Abstract:
In a data communication system, data is transmitted from a control device to a communication interface and from there via a communication bus to additional communication interfaces of trigger devices. The communication interface on the control device side has inputs, to which signals from said control device and a disarming switch can be assigned. The disarming switch can be circumvented by a bypass switch which is controlled by the control device. The state of the signal at the inputs of the communication interface on the control device side is transmitted to coresponding outputs of the communication interfaces of the triggger devices. A trigger device has a safety unit which is used to test at least one trigger unit, when the state of the signal of the outputs authorizes such a test and the trigger voltage source is not yet charged wth the full trigger voltage. In said state, the safety unit also blocks triggering as soon as the trigger voltage has been reached. The inventive system ensures a high degree of functional safety and flexibility.

Description:
CLAIM FOR PRIORITY 
   This application is a national stage of PCT/DE00/04410, published in the German language on Jun. 21, 2001, which claims the benefit of priority to German Application No. DE 199 60 261.1, filed on Dec. 14, 1999. 

   TECHNICAL FIELD OF THE INVENTION 
   The invention relates to a system for controlling the operation of modules by transmitting information from a control device via a databus, and in particular for controlling the operation of firing devices of a vehicle occupant protection apparatus in a motor vehicle. The invention also relates to a firing device for connection to the communications bus of such a system and a safety circuit for a firing device of a vehicle occupant protection system. 
   BACKGROUND OF THE INVENTION 
   A conventional system is disclosed in DE 197 39 808 A1. In this system, the code words which are transmitted from the control device to the communications interface contain an information section and an error-detection section which contains, for example, the sum of bits of the information section. The information packet contains a bit which corresponds to the presence or non-presence of a safing signal generated by a safing switch or safing sensor. If the code word transmitted by the control device is to fire firing devices of a motor vehicle occupant protection system, it contains, at a predetermined place in the information packet, a bit which corresponds to the presence of the safing signal, i.e. requires the safing switch to be closed. This information bit is replaced in the communications interface by the information relating to the safing signal which is actually present at the safing input so that, for example when there is information contained in the code word relating to the closed safing switch but when there is an absence of the safing signal at the safing input of the communications interface, the sum value in the code word no longer corresponds to the sum of the information packet and the code word can be detected as faulty, as a result of which the firing devices do not fire. 
   In the known system, the safing signal which is present at the safing input thus permits a safing function to be integrated into airbag firing systems which operate with bus systems. When the safing switch is opened, firing is reliably prevented. However, in the known system, it is not possible to distinguish between firing instructions for different firing devices, for example firing devices for side airbags and firing devices for front airbags. Furthermore, all the firing devices can be fired only if the safing switch is closed. 
   SUMMARY OF THE INVENTION 
   The invention discloses developing a system in such a way that a large degree of flexibility and reliability in terms of the actuation capability of the individual modules is provided. 
   In one embodiment of: the system according to the invention, at the control-device-end communications interface, a plurality of inputs whose signal assignment is transmitted to corresponding outputs of the module-end communications interface, information is present at the module end which can be used in a wide variety of ways to enable and disable functions which are to be triggered by means of the data transmitted by the control module. In this way, flexible actuation of the individual module is possible. The transmission of the transmitted data and the information in the code words can be protected in a similar way to that in the method according to DE 197 39 808, mentioned at the beginning, check bits contained in the code words for checking the correctness of the information both increasing the reliability of the transmission and enabling faults of the control device to be detected. The number of inputs of the control-device-end communications interface to which signals can be applied can be different from the number of the module-end communications interface. 
   In one aspect of the invention, it is possible to enable functions of the modules as a function of the switch state of the safing switch. 
   In another aspect of the invention, the modules can advantageously be addressed selectively by means of module-specific codes, as a result of which the flexibility and reliability of their actuation capability is increased further. 
   In another embodiment of the invention, a signal state is brought about which corresponds, on the one hand, to the closed safing switch, as a result of which specific functions are enabled, and which corresponds, on the other hand, to the safing switch closed by means of a test signal, and in addition to the presence of a test signal, as a result of which functions, in particular test functions in which one or more modules are in the same enabled state as in the case of a closed safing switch, can take place. 
   The test output, in another aspect of the invention, of the module-end communications interface permits selective execution of functional scopes, irrespective of the state of other outputs which are present. 
   In still another aspect of the invention, there is a way of triggering the individual safety devices for a vehicle occupant protection system of a vehicle which is suitable for practical conditions. 
   In yet another aspect of the invention, there is a large degree of reliability of the triggering of the safety devices to be triggered in the event of a front-end impact against malfunctions of the control device. In addition, as is explained further below, the safety devices which are to be triggered in the event of a front-end impact can be checked. 
   In still another an embodiment of the system, no separate test input of the control-device-end communications interface is provided. 
   In one aspect of the invention, additional functional reliability advantages to be obtained by virtue of the fact that, for example, a firing signal is generated in the control device if the safing input has experienced a level change. 
   In still another aspect of the invention, the basic design of a first advantageous embodiment of a firing device for connection to the communications bus: of the system according to the invention. The embodiment of the firing device according to the invention ensures that a plurality of identical firing devices, embodied as what are referred to as “smart squibbs”, can be connected to the communications bus and selectively triggered. 
   In another embodiment, a firing device with whose safety circuit it is possible to carry out functional checking as long as the firing voltage source is still not charged to its firing voltage. If a test signal is present at the same time as a control signal, firing of the firing device is prevented. 
   According to one aspect, the safety switch, which constitutes a central safety element of the system, is advantageously monitored. 
   The invention is suitable for all systems of the generic type in which slave modules are to be controlled by a master module via a databus as flexibly as possible and with a high degree of functional reliability. The invention is particularly suitable for use in vehicle occupant protection systems. 

