TM 9-2320-363-20-1
CENTRAL TIRE INFLATION SYSTEM (CTIS) (M917A1 AND M917A1 W/MCS)
CTIS is used to regulate tire pressure at all wheels. This allows operation of the dump truck on all road surfaces
across a wide variety of terrain, including off road, and when vehicle is stuck due to extreme conditions.
CTIS uses air from the dump truck's air system. Air is routed to the wheels via a dedicated pneumatic system
plumbed from the vehicle's wet tank. An Operator Control Panel (OCP) and Electronic Control Unit module is mounted to
the shift tower inside the cab.
Four air pressures have been programmed into CTIS:
Highway
90 psi (at 60 mph overspeed takes effect)
Cross-country
55 psi (at 40 mph overspeed takes effect)
Sand
40 psi (at 25 mph overspeed takes effect)
Emergency
30 psi (at 10 mph overspeed takes effect)
When the engine is started, tire pressures will be pressures LAST ACHIEVED when vehicle was operated.
Major components of the system are:
OCP/Electronic Control Unit
The OCP allows for operator selection of tire pressures based on road
Modular unit mounted on the
conditions and displays service codes and system status. The ECU is
Shift Tower
The ECU is the control center for the entire CTIS.
Wheel Valves
Located at each wheel end (at outer wheel of dual wheels). Provides for
inflation of tires from the vehicle's air supply via the Pneumatic Control
Unit, and deflation of tires upon system demand.
Pneumatic Control Unit
A solenoid controlled manifold that receives commands from the ECU
and controls the air system. Also contains the pressure transducer
which transmits pressure readings to the ECU. The unit delivers the
proper control signal to the
appropriate channel.
Pressure Switch
Acts as an electronic brake priority switch. It prevents CTIS from
consuming air from the wet tank until the air brake system is fully
charged. Therefore, CTIS safeguards safe operating pressures in the
primary and secondary tanks.
Speed Sensor
Provides the ECU with vehicle speed information.
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