Structural Analysis

With more and more trucks and SUV's on the roads, vehicle bumper height incompatibility becomes of ever more concern. [ Over Ride ] A car can easily slide under the bumper of a truck without its main structure being engaged. A car relies on deformation of its frame rails to absorb energy and, in case of single point sensing, to pass the crash pulse on to the crash sensor, mounted in the passenger compartment. Crash tests are such that one can always rely on the bumper being hit. Since the bumper beam is attached to the frame rails, one can always rely on at least one frame rail absorbing energy and transmitting the impact pulse into the passenger compartment.
[ Frame Rail ] In case of a bumper over ride, the bumper beam and frame rails are not involved in the crash. Typically the engine of the car will eventually hit the bumper of the truck or the bumper of the car will hit the rear axle of the truck. If no special precautions would be taken, this could lead to a late deployment of the airbag. Vehicles employing single point sensing therefore require a stiff upper structure such that it can propagate the impact pulse to the passenger compartment in case of a bumper over ride condition. Structural analysis, using explicit finite element analysis codes such as DYNA3D or Pam-Crash, is used to study the stiffness and energy absorbing capabilities of the vehicle structure.
[ Crushed Rail ] BORDER=0 Using computer analysis, many different crash scenarios can be studied without the need for costly prototypes being consumed in crash testing. The structure can be optimized to have enough rigidity to propagate the impact pulse to the main structure of the vehicle.

If the structural enhancements necessary to counter bumper over ride work out too heavy for a particular vehicle, then one can use additional crash sensors, located in the front of the vehicle structure. These crush zone sensors could be placed between the radiator and the head lights to assure that the crash is detected in a timely fashion.

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