Restraint systems are the fundamental features that help protect occupants in the event of an accident. Important restraint system components to understand include:
The primary restraint system in every vehicle is the seat belt system. Using seat belts is the most effective way you can reduce the likelihood of making contact with interior components or being ejected from the vehicle in the event of a crash.
3-Point Seat Belts
For decades, all motor vehicles have used some form of restraint system to reduce the likelihood of ejection and occupant contact with interior components. Many years ago, the only type of seat belt required was the lap belt; but in 1974, lap and shoulder belts became required by law for front outboard seat occupants. Lap and shoulder belts are referred to as 3-point belts because the restraint system is anchored to the vehicle in three places.
There is overwhelming data that support the fact that the best single protection device throughout the range of all possible collisions is the seat belt restraint system. In spite of the proven effectiveness of seat belts in reducing death and injury in automobile crashes, many Americans have been reluctant to "buckle up." As a result, all passenger cars sold in the U.S. must be supplied with "passive restraint" systems such as supplemental air bags as well.
Seat Belt Retractors
Our vehicles use two basic types of seat belt retracting devices: ELR and ALR.
ELR (Emergency Locking Retractor) seat belts allow belt motion under normal driving conditions, but lock the belt during certain decelerations, lateral movements, and acceleration (longitudinal) movements. The action permits freedom of movement for occupants during driving situations, but provides a locked seat belt in an emergency situation, such as a collision or hard braking.
ALR (Automatic Locking Retractor) seat belts include both ELR and ALR modes. When the ALR mode is activated, the seat belt remains locked at all times. The ALR function allows a child safety seat to be installed with the seat belt without using a locking clip. When the belt is pulled out to its full extension from the retractor, it will switch to the ALR mode. After it has been unbuckled from the child restraint seat and returned to its retractor, it will again function as an ELR retractor.
ELR-only seat belts are used exclusively for driver's seats. Generally, front-passenger and rear 3-point seat belts can be set to operate in either the ELR or ALR mode.
In addition to the ALR mode, permanent tether anchors located either on the rear parcel shelf or in the rear cargo area provide secure attachment points for installing a child restraint seat that requires a tether anchor.
Pretensioners and Load Limiters
The front seat belts of all our vehicles incorporate pretensioners and load limiters.
In collisions where the front air bags deploy, pretensioners tighten the front seat belts during impact to help provide better energy dissipation. The same sensor system that signals the air bags to deploy also sends a signal to a gas generator for the pretensioner. Expanding gas causes the mechanism to retract the seat belt webbing a limited amount to minimize the forward movement of the occupant's torso. The process takes only about 0.01 second and precedes actual inflation of the air bag by a few milliseconds (a few thousandths of a second).
Load limiters help minimize the peak force that an occupant will experience when restrained by the seat belt in a severe frontal collision. The load limiter helps manage the crash energy by allowing a slight extension of the seat belt when the forces of the restraint system reach a predetermined force level. The end result is a more controlled amount of force being exerted on the occupant's body.
Pre-Crash Seat Belts
Under severe braking conditions or under certain combinations of speed and steering input, the pre-crash system gently tightens the front seat belts, then releases this tension if braking stops and no impact occurs.
Unlike pretensioners, which are a one-time-use system linked to air bag deployment, the pre-crash system can apply and release belt tension as often as required during vehicle operation.
The system is designed to improve driver and front-passenger positioning in case of air bag deployment. Nissan Motor Co. Ltd. is the patent-holder for this technology and licenses it to other companies in the interest of sharing safety technology.
Front-Seat Active Head Restraints
In rear-impact collisions, the vehicle occupant's body is pushed forward by the seat while his or her unsupported head remains in essentially the same position, resulting in a head-torso misalignment, which is the main cause of whiplash neck injuries.
The Active Head Restraint helps reduce whiplash neck injuries in certain rear-end collisions by mechanically moving the head restraint upward and forward to help support the occupant's head.
Typically, the springs in the seat structure return the head restraint to its normal position after the collision (unless the collision is severe).
Analysis of test data obtained in volunteer medical experiments with a prototype seat found that the Active Head Restraint provides specific benefits to the three primary movements in the neck during rear-end collisions:
Vertical stretching of the neck was reduced by about 35%.
The Neck Injury Criterion value, an index of the severity of the head's backward movement, was reduced by about 65%.
The backward rotational angle of the head, resulting from the neck bending backward, was reduced about 35%.
According to some published reports, more than half of all child restraint seats are improperly installed or used. To make installation easier, a new type of child restraint seat and mounting system was developed, called LATCH (Lower Anchors and Tethers for Children).
The LATCH mounting system consists of anchor points (located in the lower outboard rear seating positions where the seatback and seat cushion meet) and a top tether anchor. They allow the placement of LATCH-compatible child restraint seats in the rear seats.
LATCH-compatible child restraint seats allow easy and secure attachment without the need for ALR seat belts or locking clips.
Owners should check their child restraint seat for a label saying it is compatible with the LATCH system. However, our vehicles still provide ALR seat belts and child restraint seat top tether anchors to accommodate other types of child restraint seats.
A label is attached to the seatback to help users locate the lower anchors. (Review the appropriate owner's manuals for more about the installation process for LATCH system child restraint seats.)
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