GB2263571A

GB2263571A - Triggering device for a vehicle safety device

Info

Publication number: GB2263571A
Application number: GB9300146A
Authority: GB
Inventors: Thomas Goernig; Juergen W Damisch
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 1992-01-21
Filing date: 1993-01-06
Publication date: 1993-07-28
Anticipated expiration: 2013-01-06
Also published as: GB9300146D0; GB2263571B; DE4207153C2; KR930016291A; FR2686303A1; FR2686303B1; JP3388793B2; JPH068792A; KR100283822B1; DE4207153A1

Description

2263571 A tripping Device for a Vehicle Safety Device The invention

relates to a tripping device for a vehicle safety device comprising an acceleration sensor responsive to the instantaneous acceleration and for the output of an acceleration signal, means for producing first, second and/or third signals, which are derived from the ac celeration signal, means for starting processing as soon as the first signal, which is derived from the acceleration, has attained a start threshold value and means for triggering the safety device as soon as the second signal derived from the acceleration has exceeded a threshold value within a predetermined trigger time interval. 1 Known trigger devices for vehicle safety devices, as for instance airbags, operate in the following steps. When an acceleration signal (a) of an acceleration sensor has reached a predetermined starting threshold value (a,), integration of the acceleration signal above this threshold value (a,) is commenced. In the event of the integration value (v) attaining another, predetermined threshold value (v,), the vehicle safety device is operated that is to say for instance the airbaq is inflated. As soon as the integrated signal drops back to 0,.the integration operation is inter rupted as long as the acceleration signal remains below the starting threshold value (a,).

The starting threshold value is set to be as high as possible in order to prevent triggering in response to non-critical blows or knocks. On the other hand it is necessary for the level of the threshold value to be set sufficiently low to cause triggering in a case in which an impact pulse due to an actual collision occurs. Similar criteria apply for the selection of the threshold value v,.

A triggering device of the type initially mentioned for a passive vehicle safety device is for example disclosed in the German patent publi- cation 3,816,591 C2.

Triggering devices of this type have the disadvantage that for instance knocks or jerks adjacent to the sensor, as for example on adjustment and locking in position of an adjustable steering column, may lead to an impulse to which the above mentioned triggering device will respond. In 1 such a case the vehicle safety device would be tripped, i.e. for example an airbag would be inflated or a belt pretensioner operated, in vain.

One object of the present invention is consequently to provide such a further development of a device of the sort noted initially that triggering of the respective vehicle safety device only occurs in a genuine hazard situation, that is to say in a traffic accident.

In accordance with the invention this object is to be attained taking a device of the type initially mentioned as a starting point by adopting the features of the characterizing part of claim 1. In accordance with this the entire processing operation commences with a testing interval which is followed by the triggering time interval. Furthermore means are provided, which terminate the processing operation as soon as the third signal derived from the acceleration reaches or, respectively, exceeds a predetermined threshold value within this testing time interval.

This design in accordance with the invention is based on the realisa- tion that a jerk resulting from a blow or knock on the vehicle lasts a much shorter period of time than an impact due to a collision. This is something which may be clearly seen from the changes with time of the acceleration signals or signals derived therefrom. In accordance with the design of the invention triggering of the safety device is prevented or overridden, in the event of the acceleration signal or a value derived from it, for instance its time integral, rising excessively rapidly.

The first signal derived from the acceleration can be identical with or proportional to the acceleration signal. The second signal derived from the acceleration may be proportional to the time integral of an acceleration signal exceeding a certain acceleration value. The third signal derived from the acceleration may be identical to the second signal derived from the acceleration.

In accordance with a further advantageous development of the inven- tion the second and/or the third signals derived from the acceleration may be reset to zero before processing is restarted.

An other advantageous feature of the invention is such that means are provided for terminating the processing operation as soon as the second or the third signal derived from the acceleration has dropped to a predetermined interruption threshold value.

Preferably the length of the processing operation is unlimited. In this respect the second signal derived from the acceleration is formed by integration of the acceleration signal values, which are above a certain acceleration value. Owing to the limited possibility of storing the logged data the continuously logged acceleration signal may only be stored for a 2 certain length of time corresponding to the maximum storage capacity. When the storage capacity is exhausted, the first acceleration values in the memory means are erased in order to provide new storage capacity of the new signal to be logged therein.

in accordance with a more particularly advantageous form of the in vention the testing time interval is set at 3 to 6 ms.

Further advantageous developments and convenient forms of the inven tion will be understood from the following in conjunction with the accompa nying drawings.

Figures 1 and 2 Figures 3 and 4 Figure 5 are graphs of an impact pulse arising owing to a collision.

are graphs of a pulse arising from a blow or knock.

is a block diagram to indicate the manner of functioning of one working embodiment of the triggering device in accordance with the invention.

Figure 1 shows an acceleration against time graph of the typical impact pulse signal as detected by an acceleration sensor and as produced in a traffic collision. In accordance with one working embodiment of the invention the first signal derived from the acceleration signal is the acceleration signal itself or a signal proportional to it. This form of signal is depicted in figure 1.

In figure 2 the values derived from the acceleration signal form are graphed. In this respect it is a question of the speed changes integrated with respect to time. One curve (fadt) corresponds to the integration of the detected acceleration value. A further curve plotted in figure 2 corresponds to the integration of an acceleration value, which is respectively decreased by a previously set acceleration threshold value (f(a-al)dt). In accordance with the working embodiment presently being considered the form of the integral f(a-al) dt is employed as the second and third values of the detected acceleration.