   
     The invention is explained further below by way of example and with further details with reference to the darwings, in which: 
       FIG. 1  shows a block circuit diagram of a first embodiment of the system according to the invention. 
       FIG. 2  shows a block circuit diagram of a firing device. 
       FIG. 3  shows a circuit diagram explaining the function of the firing device according to FIG.  2 . 
       FIG. 4  shows a block circuit diagram of a second embodiment of the system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   According to  FIG. 1 , a control device  2  of a vehicle occupant protection system is connected via a data line  4  to a communications interface  6  which is connected to firing devices  9 ,  10  via a communications bus  8 . The firing devices are embodied as what are referred to as “smart squibbs” which have their own communications interface  12  and whose design is explained by reference to  FIGS. 2 and 3 . The system has a plurality of firing devices which are to be fired selectively on an individual basis or in groups in the event of a front-end impact, a side impact, a roll-over etc. 
   The control device  2  controls a microprocessor which has associated memories and which determines instructions and/or information from sensor input signals  22  which are generated by different acceleration sensors, said instructions and/or information being fed to the communications interface  6  via the data line  4 . 
   In addition, a safing switch  26  which forms a redundancy switch and which closes by means of a predetermined vehicle deceleration so that, when the safing switch  26  is closed, current flows from a voltage source  28 , with for example 5 volts, through a resistor  30  and the safing switch  26  so that a safing signal is present at a safing pin or safing input  32  of the communications interface  6  which is connected to the connection between the safing switch  26  and the resistor  30 . In parallel with the safing switch  26  there is a normally open bypass switch  34  which is formed, for example, by a transistor and which is connected to a voltage divider circuit formed from two resistors  36  and  38  connected in series. The one resistor  38  is connected to ground and the other resistor  36  is connected to a test output  40  of the control device  2 , which is in turn connected to a test input  42  of the communications interface  6 . 
   The connection between the safing switch  26  and the resistor  30  is additionally connected to an input  44  of the control device  2 . 
   The control device  2  also has a control output  46  which is connected to a further pin or a control input  48  of the communications interface  6 . 
   The design and function of the individually described components and function blocks are known per se and are not explained. 
   The transmission of the information of the instructions of the control device  2  and of the signal states of the inputs  32 ,  42  and  48  which are sent via the data line  4  takes place in a manner known per se, it being possible for this data to be checked for correctness in a manner known per se by means of the division of the individual code words into information packets and check packets. If it is detected, for example, in the communications interface  6  that the input  42  has a signal applied to it, but this is not the case at the input  32 , a fault in the system can be identified immediately by acknowledgement by the data line  4  to the control device  2 . Furthermore, the control device  2  can be embodied, for example, in such a way that it sends a firing instruction for firing the firing device  18  or devices  18  only if a safing signal is present at its input  44 . Furthermore, the transmission of a firing instruction can additionally be protected by the fact that a firing pulse is transmitted only after a signal change has been detected at the input  44  or at the input  32  without a signal change being present at the input  42 . 
   If, for example in the case of test signal generated as a result of a fault in the control device  2 , i.e. test input  42  with a signal applied to it, a firing signal is transmitted via the data line  4 , this does not cause the firing device to fire as explained below because the test input  42  forms a DISABLE input. In this way, it is at least largely possible to prevent faults in the firing device  2  leading to inadvertent firing of a firing device. 
   The design of an advantageous exemplary embodiment of the firing devices  9 ,  10  which are advantageously embodied in the same way is described below with reference to FIG.  2 . 
