Eaton Compressor & Fabrication C-STOV-MC001-E1 - Manual (Page 92)

92 EATON Char-Lynn Steering Catalog C-STOV-MC001-E1 July 2006
Sizing and
Application
Ackermann Type
Steering Continued
Step Three:
Selecting Steering
Unit Displacement
Before proceeding further, a decision must be made as to the
number of steering wheel revolutions desired for the application
to steer the axle from full one side to the other. Depending on
vehicle usage, this will vary, normally 2 1/2
to 5 1/2 with 4 being a good typical value
Displ. = V
N
V = Volume full stroke
N = number of steering wheel revolutions lock
to lock
Once this calculation is
complete, select the closest standard steering unit displacement
from the catalog information.
Now the number of steering wheel revolutions should be
recalculated.
N =
V
displ.
displ. = Steering unit displacement per revolution.
Note: for different cylinder applications, the cylinder volume will
be different for right and left turns and the value N will vary
accordingly.
Step Four:
Calculating Required
Pump Flow
Pump sizing is important to assure adequate power for steering
under all operating conditions. The required pump flow can be
calculated by the following equation.
QP =
Rmax. x displ.
Q
P
(L/min): Required pump flow.
Rmax = Max. steering wheel input of steering control
unit (SCU).
displ. = Displacement of steering control unit per
revolution.
Before proceeding to evaluation required pump flow the
maximum required steering wheel speed must be determined.
Typically 120 revolutions per minute (RPM) is used for Rmax.
• It is important at engine
low idle condition that the maximum steering wheel speed
should be more
than 60 rpm.
• For engine normal idle
condition, maximum steering wheel speed should be more
than
100 rpm if possible.
• When using open center SCU connected with pump directly,
maximum pump flow should be less than
1.4 times of SCU rated
flow. Higher flow into SCU increases pressure-loss of the
steering system. If higher flow is unavoidable, install a flow
divider valve into the system or use a load sensing system.