Abstract:
A vehicle occupant restraint deployment control for a multi-stage restraint senses a longitudinal acceleration of a vehicle passenger compartment and generates a first stage deployment signal in response to a predetermined value of a longitudinal velocity derived from the longitudinal acceleration. The control is further responsive to a sensed lateral acceleration of the vehicle passenger compartment to generate a second stage deployment signal, provided that the first stage deployment signal has also been generated.

Description:
TECHNICAL FIELD  
         [0001]    The technical field of this invention is the control of vehicle occupant restraint deployment.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known that a vehicle occupant restraint deployment control may provide different levels of restraint deployment based on crash severity. For example, a first stage deployment may be commanded if a velocity derived from a vehicle passenger compartment located accelerometer exceeds a threshold value within a predetermined time period after the beginning of a detected possible crash event; but a second stage deployment, providing a greater level of protection in a more severe crash, is commanded if an additional criterion signifying a more severe crash is detected. Such an additional criterion may be, for example, a predetermined magnitude of the time rate of change of longitudinal acceleration (“jerk”) or predetermined magnitudes of “oscillation” and longitudinal velocity as described in copending patent application U.S. Ser. No. 09/690,141 Dual Stage Occupant Restraint Control Method for Motor Vehicle, filed Oct. 16, 2000 and assigned to the assignee of this application. Such criteria are derived from the sensed longitudinal acceleration of the vehicle passenger compartment.  
           [0003]    But vehicle crashes are not always directly frontal; many crashes are angle crashes in which the acceleration produced by the crash has a significant lateral component. In such crashes, the total energy of the crash will generally be greater than would be indicated by a purely longitudinal acceleration sensor. Although some prior art crash controls are described as using a lateral motion sensor to supplement a deploy/no deploy decision; the methods described generally involve mathematically intensive vector calculations to determine a value used in a primary deployment decision.  
         SUMMARY OF THE INVENTION  
         [0004]    A vehicle occupant restraint control senses a longitudinal acceleration of a vehicle passenger compartment and processes the longitudinal acceleration to provide a first stage deployment function signal, for example a longitudinal velocity signal. Generation of a first stage deployment signal is based on a predetermined criterion of the first stage deployment function signal, for example the longitudinal velocity exceeding a boundary curve. The control further senses a lateral acceleration of the vehicle passenger compartment and generates a second stage deployment signal based on a predetermined criterion of the sensed lateral acceleration, for example the lateral acceleration exceeding a boundary curve, and further based on generation of the first stage deployment signal. A first stage deployment is dependent on generation of the first stage deployment signal; and a second stage deployment is dependent on generation of the second stage deployment signal.  
           [0005]    Thus, a crash event which would be determined to require a first stage deployment on the basis of a monitored longitudinal dynamic parameter may be upgraded to also require a second stage deployment based on significant lateral acceleration indicating an angle crash, without need for vector calculations of the monitored longitudinal dynamic parameter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a schematic diagram of a vehicle having an occupant restraint system with a deployment control according to this invention.  
         [0007]    [0007]FIGS. 2A and 2B show a computer flow chart partially illustrating the operation of the deployment control in the system of FIG. 1.  
         [0008]    [0008]FIG. 3 shows plots of lateral acceleration and a boundary curve for comparison therewith as a function of event duration for several potential crash events.  
         [0009]    [0009]FIG. 4 shows a computer flow chart partially illustrating the operation of the deployment control in the system of FIG. 1. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]    Referring to FIG. 1, a motor vehicle  10  has a passenger area or compartment  12  containing a deployable restraint apparatus  14  and a deployment control  16 . Deployment control  16  includes a microcomputer  18 , a longitudinal accelerometer  20  and a lateral accelerometer  22 , each of the accelerometers providing an output signal to microcomputer  18 , and microcomputer  18  provides a multiple stage deployment signal to restraint apparatus  14  which may initiate, for example, first stage deployment or second stage deployment. The multiple stage capability of the deployment signal controls restraint deployment to protect occupants in crashes of different severity by varying such restraint characteristics as the number of inflatable restraint devices deployed, the speed of their deployment, the pressure generated by the restraint, or any other characteristic(s) known in the art.  
         [0011]    Microcomputer  18  is provided with a stored program for controlling deployment of restraint apparatus  14  in response to signals from accelerometers  20  and  22 . This program is described with reference to the flow chart of FIG. 2. Program DEPLOY begins at step  40  by sampling the longitudinal and lateral acceleration signals from acceleration sensors  20  and  22 , as well as any other vehicle parameters that might be required in a particular system. At step  42 , the program derives the longitudinal velocity and whatever other parameters are required for the first stage and second stage deployment tests from the sensed parameters. The longitudinal velocity may be derived, for example, by digitally integrating the sensed longitudinal acceleration to provide a value use in a first stage deployment test. Parameters for the second stage test might include derived values for longitudinal jerk and oscillation as described in the aforementioned patent application U.S. Ser. No. 09/690,141 and/or U.S. Pat. No. 5,483,449. In addition, immunity measures such as an Event Progression Measure (EPM) or a Rough Road Measure (RRM), as described in the referenced application may be derived at this step. These second stage test and immunity measure parameters are optional with respect to this invention.  