   The communications interface  12  which is connected to the communications bus  8  has a safing output  32   1 , a test output  42   1  and a control output  48   1 . The code words which are transmitted via the communications bus  8  are each read out by the communications interface  12  in such a way that the signal state at the outputs  32   1 ,  42   1  and  48   1 , corresponds to the signal states at the inputs  32 ,  42 ,  48  of the communications interface  6 . 
   In the firing device  16  there is a switching device  50  whose inputs are connected to the outputs  32   1  and  48   1 . A firing signal output  52  of the communications interface  12 , to which firing signal output  52  a firing signal sent by the control device  2  via the data line  4  is transmitted, is connected to a firing input  53 . A code input  54  is connected to a code signal output  55  which conducts identification signals and code signals which are individually assigned to the firing devices and are transmitted by the control device  2 . 
   The firing devices are each provided with an individual code, for example by programming a memory contained in them so that they detect a code signal which is respectively assigned to them. 
   The coding of a firing device can also be carried out by virtue of the fact that a resistor, at which a predetermined voltage drops when the code signal is present, is connected downstream of the code input  54 , said voltage serving to activate a code switch. The presence or intactness of such a resistor can be checked from the control device  2 , as a result of which the functional reliability of the system is further improved. 
   The further design and function of the switching device  50  is explained with reference to FIG.  3 : 
   The input of a code switch  56  is connected to a firing voltage source  58 . The code switch  56  has two outputs, of which one is connected to the input of a firing switch  60  via a control switch  56  which can be driven by the control output  48   1 , and the other is connected to the input of the firing switch  60  via a safing switch  61  which can be driven from the safing output  32   1 . The output of the firing switch  60  is connected to a firing unit  62 , embodied for example as a firing cap. 
   The function of the switching device  50  which is described is such that the code: signal present at the input  54  defines the control-device-specific positioning of the code switch  56 , i.e. whether the branch with the control switch  59  or the branch with the safing switch  61  is activated. When the control switch  59  is activated, a control signal which is present at the control output  48 , leads to the closing of the control switch  59  so that a firing signal  53  which closes the firing switch  60  fires the firing unit  62  when the firing voltage source  58  is charged. On the other hand, when the safing switch  61  is activated, a signal at the safing output  32   1  causes the firing output  62  to fire when there is a firing signal. 
   If a plurality of firing devices equipped with the control circuit  50  described are connected to the communications bus  8 , it is therefore possible to determine by means of the code signal whether the firing devices are activated via the control output  48   1  and/or the safing output  32   1  so that they fire correspondingly. 
   An exemplary assignment is that firing devices which are activated via the control output  48   1  are firing devices which fire when there is a side impact, whereas firing devices which are to fire in the event of a front-end impact are activated via the safing output  32   1 . The switches  59  and  61  thus constitute, in a certain way, safing switches which are assigned to a side impact or a front-end impact. In addition, the firing device contains a safety switching device  63  with an AND element  64  whose inputs are connected to the firing voltage source  58  and the test output  48   1  and whose output is connected to the input of a safety switch  66  which is formed, for example, from a transistor. The safety switch  66  connects the safing output  32   1  to ground when there is a signal from the AND element  64  so that a signal which is present at the safing output  32   1  becomes ineffective for the switching device  50 . In order to monitor the state of the safety switch  66  or of the safing output  32   1 , a monitoring device  68  is provided whose output signal is displayed immediately and/or can be sensed additionally by the control device  2 . 
   The design and function of the individual assemblies or functional elements are known per se and are therefore not explained in particular. 
