Abstract:
The invention relates to a method of vehicle collision severity discrimination for actuating a safety device at an occupant location in the vehicle. The method provides steps for providing a plurality of velocity and load level trigger values, including velocity and load level pairs, indicating a plurality of threshold conditions for actuating the safety device at an occupant location. Vehicle velocity and load are monitored so that at the instant of a collision a severity evaluation may be made, particularly where the potential for vehicle crush ameliorates the potential danger to the occupants. Responsive to selected vehicle conditions, a collision indication signal is generated Responsive to generation of a collision indication signal, vehicle velocity, vehicle load, or both, are compared to threshold conditions for actuation of the safety device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to systems and methods for triggering the deployment or actuation of vehicle occupant safety devices, including particularly supplemental inflatable restraint systems such as air bags. 
     2. Description of the Prior Art 
     A variety of systems for initiating action of passive occupant safety devices for vehicles is well known in the art It bas long been recognized that the deployment decision for each of several safety devices which may be installed on a vehicle, such as airbags, safety belt pretensioners and seat pull down devices, is not one that should be based on a simple determination that a collision has occurred, but should take into account the severity of the collision, the vehicle occupants&#39; positions and whether the vehicle occupants are using safety belts. For example, the unnecessary deployment of airbags can compromise driver control of a vehicle at a time when maintaining control is more important to avoiding injury than isolation from acceleration. 
     Typically, crash detection is based on a proxy device for a crash sensor, such as an accelerometer. However, for a number of reasons, raw peak acceleration measured by an accelerometer does not provide a good indication of whether a collision has occurred, or for that matter, the degree of severity of the collision. Short duration, high acceleration transients produced by road shock can generate g forces briefly comparable to g forces produced in an accident. Accordingly, acceleration signals have been subjected to filtering and threshold tests to qualify the signal as indicative of a collision involving the vehicle. Various systems have been proposed providing sophisticated mathematical treatments of acceleration, both to determine if a collision has occurred and to measure the degree of severity of the collision. U.S. Pat. No. 5,430,649 to Cashler et al., teaches a crash severity indication based on a series of treatments on basic acceleration data, which are intended to determine, among other things, whether an object which the vehicle impacted with was a pole or whether the collision occurred at a pronounced angle, i.e. the collision was a glancing one. 
     Crash severity is a preferred basis for the decision to deploy airbags in a collision, rather than a simple determination that a collision has occurred. However, the concept of crash severity is a somewhat nebulous one in practice. The primary object of an occupant. restraint system is to protect the occupants of the vehicle from injury. Thus crash severity should be defined in terms of the danger it poses to the occupants, and not the degree of damage to the vehicle. An accident which crushes a good deal of the front end of a vehicle may be less severe for the occupants than an accident which does not result in extensive vehicle crush. When a vehicle is crushed, much of the energy of the collision may be absorbed by the vehicle, rather than being transferred to the passenger compartment 
     In passenger cars, where the vehicle gross weight may well be only one or two hundred kilograms more than an empty vehicle weight of over a thousand kilograms, crush may be readily predicted by considering only vehicle deceleration (as well as its duration and the time rate of change of deceleration) caused by the impact. In commercial delivery vehicles, such as trucks, vehicle load can contribute a substantial proportion of a vehicle&#39;s gross weight and contribute to greater crush in accidents. Safety device deployment schemes devised for automobiles which discount changes in vehicle weight may not be appropriate for trucks due to the greatly varying loads carried by trucks. 
     What is desirable then is a safety device deployment control mechanism which can assess collision severity using selected vehicle conditions as inputs as part of a decision process relating to when and if a safety devise is deployed. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a method and system for the control of airbags and similar safety devices in vehicles which avoids unnecessary or untimely deployment of the devices. 
     It is another object of the present invention to provide for discrimination in determining severity of collisions in terms of energy transferred to occupant locations. 
     The present invention provides for meeting these and other objectives by providing a system and method of vehicle collision severity discrimination to control actuation of safety devices for an occupant location in the vehicle. The method provides steps for providing a plurality of velocity and load level trigger values which function as threshold conditions for the actuation of safety devices at an occupant location. Vehicle velocity and load are monitored so that at the instant of a collision an evaluation of severity may be made, particularly where the potential for vehicle crush ameliorates the potential danger to the occupants. Responsive to selected vehicle conditions, a collision indication signal is generated. Responsive to generation of a collision indication signal, vehicle velocity, vehicle load, or both, are compared to threshold conditions for actuation of the safety device. 