         [0012]    At step  44 , program DEPLOY now determines whether an Event flag is set. The Event flag indicates that the system has determined that a possible crash event is in progress. The prior art is acquainted with many ways of accomplishing this; one particular method is testing the sensed acceleration value against a predetermined value somewhat higher than that produced in normal braking; e.g., about 2 g&#39;s. If program DEPLOY determines at step  44  that an EVENT flag is not set, then there is no possible crash event initiated; and the program skips the rest of the steps described herein. But if the EVENT flag is set, the program proceeds to step  46 , wherein a group of tests are performed to determine if first stage deployment is required. These tests may include any tests known in the prior art for determining a first stage restraint deployment. An example combination is found in the above referenced patent application Ser. No. 09/690,141, with a primary comparison of the derived longitudinal velocity against a threshold value of a boundary threshold curve, the value varying along the boundary curve with time elapsed from the initiation of the crash event in the manner shown in the prior art. The immunity measure comparisons, if included, are also performed at this point so as to prevent undesired restraint deployment in special cases. If the tests indicate the desirability of first stage deployment, the 1st Stage Deploy flag is set at stage  48 ; if not, step  48  is skipped.  
         [0013]    The program next determines if second stage deployment is required. This begins at step  50 , wherein the sensed lateral acceleration exceeds a threshold value of a boundary curve. This process is illustrated by the chart of FIG. 3, wherein the vertical axis represents sensed lateral acceleration and the horizontal axis represents event duration, that is, the time elapsed since the initiation of a detected possible crash event. A possible second stage deployment will be indicated if the sensed lateral acceleration goes above dashed line  60 , which represents the boundary curve for lateral acceleration as a function of event duration. Curve  62  represents a longitudinal crash event, with no lateral component, and thus essentially follows the horizontal axis. Curve  64  represents a low acceleration, low angle crash, in which sensed lateral acceleration does not exceed boundary curve  60  at any time during the event. Neither of these curves signal desirability of a second stage deployment. But curve  66 , representing a high acceleration, angle crash, goes above boundary curve  60  early during the event. Thus, curve  66  would signal a possible second stage crash.  
         [0014]    If a possible second stage crash event is not indicated at step  50 , the program proceeds to step  52 , wherein other, optional second stage criteria and/or immunity measures are tested, as an alternative test to that performed at step  50 . Such second stage criteria are described in more detail in the above-referenced patent application and other prior art. If neither of steps  50  and  52  results in an indicated second stage crash event, the program returns without setting the 2nd Stage flag. But if either of the steps does indicate a second stage crash event, the program proceeds to determine, at step  54 , if the 1st Stage flag is set. If it is not, the program returns without setting the 2nd Stage flag. But if it is, the 2nd Stage Deploy flag is set at step  56  before the program returns. Thus, a second stage deployment cannot occur unless a first stage deployment is also indicated.  
         [0015]    At step  58 , the program coordinates the first and second stage deployment by running a subroutine shown in FIG. 4. At step  60 , the 1st Stage Deploy flag is checked. If it is not set, the remainder of the subroutine is skipped. But if the 1st Stage Deploy flag is set, the subroutine proceeds to step  62 , at which it is determined if the Event Duration has exceeded a Maximum value for first stage deployment. If it has, the 1st Stage Deploy flag is reset at step  64 ; and the subroutine is then exited. But if it has not, first stage deployment is initiated at step  66 .  
         [0016]    The subroutine then checks the 2nd Stage Deploy flag at step  68 . If it is not set, the subroutine is exited; but if the 2nd Stage Deploy flag is set, the subroutine proceeds to step  70 . At step  70 , the subroutine determines if first stage deployment has existed for at least a minimum duration Min. After the initiation of first stage deployment in response to the setting of the 1st Stage Deploy flag, many types of restraint apparatus require a predetermined minimum time to elapse before second stage deployment may be initiated. An example of such a system is a single inflatable bag with separate first stage and second stage inflators. With such a system, the initiation of second stage deployment must be delayed for that predetermined period of time relative to the initiation of first stage deployment. Thus, from step  70 , if the minimum time has not elapsed, the subroutine is exited. But if the minimum time has elapsed, the subroutine proceeds to step  72 .  
         [0017]    At step  72 , the subroutine determines if the Event Duration has exceeded a second stage maximum duration. There is a time limit, measured from the beginning of the potential crash event, in which second stage deployment may be usefully initiated. Once that time limit is reached, no second stage deployment will be initiated, regardless of the 2nd Stage Deploy flag. Thus, from step  72 , if the Event Duration exceeds 2nd Stage Max, the 2nd Stage Deploy flag is reset at step  74  and the subroutine exited. But if the 2nd Stage Max duration has not been exceeded, a second stage deployment is initiated at step  76  before the subroutine is exited.