mechanism may in this case be indicated by an optical display, in particularly by a luminous diode. 
     A use of such a construction which takes safety as well as comfort into account is connected with high costs because the expenditures that are required for checking whether the child safety lock is actually switched on are considerable because an electric switch has to be mounted at the corresponding door lock which, via a twin-core cable, switches the control light arranged in the area of the switching element as an &#34;acknowledgement&#34;. 
     It is therefore an objective of the invention to develop a locking mechanism of the above type with a minimum use of electromechanical switching and circuit elements and expenditures in a more cost-effective manner than heretofore provided. 
     According to the invention, the above-noted objective is achieved by advantageously arranging the display mechanism in a portion of the circuit for controlling the locks so that it is not necessary to provide an additional switch in each door lock including the holding means and an additional circuit line. 
     In especially preferred embodiments, the display means is connected in series with a p-n-p transistor having its base and collector connected respectively to &#34;off&#34; lines of the locking device circuits. 
    
    
     Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment in accordance with the present invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a basic wiring diagram of a safety door locking arrangement constructed according to a preferred embodiment of the invention; and 
     FIG. 2 schematically depicts a preferred embodiment of a switching element used to control the circuit of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In FIG. 1, a switching element 1 is shown which is preferably installed within the reach of the vehicle driver in the dashboard or in the center console. On the one hand, the switching element 1 has a movable contact 1.1, which is on the plus potential of the vehicle voltage system, and on the other hand, it has two fixed contacts 1.2 and 1.3, where at the fixed OFF contact 1.2, the OFF-lines 2.1 and 3.1 of the electric-motor-driven control units 2 and 3 which are separate from one another for the right and left rear door, are connected, while the ON switching lines 2.2 and 3.2 are connected to the fixed ON contact 1.3. Via the control units 2 and 3, the locking mechanisms (child safety locks) of the rear door locks are mechanically operated in a manner that is not shown in detail, as many such locks per se are known in the art, and the door locks are locked or unlocked. 
     A double pole or double throw changing switch 4 is installed into the control unit 2, and a double throw changing switch 5 is installed into the control unit 3, in which case the motor winding 2.0 of the control unit 2 is connected to the movable contact 4.1 and 4.2 of the double pole changing switch 4, and the motor winding 3.0 of the control unit 3 is connected to the movable contacts 5.1 and 5.2 of the double pole changing switch 5. The ON switching lines 2.2 and 3.2 are connected with the fixed contacts 4.3 and 5.3 of the double throw changing switches 4 and 5, while the OFF switching lines 2.1 and 3.1 are connected to the fixed contacts 4.4 and 5.4. An additional jointly switched fixed contact 4.5 and 5.5 of the double throw changing switches 4 and 5 is in each case connected to ground. Via a preferably mechanical functional connection 4.6 and 5.6, the double pole changing switch 4 is connected with the control unit 2 and the double pole changing switch 5 is connected with the control unit 3. For the separation of the two circuits, one diode 6 and 7 respectively is placed in the OFF switching lines 2.1 and 3.1. In addition, between the movable contact 1.1 of the switching element 1 located on the plus potential and the OFF switching line 2.1 of the control unit 2, a luminous diode 8 is switched in series with the emitter-collector line of a p-n-p transistor 9, the base of which via a resistor 9.1 is connected with the OFF switching line 3.1 of the other control unit 3. 
     The method of operation of the mechanism is as follows starting from an unlocked position of the door locks (the child safety lock is turned off). The movable contact 1.1 of the switching element 1 is connected to the fixed contact 1.2 and the movable contacts 4.1 and 4.2 of the double throw changing switch 4 are connected to the fixed contact 4.3 and at the grounding contact 4.5, and the movable contacts 5.1 and 5.2 of the double throw changing switch 5 are connected to the fixed contact 5.3 and at the grounding contact 5.5 (in FIG. 1, this switching condition is shown by the interrupted line showing the position of the movable contact). 
     When now, for the locking of the rear door locks, thus for the switching-on of the child safety lock, by means of the operation of the switching element 1, its movable contact 1.1 is switched from the fixed contact 1.2 to the fixed contact 1.3 to close a circuit (plus potential 1.1 - 1.3 - 2.2 - 4.3 - 4.1 - 2.0 - 4.2 - 4.5 - ground) for the operation of control unit 2, on the one hand, and, on the other hand, a circuit (plus potential - 1.1 - 1.3 - 3.2 - 5.3 - 5.1 - 3.0 - 5.2 - 5.5 - ground) for operation of the control unit 3. Thus the motor operators are activated to bring the locking mechanisms into a position which locks the doors. When the locked position (final position) is reached, the control unit 2, via the mechanical functional connection 4.6, switches the movable contact 4.1 from the fixed contact 4.3 to the ground 4.5, and the movable contact 4.2 from the ground contact 4.5 to the fixed contact 4.4. In the same way, the control unit 3, via the mechanical functional connection 5.6, switches the movable contact 5.1 from the fixed contact 5.3 to the ground contact 5.5, and the movable contact 5.2 is switched from the ground contact 5.5 to the fixed contact 5.4. As a result the motor operators of the countrol units are switched off and are simultaneously switched in such a way that when they are activated again, they run in reverse rotational direction. 
     Now, the OFF switching line 2.1 via 4.4 - 4.2 - 2.0 - 4.1 - 4.5 as well as the OFF switching line 3.1 via 5.4 -5.2 - 3.0 - 5.1 - 5.5 are connected to ground, thus controlling the transistor 9 and switching it to pass. The circuit for the control light 8 is thus closed, and its being on signalizes the locked condition of the door locks (child safety lock switched on). When only one control light is used according to the preferred illustrated embodiment, it is especially significant that the transistor 9 can only be controlled when both control units have actually switched and thus both OFF switching lines 2.1 and 3.1 are grounded. Therefore, when one control unit has not switched, there is no ground connection at one OFF switching line, and either the transistor cannot be controlled or the circuit for the control light cannot be closed. 
     Other embodiments are contemplated with separate control lights for each lock. 
     In order to protect the locking mechanism against an unauthorized or unintentional operation with respect to unlocking, a further development of the invention is especially advantageous in which an unlocking is only possible when, along with the operation of the switching element developed as a touch contact switch, a second switch or touch contact switch must be operated, for example, the door contact switch for the interior lighting which is closed when the front doors are opened. 
     If the motor vehicle is equipped with electrical window lifting means at the rear doors and has a switch by means of which the rear window lifting means can be secured against unauthorized use, the control element may also be secured via this switch. 
     Further, in an especially preferred embodiment, the control element is developed as a press switch. It is developed in such a way that, for the unlocking, it can be switched from its ON to the OFF position only by releasing a safety lock. As shown in FIG. 2, the control element 1 developed as the press switch for this purpose has a pressure plate 1.4 having an opening 1.5. When the pressure plate 1.4 is pressed and thus the switching connection 1.1 - 1.3 is made, the pressure plate 1.4 in this pressed condition is stopped by means of a safety lock arranged in the switch, said safety lock only being able to be released again by means of the insertion of an object 10 (such as a pin or the ignition key) into the opening 1.5 provided for this purpose. After it has been unlocked, the pressure plate 1.4 then jumps back into its starting position, establishing the switching connection 1.1 - 1.2 and unlocking the locking devices. The specially preferred embodiment illustrated in FIG. 2 provides protection against the unauthorized actuation of the control element 1. 
     Although the present invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.