21
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Axial Piston Pumps, Motors, and Transmissions
Series 70 / 15 Series
Component Selection (Continued)
Because there are no system pressure relief valves in
Series 70 units and many 15 Series transmissions,
the maximum hydrostatic motor torque should occur
at the vehicle wheel slip condition. Because of weight
transfer from pushing or pulling implements, it may be
difficult to determine the true weight on the drive
wheels at wheel slip. Experience has shown that the
values listed under “Maximum Pull Ratio” in the
above table can be used to determine the maximum
tractive effort. The maximum hydrostatic motor torque
can be calculated using the following equation:
Max. Motor Torque
(lbf•in)
=
Maximum PR x GVW x LR
FDR x FD eff
Where:
PR
= Pull Ratio
GVW
= Gross Vehicle Weight in lbs.
LR
= Tire Loaded Radius in inches
FDR
= Transaxle Final Drive Ratio
FD eff
= Transaxle Final Drive Efficiency
Vehicles generally operate at the maximum tractive
effort condition less than 2% of their life, therefore it
is necessary to select a transmission which will give
adequate life under typical operating conditions. If a
duty cycle for the transmission is known, Sauer-
Sundstrand can assist in calculating a weighted aver-
age or root cubic mean motor torque and can esti-
mate the life expectancy of the transmission se-
lected.
If the vehicle duty cycle is not known, then the values
in the accompanying table listed under typical oper-
ating conditions can be used in the following equation
for the motor torque determination. If the life is not
adequate, the transaxle final drive ratio or tire size
may need to be changed, or the next larger transmis-
sion may be needed. Contact Sauer-Sundstrand for
assistance in the correct transmission selection.
Typical Operating
Motor Torque (lbf•in)
=
Typ. PR x GVW x LR
FDR x FD eff
Where:
Typ. PR = Typical Pull Ratio
GVW
= Gross Vehicle Weight in lbs.
LR
= Tire Loaded Radius in inches
FDR
= Transaxle Final Drive Ratio
FD eff
= Transaxle Final Drive Efficiency
Series 70 / 15 Series Transmission System
Operating Pressure Limits (and
Corresponding Motor Output Torques) for
5 Year Life Expectancy
Pressure in psi (Torque in lbf•in)
Typical Continuous Operating Limits
Usage
Product
Hrs./Yr.
BDU-10L
BDU-21L
15 Series
100
1300 (115) 1300 (250) 3000 (410)
200
1000 (85)
1000 (190) 2600 (350)
300
800 (70)
800 (155)
2000 (270)
400
650 (55)
650 (125)
1500 (195)
Maximum Operating Limits
Usage
Product
Hrs./Yr.
BDU-10L
BDU-21L
15 Series
100
2100 (180) 2100 (400) 4500 (610)
200
2100 (180) 2100 (400) 4500 (610)
300
1900 (170) 1900 (380) 4000 (525)
400
1800 (160) 1800 (355) 3600 (480)
NOTE: Operation at these pressure and output torque
limits (under normal conditions) will give a
five year life expectancy, assuming recom-
mended maintenance procedures are fol-
lowed. In the event that an extreme duty cycle
is anticipated, consult Sauer-Sundstrand.
Summary of Contents for 2001 950
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