   The function of the safety device  63  is explained below. It is assumed here that, after the system is switched on, for example via the communications bus  8 , the firing voltage source  58  is gradually charged to the firing voltage. 
   The safing output  32   1  may have a safing signal (front-end impact) applied to it so that when there is a corresponding code the switch  61  is closed and the firing unit  62  fires when there is a firing signal if the test output  42   1  does not have a signal applied to it. However, if a test signal is present and the firing voltage source  58  is charged to its firing voltage, the AND element  64  supplies an output signal, as a result of which the safety switch  66  closes and connects the safing output  32 , to ground, as a result of which in turn the switch  60  is prevented from closing. A test signal thus constitutes an ENABLE signal in terms of the firing. If the firing voltage source  58  has still not reached the firing voltage after the system is put into operation (the firing voltage source  58  contains a charging capacitor), the AND element  64  does not supply an output signal because there is inequality between the voltage at the test output  42   1  and the voltage of the firing voltage source  58  in this state. It is in any case impossible for the firing device  18  to fire with inadequate voltage. However, by using a firing pulse or test pulse generated by the control device it is possible to test the firing unit  68  because the switches  56 ,  61  and  60  bring about a current path from the voltage source  58  to the firing unit  62 . 
   If a plurality of firing devices are connected in accordance with  FIG. 2  to the communications bus  8  in  FIG. 1 , a vehicle occupant protection system can thus be brought about in which a number of firing devices (closed switch  61 ) fire only when there is a front-end impact (safing output  32   1 ), and other firing devices (switch  59  closed) fire when there are impacts other than front-end impacts, the firing of said firing devices being secured via the control output  48   1 . The control devices which fire when there is a front-end impact can be additionally checked in terms of their function using the test output  32   1 , firing being reliably prevented when there is a functional check. 
   It goes without saying that the system described can be changed in different ways. For example, it is not absolutely necessary to integrate a firing-device-specific identification; however, it increases the flexibility of the system because firing devices can be addressed selectively. The switching device  50  can contain a plurality of switches so that it is possible, for example, to fire all the firing devices in the case of a front-end impact, whereas only respectively assigned firing devices are fired in the case of other impacts. Alternatively, it is also possible to use other firing devices which are connected to a common communications interface  12 . 
   The firing input  53  can be dispensed with if the firing signal comes directly via the output  48   1  or  32   1  and closes corresponding switches which connected the firing voltage source to the firing unit. 
   It goes without saying that the block circuit diagram in  FIG. 2  is also schematic and can be modified in various ways. For example, a plurality of firing units may be provided per firing device.  FIG. 4  shows a modified embodiment of the system according to  FIG. 1 , the same reference symbols being used for functionally similar parts. 
   The essential difference from the embodiment according to FIG.  3  and that according to  FIG. 1  is that in the embodiment according to  FIG. 3  the test input  42  is absent and in its place the test output  40  is connected via a further voltage divider circuit with resistors  70  and  72  to a switch  74  which is formed, for example, by a transistor, can be actuated electronically and is connected to the control input  48 . 
   The circuit ensures that when a test pulse generated by the control device  2  is present at the test output  40  or when there is a pulse at the output  40  (which does not necessarily need to be a test output) for closing the switches  34  and  74  at the inputs  32  and  48 , in each case the same voltages or signals are present as when the safing switch  26  closes or when there is a control signal present at the control output  46 . 
   With only two pins or inputs  32  and  48  of the communications interface  6  to which corresponding outputs  32   1  and  48   1  of the decoding device  10  correspond, it is possible to secure four functional scopes, for example according to the following table: 
   
