Figure 8. CIV in deep snow.
of the CIV. The snow in these tests was about 36 cm
using the CIV with load cells mounted only on the
deep, which is about equal to the undeflected
front axle. He used two different indirect methods
radius of the tires. Figure 7 shows how the snow
to accomplish this. In one procedure, he drove the
piled up in front of a wheel, although it is not clear
front wheels at a steady speed and assumed that
whether this snow came from under the vehicle or
the measured force on the front load cells was
was pushed up from the area in front of the tire
equal to the trailing tire resistance (the measured
(note the "bow wave" in front of the CIV in Fig. 8).
forces for the CIV are analyzed below). A compari-
Because of the difficulty of towing the CIV in
son of these measurements are made with those of
snow this deep, it was disconnected from the tow
tests 0125h and 0125i in Figure 9, which shows all
vehicle and driven in front-wheel drive. It became
the values falling in the same range.
immobilized when the snow piled up in front of
To see if the rear coefficients were related to the
the bumper (Fig. 8), so that tire chains had to be
slip of a preceding driven wheel, the leading tire's
installed on the front wheels. This, and slightly
Differential Interface Velocity (DIV) was compared
shallower snow in the succeeding area, allowed
with the trailing tire resistance coefficients. There
some data to be collected. Tests 0125h and 0125i
did not appear to be any clear cause and effect.
yielded trailing tire resistance behind a driven tire.
The trailing tire resistance coefficients were 0.064,
Undercarriage drag
0.057, 0.064 and 0.077 for the left and right sides of
Figure 10 shows a force balance on the entire
tests 0125h and 0125i respectively. These values
vehicle (neglecting air resistance); once the vehicle
and those of tests 0125f and 0125g are much higher
is moving at a steady speed, the sum of forces
than those measured in the other tests; this is most
should be zero. If the CIV is driven at a steady
likely attributable to snow falling back into the rut
speed, the load cells on the driven axles measure
behind the front wheels in deep snow, or in the
the resistance to motion felt by the rest of the
case of tests 0125h and 0125i, attributable to the
vehicle (i.e., the net traction measured by these
disruption of the packed snow rut by a preceding
load cells must equal the sum of all the other
driven tire. (A preceding driven tire disrupts the
resistances). Since some of the CIV undercarriage
snow through the effects of wheel slip; compared
was dragging in the deep snow tests, undercar-
to the effects of a freely rolling wheel, the snow in
riage drag can be estimated. Minimum ground
the bottom of the rut is made uneven and looser.)
clearance for the CIV is 14.0 cm for the torsion bar
Blaisdell (1987) measured trailing tire resistance
brackets and 19.1 cm for the front differential, and
11
Previous Page
