Vittorio Castelli

A COMPLETE FRONTAL CRASH SENSOR SYSTEM - 1

This is the first paper in a new series. The main goal is to determine a coherent theory of sensing frontal crashes and the resulting required properties of future airbag sensor systems. In this paper a general theory of crash sensing is developed by combining conclusions from previous papers with new analysis. The key features of future systems should be as follows: (1) crush zone sensors which sense relevant impacts to alt portions of the vehicle front; (2) an occupant position sensor as an input to the sensing system; and (3) a mechanical safing/arming sensor having a long dwell. It is further concluded that cars should be designed so that only impacts involving the front of the vehicle need be sensed for the deployment of frontal protection airbags. A sensor system is presented which has the required features. For the covering abstract of the conference see IRRD 886366.

Vehicle Occupant Position Sensing

This paper, originally published in 1994, discusses some of the problems associated with crash sensors, including the difficulties in sensing occupants and objects located in the vehicle. Current sensor systems make no allowance for occupants that are wearing seatbelts, for rear facing child seats located on the front passenger seat or for unoccupied seats. In some crashes, sensors trigger late and the occupant has moved to a position near to the airbag deployment cover. Although the required sensor triggering time is now determined by assuming that the occupant is an averaged-size male sitting in the mid-seating position, 70% of vehicle occupants are smaller and, on average, sit closer to the airbag. An occupant presence and position sensor could reduce the risks posed by these situations. Several technologies exist that will permit a measurement to be made of the position and velocity of the occupant. Once in place, these sensors that map vehicle occupants could offer other safety and comfort benefits, such as monitoring driver behavior or adjusting the heating and air conditioning.

Characterization of the Cross-Axis Acceleration Crash Sensor Environment and Test Method

Crash sensors for use in deploying air bags operate in an environment of severe vibrations, not only along the longitudinal axis of the sensor, but also in the transverse vertical and lateral axes. These vibrations can have a detrimental effect on some crash sensor designs. Various methods using Fourier analysis have failed to provide a characterization of cross-axis vibrations. A technique using shock spectrum analysis has been developed which can be used to characterize these vibrations. This work has caused the development of a specification for laboratory testing of the sensitivity of a sensor to cross-axis vibrations. This paper presents the underlying theoretical basis for the shock spectrum technique, the results of applying the technique to a library of crash data, and a recommended specification for laboratory sensor testing for sensors mounted in the crush zone and non-crush zone. For the covering abstract of the conference see IRRD 886366.

SENSING SIDE IMPACTS

Now that airbags are the accepted solution for protecting occupants in frontal impacts, and now that safety sells cars, it is natural to look closely at the second largest killer of automobile occupants, side impacts. This paper develops the theory of sensing side impacts based on the assumption that airbags will soon be used for side impact protection. The trade-offs between the various sensor technologies are discussed including electronic and mechanical sensors. For mechanical sensors, fluid damped, undamped and crush sensing switches are compared. Finally, the requirements for a successful predictive sensor are presented. (A) For the covering abstract of the conference see IRRD 894848.

PERFORMANCE OF A CRUSH SENSOR FOR USE WITH AUTOMOTIVE AIR BAG SYSTEMS

In earlier SAE papers the authors demonstrated that the ideal crash sensor for use in the crush zone has a constant velocity change response, and various sensors are now in use which perform as acceleration integrators. Further study of sensor performance, however, has shown that crush zone sensors function by being struck by crushed material which is forced rearward during the crash. This observation has led to the design of an inexpensive sensor which measures crush instead of velocity. The crush of the vehicle is used as an accurate indicator of the severity of the crash. This paper presents the theoretical basis for a sensor which initiates air bag deployment when the crush of the vehicle exceeds a pre-selected amount. In a companion SAE paper, the authors have demonstrated that single point sensing in the passenger compartment may result in late air bag deployment on soft crashes, and, therefore, sensing in the crush zone is required. Crush sensors, such as described in this paper, have significant performance advantages over current generation sensors and can be used either alone or in conjunction with electronic passenger compartment sensors.