Torque Sharing - Woodward 723PLUS Technical Manual

723PLUS Digital Marine Control Manual 26482
Maximum Fuel Limiting
The maximum fuel limit is an absolute actuator driver output limit and is active at
all times. This is the maximum actuator driver output the 723PLUS control will
allow under any conditions, and can be used to limit engine horsepower. It can
also be used as a troubleshooting tool to block the fuel rack during unstable
conditions. The max fuel limit set point is found in service mode, under the
header H**START/MAX LIMITS**, at prompt 03 MAXIMUM FUEL LIMIT. To
disable the maximum fuel limit function, set the limit at 100%.

Torque Sharing

The third primary function of this 723PLUS control is to share load equally
between two engines that are mechanically connected through a common
gearbox or reduction gear. Torque sharing is done electronically. The two
723PLUS controls communicate torque, and other information needed for torque
sharing, over the redundant Control LON channels. Torque sharing signals,
produced within each 723PLUS, are used to maintain equal torque on both
engines. Each 723PLUS control compares its specific TORQUE INPUT % to the
companion torque sharing signal and applies a bias (±) to the speed reference.
This bias changes engine load until it matches the torque sharing signal. The
torque sharing bias of the speed reference is zero once both engines are
clutched in and sharing load equally or when only one engine is clutched in.
Control LON Lines
The Control LON lines provide the link for communicating load and operational
status (e.g., running, clutched in, slave, etc.) between the two 723PLUS controls.
The TORQUE SIGNALS of both engines are sent and received over the Control
LON lines to do torque sharing. A torque sharing signal, proportional to the total
load on both units, is independently produced within each 723PLUS control. The
723PLUS control simultaneously biases and uses this internal torque sharing
signal.
An internal switch isolates the 723PLUS control from the torque sharing signal
until the unit is ready to begin torque sharing. This is done shortly after a
clutching operation begins. If this is the first unit being clutched, the torque
sharing switch closes immediately after the clutch closes. If this is the second
unit being clutched, the engine speeds are matched (synchronized), then the
clutch is closed. The 723PLUS control then begins to soft load the second engine
until its torque equals, within 5%, the internal torque sharing signal. At this point
the internal torque sharing switch closes and the two 723PLUS controls begin
operating in the torque sharing mode. In the torque sharing mode, torque on
each engine is regulated to make the TORQUE SIGNALS of both engines match
each other equally. Both 723PLUS controls now operate as one unit and use
only the speed reference of the master (first engine clutched in) 723PLUS
control.
32 Woodward