WO1990002673A1

WO1990002673A1 - Apparatus for triggering a vehicle safety system

Info

Publication number: WO1990002673A1
Application number: PCT/EP1988/000820
Authority: WO
Inventors: Hartmut Schumacher; Norbert Crispin; Bernhard Mattes
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1988-09-09
Filing date: 1988-09-09
Publication date: 1990-03-22
Anticipated expiration: 1991-03-09

Abstract

A triggering unit for supplying electrical energy to an igniter (28) for inflating an inflatable restraining device in a vehicle has a storage capacitor (C1) which is connectable to an igniter (30) of the initiation element (28) by means of two switches (S1, S2) connected in series with the initiation element. Each switch (S1, S2) is closable independently of the other by means of an associated control device (CU1, CU2) which receive signals from respective sensors (SR1, SR2) and determine whether a crash condition has occurred. Only when both control devices (CU1, CU2) determine the occurrence of a crash condition simultaneously are both switches closed and energy is supplied to the initiation element (28). Each switch (S1, S2) is closable periodically, and the energy (ΔE) supplied to the initiation element (28) during simultaneous closure of the switches is less than the firing energy of the igniter (30). A capacitor (CF) in series with the igniter (30) ensures that the igniter cannot be fired by a d.c. voltage e.g. by a short-circuit to the vehicle battery.

Description

DESCRIPTION

APPARATUS FOR TRIGGERING A VEHICLE SAFETY SYSTEM

Prior Art

The present invention relates to an apparatus for triggering a vehicle safety system of the kind described in the precharacterising clauses of claims 1, 3 and 6 respectively.

In electronic restraining systems in vehicles, e.g. an inflatable air bag to restrain an occupant in

the event of a crash, the system normally takes the form of one or more sensors which detect the

deceleration of the vehicle and a control unit to monitor signals from the one or each sensor and to supply an electrical signal to fire electrically an igniter to inflate the bag if the control unit

determines that a crash condition has occurred

which requires the protection by the restraining system. There is a requirement for the system to be able to trigger the safety function very rapidly in the event of such a crash. However, it is also necessary that the restraining system should not be inadvertently actuated, for example in the event that a crash condition is incorrectly detected or if a short circuit occurs.

It is an object of the present invention to provide an initiation element and triggering apparatus for inflating an inflatable restraining device which

overcomes the aforementioned disadvantages.

Advantages of the Invention

The above object is achieved by adopting the features set forth in claim 1. This has the advantage that the initiation element cannot be fired by direct appl ication of a d.c. voltage, e.g. the battery voltage of a car. Conventional systems lead to deployment in this case. A further advantage is that the initiation element can still be triggered despite a short circuit to the battery voltage or to ground on the leads

supplying energy to the element.

The above object is also achieved by adopting the features set forth in claim 3. This has the advantage that firing of the initiation element is only possible by rhythmic, simultaneous triggering of the switches, in contrast to existing systems, in which a single

triggering command is sufficient. Thus, since rhythmic, simultaneous triggering of the switches is required and triggering of fewer than all of them is insufficient to fire the initiation element, there is increased

protection against incorrect triggering in the event of a fault.

The above object is also achieved by adopting the features set forth in claim 6. This has the further advantage that even after firing has been initiated, it is still possible to cancel the operation before firing occurs. This is particularly useful in the event of, for example, spurious firing signals.

The present invention has the further advantage that, in contrast to the prior art devices, short- circuits of the igniter or short-circuits to ground in the leads connecting the triggering unit and the

initiation element do not cause discharging of the energy reserve in the firing operation, thus removing the requirement for an energy reserve for each

initiation circuit .

Moreover, in the present invention, testing of the triggering circuit requires only a measuring resistor, and the tested components are tested directly.