In the example illustrated in figures 1 and 2 the triggering device detects the attainment of a predetermined acceleration threshold value a, (see figure 1) at a point in time ti. Therefore the processing operation, which extends over the time interval t, tV is started. That is to say in a so-called testing time interval tl t2 a test is made to see whether the derived signal (f(a-al) dt) has reached a predetermined threshold level v, or not. In the case illustrated in figure 2 the derived signal does not attain the predetermined threshold value vi within the testing interval t, 3 - t., said threshold value v, only being reached at a point in time, which is within the time interval t, - t3. The point in time at which the threshold value vi is reached is denoted tt on the time axis. Because the point in time is within the triggering time interval t2 t3, the vehicle safety device (for instance in the form of an airbag) is tripped. In figure 3 and figure 4 changes in the signal corresponding to an impact pulse detected by the acceleration sensor is plotted. As shown in figure 3, at the point.in time t the threshold value a, is attained the therefore the processing or evaluating operation t, t3 is started. In the working embodiment being considered herein t3 is not specified exactly so that t3 - w. As shown in figure 4, the value (f(a-al) dt) derived from the acceleration increases very rapidly, that is to say even within the testing interval, it reaches the threshold value (v,). This point in time is denoted as ts,' on the time coordinate in figure 4. At this point in time the processing operation is terminated and the signal derived from the acceleration, i. e. f(a-a,)dt is reset to 0. This point in time is simultaneously the new starting point for a further processing operation, which is denoted t 111 on the time coordinate in figure 4. Within the testing time interval t 1 t2- lasting approximately 3 to 6 ms. the threshold value vi is not reached again in the illustrated working embodiment. However the derived signal value decays very rapidly to reach 0 at the point time t,2' ' This means that in the case of the working embodiment considered herein there is as well an interruption of the processing operation so that in this case example in accordance with figures 3 and 4 the triggering device does not trip the vehicle safety device.

In figure 5 a flow chart will be seen for explaining a working embodiment of the triggering device in accordance with the invention. Reference 10 denotes an acceleration sensor of known design. The acceleration signal a is decreased at 12 by the threshold value a,. At 24 testing is performed to check whether the value (a-a,) is larger than 0. If this is the case a start command is sent to the integrator 14 so that the value (aa,) detected here is integrated. Simultaneously a start pulse is sent to the timing member 32 by means of which the testing time interval tc is set. The value coming from the integrator 14 is tested in the comparator 26 to see if it has reached 0 or not. If it has attained 0, then via the ORgate 28 a stop and reset signal is sent to the integrator 14. On the other hand a reset signal is also sent to the timing member 32. The value v coming from the integrator is decreased in the subtracting member 16 by the threshold value v,. In the matching member 18 testing is then performed to see if the value (v-v,) is greater than 0. If this is the case, a signal is 4 sent to the AND-gate 20. If the timing member 32 simultaneously sends a blocking signal to the AND-gate 20, that is to say the testing time interval has run to an end in the meantime, a triggering signal is sent to the safety device 22. If the testing time has not yet run to an end, the second AND-condition will not have been fulfilled at the AND-gate 20 so that the safety device 22 is not tripped. However in this case a second ANDcondition will have been satisfied at the AND-gate 30 so that via the ORgate 28 a corresponding stop command will be sent to the integrator 14 and a reset command will be sent to the timing member 32.

Claims

1. A tripping device for a vehicle safety device comprising an acceleration sensor responsive to the instantaneous acceleration and for the output of an acceleration signal (a), means for producing first, second and/or third signals, which are derived from the acceleration signal (a), means for starting processing (tl - t.) as soon as the first signal (a), which is derived from the acceleration, has attained a start threshold value (a,) and means for triggering the safety device as soon as the second signal (v) derived from the acceleration has exceeded a threshold value (v,) within a predetermined trigger time interval (t2 - t 3)l characterized in that that the entire processing operation (t, - t3) is adapted to commence with a testing time interval (tl - t2) which is followed by a triggering time interval (t

2 - t,,) and in that means are provided adapted to interrupt said processing operation as soon as the third signal (v) derived from the acceleration has reached or exceeded a predetermined threshold value (vi within the testing interval (tl - t2) ' 2. The triggering device as claimed in claim 1, characterized in that the first signal derived from the acceleration is identical with or propor- 6 tional to the acceleration signal (a).

3. The triggering device as claimed in claim 1 or in claim 2, characterized in that the second signal (v) derived from the acceleration is proportional to the time integral of the acceleration signal (a) above a predetermined integration value (al)(ft(a-al)dt)..

4. The triggering device as claimed in claim 3, characterized in that the third signal derived from the acceleration is identical with the second signal (v) derived from the acceleration.

5. The triggering device as claimed in any one of the claims 1 through 4, characterized in that the second signal and the third signal derived from the acceleration are preferably reset to 0 before a processing operation (tl t 3) is recommenced.

6. The triggering device as claimed in any one of the claims 1 through 5, characterized by means for the termination of the processing operation as soon as the second or the third signal (v) derived from the acceleration has fallen to a predetermined termination threshold value (0).

7. The triggering device as claimed in any one of the claims 1 through 6, characterized in that the duration of the processing operation is unlimited (t3 - co) and in that the second signal (v) derived from the acceleration is formed by integration of the acceleration signal (a) above a predetermined value (a,).

8. The triggering device as claimed in any one of the c.laims 1 through 7, characterized in that the testing time interval (tl - t 2) i s set at 3 to 6 ms.

9. A triggering device for a vehicle safety device, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

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