Land vehicles: bodies and tops – Bodies – Seats with body modifications
Reexamination Certificate
2001-03-15
2002-08-20
Gordon, Stephen T. (Department: 3612)
Land vehicles: bodies and tops
Bodies
Seats with body modifications
C297S216140, C297S216150, C297S216160, C297S216180, C297S216190
Reexamination Certificate
active
06435592
ABSTRACT:
TECHNICAL AREA
This invention refers to a device for counteracting injury to a person sitting in a seat in a vehicle, primarily a so called whiplash injury, which can occur due to a rapid change in velocity, such as a collision, from the rear.
BACKGROUND OF THE INVENTION
A whiplash injury is a soft tissue injury which can occur on account of violent acceleration and/or deceleration applied to the cervical spine. The classic case where these kinds of neck injuries occur is when sitting in a car which is subjected to a rear-end impact, but can also occur in other activities than car driving, such as in participating in certain sports.
According to demands from insurance companies, 16,000 claims are sent to the insurance companies every year because of rear-end impacts in Sweden alone. Of these cases, 1,500-2,000 sustain permanent injury and 100-200 have to be given a disability pension. Whiplash injury is the most common type of injury resulting in compensation from the insurance companies. When head restraints, popularly termed head rests, became standard in cars, there were considerable hopes that whiplash injuries would disappear. The disappointing result was that the risk of permanent injury only fell by less than 20%, which shows that the problem largely remains.
Several researchers agree that the following factors and situations are of decisive importance for the question of whether a collision will cause whiplash injury or not:
(a) The distance between the head and the head restraint, and the vertical location of the head restraint.
(b) The magnitude of the collision, the crash pulse.
(c) The stiffness of the car. A stiff car gives greater acceleration, and thus higher forces.
(d) The angle of the backrest
(e) The muscular strength of the individual, in combination with the length of the cervical spine.
(f) If the person is prepared, and tensions his neck muscles back against the head restraint before the collision, the risk of whiplash injury is minimal.
(g) Small children who travel in rearward-facing child seats are subjected to the same or greater forces in a front-end crash than adults who are subjected to a rear-end collision. Despite this, children seldom suffer from neck injury in a front-end collision. Children very seldom sustain whiplash injuries.
(h) Women are subjected to about a 50% greater risk than men of suffering whiplash injury in a rear-end collision. Statistics from the same type of car.
(i) It has been found that the injury frequency is lower in older cars, where the seat backrest collapses in a rear-end collision, compared with newer cars with stronger seats (as reported by the Swedish Road and Transport Research Institute).
(j) People in the back seat are only subject to half the risk of sustaining neck injuries compared with people in the front seat. This is despite the fact that head restraints are frequently not provided for the rear seats.
(k) “Bouncy” seats entail a greater risk of whiplash injury.
(l) About 25% of all whiplash injuries occur in front-end collisions.
(m) Passengers in a 4-door vehicle have a 20% higher incidence of whiplash injury compared to passengers in a car which is identical, except that it only has 2 doors. The only difference is that on the 2-door car, the B pillars are located 270 mm further back, compared with the 4-door model. This affects the position of the upper seat belt anchorage.
The last five points indicate that the risk of sustaining a whiplash injury are greatest when the head is thrown forwards as far as it will go (hyperflexion), which occurs after about 400 ms. Regardless of when the injury occurs, the risk is considerably reduced if the acceleration of the seat is minimized.
In recent years, research in this area has been intensified, which has led to new theories and experience related to the cause of whiplash injury. Several theories and initiatives have been found to be incorrect and have therefore now been rejected. This means now that there are old technical solutions which do not solve the problem.
Since the person sits completely still at the start of the crash sequence, the solution to should be based on a system or device which reduces the acceleration to less than 4 g, since it has been found that whiplash injury is avoided at accelerations below 4 g. This has been demonstrated in experiments on volunteers (please refer to “Comparison of head-neck kinematics during rear-end impact between standard Hybrid III RID neck, volunteers and pmtos”). By allowing the entire seat to move backwards on a sledge-like element in the car during the instant of collision, the acceleration can be reduced to less than 4 g. Through lower acceleration, lower forces are experienced, which lead to a strongly reduced risk of injury.
In crash tests performed and reported by the Volvo Car Corporation, acceleration and velocity values in a typical rear-end collision were found to have the values shown in the graphs of
FIGS. 1 and 2
.
FIGS. 3-8
show the crash sequence in the first 400 milliseconds, where
FIG. 3
shows the crash sequence at time 0 milliseconds (ms), where the person is in the initial position and is thus not affected by any acceleration due to collision etc.
FIG. 4
shows the crash sequence at a time of 50 ms, when the acceleration has reached its peak after only 10 ms. The speed of the car increases more or less linearly and has reached its top speed after about 50 ms on account of the collision. The body initially moves straight backwards without any mutual displacement of members. At 50 ms, the person's neck muscles begin to tense in a reflex action to counteract the rearward movement of the person's head. This is regarded as being a decisive factor when the sequence is studied. All studies involving acceleration greater than 5 g have been done on dummies, cadavers etc.
FIG. 5
shows the crash sequence at a time of about 100 ms, when the relative movement begins. The shoulders stop and the head and lower body continue to move backwards. This has been proven by researchers at the Chalmers University of Technology and others. They found that this is because the backrest is stiffer at the top, due to the cross beam in the backrest frame which unites the right and left sides of the backrest. At the same time, the mass of the body is greater in the pelvic area than in the shoulder area. There are theories that whiplash injury is caused by this effect, due to the rapid increase in pressure in the cervical spinal canal, which occurs when the head moves backwards and the volume of the cervical spinal canal decreases in a very short space of time due to the extension. This leads to an increase in pressure in the cervical spinal canal which can cause bleeding in the blood vessels around the spinal canal (myelorrhagia). Experiments have been performed on pigs at Chalmers University of Technology, in which the increase in pressure in the cervical spinal canal due to forced rapid extension was measured. Another probable source of injury would be the damage caused by the shear stress in the neck, which occurs when the head wants to move back relative to the shoulders. This effect is similar to a pack of cards lying on a table when you move the upper part of the pack sideways. The cards illustrate the disks in the cervical spine. Between 100-200 ms, the neck muscles have reached their maximum force in trying to stop the rearward movement of the head. This muscle force represents a bending moment equivalent to a force of up to 300 N at eye height.
FIG. 6
shows the crash sequence at 200 ms when the head has moved back as far as it goes, relative to the backrest and head restraint. The neck muscles are still at maximum tension. The backrest and head restraint are bent back to a maximum, and like a big spring, they will soon throw the head and torso forwards with great force.
FIG. 7
shows the crash sequence at 300 ms, when the head has about twice the speed of the car and seat. The neck muscles are still at maximum tension, which means that the acceleration of the head continues. It is probable that t
Autoliv Development AB
Gordon Stephen T.
Gutman Hilary L.
Klarquist & Sparkman, LLP
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