    
    
     DRAWINGS 
     FIG. 1 is a graphical depiction of comparative crash pulse data measured near an occupant seat for a conventional truck at differing loads and velocities at the moment of impact; 
     FIG. 2 is a simplified top plan view of a commercial class motor vehicle; 
     FIGS. 3A and 3B are graphs illustrating theoretical trigger envelopes for a safety device at an occupant location for the commercial vehicle of FIG. 2; 
     FIG. 4 is a graph illustrating a trigger envelope for safety devices in accordance with the preferred embodiment; 
     FIG. 5 is a schematic illustration of a safety device actuation system; and 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The relative motion vectors for two colliding objects, and the load or mass of one of the objects, may be used to predict crush to an object resulting from the collision. For a conventional truck, a heavy load can contribute to crush of the engine compartment forward of the occupants&#39; location, resulting in transfer of a smaller crash pulse to the passenger compartment. 
     Turning to the Figures, several aspects of the invention are shown with like numbers referring to like features. FIG. 1 is a graphical illustration of the effects of varying degrees of crush, contrasted by comparing the crash pulse transmitted to the base of a “B” pillar for a representative, conventional truck. The B pillar is located approximately the same distance from the front end of the truck as the vehicle&#39;s front seats. The graph compares acceleration at the B pillar against time for an unloaded truck traveling at 20 miles per hour and the acceleration at the B pillar of the truck, fully loaded, traveling at 30 miles per hour. Little if any crush occurs for the unloaded truck, with acceleration peaking at just greater than 50 g&#39;s between 10 and 20 ms. after the collision. For a loaded truck, peak acceleration is just under 50 g&#39;s and occurs at between 70 ms. and 80 ms., notwithstanding a truck speed 10 mph greater than for the unloaded truck. The delay in the timing of the maximum crash pulse intensity at the B pillar after an accident and the reduction in its intensity stem from crushing of the engine compartment of the truck forward of the occupant location. Vehicle crush implies that different parts of the vehicle will observe different degrees of acceleration and different maximum amounts of acceleration. Evidence suggests that the pattern observed for a conventional truck may not occur at the occupants&#39; usual location in a cab over engine truck configuration, although the present invention can still be applied to such configurations and other vehicles advantageously. 
     FIG. 2 is a simplified top plan view of a commercial vehicle  10  incorporating an actuation control system for an occupant safety device such as an airbag  25 . Vehicle  10  has three basic sections, a forward crush zone  12  in which an engine  14  is located, a passenger cab  16 , and a cargo zone or load bearing region  18 . 
     A passenger or driver may be located on a seat  20 , located within the passenger compartment  16 . Associated with seat  20  are seat weight sensor  22  or another suitable device used to determine if the occupant location is in fact occupied. Seat  20  includes a physically associated safety belt, usage of which is monitored by a sensor  24 . Actuable safety device system  25  is located in proximity to seat  20  to protect an occupant of the seat in the event of actuation of the safety device. Typically safety device system  25  includes an airbag located between a passenger location and the front end of vehicle  10  to prevent injury to the passenger in the case of a front end collision. However, safety device system  25  may also include a seat pull down device, safety belt pretensioner, or combination of elements, some or all of which may be actuated in response to indication of a collision. For example, if the occupant is using a safety belt, both a seat pull down device and an airbag may be actuated. If, however, the occupant is not wearing a safety belt, retracting the seat is not done. It is not necessary that the trigger levels in terms of vehicle weight and speed be the same for different actuable safety devices, or that they be the same for different occupant locations. Vehicle conditions may also be used to determine the timing of the actuation of safety devices due to delay of the maximum crash pulse in reaching an occupant location in addition to use in determining if deployment is to occur. 
     A safety device controller  27  provides response to a collision indication for the control of safety device system  25 . Safety device controller  27  communicates with several sensors disposed on vehicle  10  over any suitable communications link (not shown). The sensor array includes sensors both for detecting the occurrence of a collision and sensors monitoring vehicle conditions indicative of the proportion of collision energy vehicle  10  is likely to absorb through deformation in case of an accident Among the sensors monitored are an accelerometer  30  used to detect the occurrence of a collision. Alternatively a strain gauge or other device may be used in the crush zone  12  to provide indication of an accident (not shown). A velocity sensor  26  is disposed to measure vehicle speed from one of wheels  29 . A plurality of weight sensing elements  28 A- 28 D are positioned around cargo zone  18  to permit an estimation of vehicle gross weight and accordingly whether vehicle conditions will result in crushing the vehicle. 
     A data communication system (not shown) transmits data from velocity sensor  26 , weight sensors  28 A- 28 D, accelerometer  30 , occupant sensor  22 , and safety belt use sensor  24  to safety device controller  27 . Controller  27  may also monitor actuable safety device system  25  status. Controller  27  monitors the several sensors to determine which of one or more actuable devices which are part of safety device system  25  are to be actuated or the timing of its actuation. 
