TRIGGERING DEVICE FOR A VEHICLE OCCUPANT RESTRAINING SYSTEM

Abstract: A triggering device for a vehicle occupant restraining system having a plurality of occupant restraining devices (BT1; BT2) for restraining an occupant in the event of a crash has an acceleration sensor (10) and control means (12; 12') for determining a crash condition on the basis of signals received from the sensor and for triggering the restraining system upon such a determination. The triggering of each restraining device (BT1; BT2) is controlled by a switch (22; 24) which is actuable by fastening an associated seat belt. The associated restraining device (BT1; BT2) may therefore only be triggered when the associated seat belt is fastened.

Description: DESCRIPTION IEIGGERING_DEyiCE_FOR_A_ EHICLE_OCCyPANT EESTRA1N1NG_SYSTEM S ate_of_the_Art The present invention relates to a triggering device for a vehicle occupant restraining system in accordance with the pre-characterising clause of claim 1. In vehicle occupant restraining systems, such as seat belt tensioners and inflatable air bags, an acceleration sensor determines the deceleration of the vehicle, and if it is determined that the deceleration exceeds a predetermined threshold value, i.e. that a crash condition exists, then the occupant restraining system is actuated, e.g. the seat belts are tensioned or the vehicle air bags are inflated. However, it is desirable to permit triggering of only those restraining systems which are actually required. For example, if the passenger seat is not occupied, then it is preferable that the associated restraining system is not triggered in the event of a crash. One reason for this is to reduce repair costs of a vehicle after an impact. It is thus an object of the present invention to provide a triggering device for a vehicle occupant restraining system which actuates only those restraining systems necessary to restrain the occupants, and which would not be triggered if the position associated with a particular restraining system was not occupied. Advanta2es__0f_the_I.nvent.i0n The above object is achieved by adopting the features set forth in claim 1. In this way, a restraining device may only be triggered when the seat belt associated with that particular restraining device is used. Also, the present invention allows triggering of the or each restraining system even in the event of faults in the electrical circuits. Also, since existing restraining systems, for example seat belt tensioning devices, currently in production do not include interrogation of external switches for preventing or releasing triggering of the seat belt tensioner, the present invention is downwardly compatible with earlier systems, which reduces the number of spare parts which need to be stocked and ensures fail safe operation in service stations. Further advantages are obtained by the features of claims 2 to 5. Drawings By way of example only, a specific embodiment of the present invention will now be described, with reference to the accompanying drawings, which: Fig. 1 is a schematic diagram of a triggering device for a vehicle occupant restraining system in accordance with the present invention; and Fig. 2 is a circuit diagram of a device for triggering a vehicle occupant restraining system, in accordance with the present invention. Referring firstly to the schematic arrangement of Fig. 1, the triggering system in accordance with the present invention comprises an acceleration sensor 10 which feeds integrated acceleration signals __ v into a first comparator 12, which determines, in accordance with predetermined characteristics, whether a crash condition has occurred, on the basis of the incoming Δv signal. In the event of a crash condition, the first comparator 12 outputs a signal X to each of first and second circuits, as illustrated as being effectively AND gates A j , A 2 , associated with the driver's occupant safety system (in this case a seat belt tensioner) and a passenger's occupant safety system (also a seat belt tensioner in this case) respectively. Each of the second and third comparators 14, 16 controls, via the AND gates A j , A 2 , an associated transistor switch 18, 20, each of which controls the associated belt tensioning device (illustrated schematically as BT1, BT2 respectively) . Each of the AND gates A j , A 2 also receives a signal from an associated seat belt lock contact switch 22, 24 via a comparator 14, 16. These switches are normally closed, but are opened by the insertion of the seat belt buckle into the associated socket. Each of the seat belt lock contact switches 22, 24 is connected in series with a first resistor R S1 and in parallel with a second resistor R S2 . The result of this is that a higher voltage is fed to the respective comparator 14, 16 when the belt buckle is inserted, i.e. when the contact switches 22, 24 are opened. In use, the acceleration sensor 10 and the first comparator 12 produce a crash signal X in the event of a crash condition, and this signal is fed to each of the AND gates A- j , A 2 . However, the AND gates A j , A 2 will only output a signal to the respective transistor switches 18, 20, thereby activating the seat belt tensioning devices, if the other signal