increased by only 11% (35.9–38.7 Nm) from L1P2 to L1P3, but the
severeness increased by 182%. The results showed that greater gear
setting of the transmission and PTO caused greater severeness on
the transmission input shaft, which was different from the result of
Kim et al. (2000) of only the greater PTO gear setting resulting in
greater severeness of the transmission in rotary tillage. It may be
attributed to that the ground speed (3.77 km h1
) used by Kim
et al. (2000) was relatively fast for rotary tillage. If the ground
speed is too fast, the rotavator would likely walk on the soil,
causing a decrease in transmission load as the ground speed was
increased.
Fig. 6(b) shows the severeness of the PTO input shaft. The
results were similar in the case of the transmission input shaft. The
speed-combination of L1P1 resulted in the smallest severeness,
and the severeness increased when the combined speed increased.
It should be noted that the severeness increased significantly by
1078–1655% when the PTO rotational speed increased by 185% as
the PTO gear was shifted from P1 to P3 at the same ground speed.
The severeness increased by 139–213% when the ground speed
increased by 201% as the transmission gear was shifted from L1 to
L3 at the same PTO rotational speed. Also, the average load was not
statistically different as the ground speed increased. The results
showed that the load on the PTO input shaft was affected more
significantly by the PTO rotational speed rather than by the ground
speed.
4. Summary and conclusions
This study was conducted to analyze effects of the gear
selection on load acting on the transmission and PTO input shafts
of a 75 kW agricultural tractor during rotary tillage. First, the loads
acting on the transmission and PTO input shafts were measured
during rotary tillage. Rotary tillage was conducted at three ground
speeds and three PTO rotational speeds under upland field sites
with the same soil conditions. Second, loads on the transmission
and PTO input shafts were evaluated. The results showed that the
average torque on the transmission input shaft increased
significantly as the ground speed increased from L1 to L3 at the
same PTO rotational speed. Also, the average torque on the PTO
input shaft increased as the PTO rotational speed increased at the
same ground speed.
Finally, load severeness of the transmission and PTO input
shafts were evaluated. Severeness levels of the transmission and
PTO input shafts increased as both the ground speed and PTO
rotational speed increased. The severeness of the transmission
input shaft increased by 573–746% when the ground speed
increased by 201% as the transmission gear was shifted from L1 to
L3 at the same PTO rotational speed. At the same ground speed, the
severeness increased by 187–340% when the PTO rotational speed
increased by 185% as the PTO gear was shifted from P1 to P3. The
fatigue life of the transmission input shaft decreased when the
combined speed increased, and effects of the ground speed were
more significant. The severeness of the PTO shaft increased
significantly by 1078–1655% when the PTO rotational speed
increased by 185% as the PTO gear was shifted from P1 to P3 at the
constant ground speed. The severeness increased by 139–213%
when the ground speed increased by 201% as the transmission gear
was shifted from L1 to L3 at the same PTO rotational speed. The
fatigue life of the PTO shaft was similar in the case of the
transmission input shaft.
Farmers tend to conduct rotary tillage operation at greater
travel speeds for greater field efficiency (i.e., less time) and greater
PTO rotational speeds for finer tilth. Greater travel and PTO speeds,
however, would cause greater loads on and shorter fatigue life of
the input shafts. Furthermore, greater speeds may cause unfavorable
soil conditions after the tillage operation. For example,
improper fast travel speeds may lead to coarser soil conditions,
while too fast PTO rotational speeds may lead to finer soil
conditions, than favorable tilth for better crop growth and less
environmental concerns such as soil erosion. Farmers need to
select an optimum gear setting for their crop and soil conditions,
considering not only field efficiency but load severeness of the
major power transmission parts.