     FIG. 3A is a graphical illustration of a theoretical actuation envelope for an airbag mounted on a conventionally configured vehicle having a forward mounted engine. In the preferred embodiment, vehicle load and vehicle velocity are monitored. The graphs thus arc depicted as a function in one variable, with velocity on the Y-axis and weight on the X-axis. That is, velocities at which (or above) actuable restraint devices are determined as a function of the weight of the vehicle load. Two envelopes,  42  and  44 , are depicted. Envelopes  42  and  44  illustrate that for a conventional truck, higher initial vehicle speeds can be tolerated in an accident with increasing vehicle weight without need to deploy a supplemental restraint. Envelope  42  is utilized if the person at an occupant location is wearing a safety belt. Envelope  42  is illustrated as a generally increasing function against weight from V min1 , the minimum velocity for which the airbag or other safety device is activated, to V max1 , above which velocity an airbag or other safety device is always actuated. In this illustration, the decision is simply whether or not to deploy an airbag and not timing of that deployment. 
     Envelope  44 , is utilized where the person to be protected is not wearing a safety belt and the actuable safety device is of a type useful in protecting unbelted occupants, such as an airbag. Envelope  44  illustrates that actuation velocities are universally below those indicated by envelope  42 , but again the envelope is an increasing function of vehicle weight, indicating the increasing capacity of the system to absorb deceleration forces by crush of the vehicle forward of an occupant&#39;s location. The precise slope and shape of the envelopes for a particular vehicle type are sui generis. The non-zero slope portion of envelope  42  or envelope  44  may reflect constant peak energy transfer rates or accelerations experienced at a vehicle B pillar. Or, the envelopes may reflect a judgment regarding total energy transferred in a limited time among other factors. 
     Envelopes for engine forward designs typically allow a greater velocity before actuation as vehicle weight increases, up to a maximum velocity. Nor will the envelopes for unbelted passengers necessarily parallel those for belted passengers. The envelopes for different types of safety devices may differ as well, with seat pull down occuring at different speed weight combinations than airbag deployment. 
     Envelopes for some cab over engine designs may exhibit a declining allowed vehicle velocity with increases in truck gross weight. The lack of a substantial crush zone forward of the passenger compartment may produce such a result although specific curves must be developed for each vehicle type. 
     As illustrated in FIG. 3B, in a preferred embodiment of the invention, installed on a conventional, engine forward truck, deployment of a safety device is controlled by reference to a selected envelope defined by three zones of response  46 ,  47  and  48 . Here an airbag is deployed if weight is less than W 1  velocity exceeds V 1 , if velocity excels V 2  and weightr is greater than W 1 , but less than W 2 , and if velocity exceeds V 3 , but not otherwise. 
     FIG. 4 is a schematic illustration of the relationships among the components utilized for controlling safety device system  25 . An accelerometer  30  provides a raw signal directly to a processor incorporated within actuation control system  27 , which is subjected to qualification conditions to generate indication of a collision. Alternatively, or In supplement to accelerometer  30 , an auxiliary crush zone crash sensor  32  may be provided. Again the signal is provided directly to actuation control system  27  where the appropriate algorithm may be provided to qualify the raw signal. System  27  may provide for each occupant location independently. Accordingly, actuation control system  27  receives inputs from an occupant sensor  22  and a safety belt usage sensor  24  for each occupant location. 
     While more complex sensing regimes are conceivable, a velocity sensor  26  and load sensors  28  provide good predictors of truck crush potential in an accident, particularly with a fixed obstacle. Advantages are still obtained even for collisions with other trucks by making the envelopes conservative. 
     FIG. 5 illustrates one way of handling of signals from the assorted sensors. An accelerometer crash sensor signal  50  and an auxiliary crush zone crash sensor signal  52  (if present) are used to generate a collision indication signal by a collision indication qualification process  54 , the particulars of which form no part of the present invention. Numerous examples in the prior art provide sophisticated mathematical treatments of acceleration to discern road noise from an actual collision. 
     The state of an occupant occupation signal  56  and an occupant safety belt usage signal  58  are applied to a select thresholds  60  process, which, in the preferred embodiment determines the appropriate table for use. A velocity signal  62  and a vehicle load signal  64  are applied to a threshold compare process  66 , which uses the variable signal inputs into the table selected by the thresholds selection process  60  and completes the comparison into the table to determine whether to generate an actuation signal. 
     The present invention provides an actuation system for a supplemental restraint system such as airbag or seat pull down mechanism by evaluating occupant circumstances as well as vehicle load and velocity at the moment a collision occurs. A determination of collision severity using vehicle condition as an input avoids unnecessary or untimely deployment of safety systems, potentially under conditions where non deployment may enhance safety. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.