Komatsu 930E-2, Shop Manual

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Propel Torque Control
This software function commands the appropriate mo-
tor torque to the inverters during propel. The torque
command is primarily a function of the accel pedal
position and is limited by the physical constraints of the
system.
Each wheel torque is computed independently be-
cause the wheels may be operating at different
speeds. Each torque command is adjusted to account
for the following constraints:
•
Speed Override
The propulsion system will attempt to limit truck
speed to the design envelope of the wheel motors.
As such, the torque command will be modulated as
the truck speed approaches the motor overspeed
limit so that this limit is not exceeded if possible.
Note, however, that steady state operation is kept
as close to the overspeed limit as possible without
exceeding it.
•
Motor Torque Limits
The torque command will be constrained to the
operating envelope of the inverters and the traction
motors. The maximum torque that can be com-
manded is dependent on motor speed and on DC
link voltage.
•
Gear Stress
The torque commanded will not exceed that which
will produce excess gear stress.
•
Horsepower Available
The horsepower available will be estimated from
the engine speed. Parasitic loads are taken into
account. The torque will be limited such that the
engine does not overload.
•
Jerk Limit
The torque command will be slew-rate limited to
prevent jerking motion.
•
Wheel Spin
In the event that the inverters detect a wheel spin
condition and reduce torque in the slipping wheel,
the motor torque in the other wheel may be in-
creased within the above constraints such that as
much of the total desired torque as possible is
maintained.
Retard Torque Control
The retard system converts braking torque from the
wheel motors to energy dissipated in the resistor grid.
The requested retard torque is based on the following
three sources:
•
Retard Foot Pedal or Lever
The maximum short time retard torque (at any
speed, hence the constant torque level) will be
scaled (linearly) by the retard foot pedal input
(RPINHI) to produce the foot pedal retard torque
call.
•
Overspeed
While overspeed is active, the full available retard
torque will be requested.
•
Retard Speed Control
While RSC is active, the RSC retard torque call will
be adjusted to control truck speed to the RSC set
point. Retard speed control will not request any
retard torque if RSC is not active.
The maximum torque call from the above three
sources will be selected as the retard torque call.
Retard Torque Limits are as follows:
1. The retard torque call will be limited to the maxi-
mum torque level based on speed.
2. The retard torque call will be limited to the maxi-
mum torque level available within the thermal
constraints of the motors.
3. The retard torque call will be limited as needed to
prevent overvoltage on the DC link.
4. While in retard, the minimum retard torque call will
provide enough power to support at least one grid
with 600 volts on the DC link. Retard will be
dropped if the torque call falls below this value.
5. At low speed, the available retard torque will be
ramped to zero.
Wheel Slide Control
The inverters prevent wheel slide by limiting torque to
maintain wheel speeds above preset limits. These
preset limits are a function of truck speed and the
allowable creep; additional compensation will be ap-
plied to provide for differences between wheel speeds
during turns.
E02014 3/01 Electrical Propulsion System Components E2-35