received by the comparator 14, 16 from the respective seat belt lock contact switch indicates that the switch is open, i.e. that the seat belt buckle is inserted and that the seat is occupied. This can be determined by measuring the other input in the respective comparator 14, 16, a lower voltage indicating that the switch is closed, and a higher voltage indicating that the switch is open and the seat belt buckle is inserted. Thus, two conditions are necessary for the actuation of a particular seat belt tensioning device, namely that a crash condition has occurred and furthermore that the seat associated with to that seat belt tensioning device is occupied. In particular, if the comparator 14, 16 determines that the switch is closed, i.e. that the associated seat is not occupied, then the associated belt tensioning device will not be actuated. It should be noted that actuation of the belt tensioning devices BT1, BT2 are independent of one another. Thus, if the seat belt buckle of only one seat belt is inserted, only the belt tensioning device associated with that fastened seat belt is actuable in the event of a crash. A concrete example of the present invention is illustrated in Fig. 2. The arrangement comprises an acceleration sensor 10 which is connected via a low-pass filter (R* | 8 > R- j g-. C 14 ) for integration of the output signal, to an amplifier 30 with high-pass behaviour for amplifying the filtered, integrated acceleration (Δv) signal. This amplifier compensates for the sensitivity tolerance of the acceleration sensor 10, and for other tolerances in the evaluation circuit. The arrangement also comprises a conventional voltage regulator 32 with associated conventional components (diodes D, Zener diodes ZD, capacitors C, resistors R) which produces an accurate, regulated voltage which is input to a comparator arrangement 12', which comprises a Δv threshold comparator 34 and a prolongation means in the form of a comparator 35, resistor R 9 , and capacitor C 6 . An acceleration- dependent switch S connects the belt tensioning devices BT1, BT2 to positive supply voltage in case of its closure. The switch S is adapted to close under deceleration, and helps to guard against inadvertent triggerings of the belt tensioners by the electronics. The output from the amplifier 30 is also input into the v comparator 34, and it is the comparator arrangement 12' which thus determines whether a crash condition has occurred, namely if the signal from the high-pass amplifier 30 is greater than the steady regulated voltage by a predetermined amount, then the comparator arrangement 12' outputs a signal. In conventional systems, this would simply be used to turn on a transistor switch and thereby activate all the occupant restraining systems of the vehicle. However, it will be appreciated that in this case the one signal would actuate a__ the safety systems, irrespective of whether the associated seats were occupied. In contrast, the output from the comparator 12' is input to each of two output stage logic units 36, 38, and it is the output of the logic units which controls the state of the respective transistor switches 18, 20. Each output stage logic unit 36, 38 also receives a signal from an associated respective seat belt buckle contact switch, the unit 36 receiving its signal from the driver's switch 22, and the unit 38 receiving its signal from the passenger switch 24. It should be noted that any number of such switches can be provided in the vehicle, corresponding to the number of people which the vehicle is designed to carry. Referring firstly to the driver's switch 22, as explained previously this is connected in series with a first resistor R S1 and in parallel with a second resistor R S2 . The output from the resistor R s1 is fed into the inverting input of a comparator 40, the non- inverting input receiving a constant voltage input from the voltage regulator 32. The output from the comparator 40 is fed into the inverting input of the logic unit 36 where it is compared with the output from the comparator 12' which is fed into the non-inverting input of the logic unit 36. A similar arrangement is effected with the passenger switch 24, the output from the switch being connected to a further comparator 42, identical to the comparator 40, the non-inverting input of the comparator 42 also receiving constant voltage from the voltage regulator 32. The output of the further comparator 42 is fed into the inverting input of the logic unit 38, where it is compared with the output of the comparator 12', which is fed into the non-inverting input thereof. The system will now be described with reference to the driver's switch 22, and the passenger switch 24 operates in a similar fashion. The acceleration sensor 10 continuously monitors the acceleration of the vehicle, and feeds the integrated acceleration signal into the Δv amplifier 30. When the Δv amplifier 30 determines that a crash condition has occurred, a signal is output to the comparator 34 of the comparator unit 12'. When the mechanical acceleration-dependent switch S also determines that the vehicle is decelerating, it closes and provides a connection of the seat belt tensioning devices BT1, BT2 to the positive