MoTeC SDC3 - Manual (Page 6)

MoTeC SDC3 4 Functionality
Slip Control
The slip control strategy detects slip (i.e.: rear speed ≠ front speed) and increases diff lock to maintain slip close
to the value specified in the Desired Slip table. The Desired Slip table specifies the value above which additional
diff lock will be applied, according to the slip control setup parameters.
The calculation of lock percentage for slip control is determined by the Slip Control Range and Max Slip Control
Lock
parameters which apply to all user modes.
The following algorithm determines the %lock for slip control. The desired slip is the output from the Desired Slip
table.
IF Rear Speed > Front Speed
THEN Measured Slip = Rear Speed – Front Speed
ELSE Measured Slip = Front Speed – Rear Speed
Slip Control Factor = (Measured Slip – Desired Slip) / Slip Control Range
Constrain Slip Control Factor to the range 0 to 1
Slip Diff Lock = Slip Control Factor * Max Slip Control Lock
NOTE: Slip is specified as speed difference between front and rear wheels, not as a ratio of the speeds.
The addition of the calculated slip diff lock percentage is shown in the lock percentage strategy above.
Slip control example
Max slip control = 10% lock
Slip control range = 20 km/h
Desired slip (from Desired Slip table) = 10km/h
For a measured slip of 15km/h, slip diff lock = ((15 – 10) / 20) * 10 = 2.5%
For a measured slip of 30km/h or above, slip diff lock = 10%
For information on configuring the slip control parameters, see Setup | User Modes in the SDC Manager section.
Diff Control Methods
The SDC3 implements two methods of driving the centre differential, selectable in the configuration.
Current Control
Current output control regulates the solenoid current waveform by setting a minimum current and ripple factor for
a particular lock percentage. The parameters for this control mode are pre-configured for the factory centre diff
solenoid and should not be changed. This is the recommended mode of operation.
Duty Cycle Control
Duty cycle output control provides a PWM solenoid drive from 0 to 100% duty cycle for 0 to 100% calculated lock.
The frequency of the drive pulses changes linearly between specified frequencies for 0% 100% lock. This mode
is not recommended as the effective diff lock will change with diff temperature.
An absolute limit for solenoid current can be configured for either control method, and is pre-configured for the
factory centre diff solenoid.
For information on configuring the diff control method, see Setup | Output in the SDC Manager section.