GB2198571A - Event sequence indicator for a vehicle crash bag system - Google Patents

Description

"Event seauence indicator The invention relates to airbags for vehicle, and to a device which determines whether or not the airbas was set off in an accident.

Airbags have proven effective in preventing drivers and passengers from being impaled on steering columns, smashed against dashboards and ejected through windscreens during vehicular accidents. However in several cases of cars equipped with airbags where the airbags have been deployed, the driver of the vehicle has claimed that the airbag went off inadvertently and caused him to have the accident. There have been reports of inadvertent deployments of the airbags caused by radio interference.

Present airbag systems have no device for positively determining whether the airbag was set off by the sensor in response to an accident at the time the airbag was deployed or somehow went off by itself.

That information is essential in determining the manufacturer's liability if a user of the vehicle asserts that an airbag caused the accident. The correct determination of liability is vital to the manufacturer's survival.

Some airbag systems have a diagnostic system which indicates whether an electric current was sent to the inflator after an accident was sensed, but that does not positively indicate that the gas generator was started after an accident occurred.

A device was disclosed in United States Patent No. 3,915,474 for solving this problem. That "recording mechanism for a safety device used in a motor vehicle" has not been adopted, primarily because of its large size. Such a recording mechanism, if it is to be usable in practice, must not contribute significantly to the size or weight of the airbag systems. Any attempt to miniaturize that previously proposed device, however, results in a problem that in some vigorous crashes the piston will rebound off the end of the cylinder and return to its initial position before the gases from the inflator have had time to arrest the motion of the sensing means. Thus, in a miniaturized version, the device can give a false reading.The problem arises from the fact that it takes as much s 15 milliseconds from the time at which the sensor indicates that the airbag should be deployed to the time at which there is significant gas pressure in the inflator.

The invention provides a device for indicating if an airbag inflator for a vehicle was set off in an accident, which comprises a vessel enclosed at both ends which is arranged to be inserted into an airbag inflator housing with an axis of the substantially aligned with the axis of the vehicle; an object capable of moving along the axis of said vessel in response to a deceleration of the vehicle in excess of a predetermined level; means for exerting a force on the object to prevent it from moving along the axis unless the deceleration of the vehicle exceeds a predetermined level; and means for entrapping the object during its movement along the said axis of the vessel and preventing further movement of the object once a primer of the airbag inflator is activated.

The invention also provides an indicator device for determining that a vehicle was crashing when deployment of a safety device was initiated comprising: means for sensing that a vehicle is in a crash; means for sensing initiation of a primer used to initiate the said safety device; and means for recording that the crash preceded the initiation of the primer.

The primer or squib gas, which is used in accordance with the invention to stop the motion of the sensing mass or piston, provides a usable gays pressure in 1 to 2 milliseconds after sensor firing.

A principal object of the present invention is to provide a miniature device which indicates that an automobile was in an accident at the time the airbag was deployed.

Another object of the invention is to provide a miniature device which indicates independently of the crash sensor that an automobile was in an accident at the time the airbag was deployed. This can provide correct information if the sensor itself was defective.

An additional object is to provide a means for positively ruling out the manufacturer's liability when an airbag is deployed during the course of an accident.

An additional object of the invention is to provide a method of determining whether a vehicle was in a crash when deployment of a safety device was initiated.

Yet another object of the present invention is to provide a device that is small, light in weight, and relatively inexpensive to manufacture and assemble.

One form of indicating device constructed in accordance with the invention will now be described by way of example only with reference to the accompanying drawings, in which like reference numerals indicate corresponding parts thoughout the several views, and in which: Figure 1 is a view showing airbags mounted on a steering wheel and on a dashboard of a vehicle; Figure 2 is a cutaway view of an airbag system as shown in Figure 1, with the inflator broken away and removed; Figure 3 is a cross-sectional view of an inflator as shown in Figure 2, with an event sequence indicator inside a sensor which is, in turn, inside the inflator.

Figure 4 is a perspective view of the outside of an indicator as shown in Figure 3, to a larger scale than Figure 3; Figure 5 is an axial cross-sectional view of the indicator taken along the line 5-5 in Figure 4, showing it in a rest condition; and Figure 6 is a view similar to Figure 5 showing the indicator after the inflator has been activated in response to an accident.

Referring to the drawings, one form of airbag safety restraint system 7 includes a gas generator or inflator 8 mounted inside a housing 9 for the folded airbag 12. Within the- gas generator 8 is an event sequence indicator 10.

Referring especially to Figure 5, the indicator 10 consists essentially of a tube 20 containing a ball 30 and a spring 40. The tube has a flange 50 to assist in positioning the tube inside the gas generator 8 of an airbag.

