Control Method for Variable Level Airbag Inflation

This invention relates to an automotive supplemental restraint system having multi-stage inflation and particularly to a control method to triggering inflation of each stage.

To afford occupant protection in motor vehicles it is a common practice to provide air bags which are quickly inflated,when a crash is sensed by an accelerometer and associated controller. Such controllers are able to measure the severity of the crash and the velocity change by analyzing the acceleration so that the airbag inflation is optimally timed. Typically the airbag is deployed by firing a pyrotechnic device which releases or produces gas for inflation at a fixed rate, so that deployment is the same for every type of crash, except for the timing. Further improvement in the deployment can be made by controlling the rate of deployment over time. One way of accomplishing this is by multilevel inflation or variable level inflation.

It has been proposed to include two or more inflators in an airbag and to inflate the airbag in stages by triggering inflators in succession. An optimum control for each inflation is desired.

It is therefore an object of the invention to control the firing of multiple airbag inflators to optimize the effect of the airbag for each type of crash at different impact speeds.

The invention is carried out by triggering the first one of the inflators by a conventional control algorithm which evaluates the severity of the crash to determine whether to deploy the airbag and when to fire the inflator. In the course of this determination the controller detects when the acceleration reaches a threshold, then invokes the deployment algorithm which calculates a deployment time and the velocity change at the deployment time determined by integrating the acceleration. The algorithm for the second stage then evaluates severity of the crash on the basis of the deployment time and velocity at the deployment time. In the case of a very severe crash the second inflator is fired immediately. For a moderately severe crash the second inflator is fired after a time delay; the delay is a function of the first stage deployment time and/or the velocity at the first stage deployment time. For a less severe crash the second inflator is not fired at all. If the system has an additional inflator, the same logic is used to determine its firing based on the deployment time of the second inflator and the velocity at that time. In other words, the system re-determines crash severity as of the time of the inflating of the second stage, and deploys the additional inflator when justified by the re-determined crash severity.

The above and other advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein like references refer to like parts and wherein:

FIG. 1 is a schematic diagram of a supplemental restraint system with multi-stage inflation;

FIGS. 2 and 3 are graphs of deployment time and velocity vs. crash severity;

FIG. 4 is a graph of time interval between deployments vs. crash severity, according to the invention;

FIG. 5 is a graph of the time interval for subsequent deployment vs. the first stage inflation triggering time, according to the invention;

FIG. 6 is a graph of the time interval for subsequent deployment vs. the first stage inflation triggering time, according to the invention; and

FIG. 7 is a flow chart representing an algorithm for determining time interval for subsequent deployment according to the invention.

FIG. 1 shows a supplemental inflatable restraint (SIR) system comprising an accelerometer or sensor 10, a hardware low-pass filter 12, a micro-controller 14, and a SIR deployment system 16. The elements 10-14 may be generally conventional, except for the functionality of the microcontroller 14 under the direction of the control software described herein.

The deployment system 16, however, has a plurality of inflators 18 which are controlled by the micro-controller 14 to inflate the airbag in stages, or simultaneously, or perhaps only one or two are inflated, depending on the crash severity. Each inflator, when fired produces sufficient gas to partially inflate the air bag and all the inflators together can produce the amount of gas equivalent to a conventional single stage inflator. If, for example, two inflators are provided, the first one to inflate may produce 60% to 80% of the gas for complete inflation and the second inflator, if used, supplies the remainder. Thus a partially or fully inflated airbag can be deployed immediately, or full inflation is attained over a longer time period by deployment in two successive stages. Each inflator 18 is coupled to an I/O port 20 of the micro-controller.

The accelerometer 10 provides an analog electrical signal corresponding to the acceleration along the longitudinal axis of the vehicle. The acceleration signal is supplied to the filter 12 to form a filtered acceleration signal which is applied as an input to an A/D port 22 of the micro-controller for analysis according to this invention and further according to previously known SIR methods. In addition to the I/O ports 20 and the A/D port 22, the micro-controller 14 comprises conventional electronic componentry, including a microprocessor and random access and read-only memories.

Conventional single stage inflation controllers initiate a deployment algorithm when the filtered acceleration signal reaches a threshold. The algorithm processes the acceleration signal to determine whether to deploy and calculates the velocity V.sub.D of a vehicle occupant relative to the vehicle at deployment and the time T.sub.D of deployment measured from the threshold crossing. These two parameters are well known in the art and are generally available in conventional SIR systems of various manufacturers. These parameters will be used in a subsequent stage to determine crash severity and then whether to deploy another stage and when to do it.

