03-01-2011, 06:53 PM
WHIPLASH PROTECTION SYSTEM
Submitted by:
SATYA SHANKER M.
DEPARTMENT OF MECHANICAL ENGINEERING
COLLEGE OF ENGINEERING TRIVANDRUM
August 2010
Submitted by:
SATYA SHANKER M.
DEPARTMENT OF MECHANICAL ENGINEERING
COLLEGE OF ENGINEERING TRIVANDRUM
August 2010
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ABSTRACT
If you are involved in a rear-end car accident, statistics tell us that you
have a one in four chance of sustaining a whiplash injury. Whiplash is caused
when the head is very quickly jerked backward and forward at the moment of
collision, resulting in damage to the muscles and ligaments in the neck. It is a
long-overlooked injury which causes pain and misery for thousands of people
each year. For many years, the fact that it was difficult to detect physically
whiplash injury and whiplash sufferers were dismissed as being hypochondriacs
or malingerers, and could not get any treatment. So what can be done to prevent
some of the estimated 200,000 whiplash injuries that occur in car accidents each
year?
WHIPS are an integrated safety system for avoiding neck injuries and are
one of the most effective in the market. In the event of a powerful rear end
collision the backrests and head restraints in the front seats follow the
movements of the seat occupant’s body. The occupants are pulled tightly into the
contours of the orthopedic-designed seats and headrests, limiting movement of
the neck and back, which cause neck and back injuries to occur. Whiplash
Protection System (WHIPS) is designed to help protect occupants in the event of
a rear-end collision.
It can be concluded that seats aimed at preventing whiplash injuries in
general also lower the risk in real-life crashes. Furthermore it can be concluded
that results from existing consumer crash test programs for whiplash correlate
with real life injury outcome. TABLE OF CONTENTS
ABSTRACT V
LIST OF FIGURES VII
1.0 INTRODUCTION 1
2.0 WHIPLASH INJURY 3
3.0 DESIGN CONCEPTS 4
4.0 REACTIVE HEAD RESTRAINTS-RHR 5
4.1 PENDULUM SYSTEM 6
4.2 SPRING ACTIVATED 6
4.3 PYROTECHNIC HEAD RESTRAINT 7
5.0 PRO-ACTIVE HEAD RESTRAINTS 8
6.0 INFLATABLE HEAD RESTRAINTS-IHR 10
7.0 REACTIVE SEAT- RAS 12
8.0 THE WHIPLASH TEST 14
9.0 CONCLUSION 15
10.0 REFERENCE 16
VII
LIST OF FIGURES
Fig 1 Whiplash Protection System 1
Fig 2 Whiplash Injury 3
Fig 3 Reactive Head Restrainers 5
Fig 4 Pro-Active Head Restraints 8
Fig 5 Pro-Active Head Restraints (Activated) 9
Fig 6 Inflatable Head Restraints 10
Fig 7 Airbag Inflator 10
Fig 8 Reactive Seat 12
Fig 9 Whips Operation 13
Fig 10 Whiplash Testing Apparatus 14
1
1.0 INTRODUCTION
Fig. 1 Whiplash Protection System
Whiplash preventive measures
have so far been focused on
developments of the seat. Since the
70s head restraints have been
implemented more and more frequently. To date all seating positions in most
car models are fitted with head restraints. The whiplash injury reducing
effects of head restraints have been shown to be relatively low, between 5%
and 15%. In order to increase the vehicle crashworthiness in high-speed rear
end crashes, vehicle seats have become stiffer since the late 80s. Stiffer seats
have probably increased the whiplash injury risks in low-speed rear-end
crashes. Based on this knowledge more advanced whiplash protection
devices have been introduced in the market. The better protection is
achieved through improved geometry and dynamic properties of the head
restraint or by active devices that move in a crash as the body loads the seat.
The main ways to lower the whiplash injury risk are to minimize the relative
motion between head and torso, to control energy transfer between the seat
and the body and to absorb energy in the seat back.
