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The mechanical properties
of polyvinyl alcohol (PVA) films prepared by evaporating water from freeze/thaw
cycled gel were investigated as a function of the number of freeze/thaw cycles.
The maximum stress of the PVA film prepared by freeze/thaw cycling was larger
than that prepared without the freeze/thaw cycle process. The largest maximum
stress was 46.2 MPa for a film prepared with 10 freeze/thaw cycles, which was twice as large as
that for a cast PVA film without freeze/thaw cycling (22.3 MPa). This is due to the
formation of small crystallites during the freeze/thaw cycle process. Furthermore,
when the film was annealed at 130°C, the maximum stress was as high as 181 MPa
which was comparable to that for
PVA films prepared using additives. The crystallinity is not the main factor
that determines the maximum stress for either the non-annealed or annealed
freeze/thaw cycled films, but the glass transition temperature is well
correlated with the maximum stress, irrespective of the annealing process. This
is due to the different molecular morphology; the non-annealed freeze/thaw cycled film
consists of many small crystallites, but the annealed film consists of larger
crystallites formed during the annealing process.
It has been
reported that steering systems with derivative terms have a heightened lateral
acceleration and yaw rate response in the normal driving range. However, in
ranges where the lateral acceleration is high, the cornering force of the front
wheels decreases and hence becomes less effective. Therefore, we applied
traction control for the inner and outer wheels based on the steering angle
velocity to improve the steering effectiveness at high lateral accelerations.
An experiment using a driving simulator showed that the vehicle’s yaw rate
response improved for a double lane change to avoid a hazard; this improves
hazard avoidance performance. Regarding improved vehicle control in the
cornering margins, traction control for the inner and outer wheels is being
developed further, and much research and development has been reported.
However, in the total skid margin, where few margin remains in the forward and
reverse drive forces on the tires, spinout is unavoidable. Therefore, we
applied tire camber angle control to improve vehicle maneuverability in the
total skid margin. An experiment using a driving simulator has confirmed that
the vehicle’s lateral acceleration at the turning limit can be improved by
controlling the camber angle. Because of this, camber angle control promises to
be more effective than traction control for the inner and outer wheels. By
applying this type of steering control, it is possible to increase maneuverability
and stability in the cornering margins.
variable steering characteristics have long been studied and compared with
those having typical fixed gear ratio steering, and the variable gear ratio
properties are reported to have improved maneuverability and stability in
high-speed lane changes and on slippery low-friction road surfaces. However, it
is not clear how gear ratios should be set for individual vehicle characteristics.
Therefore, the present study has investigated a variable steering gear system
using body slip angle feedback for the purpose of improved maneuverability and
stability in the critical cornering range and upwards, in excess of the
critical limit, and into the countersteer range. The results of a driving
simulator experiment show that the steering effect improves and maneuverability
and stability increase in the critical cornering range and upwards, in excess
of the critical limit, and into the countersteer range by applying
linear-variable control to the steering ratio from a body slip angle of 5?.
This result is seen both in double lane changes, such as in hazard avoidance,
and in J-turns with long drifting. Moreover, it shows an improvement in drift
controllability through prompt countersteering. Overall, the present system can
enhance the driver’s hazard avoidance capability.