As indicated in FIGS. 2 and 3, the parameters T.sub.D and V.sub.D are generally small values for very severe crashes. They are small since a more severe crash should result in earlier deployment, and the short period gives less time for the accumulation of velocity. Thus these parameters are suitable candidates for crash severity indicators. Thus they can be used to determine the interval T.sub.INT between the first and second inflators (and between each stage and the next one). It is reasonable to choose a short time interval for more severe crashes and a longer interval for less severe crashes as shown in FIG. 4. It has been found that for the most severe cases the time interval T.sub.INT should be zero so that the second inflation is triggered immediately. On the other hand, when the crash is not severe the second (or subsequent) inflation should not occur at all. For the intermediate case of moderate crash severity, the time interval should be varied as a function of severity.

FIG. 5 shows the example of T.sub.INT for the three regions of crash severity. A deployment time threshold T.sub.A defining a crash severity limit is empirically determined and marks the boundary of very severe and moderately severe crashes; a time T.sub.B is determined as the boundary of moderate and not severe crashes. It has been found to be desirable to deploy the second inflator immediately after the first when T.sub.D is less than time threshold T.sub.A so that T.sub.INT is set to zero. For deployment times between T.sub.A and T.sub.B, however, the time interval T.sub.INT increases with T.sub.D. A linear or proportional function is chosen for simplicity although another increasing function may be used. Thus the time interval increases from 0 at T.sub.A to an empirical limit T.sub.LIM.sbsb.--.sub.T at T.sub.B which sets the maximum allow delay between the first and second deployment times. For deployment times greater than T.sub.B, the crash is not severe and there is no deployment of the second inflator. A similar function is shown in FIG. 6 for the time interval T.sub.INT as a function of velocity V.sub.D. Boundary points V.sub.A and V.sub.B are empirically chosen to define the three severity regions and a time limit T.sub.LIM.sbsb.--.sub.V is determined.

The algorithm for determining the time interval between the first and second inflator deployments is shown in the flow chart of FIG. 7 wherein the functional description of each block in the chart is accompanied by a number in angle brackets <nn> which corresponds to the reference number of the block. The micro-controller is programmed to process the software loop periodically, say at a rate of 1600 to 2000 Hz, to repeatedly sample the acceleration signal produced by the sensor <30>. If it is determined that the acceleration exceeds a threshold <32> a deployment algorithm is entered to determine if first stage deployment is justified <34>. At the same time, the parameters T.sub.D and V.sub.D are produced if a decision is made to deploy the airbag. Thus far the methodology is exactly the same as conventional algorithms for single stage systems. Then if the first stage is commanded to be deployed, the parameters T.sub.D and V.sub.D are used to determine when, if ever, to trigger the second stage inflator. If the deployment time is greater than the value T.sub.B or if the velocity at that time is greater than V.sub.B <38>, the crash is not severe and the second stage inflation is withheld <40>. As a result, the airbag is softer than if it were fully inflated but is adequate for the less severe crash. If the step 38 conditions are not met, it is next determined if the deployment time is less than the threshold value T.sub.A <42> and if so the time interval is set to zero for immediate inflation <44> because the crash is very severe and the airbag is fully inflated, just as it is in a single stage system. If the step 42 condition is not true, it is next determined whether the deployment time is between T.sub.A and T.sub.B AND the velocity is less than V.sub.A <46>. If so, the time interval is calculated to be proportional to the difference between the value T.sub.A and the parameter T.sub.D, or T.sub.INT =T.sub.LIM.sbsb.--.sub.T *(T.sub.D -T.sub.A)/(T.sub.B -T.sub.A) <48>. If the condition of step 46 is not met, then it is determined if the deployment time is between T.sub.A and T.sub.B AND the velocity is between V.sub.A and V.sub.B <50>. If so, the time interval is selected to the smaller of the values T.sub.LIM.sbsb.--.sub.T *(T.sub.D -T.sub.A)/(T.sub.B -T.sub.A) and T.sub.LIM.sbsb.--.sub.V *(V.sub.D -V.sub.A)/(V.sub.B -V.sub.A) <52 >.

By including a conventional SIR algorithm as the initial part of the multi-stage control algorithm the ability to discriminate a crash in a timely manner with immunity to rough road and other abuse events is preserved. In addition, parameters developed within the initial crash sensing algorithm are employed in determining deployment of a subsequent stage, thereby economizing on the processing burden. It will thus be seen that the control for two or more additional stages is effected simply without additional SIR hardware and only minimal software. The effect of the algorithm is to maintain the rapid full inflation of an air bag for severe crashes but to provide a softer or more slowly inflating airbag for less severe conditions.