Nowadays several systems exist, for example RHR or AHR (Reactive
Head Restraint or Active Head Restraint) in several car models, RAS
(Reactive Seat) in Volvo and Jaguar, WIL (Whiplash Injury Lessening) in
Toyota. RHR was firstly introduced in Saab cars in 1998 (SAHR), and is
today the most common whiplash protection concept on the market. It exists
in several models in Audi, Ford, Mercedes, Nissan, Opel, Skoda, Seat and
Volks Wagon. RHR is a mechanical system that actively moves the head 2
restraint up and closer to the head and in a crash. Saab apart from the head
restraint has also designed the seat back structure to better support the torso
in a rear end crash. Whips were first introduced in Volvo cars in 1999. The
seat back is in a crash moved rearwards and yields in a controlled way to
absorb energy.
The Toyota system WIL has no active parts and is only working with
improved geometry and softer seat back. Ford has also introduced seats
without active or reactive parts in the headrest, but with an improved design
aimed at preventing whiplash injury. Studies have been presented showing
the effect of the Saab RHR and Volvo Whips indicating an injury reducing
effect of approximately 40-50%. Apart from that the information of real-life
performance of different systems is limited.
In recent years some consumer rating programs have been developed and
introduced. In 2003 Folksam and the Swedish Road Administration (SRA)
started crash testing of car seats, where each seat is exposed to three
different tests. Also the German ADAC started crash testing of car seats using
multiple tests for each seat. In 2004 the insurance initiative IIWPG
(International Insurance Whiplash Prevention Group) started consumer
crash testing in Europe and in the USA. In those tests each seat was exposed
to one test. Studies of the correlation between crash test results and real-life
performance is rare. 3
2.0 WHIPLASH INJURY
Whiplash is the most common injury in car crashes, and the
debilitating and painful symptoms associated with neck strain are a costly
burden on the insurance industry, and the general public. There are now
over 400,000 whiplash injury claims annually. Although the majority of
injuries are only minor, in a minority of cases the injury can lead to long term
pain over many months. Around 1% of injured occupants suffer permanent
impairment leading to a lifetime misery.
Fig. 2 Whiplash Injury
Whiplash is thought to occur during the rapid differential movement of
the body relative to the head, when the seat moves forward in a rear-end
crash and the head doesn’t, because the head is not supported by the head
restraint. Finally, during the impact phase, the head catches up with the
body, but in the meantime, the neck has been forced into an ‘S’ shape. This is
where many researchers believe that the whiplash injury occurs. Although
researchers still do not fully understand the mechanisms of whiplash injury,
many agree that the risk of injury can be reduced through good seat design.
The key to effective whiplash injury prevention is the car’s seat, and in
particular, the size and placement of the head restraint and its ability to lock. 4
3.0 DESIGN CONCEPTS
It is important to arrange the sitting posture of the occupant as
straight up as possible, because a slouching posture will keep the occupant’s
head distant from the head restraint. The locus of adjusting the head
restraint is designed to move almost vertically. This is because, when driving,
the backs of head, depending upon the body size of the occupants, are
located almost on the same vertical axis.
Geometry of The Head Restraint and Seat Back First, for the low-speed
rear end collisions, the head restraint, especially the metal frame, is moved
forward and upward. But it has some limitations, because if the head
restraint is too near the head it interferes with the occupant’s head and
causes discomfort while driving. Second, the upper part of the seat back
frame is moved rearward away from the upper torso with the seat surface
remaining to support the upper torso the same way as in the original seat
design, and also raised along with the head restraint. During rear end
collisions the upper torso mildly sinks into the seat back, and when the upper
torso stops and starts to rebound, at the maximum deformation of the seat
back, the head is restrained naturally by the head restraint. Therefore head
and torso move in harmony, and head stops and starts to rebound
simultaneously with the torso (less whiplash movement). The pelvic support
at lower part of the seat back frame initiates the lower torso to rebound first,
and therefore helps to prevent the neck extension motion through its relative
flexion motion. Position the head restraint, as high as the top of the
occupant’s head is not necessary. The reason is because it is not the pad but
the frame of the head restraint which sustains the occupant’s head during
rear end collisions. The head restraint height (H) of approximately 8OOmm
parallel with the torso line is sufficient. 5
4.0 REACTIVE HEAD RESTRAINTS - RHR
The RHR system was introduced in 1997 as the world's first active,
anti-whiplash head restraint and is standard equipment in all car models. It
also provides multiple adjustment points to allow the head restraint to be
ideally positioned for most front-seat occupants. Real-life crash statistics
show that necks injuries are one of the most common results of rear-end
collisions, even at relatively low speeds. The triggering factor in these
whiplash injuries is the violent movement of the head in relation to the body
during an impact from behind, often leaving victims with long-term pain in
the event of a rear-end collision.
