Abstract
Horizontal crash at road and rail vehicles generates human and material injuries, many of them with important negative effects.
Damper in bumper a known solution for vehicles protection at crash is realized with different damping devices, from passive elements to actuators. Usually the devices are tuned for 5 km/h crash speed.
After collision the passive solutions destroy and must be removed with other new devices. The solutions using standard shock absorbers and actuators are improper the first dissipating insufficient energy and actuators being more expensive and having a long reaction time so the damping coefficient changing is realized in too low steps.
VZN damper concept granted with European Patent EP 1 190 184 and Romanian Patent RO 1 18546, characterized by progressive damping coefficients with the stroke is a great opportunity to realize simple and cheap protection at crash, due to its capacity to realize constant damping force without mechanisms and electronics. It is necessary only to tune accordingly VZN damping characteristic to this desiderate.
VZN concept consist of a piston rod attached to a piston without valves moving inside inner cylinder close at both ends and filled at rebound and compression by specific filling valves placed in upper /bottom lids or on the ends of the inner cylinder. The damping effect is realized by valves or in cheap solution by metering orifices (holes/slots) placed sideways inner cylinder in convenient position. Due to this structure VZN tuning for constant damping force at different piston speed can be realize both with identical metering holes/slots placed at optimal distances, or placing metering holes/slots of different areas at equal distances. The numbers of metering holes/slots are enough such the steps speed evolution be practical continuous and thus the damping force be practical constant. The VZN behaviour is increased by new components e.g. levelling pistons, double guiding elements and balancing solutions.
Paper presents the theory used to dimension VZN damper placing metering orifices at equal distances, a practical device with levelling piston and simulation comparative to standard one.
The standard damper dissipates 30÷40% lower energy comparative to VZN one. This means in the same situation in which VZN damper reduces constant speed from 30, respectively 20 [km/h] to zero, the standard dampers reduces speed up to 14, respectively 11[km/h], then collapsing the vehicle.
Keywords: progressive damping, VZN, crash, passenger protection, body protection