During rear end collisions, the part of body below neck(torso), moves forward and part above the neck(head), moves in opposite direction due to inertia effect resulting in whiplash injury. The whiplash causes head injury due to fracture of ligaments in the neck portion of body. About 59% of whiplash patients undergo disability and leads to long-lasting symptoms. The system used for whiplash protection reduces head and head rest contact distance (back set) to prevent complete extension in neck region.
Existing whiplash protection system employed to prevent neck injuries has a downside that use of pyrotechnical actuator leads to complex mechanism and needs to be replaced each time after the collision event leading to high maintenance cost.
These drawbacks are eliminated by the smart active head restraint system which adapts itself to minimize back set distance during rear collision, consisting of shape memory alloy (SMA) spring actuation system integrated with mechanical linkage mechanism for the forward motion of headrest during crash event by 50mm within 60ms.
SMA actuation system consists of nitinol spring actuator along with bias steel spring in antagonistic arrangement, this system functions to lock the front and rear part of headrest. Once the SMA actuation system is triggered by electrical signal, it unlocks both the parts of headrest during crash event, prestressed spring inside headrest moves mechanical linkages forward. The forward movement of the mechanical linkage leads to forward motion of front part of head rest, resulting in reduced back set distance (<5mm) in 60ms, thus mitigating whiplash injury. The system is coupled with airbag crash module to sense crash and perform the triggering action by supplying electric current to SMA actuator.
The unique design of SMA actuation system based on pull-only mechanism (unlocks only when electric current is supplied to nitinol spring), helps to prevent the actuation of system even when unknown external force is applied on headrest.
The benefits of pro-active smart head restraint design include: - compact system contained within head restraint, rapid actuation response of nitinol actuator in 30ms, Irreplaceable head restraint system which can be manually set again after crash unlike pyrotechnic actuators resulting in reduced overall operating cost by 40%, Lightweight actuation system of 120 gm leading to weight reduction of 65% compared to existing systems, Reliable system with use of high strength nylon polymers to withstand the impact force during collision, Easy re-installation of the system without the use of any tools.
The shape memory spring actuator can be easily manufactured using shape setting process in vacuum furnace at a temperature of 550°C for 25 minutes, while its polycarbonate housing with simple design can be injection molded. The mechanical linkages along with its front and rear supports made of nylon can also be injection molded due to its simple construction reducing overall development cost.
The proposed system is focused towards the safety of occupants leading to intelligent vehicle safety system which hikes its potential of implementation in commercial vehicles due to overall less development and operating cost with lightweight system.