Fig. 3 Reactive Head Restrainer
The RHR system is designed to limit the head movement of the
occupant during the impact, helping to reduce the risk of whiplash injuries.
The system is entirely mechanical and is based on the lever principle. An
upper padded support is connected to a pressure plate in the backrest of the
seat. In some rear collisions, the occupant's body will be forced by the crash
pulse into the backrest, which moves the pressure plate towards the rear.
Subsequently, the head restraint is moved up and forward to "catch" the
occupant's head before the whiplash movement can start. The precise
activation of the system is determined by the force with which the occupant's
back is forced against the backrest, the magnitude of the collision forces and
by the occupant's weight.
A benefit of the mechanical RHR system is that in most crashes it 6
needs no repairs to restore it to operational condition after it has been
activated. The head restraint automatically reverts to its initial position and
is immediately ready to operate again. As whiplash injuries usually occur in
low-speed collisions in which the vehicle may sustain only limited damage,
the active head restraint does not increase the cost of the repairs needed after
the crash. RHR for even faster activation in rear impacts at lower speeds. The
head restraint is activated as soon as the lower back is pressed into the
seatback by the occupant's inertia during a rear impact. There are three types
of reactive head restraints available in the market. They are:
4.1 Pendulum System
The whiplash protection system used on Audi and Saab vehicles is a
mechanical pendulum. When the occupant moves rearward their torso
pushes against the plate. That moves the head restraint upward and forward.
This reduces the distance between the occupants head and the head restraint
along with providing support and reducing injury to the occupants head.
Springs in the seat structure return the head restraint to the normal position.
4.2 Spring Activated
2005 Mercedes Benz M Class features an optional spring actuated
system for whiplash protection. If the sensing system detects a rear collision
within a specific impact severity, it releases a pre tensioned spring inside
head restraints. This cause the head restraints to move immediately forward
by about 40 mm and upward by 30mm.this movement is designed to support
the head of the front seat occupants at an early stage lowering the possibility
of whiplash injury. After activation the head restraints can be unlocked and
returned to the original position using a tool supplied within the vehicle.
7
4.3 Pyrotechnic head restraint
The pyrotechnic head restraint on the newer BMW 7 series is unique.
In this system a compressed gas cartridge at the base of the head rest frame
activates during a rear collision, moving the headrest upward rather
abruptly. The gas cartridge can be replaced and the system reset if there is no
further damage.
Active head rests on a mechanical basis are more complicated in design
and function. The mechanism has to be highly sophisticated in order to avoid
larger head rests. This means that a lot of additional parts are required
compared to the inflatable head rest. For the described mechanical solutions
the optimization of the operating parts is quite difficult. Also a too aggressive
mechanical system results in additional neck loads, especially in situations
where the head is close to the head rest, but serious loads to the occupant
were never reached in various number of tests in different head to head rest
positions. 8
5.0 PRO-ACTIVE HEAD RESTRAINTS
Although many seats are now rated as ‘Good’ the manufacturers are
using a wide variety of designs, and these work in different ways. Many
drivers are often ‘out of position’ in an accident – for example, they are
leaning forward to see around a corner at a junction. The Pro-Active Head
Restraint technologies can offer additional protection in complex, out of
position situations, such as roundabouts or junctions. Pro-Active Head
Restraints (PAHR) are a recent technology used by manufacturers to help
prevent whiplash injuries. Both Mercedes and BMW fit PAHR systems.
These systems are designed to reduce the risk of neck injury in a rear crash
by preventing the differential movement of the head and neck.
Fig. 4 Pro-Active Head Restraints
The Pro-Active Head Restraints are linked to an electronic control unit.
