| HYGETM
Operating Principle
Each of the systems in the HYGE line of automotive
safety test equipment includes a HYGE actuator.
The HYGE unit develops its powerful, repeatable
thrust through differential gas pressure acting on the two faces
of a thrust piston in a closed cylinder. The cylinder is separated
into two chambers by an orifice plate. The area of one entire
piston face is exposed to the gas pressure in chamber A. On the
other side of the piston, only the smaller area within the seal
is exposed through the orifice opening to the gas pressure in
chamber B.
In preparation
for firing, compressed gas is introduced into chamber B until
the forces on the thrust piston are equalized. Any further increase
in the pressure in chamber B upsets this equilibrium, opens the
seal at the orifice, moves the piston away from the orifice plate,
and instantly exposes the entire piston area to the gas pressure
in chamber B. A controlled thrust on the piston results. Transmitted
by a thrust column, this limited-duration thrust acts upon a test
specimen to produce an accurately predictable acceleration or
velocity.
The thrust
and the mass of the specimen govern acceleration of the specimen.
To produce a given acceleration waveform, a specific metering
pin is attached to the thrust piston and projects through the
orifice into chamber B. The contour of the pin meters the flow
of gas through the orifice, regulating the acceleration and making
the utilized thrust precisely repeatable.
When the
unit is used as a velocity generator, the necessary control is
obtained by changing the pressure magnitudes.
The HYGE
principle, as applied to safety testing, simulates the longitudinal
deceleration conditions of an actual impact, but in reverse. Prior
to an actual crash, the test vehicle and manikin each move at
constant velocity. At impact they are stopped very rapidly. With
the HYGE system, the test vehicle assembly and the
manikin are initially at zero velocity. This situation simulates
the constant velocity conditions prior to an actual crash. The
programmed rapid acceleration of the HYGE sled drives
the automobile assembly out from under the manikin and produces
a response similar to that caused by the rapid deceleration of
a moving vehicle. The acceleration and deceleration effects are
interchangeable because the acceleration-time relationships are
essentially the same in both cases. The illustration below shows
the velocity and acceleration relationships between an actual
crash impact and a HYGE simulation.
Some significant
advantages of the application of the HYGE principle to
crash simulation testing are:
1. The
manikin can be accurately positioned prior to the test and the
position will remain unchanged until the instant of impact.
2. Prior to impact, the manikin and the seat assembly are not
subjected to forces caused by compressed seat springs or energy
stored in the manikin.
3. The zero acceleration level of the manikin prior to impact
closely simulates real constant velocity conditions.
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