By way of example only, a specific embodiment of the present invention will now be described, with reference to the accompanying drawings, in which:- Fig. 1 is a circuit diagram of an embodiment of triggering unit in accordance with the present

invention, connected to an embodiment of initiation element in accordance with the present invention;

Figs. 2a to 2d are plots of two switch states, the voltage across an igniter and the voltage across a measuring resistor respectively of the circuit of

Fig. 1, during a normal firing condition; and

Figs. 3a to 3d are plots of two switch states, the voltage across an igniter and the voltage across a measuring resistor respectively of the circuit of

Fig. 1, during a firing condition in which a short circuit is present in the circuit.

Referring firstly to Fig. 1, the triggering unit comprises a source of power 10 from a battery which feeds current via a switching regulator 12 and forward- biassed diode 14 to an energy reserve capacitor C₁, which is charged by the switching regulator 12 in a known manner to a vo l tage V_{E R} , whi ch in thi s cas e i s twice the value V_B of the power source 10. One side of the capacitor C₁ is connected to one terminal of each of two switches S ₁, So and also to an analog to digital converter (ADC)20. The other side of the capacitor is connected to ground E, to the ADC 20 via a measuring resistor 22 and also to the remaining terminal b of each of the switches S₁, S₂ via the measuring resistor 22.

The switches S ₁, S₂ form part of a circuit with an initiation element 28, each switch being connected to the initiation element by means of a respective

coupling capacitor C_C1, C_{C 2} . Each C_C1, C_C2 is

bridged by a respective high-value resistor R₁, R₂, and the initiation element 28 is bridged by a high- value resistor R₃ . The initiation element 28

comprises a conventional igniter 30 in series with a firing capacitor C_F. As will be explained in more detail hereinafter, the switches S₁, S₂ act to

reverse the polarity of the initiation element 28 when actuated simultaneously, thereby causing the igniter 30 to fire a gas generator and by this to inflate an air bag. The high-value resistors R₁, R₂ and R₃ serve to discharge their respective capacitors C_{C 1}, C_C2 and C_F very slowly when the system is at rest.

The ADG monitors the initiation element 28, the leads 32 which connect the initiation element to the triggering unit, and the switches S₁, S₂, by measuring the voltage V_M across the measuring resistor 22. The digital signal from the ADC 20 is fed to each of two control units CU ₁ , CU₂ , the control unit CU₂ also receiving the digital V_M signal from the other control unit CU₁.

Each control unit CU₁, CU₂ receives evaluation signals from a respective sensor SR₁, SR₂. The sensors detect signals, e.g. acceleration of the vehicle along a given axis, which can determine when a crash condition has occurred, e.g. when the deceleration along an axis exceeds a threshold value. The control units CU₁, CU₂ continuously monitor the signals from the respective sensors SR₁, SR₂ and determine whether a crash

condition has occurred.

If the signals from the sensors SR₁, SR₂ are such that the control units determine that a crash condition has occurred, the control unit CU₁ triggers switch S₁, and simultaneously the other control unit CU₂ triggers switch S₂. This is illustrated in Figs. 2a and 2b and as a result a voltage pulse V_INF is produced across the igniter 30 in each timing phase ΔT corresponding to the simultaneous actuation of the two switches S₁, S₂. The peak value of the voltage, V_INF is:

where R _INF is the resistance of the inflation capsule

(igniter) 30. Of course, the initial voltage pulse A in only half this magntiude. The peak power pulse applied to the inflation capsule is thus 4

and thus the energy applied during each period T of simultaneous closing if the switches S₁, S₂ is:

T

For U_ER c constant (which occurs for C_ER >> C_F)

and for ΔT >>

(e.g. Δ T = 5

> .

the following proximation is true:

Putting

*= (R_INF + R_M).C_TOT (C_TOT = total capacitanc))

(assuming C_C1 = C_C2 = C_c).

Putting C_TOT

C_F (i.e. C_C » C_F), the following

approximation applies:

Thus, during each period of time T for which the switches are simultaneously closed, a fixed amount of energy Δ E is applied to the inflation capsule 30. When the total amount of energy applied to the inflation capsule 30 exceeds the firing energy , the capsule is actuated and inflation of the air bag is effected.

