Page 577 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CHAP TER 1 7. 1 Vehicle safety

in the sizes and physical proportions of drivers, biaxial
adjustment (vertical and longitudinal) of the positions
of both the seat and steering wheel can contribute
significantly to comfort.
For the prevention of whiplash injury of the spine in
a rear end impact, the conventional headrest is not fully
effective. According to Volvo, the spine may be affected
throughout its length, so the shape and restraint offered
by the whole of the seat back is relevant. To this end
Volvo have been concentrating on:
1. Controlled resilience of the squab cushion and
installation of a new recliner system to reduce the
severity of a rear end impact pulse on the spine.
2. Reducing to a minimum movement of all parts of the
spine relative to each other, by providing good sup- Axis of
port from the base right up the spine to the head, so pivot
that, throughout the impact, the curvature of the
spine changes as little as possible.
3. Reducing to a minimum the forward rebound of the Fig. 17.1-20 The Saab seat designed to prevent spinal damage
occupant from the seat into the seat belt. due to whiplash. At the lower end of the pivoted lever is a pad
against which, during a rear end impact, the shoulders push to
The outcome of design on these three principles is what swing the head rest at the upper end of the lever forwards about
Volvo calls the WHIPS seat. In a rear end impact with the pivot to support the head. Stops, not shown here, limit the
a conventional seat, the occupant is first accelerated motion of the lever.
forward. This causes him to sink into the resilient trim on
the squab and then rebound forward against the seat belt.
In the meantime, his head is supported by the head rest. range of rearward vision. If left in the lowered position,
With Volvo’s new system, the forces between the body of however, they are very uncomfortable so, as soon as
the occupant and the seat squab activate the WHIPS passengers enter the seats, they are obliged to elevate
system. The new recliner allows the squab to move them to the position in which they will provide adequate
backwards, and therefore reduces the forces between it protection from spinal whiplash.
and the body without increasing the distance between
the head and its restraint. Additionally, the seat squab
bends backwards to reduce further the g-force on the 17.1.22 The pedal controls
body. The overall result is a reduction also in the energy
available to induce rebound. Inappropriate pedal arrangement can have a significant
A safety seat introduced by Saab has what they term effect on driver fatigue as well as directly cause acci-
the Pro-tech self-aligning head restraint. Their aim is at dents. To enable the driver to differentiate easily be-
providing uniform support throughout the whole length tween the brake, clutch and accelerator controls, the pad
of the spine. In a rear end impact, this seat back absorbs on the accelerator pedal should be positioned directly
energy by allowing the lower part of the spine and back to beneath the ball of the driver’s right foot, when resting in
sink into it in a controlled manner, an action likened by its natural position. It should be slightly convex so that
Saab to the catching of a ball in a padded, gloved hand. the driver can easily pivot his foot about his heel to de-
The rearward movement of the occupant’s body is press the pedal, with just enough friction between the
reacted by a pressure plate in the squab. This plate is sole of his foot and the pedal to enable him to maintain
connected to the lower end of a vertical pivoted lever, the a steady throttle opening when needed. The range of
upper end of which pushes the head rest forward until angular movement must be large enough to avoid jerky
the moments about the pivot balance, to counteract the operation of the throttle and, over virtually all its range,
tendency to whiplash, Fig. 17.1-20. Saab claim that, with the feel-back should be linearly progressive and pro-
this system, the head rest can be set in a lower position portional to throttle opening. In some instances, when
than would otherwise be safe. the throttle is just cracking open, the movement of the
For the rear seats of some of their models, Saab pro- pedal relative to that of the throttle may be increased to
vide vertically adjustable head rests which can be avoid jerky take-off from rest.
lowered by the driver when it is not carrying passengers For rapidity and ease use in an emergency, the brake
in them. In this way he is assured of the best possible pedal must be directly beneath the driver’s left foot.

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