When the crash sensors on the car detect a rear impact of the defined
severity, the control unit deploys the head restraint by activating preloaded
springs inside it. The front of the head restraint moves up and forward to
meet and support the head early in the crash phase, and thus helps to reduce 9
the risk of injury. The NECK-PRO system from Mercedes is fully reversible
and can then be re-set by the car owner – it can be pushed back into position
by hand. Thus, NECK-PRO can be triggered even at a very low impact
severity and offers then the full protection potential - without any repair
costs for the owner.
Fig. 5 Pro-Active Head Restraints
The advantage of the PAHR systems is that they are activated based on
input from the crash sensor – they do not rely upon the weight of the
occupant’s body moving into the seat for activation like a Reactive Head
Restraint (RHR). PAHR systems offer their protection potential regardless of
the occupant’s size and weight. The particular advantage is that if the
occupant is out of position, for example leaning forward to see around a
corner, the PAHR will still activate and offer some protection to the
occupant. This must be a benefit of these systems since the PAHR systems
deploy regardless of the occupant’s posture. 10
6.0 INFLATABLE HEAD RESTRAINTS - IHR
After analyzing the results of many math models a prototype of an
inflatable head rest was designed. An airbag is integrated in a way that the
whole head rest is enlarged. The bag is covered by foam blocks so that the
usual occupant comfort is guaranteed whilst keeping inflation noise to a non-
injurious level.
Fig. 6 Inflatable Head Restraints
The bag itself is made of a thin, nylon fabric, which is folded into the
Head Restraint. The sensor is the device that tells the bag to inflate. Inflation
happens when there is a collision force equal to running into a brick wall at
10 to 15 miles per hour (16 to 24 km per hour). A mechanical switch is
flipped when there is a mass shift that closes an electrical contact, telling the
sensors that a crash has occurred. The sensors receive information from an
accelerometer built into a microchip. The airbag's inflation system reacts
sodium nitride (NaN3) with potassium
nitrate (KNO3) to produce nitrogen gas. Hot
blasts of the nitrogen inflate the airbag. The
airbag system ignites a solid propellant,
which burns extremely rapidly to create a
large volume of gas to inflate the bag.
Fig. 7 Airbag Inflator 11
The bag then literally bursts from its storage site at up to 200 mph
(322 kph) -- faster than the blink of an eye ! A second later, the gas quickly
dissipates through tiny holes in the bag, thus deflating the bag. Even though
the whole process happens in only one-twenty-fifth of a second, the
additional time is enough to help prevent serious injury.
The inflatable head rest has proven to be a promising Alternative for
Reactive head restraint systems. Effectiveness in regard to occupant loads
and kinematics is excellent and also the deployment noise has been reduced
to a non dangerous level. In sled tests it has proven to work safe and
efficient. No negative effects to the occupant could be observed. Also there
are no restrictions for comfort, styling and safety due to the fact that the
airbag and the inflator are below the styling cover and the foam bolster of the
head rest.
12
7.0 REACTIVE SEAT- RAS
Volvo introduces a reactive seat called whips in the 2000 model. This
system is built into the hinges of the seatback on the two front seats. With
this system, head positioned with occupant’s rearward movement. In several
rear collisions a metal page link in the seatback hinge deform to allow more
seatback movement than normal. This absorbs some of collision energy
caused from rear impact. There are actually two movement of seat. First, the
seat moves up to protect the occupant’s head and neck then it moves back.
Fig. 8
Reactive
Seat
This protective system cushions the movement through energy-
absorbing deformation elements between the backrest and seat cushion. If a
rear-end collision occurs, the backrest follows the occupant’s rearward
movement in order to reduce the forces on the neck and spine. The RAS
provides improved spinal support by virtue of its modified backrest
characteristics and close proximity of the head restraint's position to the
occupant's head. RAS utilizes a specially designed hinge mount that attaches
the back rest to the seat bottom, which has a pre-determined rate of
rearward movement in the event of certain types of rear impacts. The 13
seatback also has a series of springs that allows the cushion to move slightly
rearward upon impact, thereby helping to cradle the body within the seat.
