System for controlling the operation of modules using information transmitted from a control device via a data bus, a trigger device and a test circuit

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

According toFIG. 1, a control device2of a vehicle occupant protection system is connected via a data line4to a communications interface6which is connected to firing devices9,10via a communications bus8. The firing devices are embodied as what are referred to as “smart squibbs” which have their own communications interface12and whose design is explained by reference toFIGS. 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 device2controls a microprocessor which has associated memories and which determines instructions and/or information from sensor input signals22which are generated by different acceleration sensors, said instructions and/or information being fed to the communications interface6via the data line4.

In addition, a safing switch26which forms a redundancy switch and which closes by means of a predetermined vehicle deceleration so that, when the safing switch26is closed, current flows from a voltage source28, with for example 5 volts, through a resistor30and the safing switch26so that a safing signal is present at a safing pin or safing input32of the communications interface6which is connected to the connection between the safing switch26and the resistor30. In parallel with the safing switch26there is a normally open bypass switch34which is formed, for example, by a transistor and which is connected to a voltage divider circuit formed from two resistors36and38connected in series. The one resistor38is connected to ground and the other resistor36is connected to a test output40of the control device2, which is in turn connected to a test input42of the communications interface6.

The connection between the safing switch26and the resistor30is additionally connected to an input44of the control device2.

The control device2also has a control output46which is connected to a further pin or a control input48of the communications interface6.

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 device2and of the signal states of the inputs32,42and48which are sent via the data line4takes 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 interface6that the input42has a signal applied to it, but this is not the case at the input32, a fault in the system can be identified immediately by acknowledgement by the data line4to the control device2. Furthermore, the control device2can be embodied, for example, in such a way that it sends a firing instruction for firing the firing device18or devices18only if a safing signal is present at its input44. 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 input44or at the input32without a signal change being present at the input42.

If, for example in the case of test signal generated as a result of a fault in the control device2, i.e. test input42with a signal applied to it, a firing signal is transmitted via the data line4, this does not cause the firing device to fire as explained below because the test input42forms a DISABLE input. In this way, it is at least largely possible to prevent faults in the firing device2leading to inadvertent firing of a firing device.

The design of an advantageous exemplary embodiment of the firing devices9,10which are advantageously embodied in the same way is described below with reference to FIG.2.

The communications interface12which is connected to the communications bus8has a safing output321, a test output421and a control output481. The code words which are transmitted via the communications bus8are each read out by the communications interface12in such a way that the signal state at the outputs321,421and481, corresponds to the signal states at the inputs32,42,48of the communications interface6.

In the firing device16there is a switching device50whose inputs are connected to the outputs321and481. A firing signal output52of the communications interface12, to which firing signal output52a firing signal sent by the control device2via the data line4is transmitted, is connected to a firing input53. A code input54is connected to a code signal output55which conducts identification signals and code signals which are individually assigned to the firing devices and are transmitted by the control device2.

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 input54, said voltage serving to activate a code switch. The presence or intactness of such a resistor can be checked from the control device2, as a result of which the functional reliability of the system is further improved.

The further design and function of the switching device50is explained with reference to FIG.3:

The input of a code switch56is connected to a firing voltage source58. The code switch56has two outputs, of which one is connected to the input of a firing switch60via a control switch56which can be driven by the control output481, and the other is connected to the input of the firing switch60via a safing switch61which can be driven from the safing output321. The output of the firing switch60is connected to a firing unit62, embodied for example as a firing cap.

The function of the switching device50which is described is such that the code: signal present at the input54defines the control-device-specific positioning of the code switch56, i.e. whether the branch with the control switch59or the branch with the safing switch61is activated. When the control switch59is activated, a control signal which is present at the control output48, leads to the closing of the control switch59so that a firing signal53which closes the firing switch60fires the firing unit62when the firing voltage source58is charged. On the other hand, when the safing switch61is activated, a signal at the safing output321causes the firing output62to fire when there is a firing signal.

