Centaur 2001 950, Руководство по обслуживанию, Страница: 435 / 450

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Axial Piston Pumps, Motors, and Transmissions Series 70 / 15 Series
Definitions of Typical Lawn and Garden and Turf Maintenance Vehicles
Lawn Tractor – Vehicle with an 8 to 16 horsepower (6
to 12 kW) gasoline engine that is used primarily for
mowing with limited drawbar capability and some
active ground engaging attachments (i.e. rotary tillers,
snowblowers). Tire diameters are typically 18 to 20 in.
(457 to 508 mm) and vehicle weights are generally
500 lbs. (227 kg) or less.
Yard Tractor – Vehicle with a 12 to 18 horsepower (9
to 13.5 kW) gasoline or diesel engine that is used
primarily for mowing with some drawbar capability
and some active ground engaging attachments (i.e.
rotary tillers, snowblowers, front blade). Tire diam-
eters are typically 20 to 23 in. (508 to 584 mm) and
vehicle weights range from 650 to 850 lbs. (295 to 386
kg).
Garden Tractor – Vehicle with a 14 to 20 horsepower
(10.5 to 15 kW) gasoline or diesel engine that is used
as a mowing or utility vehicle. Capability for using
passive ground engaging implements such as mold-
board plows and front end loaders distinguish these
tractors from yard tractors. Tire diameters are typi-
cally 23 to 28 in. (584 to 711 mm) and vehicle weights
range from 1000 to 1200 lbs. (454 to 544 kg).
Front Mount Mower – Vehicle used primarily for
mowing, where the mowing attachment is located in
front of the machine. Some have accessory attach-
ments such as brooms, snowblowers, and blades.
The vehicle is usually driven through a transmission/
transaxle arrangement and the rear wheels are
steered. Vehicle weights and tire diameters vary in
relation to the size of the mower.
Rear Engine Rider – Vehicle used primarily for mow-
ing, where the mower deck is located under the
machine. The engine is located at the rear, often
under the operator's seat. The vehicle is usually
driven through a transaxle arrangement and the front
wheels are steered. Tire diameters are typically 18 in.
(457 mm) or less, and vehicle weights are generally
500 lbs. (227 kg) or less.
Dual Path Mower – Vehicle used primarily for mowing
with some accessory attachment capability. Usually
a dual path propelled vehicle in which steering is done
by controlling the speed of each drive wheel indepen-
dently. Vehicle weights and tire diameters vary in
relation to the size of the mower.
Component Selection for Lawn and Garden or Turf Maintenance Vehicles
Selecting the proper transmission for a vehicle be-
gins with determining the maximum vehicle speed
desired and the maximum tractive effort required.
The transmission selected must meet both require-
ments.
Many lawn and garden hydrostatic transmissions are
used in conjunction with readily available transaxles.
The maximum hydrostatic motor speed can be calcu-
lated by using the following equation. The input speed
to the pump should be 10% greater than the maxi-
mum motor speed.
Max. Motor Speed (rpm) =
S x FDR x 168
LR
Where:
S = Maximum Vehicle Speed in mph
FDR = Transaxle Final Drive Ratio
LR
= Tire Loaded Radius in inches
A useful parameter for determining tractive effort is
“pull ratio”. Pull ratio is a dimensionless term that is
the ratio of tractive effort to gross vehicle weight. It is
generally constant for each class of vehicle. These
values may be used when actual vehicle tractive
efforts are not known.
Typical Pull Ratios for Lawn and Garden
Vehicles
Maximum Typical
Vehicle Class Pull Ratio Pull Ratio
Lawn Tractor 0.73 0.18
Yard Tractor 0.80 0.20
Garden Tractor 1.00* 0.23
Front Mount Mower 0.80** 0.23
Rear Engine Rider 0.50 0.16
Dual Path Mower 0.85 / 2 0.25 / 2
* Assumes weight transfer to the driving wheels
from an implement.
** Based on wheel slip for a four-wheel-drive vehicle
on dry asphalt. For mower service on turf, a ratio
of 0.62 may be more appropriate.