The APU Engine.
The APU engine is an 11.5-horsepower, overhead-valve, two-cylinder, four-
starter/generator and the primary hydraulic system pump (Figure 4).
ignition, fuel supply, preheat, start switch, and engine indicator lights
are mounted on a control box for APU operation (Figure 6).
APU Mounted in APU Compartment.
The Electrical Starter/Generator.
The electrical starter/generator starts the APU, recharges the main engine
batteries, and provides electrical power for the operation of M992
components and the supported howitzer. The starter/generator is mounted on
the APU engine drive chain housing with mounting studs, nuts, and
lockwashers. The starter/generator is driven by a combination engine drive
chain/sprocket (Figure 5).
The Primary Hydraulic System Pump.
The primary hydraulic system pump provides power for the hydraulic system
The pump is mounted onto the engine drive chain
housing by mounting bolts and is driven by the combination engine drive
Failure of the APU results in primary system failure,
making it necessary to operate the main engine backup hydraulic pump to
maintain system operation (Figure 5).