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 manekin.
3. The zero acceleration level of the manikin prior to impact
closely simulates real constant velocity conditions.