If a plurality of firing devices equipped with the control circuit50described are connected to the communications bus8, it is therefore possible to determine by means of the code signal whether the firing devices are activated via the control output481and/or the safing output321so that they fire correspondingly.

An exemplary assignment is that firing devices which are activated via the control output481are 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 output321. The switches59and61thus 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 device63with an AND element64whose inputs are connected to the firing voltage source58and the test output481and whose output is connected to the input of a safety switch66which is formed, for example, from a transistor. The safety switch66connects the safing output321to ground when there is a signal from the AND element64so that a signal which is present at the safing output321becomes ineffective for the switching device50. In order to monitor the state of the safety switch66or of the safing output321, a monitoring device68is provided whose output signal is displayed immediately and/or can be sensed additionally by the control device2.

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 device63is explained below. It is assumed here that, after the system is switched on, for example via the communications bus8, the firing voltage source58is gradually charged to the firing voltage.

The safing output321may have a safing signal (front-end impact) applied to it so that when there is a corresponding code the switch61is closed and the firing unit62fires when there is a firing signal if the test output421does not have a signal applied to it. However, if a test signal is present and the firing voltage source58is charged to its firing voltage, the AND element64supplies an output signal, as a result of which the safety switch66closes and connects the safing output32, to ground, as a result of which in turn the switch60is prevented from closing. A test signal thus constitutes an ENABLE signal in terms of the firing. If the firing voltage source58has still not reached the firing voltage after the system is put into operation (the firing voltage source58contains a charging capacitor), the AND element64does not supply an output signal because there is inequality between the voltage at the test output421and the voltage of the firing voltage source58in this state. It is in any case impossible for the firing device18to 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 unit68because the switches56,61and60bring about a current path from the voltage source58to the firing unit62.

If a plurality of firing devices are connected in accordance withFIG. 2to the communications bus8inFIG. 1, a vehicle occupant protection system can thus be brought about in which a number of firing devices (closed switch61) fire only when there is a front-end impact (safing output321), and other firing devices (switch59closed) fire when there are impacts other than front-end impacts, the firing of said firing devices being secured via the control output481. The control devices which fire when there is a front-end impact can be additionally checked in terms of their function using the test output321, 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 device50can 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 interface12.

The firing input53can be dispensed with if the firing signal comes directly via the output481or321and closes corresponding switches which connected the firing voltage source to the firing unit.

It goes without saying that the block circuit diagram inFIG. 2is also schematic and can be modified in various ways. For example, a plurality of firing units may be provided per firing device.FIG. 4shows a modified embodiment of the system according toFIG. 1, the same reference symbols being used for functionally similar parts.

The essential difference from the embodiment according to FIG.3and that according toFIG. 1is that in the embodiment according toFIG. 3the test input42is absent and in its place the test output40is connected via a further voltage divider circuit with resistors70and72to a switch74which is formed, for example, by a transistor, can be actuated electronically and is connected to the control input48.

The circuit ensures that when a test pulse generated by the control device2is present at the test output40or when there is a pulse at the output40(which does not necessarily need to be a test output) for closing the switches34and74at the inputs32and48, in each case the same voltages or signals are present as when the safing switch26closes or when there is a control signal present at the control output46.

With only two pins or inputs32and48of the communications interface6to which corresponding outputs321and481of the decoding device10correspond, it is possible to secure four functional scopes, for example according to the following table:

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 output40in the embodiment according toFIG. 3is 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 outputs321and481.

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 interface6which are transmitted via the communications bus8to the communications interface12and 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 inFIG. 2, be embodied with three outputs, and the applications of signals to the inputs32and48of the control device ofFIG. 4, which are transmitted via the communications bus, can be converted into the following applications of signals by appropriately embodying the communications interface12:

As a result, with the embodiment of the control device and of the circuits connected downstream of it according to FIG.1and the embodiment of the firing device according toFIG. 2it 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 inputs32and48and their signal state being as indicated in the table above. The information contained in the (control and signal) bits is converted in the communications interface12into the application of signals to the outputs321,481and421which is indicated in the table.