     
       
             
             
             
             
           
         
             
                 
             
             
               State 
               Safing input 32 
               Control input 48 
               Enabling/disabling 
             
             
                 
             
           
           
             
               I 
               0 
               0 
               Enabling test 
             
             
                 
                 
                 
               Firing in case of 
             
             
                 
                 
                 
               front-end impact 
             
             
               II 
               0 
               1 
               Enabling firing in 
             
             
                 
                 
                 
               case of non-front- 
             
             
                 
                 
                 
               end impact 
             
             
               III 
               1 
               0 
               Disabling of firings 
             
             
               IV 
               1 
               1 
               Enabling of firings 
             
             
                 
             
           
        
       
     
   
   As is apparent, the firing device or devices which are assigned to a front-end impact can be tested and the firing device or devices which are not assigned to a front-end impact can be fired independently of the firing devices to be fired in the event of a front-end impact. The output  40  in the embodiment according to  FIG. 3  is therefore not a test output in the true sense but rather an additional control output with which functions can be disabled or enabled. 
   The circuit of the firing device or devices is correspondingly embodied so that the corresponding functions can be disabled or enabled with the signal states explained in table 2 at their outputs  32   1  and  48   1 . 
   It goes without saying that the circuits which are explained by way of example can be modified in various ways if only the essential ideas of the invention are implemented, i.e. the generation of signal states at the control-device-end communications interface  6  which are transmitted via the communications bus  8  to the communications interface  12  and are available there for disabling or enabling functional states which are triggered by means of corresponding instructions. 
   An input of the control-device-end communications interface is connected to a safing switch, it being possible to bypass the safing switch by means of a bypass switch which can be driven by an output of the control device. The output of the safing switch is connected to an input of the control device, it being possible, in contrast to the embodiments illustrated, for this input to be inverting, i.e. to have the voltage zero applied to it when the safing switch is closed. 
   An output-end control device has a device with which it is possible to test a firing device with predetermined application of signals to the outputs of the firing-device-end communications interface as long as the voltage source has not yet reached its firing voltage, and in the state in which the test capability is enabled the firing capability is automatically disabled as soon as the voltage source has reached its firing voltage. 
   Alternatively, the communications interface of the firing devices can, as shown in  FIG. 2 , be embodied with three outputs, and the applications of signals to the inputs  32  and  48  of the control device of  FIG. 4 , which are transmitted via the communications bus, can be converted into the following applications of signals by appropriately embodying the communications interface  12 : 
   
     
       
             
             
             
           
             
             
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               K-interface 6 
               K-interface 12 
             
             
                 
               (FIG. 4) 
               (FIG. 2) 
             
           
        
         
             
                 
               State 
               32 
               48 
               32 1   
               48 1   
               42 1   
             
             
                 
                 
             
             
                 
               I 
               0 
               0 
               1 
               0 
               1 
             
             
                 
               II 
               0 
               1 
               1 
               1 
               0 
             
             
                 
               III 
               1 
               0 
               0 
               0 
               0 
             
             
                 
               IV 
               1 
               1 
               0 
               1 
               0 
             
             
                 
                 
             
           
        
       
     
   
   As a result, with the embodiment of the control device and of the circuits connected downstream of it according to FIG.  1  and the embodiment of the firing device according to  FIG. 2  it is possible to carry out all the functions explained in conjunction with these figures. 
   Only two additional bits included in the code words have to be transmitted via the communications bus, said bits corresponding in each case to one of the inputs  32  and  48  and their signal state being as indicated in the table above. The information contained in the (control and signal) bits is converted in the communications interface  12  into the application of signals to the outputs  32   1 ,  48   1  and  42   1  which is indicated in the table.