Seat Belts

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Seat Belts
Prepared by Team Roadrunner Nathan
Durham William C. Moore Benjamin Sargent
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Newtons First Law
INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
An Object in motion tends to stay in motion
unless acted upon by an out side force.
Modern Seat Belts

• Prevents occupant from being thrown from vehicle
• Applies force to rigid parts of occupants body
• Increases stopping time on body by stretching
  belt
• Places occupant in optimal crash position

Lap belt
3-Point Belt
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INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
History of Seat Belts

• 1885 First safety harness patent
• 1956 Ford offers optional
• lap belts
• 1959 Volvo makes first
• modern three
• point system
• 1963 Volvo makes three point
• system standard in US
• 1968 Two point lab belts are
• standard in US
• 1974 NHTSA requires Bohlins
• three point continuous
• loop in all new US cars

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Data from the National Highway Transportation
Safety Administration
INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
With 100 seat belt usage, about 340,000 lives
would have been saved since 1975!
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Lives saved per year as a result of seat belt
usage.
INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
As more people wear seat belts, more lives are
saved each year.
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The kinetic energy equation represents the energy
an occupant has when a vehicles stops.
INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
Including stopping distance
180 lb person with seat belt (1 ft stopping
distance) Stopping from 30 mph experiences 5419
lbs Stopping from 60 mph experiences 21,676
lbs 180 lb person without a seat belt (0.2 ft
stopping distance) Stopping from 30 mph
experiences 27,096 lbs Stopping from 60 mph
experiences 108,384 lbs
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• Retracting Device

INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
Belt webbing is retracted using a spool and a
torsional spring
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Locking Mechanisms

• There are two types of locking mechanisms
• Mechanisms triggered by vehicles movement

INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
During a car crash, the inertia forces the
weighted pendulum forward causing the pawl to
extend upward. The pawl catches a toothed
ratchet gear that is attached to the spool, thus
stopping the gear and spool from rotating
counter-clockwise.
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• Locking Mechanisms

• Mechanisms triggered by belts movement

INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
When the spool begins to spin quickly, the
weighted clutch lever (centrifugal clutch) is
driven outward contacting the cam. The contact
with the cam causes a sliding pin to move along a
grove pulling the pawl into contact with the
ratchet gear. The pawl becomes locked into the
gears teeth, causing the spool to resist all
counter-clockwise rotation.
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• Pretensioner

INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
A pretensioner pulls in on the belt to tighten
any slack in the webbing during a crash and moves
the passenger in optimal crash position. This
mechanism is used in collaboration with one of
the previous mentioned methods of locking the
spool. Pretensioners can be built around electric
motors, solenoids, or pyrotechnics. The most
popular pretensioners use pyrotechnics. The
figure below shows this type of pretensioner.
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Future Seat Belt Technology
INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
Inflatable Seat Belt
4 Point Belt Systems

• Reduces whipping
• Spreads out impact force

• Greater restraint on passengers
• torso
• Spreads out impact force

Honeywell Smart Fiber Belt

• Reduce the impact forces on a passenger

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INTRODUCTION HISTORY STATISTICS DESIGN
THEORY DESIGN FEATURES FUTURE
Any Questions?