In this embodiment, however, the length Δ T of the timing phase and the supply Δ E of energy per timing phase are selected such that the energy supplied to the inflation capsule 30 in a single timing phase T cannot exceed the firing energy. The length Δ T of the timing phase is also selected so that, bearing in mind the aforementioned condition for Δ E < firing energy, the application of energy pulses is as frequent as possible.

A very important advantage of these two conditions for Δ E and Δ T is that the firing operation can still be discontinued after it has been initiated. For example, if both control units CU₁ and CU₂

simultaneously determine that firing is required, switches S₁ and S₂ would be actuated, and energy pulses would be supplied to the capsule 30. If, before firing had occurred, one of the control units no longer

determines that firing is required, it is likely that there was previously a fault in the system or that the condition sensed by the sensors SR₁,SR₂ was only transitory, and that firing is not required. In this case, the associated switch would no longer be actuated and no further energy pulses would be applied to the capsule 30, thus preventing firing.

This is in contrast to the prior art in which, as soon as a control determines that the deceleration of the vehicle is such that a crash condition has occurred, the capsule is fired. If the control subsequently determines that firing is not required (e.g. a fault in the system or a transitory sensor signal), the firing can not then be halted.

Testing of the triggering circuit

When voltage and power pulses are applied to the inflation capsule 30, the characteristic of the voltage V_M across the measuring resistor R_M may be used to detect the presence of short circuits. The voltage characteristic is compared with a desired characteristic stored in one or both of the control units CU₁, CU₂.

The comparison is carried out on the basis of the following :

(for all cycles, cycle 1 .... n, after the first

charging cycle, since the value of the voltage in the first charging cycle T_o is half of that in subsequent cycles).

In the above,

£ C_TOT(R_INF + R_M)

* C_F( RI_NF + R_M) if it is assumed that C_TOT C_F (i.e. C_C1 = C_C2 >> C_F) . Thus, by monitoring the voltage V_M(t) across the

measuring resistor R_M, changes in the inflation capsule resistance R_INF and changes in the capacitance C_F of the firing capacitor can be determined independently of each other. For instance, if R_INF changes, both the initial amplitude of the voltage pulse V_M and the decay constant ζ of the pulse will be changed, whereas a change in C_F will affect the decay constant ζ only.

The voltage R_M is continuously monitored during voltage pulse conditions by the control units CU₁, CU₂. By determining the value of the change from the stored desired voltage characteristic, the effect on the ability of the system can be monitored and evaluated in the control units CU₁, CU₂. The various types of short circuit can be determined as follows:

A . Short circuit to ground at point A of the triggering circuit.

As shown in Fig. 3c, the voltage V_INF across the inflation capsule is zero during the first charging cycle T_o (which is before the voltage V_M is measured). In subsequent timing phases (2n-1), n=1, 2,...,n_{m ax}

(e.g. T₁, T₃) when the switches S ₁* , S₂ are in contact with the terminals b of the switches S₁, S₂ , the maximum value of V_INF is U_ER and the time constant ζ ₁ is:

In the subsequent timing phases (2n), n=1, 2,...,n_max (e.g. T₂, T₄ ) when the switches S₁, S₂ are in contact with the terminals a of the switches S₁, S₂:

an d

ζ

Thus, the characteristic of Fig. 3d appears on the measuring resistor R_M:

For odd timing phases (2n-1) :

V_M = U_ER and ζ 3 = C_C.R_M

For even timing phases (2n) : V_M = U_ER and

By measuring the changes in V_M, a short circuit at point A can thus be detected, by comparing the measured characteristic with the stored desired characteristic.

The control units can then decide whether the firing operation should be discontinued (in which case the switches S₁, S₂ cease to be actuated) or continued with a longer duration of activation to compensate for the smaller amount of energy supplied in each timing phase T.