supply voltage. This is a further necessary condition for the actuation of the belt tensionsers. In the conventional manner, a signal is output from the comparator unit 12' and input into the non-inverting inputs of the output stage logic units 36, 38. When the belt fastener is not inserted, the output voltage U 22 from the switch 22 is less than the divided output voltage U REG ,swhich causes the comparator 40 to have a high output. Thus, the output voltage U 40 from the comparator 40 is greater than the voltage U 12 from the comparator unit 12', even when the Δ v threshold has been exceeded and wants to trigger the device. However, the divider comprising resistors RJQ and R- j *- limits the voltage range from the output of the comparator unit 12' to a value which is smaller than the value U 40 from the comparator 40 which is determined by the divider R S1 , R S (in the belt fastener switch), resistor R 25 , diode D 4 and resistor R 27 (connected between diode D 4 and the output of the voltage regulator 32). Thus, if the belt fastener is not inserted, the output of the comparator 36 cannot become high, and consequently the transistor switch 18 remains inactive, and thus the belt tightening device is not actuated. When the belt fastener _s inserted, the voltage U 2 from the switch 22 is greater than the divided regulated voltage U RE6 from the voltage regulator 32. In this case, the voltage divider comprising resistors R 35 and R 28 connected to the output of the comparator 40 becomes effective, and reduces the value of the signal input from the comparator 40 into the inverting input of the comparator 36. Thus, when the output of the comparator unit 12* becomes high (when the ___ v threshold is exceeded) the output from the comparator unit 12' can become greater than the voltage U^g. In this case, the output of the output stage logic unit 36 becomes high, and the transistor switch 18 is switched on, thereby actuating the belt tensioning device BT1 to which the transistor 18 is connected. This is possible under the condition that switch S is closed. An identical operation occurs with the passenger switch 24, through its associated circuitry. The only difference is that it is the transistor switch 20 which is actuated, which controls its associated belt tensioning device BT2. Interruption in the lead from the driver's switch 22 in the vehicle, or short circuiting of this lead to positive has the same effect as if the belt fastener is inserted. This enables the system to be compatible with existing systems without the belt fastening switches. When the driver's switch 22 lead is short circuited to earth, the divider comprising resistor R 5 , diode D 4 and resistor R 27 causes the output voltage U 40 of the comparator 40 to be at a value which is smaller than the output voltage U 12 of the comparator unit 12' when the latter determines a crash condition. Thus, a triggering operation in a crash is also possible during a short circuit to earth. The above discussion of interruption and short circuiting of leads also applies to the passenger switch 24. The above embodiments have been described with reference to normally-closed switches 22, 24 which are opened upon fastening of the belts. However, normally- open switches could be used instead, with appropriate adaptation of the evaluation circuit (e.g. reversal of the logic signals). Moreover, the restraining system need not be a seat belt tensioner, but may be applied to other occupant restraining systems, e.g. inflatable air bags.

Claims: CLAIMS 1. A triggering device for a vehicle occupant restraining system having a plurality of occupant restraining devices (BT1, BT2) for restraining an occupant in the event of a crash, the triggering device comprising an acceleration sensor (10) and control means (12; 12') adapted to determine a crash condition in dependency on signals from the sensor (10) and thereby trigger the restraining system, characterised in that the triggering of each restraining device (BT1; BT2) is controlled by a respective switch (22; 24) actuable by fastening an associated restraining device may only be triggered by the control means (12; 12') when the associated seat belt is fastened. 2. A triggering device as claimed in claim 1, wherein each switch (22; 24) is operable by fastening the respective seat belt and is open when the respective belt is not fastened. 3. A triggering device as claimed in claim 1, wherein each switch (22; 24) is closable by fastening the respective seat belt and is open when the respective seat belt is not fastened. 4. A triggering device as claimed in any of claims 1 to 3, wherein the triggering of the restraining devices (BT1, BT2) is effected by means of a transistor switch (18; 20) whose conduction state is controlled by the control means (12; 12'). 5. A triggering device as claimed in any of claims 1 to 4, further comprising an acceleration-dependent mechanical switch (S) connected in series with the belt tensioning devices (BT1, BT2).

Inventors: MATTES BERNHARD, OSWALD KLAUS, REISCHLE KLAUS, MATTES, BERNHARD, OSWALD, KLAUS, REISCHLE, KLAUS
Applicants: BOSCH GMBH ROBERT, ROBERT BOSCH GMBH
Application year: 1988
Main classification: B60R22
IPC codes: B60R21, B60R22