This, combined with high-mounted head restraints, help to limit the
"whipping" motion of the head that often occurs during a rear-end impact.
A new survey from Volvo's traffic accident research team shows that
RAS reduces short-term injuries by 33 percent and long-term injuries by 54
percent. However, Volvo is not alone in drawing this conclusion; several
independent surveys reveal major reductions in whiplash injuries.
Fig. 9 Whips Operation
14
8.0 THE WHIPLASH TEST
Fig. 10 Whiplash
Testing Apparatus
The whiplash test used by international insurance research partners was
developed and is now used throughout the world. The test recreates a typical
10 M.P.H. crash on a special test machine the sort of shunt where whiplash
injuries commonly occur and features the unique BioRID whiplash dummy,
especially created to emulate the movement of a human during a rear crash.
The test assesses the forces endured by the car’s occupants during the crash
and measures the time until the head and neck are supported. The best seats
have large head restraints that can support the occupant’s head and neck
very early and can mitigate the force of the crash helping to prevent injury.
Many of the best performing seats have anti-whiplash devices that can
absorb the forces of the crash or move the head restraint automatically
during the crash to support the head early to help prevent injury. The test
measures the size of the head restraint and how close it would be to a typical
driver. It also rates the dynamic performance of the seat during the crash test
and combines these two assessments into one final, overall rating.
15
9.0 CONCLUSION
The seat, which has new design concept for reduction in whiplash injuries,
allows less motion between head and torso in the modified dummy sled tests,
and also allows less motion in volunteer sled tests. Moreover there is less
movement between each cervical vertebra. Cars fitted with advanced
whiplash protection systems had 50% lower risk of whiplash injuries leading
to long-term symptoms compared with standard seats launched after 1997.
The whiplash prevention systems, RHR, IHR or RAS, had lower risk of
whiplash injuries leading to long-term symptoms compared with standard
seats launched after 1997. A correlation was found between consumer crash
test programs and real life whiplash injury outcome. Cars with seats rated as
good in the consumer crash tests had lower risk of whiplash injuries leading
to long-term symptoms compared with seats rated poor.
With environmental and cost pressures becoming ever greater, very small or
City cars are becoming increasingly popular. City cars are designed for the
urban environment and spend the majority of their time in traffic and this is
where most whiplash injuries occur, due to low speed shunts. But no City
cars have a seat and head restraint rated as ‘GOOD’ for protection against
whiplash injuries, even though these are some of the latest designs. These
cars need the best protection because they are smaller and lighter and more
susceptible to high forces in a rear end crash. These City cars are not
equipped to protect their occupants’ necks when they have to absorb the
crash energy from larger, heavier vehicles. The only two City cars to achieve
an ‘ACCEPTABLE’ rating were the Renault Twingo and the Smart Fortwo.
The majority of the other nine City cars were rated as ‘MARGINAL’, with the
current Ford Ka and Fiat Panda rated as ‘POOR’. 16
10.0 REFERENCE
→ Paul C. Ivancica, Daohang Shab, 2009; Comparison of the whiplash injury criteria;
Journal of Accident Analysis and Prevention 42 (2010) 56–63.
→ Jakobsson, L., Isaksson-Hellman, I., Lindman, M., 2008. WHIPS (Volvo cars’
Whiplash Protection System)—the development and real-world performance.
Traffic Injury Prevention 9, 600–605.
→ RCAR-IIWPG. RCAR-IIWPG Seat/Head Restraint Evaluation Protocol.
http://rcar, 2008.
→ Siegmund, G.P., Winkelstein, B.A., Ivancic, P.C., Svensson, M.Y., Vasavada, A.,
2009. The anatomy and biomechanics of acute and chronic whiplash injury. Traffic
Injury Prevention 10, 101–112.
→ Relationship of Dynamic Seat/Head Restraint Ratings to Neck Injury Rates
Insurance Institute for Highway Safety Vehicle Research Center, Ruckersville,
Virginia, iihs.org
→ Head restraint related info http://www-nrd.nhtsa.dot.gov/pdf/nrd-
51/MiscBio/headpos.pdf
→ Thatcham Research News Volume two, issue one January, 2007