Test circuit for detection of malfunctions in an electric trigge

Details Test circuit for detection of malfunctions in an electric trigge Test circuit for detection of malfunctions in an electric trigge

1993-06-02

1996-05-07

Swarthout, Brent A.

Communications: electrical

Land vehicle alarms or indicators

Internal alarm or indicator responsive to a condition of the...

340436, 280734, 280735, 307 101, 180271, 180282, 36442405, B60Q 100

Patent

active

055150276

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a test circuit for detection of malfunctions in an electric triggering device for protection of vehicle occupants, in which the triggering devices are arranged with a first connector connected to earth and a second connector connected to a control unit for supply of a triggering current to the triggering devices when detecting a triggering condition.


BACKGROUND OF THE INVENTION

Triggering devices according to the above are used i.e. in motor vehicles for activating so-called air bags, i.e inflatable air cusions which protect the driver and passanger in the event of an accident. It is important that the condition of these triggering devices is continuously monitored so that they actually function if an accident should occur. One problem is that the resistance of various common triggering devices can vary between 1.80 and 2.50 .OMEGA.. For example, a normal tolerance zone in an application with two triggering devices connected in parallel can lie between 0.9 and 1.25 .OMEGA., outside of which range an error must be indicated.
Several test circuits for continuous monitoring of triggering devices are known. Because of the problem of the large tolerance zone of the resistance of the triggering device, use has been made of circuits in which voltage division takes place across the resistance and with detection of changes in resistance. For example, U.S. Pat. No. 4,016,426 describes test circuits which include a plurality of diodes, transistors and other electrical components. The complicated construction is due partly to the fact that the current must be limited so that the triggering devices will not be activated by the test current. This implies that the arrangement is relatively expensive to manufacture.


OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide a simple, cheap and reliable test circuit.


SOLUTION

This object is achieved according to the present invention in that the test circuit comprises a voltage regulator, a current generator connected in series between the voltage regulator and the connection of the triggering devices to the control unit for generating a test current to the triggering devices, and two voltage comparators connected between the earth connection, the connection to the control unit and the voltage regulator for detecting the voltage across the triggering devices.
Preferred embodiments of the invention are detailed in the dependent claims .


BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described in more detail with reference to the attached drawing which schematically illustrates the test circuit according to the invention.


BEST MODE OF CARRYING OUT THE INVENTION

A triggering device for a so called air bag is provided with a hot-wire whose function is to ignite a powder charge. Error in the triggering device is indicated if its resistance deviates from a resistance range. Usually two triggering devices connected in parallel in a circuit are used. The triggering of the two triggering devices occurs in parallel via a common detector. In the following, a test circuit is described in an application with two parallel connected triggering devices.
In the drawing, reference numerals 10 and 11 denote the two parallel-connected triggering devices which are arranged with a first connection 12 connected to earth 13 and a second connection 14 connected via a lead 15 to a control unit for detecting a triggering condition. The control unit is connected to the positive terminal of the vehicle's battery (not shown).
A second lead 16 connects a voltage regulator 17 via the ignition lock to the previously mentioned battery's +ve terminal and provides voltage to a current generator which comprises an operational amplifier 18 and a current amplifier 19 (transistor).
The current generator receives a suitable reference potential in a potential divider formed by two resistors 20, 21 which in turn is supplied from the voltage regulator 17. The operational amplifier 18 with additi

REFERENCES:
patent: 4016426 (1977-04-01), Nishioka
patent: 4143264 (1979-03-01), Gilbert et al.
patent: 4673912 (1987-06-01), Kumasaka et al.
patent: 4893109 (1990-01-01), Vrabel et al.
patent: 4945336 (1990-07-01), Itoh et al.
patent: 4956631 (1990-09-01), Itoh
patent: 5081442 (1992-01-01), Ito et al.
patent: 5155376 (1992-10-01), Okauo
patent: 5166880 (1992-11-01), Furui
U. Tietze Ch. Schenk, Halbleiter-Schaltungstechnik, 1983 pp. 352-353.

Affiliated with

Also associated with

Rating

Test circuit for detection of malfunctions in an electric trigge does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Test circuit for detection of malfunctions in an electric trigge, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Test circuit for detection of malfunctions in an electric trigge will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1230035