B . Short circuit to earth at point B of the triggering circuit

In this case, an analogous situation to that described for point A above occurs and is detected across the measuring resistor RM.

C. Short circuit to V_B at point A and point B of the detonation circuit

Either of these cases can be determined by

measuring V_M and comparing its characteristic with the stored desired characteristic. In this case, firing of the capsule 30 can still be effected, and the required firing energy can be supplied to the capsule by

lengthening the duration of activation by the control units CU₁, CU₂.

The invention is not restricted to the details of the foregoing embodiment. For example, the control unit CU₂ can be replaced by an analog by-pass which can

trigger the switch S₂ and which permits access to S₂ only in a fixed mono-time.

Also, it will be appreciated that it is possible to provide any number n of arrangements comprising

switches, coupling capacitors and initiation element

(28) to the energy reserve C₁. The number of measuring channels on the' ADC 20 and the triggering leads to the switches of the control units.

Each arrangement, of course, may have more than two independently closable switches, each receiving its closur signal from an associated control unit, or some of which m be accessible only in a fixed mono-time. Increasing the number of switches decreases the possibility of accidental deployment.

Claims

1. An initiation element (28) for inflating an inflatable restraining device, comprising an

electrically actuable igniter (30), and characterised by a capacitance (C_F) connected in series with the ingiter.

2. An initiation element as claimed in claim 1, wherein the element is connected to a triggering unit which is adapted to detect the occurrence of a crash condition and send an electrical signal to actuate the igniter (30).

3. A triggering unit for supplying electrical energy to an initiation element (28) for inflating an inflatable restraining device, comprising an electrical energy source (C₁), an igniter (30) and a circuit comprising connection means for connecting the

electrical energy source to the igniter in response to detection of a crash condition, characterised in that the connecting means comprises a plurality of switches (S₁, S₂ ) in series with the initiation element (28), each switch (S₁, S₂) being closable independently of the others by means of an associated control means (CU₁, CU₂) in response to determination of the occurrence of a crash condition by the associated control means.

4. A triggering unit as claimed in claim 3, wherein each control means (CU₁, CU₂) is provided with an associated sensor (SR₁, SR₂) to enable each control means to determine the occurrence of a crash condition independently of the others.

5. A triggering unit as claimed in claim 3 or claim 4 , wherein at least one switch (S₁, S₂) is

closable periodically in response to detection of a crash condition, and during connection of the

energy source (C₁) to the igniter (30) in a single closure of the or each switch, the energy (Δ E) supplied to the igniter is less than the energy

required to fire it.

6. A triggering unit for supplying electrical energy to an initiation element (28) for inflating an inflatable restraining device, comprising an electrical energy source (C₁), an igniter (30) and a circuit for connecting the energy source (C₁) to the igniter (30) in response to detection of a crash condition,

characterised in that the circuit comprises at least one switch (S₁, S₂) which is closable periodically in response to detection of a crash condition, and in that during connection of the energy source (C₁) to the igniter (30) in a single closure of the or each switch, the energy (Δ E) supplied to the igniter (30) is less than the energy required to fire it.

7. A triggering unit as claimed in claim 6, comprising a plurality of switches ( S ₁ , S₂) in series with the initiation element (28), each switch being closable periodically, independently of the other switches, by an associated control means (CU₁, CU₂) in response to determination of the occurrence of a crash condition by the associated control means (CU₁, CU₂).

8. A triggering unit as claimed in any of claims 3 to 7, further comprising monitoring means (20) for monitoring the circuit when the energy source (C₁) is connected to the igniter (30).

9. A triggering unit as claimed in claim 8, comprising means (R_m, 20) for monitoring the

characteristics of the electrical signals supplied to the igniter (30) and means for comparing the monitored characteristics with stored, desired characteristics.

10. A triggering unit as claimed in any of claims 3 to 9, in combination with an igniter (28) as claimed in claim 1 or claim 2.