A preferred form of the event sequence indicator consists of an aluminium tube 20 one inch (25 mm) long approximately 1/8 inch (3 mm) internal diameter, closed at both ends. Inside the tube are a 1/8 inch (3 mm) diameter stainless steel ball 30 and a spring 40 which exerts a force on the ball greater than the force exerted on the ball by gravity at the earth's surface.

The clearance between the ball and the tube is at least 0.003 inches (75cm) so that the tube can be made by conventional manufacturing techniques. The tube is placed inside the inflator near to the primer or squib, which could be also inside the sensor if the sensor is in the inflator, at such a location that when the primer chamber becomes pressurized the tube is subjected to the primer gas pressure. The tube 20 is so aligned in the inflator that the axis of the tube lies substantially parallel to the fore-and-aft axis of the vehicle, with the ball 30 at the rear end of the tube.

If the inflator is in the steering column, for example, the axis of the tube 20 would be parallel to the axis of the steering column.

During an accident, the car decelerates, causing the ball 30 to move forward in the tube 20, compressing the spring 40. As long as the car is experiencing a deceleration in excess of the force exerted by the spring on the ball, the ball will move away from its original location. If the primer then is ignited, the gas pressure in the primer chamber will collapse the thin walled aluminium tube trapping the ball as shown in Figure 6. Thus, for example, if the primer went off inadvertently when there was no deceleration of the vehicle, the ball would be trapped at its starting position. If, on the other hand, the car is decelerating at more than 3 g's and therefore definitely in an accident, the ball would be trapped away from its home position.

This device which would add only a few cents (a few pence) to the cost of the airbag system could in a very simple manner solve a problem which, if it were to be solved by a device external to the inflator, would require a separate sensor and some complicated circuitry.

Naturally, many other systems could be designed using oher spring-and-mass systems such as band and roller devices, pendulums, and so on, and other environmental phenomena in the primer chamber, such as heat, could be used to trap the sensing mass. If the mass were surrounded in a suitable plastics material, for example, the heat of the primer could deform the plastics to trap the sensing mass. Also, a pressure sensor having an electrical output such as a piezoelectric device or pressure switch, or a temperature sensor, could be placed in the primer chamber and used in combination with an accelerometer to detect the simultaneous presence of gas pressure or temperature in the primer chamber and deceleration of the vehicle.

An electronic circuit employing a fuse or other recording means, for example, would record if the vehicle is decelerating when pressure or temperature first appears in the primer chamber. Although more complicated than the indicator shown in the drawings, it nevertheless still gives a more accurate indication of which event occurred first, deceleration of the vehicle or ignition of the primer.

Accidents were simulated using the NHTSA (National Highway Traffic Safety Administration) and the indicator 10 which is described above with reference to the drawings. The clearance between the ball and tube for this device was .006 inches (150um). The ball had the capability of traveling .625 inches (15mm) before rebounding off the compressed spring. The spring gave an initial bias equivalent to an acceleration of the ball of 2.3 g, which increased as the ball traveled down the tube to a maximum of 8 g if the ball reached its maximum travel of .625 inches (15 mm) from the rest position.

The simulations were run by first determining the time at which a typical passenger compartment sensor would have fired in each of the crashes. Three milliseconds were added to this firing time to give the approximate time at which significant pressure would first appear in the primer chamber. The simulation model was then run and the travel of the event sequence indicator ball was recorded at the times determined above. Table I shows the results of the 20 simulations.

The first column gives the trial number; the second column gives the crash description; the third column gives the distance traveled by the mass at the time at which the pressure collapsed the tube, and the fourth column gives the results of simulations where 15 milliseconds were added to the firing time. This device would have give a false indication in cases 4, 7, 14, 15, and 16 if the inflation pressure had been used instead of the primer pressure.

TABLE 1 15 Crash Description Distance (Inches) Milliseconds 1 39./9 mph, VTB #1 0.262 0.154 Chevrolet Citation 1980 2 29.0 mph, VTV #1 0.299 0.433 Chevrolet Impala 197.8 3 30.1 mph, VTV #1 0.288 0.368 Chevrolet Impala 1978 4 48.0 mph, VTB $t1 0.256 0.000 Chevrolet Citation 1980 5 35.0 mph, VTB #1 0.244 0.389 Chevrolet Citation 1980 6 34.9 mph, ITV #1 0.262 0.446 Volkswagen Rabbit 1979 7 34.8 mph, VTB #1 0.268 0.044 Volkswagen Rabbit 1979 8 59.1 mph, ITV #2 0.246 0.575 Ford Torino 1975 9 62.3 mph, VTV #1 0.235 0.341 Dodge Sportsman Van 1979 10 62.3 mph, VTV #;2 0.273 0.199 Chevrolet Impala 1979 11 40.7 mph, VTB #1 0.275 0.230 Plymouth Fury 1975 12 25.2 mph, VTB 3Y1 0.276 0.152 Dodge Sportsman Van 1979 13 45.1 mph, VTB MR1 0.262 0.228 Volvo 244 1975 14 25.1 mph, VTB #1 0.254 0.055 Ford Van 1979 15 62.2 mph, ITV #2 0.249 0.025 Honda Civic 1975 16 63.6 mph, VTV #1 0.295 0.015 Ford Torino 1979 17 63.3 mph, VTV 82 0.259 0.264 Chevrolet Impala 1979 TABLE 1 Cont'd 15 Crash -description Distance (Inches) Milliseconds 18 40.5 mph, VTB t1 0.257 Ford Torino 1975 19 40.8 mph, VTB #1 0.215 Honda Civic 1975 20 30.0 mph, VTB #1 0.261 Ford Van 1979 VTB = Vehicle to Barrier 1 mph = 1.61 km/h or 0.447 m/s ITV = Impactor to Vehicle 1 inch = 25.4 mm VTV = Vehicle to Vehicle Only those cases in which the airbag would have been deployed were considered.

From the results here, as well as 280 cases studied, we see in all cases this ball has travelled more than 0.15 inches (3.8 mm) at the time at which it would be frozen by the collapsing tube, and thus would indicate that a crash was in progress.

In this specification, the term "primer" has been used to include the primary inflator-initiating pyrotechnic device. As such, it would include stab primers which are used in mechanically initiated inflators such as disclosed in United States Patent No. 4,580,810 and electric squibs used in electrically initiated airbag systems.

Claims (21)

What we claim is:

1. A device for indicating if an airbag inflator for a vehicle was set off in an accident, which comprises: a vessel enclosed at both ends which is arranged to be inserted into an airbag inflator housing with an axis of the substantially aligned with the axis of the vehicle; an object capable of moving along the axis of said vessel in response to a deceleration of the vehicle in excess of a predetermined level; means for exerting a force on the object to prevent it from moving along the axis un-less the deceleration of the vehicle exceeds a predetermined level; and means for entrapping the object during its movement along the said axis of the vessel and preventing further movement of the object once a primer of the airbag inflator is activated.

2. A device as claimed in claim 1, in which the means for exerting a force is a spring.

3. A device as claimed in claim 1 or claim 2, in which the said predetermined level is 1 g.

4. A device as claimed in any one of claims 1 to 3, in which the means for entrapping the said object is the collapsing of the vessel in response to the gas pressure generated by the said primer inside the inflator housing prior to inflation of the airbag.

5. A device as claimed in claim 4, in which the said vessel is of thin gauge metal.

6. A device as claimed in claim 5, in which the said metal of the vessel is aluminium.

7. A device as claimed in claim 4, in which the said vessel is of a plastics material.

8. A device as claimed in any one of claims 1 to 3, in which the means for entrapping the said object is the collapsing of said vessel in response to the heat generated inside the inflator during inflation of said airbag.

9. A device as claimed in any one of claims 1 to 8, in which the said vessel is a tube and the said object is a ball.

10. A device as claimed in claim 9, in which the ball is of stainless steel.

11. A device as claimed in any one of claims 1 to 8, in which the said object is a pendulum.

12. A device as claimed in any one of claims 1 to 8, in which the said object is a band and a roller device.

13. A diagnostic device for use in conjunction with a gas generator, comprising: means for sensing pressure caused by a primer; means for sensing deceleration; and recording means to record that deceleration was occurring when pressure caused by actuation of the primer appeared.

14. An indicator device for determining that a vehicle was crashing when deployment of a safety device was initiated comprising: means for sensing that a vehicle is in a crash; means for sensing initiation of a primer used to initiate said safety device; and means for recording that the crash preceded the initiation of the primer.

15. An indicating device substantially as hereinbefore described with reference to, and as shown in, Figures 4 to 6 of the accompanying drawings.

16. An inflator for an airbag safety device including a device as claimed in any one of claims 1 to 15.

17. An inflator substantially as hereinbefore described with reference to, and as shown in, Figures 3 to 6 of the accompanying drawings.

18. An airbag assembly with an inflator as claimed in claim 16 or claim 17.

19. An airbag assembly substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

20. A vehicle fitted with one or more airbag assemblies as claimed in claim 18 or claim 19, with the said axis of movement of the movable object generally aligned with a fore-and-aft direction of the vehicle and the object biased towards the rear of the vehicle.

21. A method for determining that a vehicle was crashing when deployment of an airbag inflator was initiated, comprising: providing an object capable of moving along an axis which is substantially aligned with the axis of the vehicle in response to deceleration of the vehicle in excess of a predetermined level; and recording the position of the said object when gas pressure is generated by a primer inside.