An Improved Cooling System for Military and Heavy Duty Vehicles

A cooling development program is described for an improved cooling system for the M551 (Armored Reconnaissance/Airborne Assault Vehicle). The M551 specification was to cool at 125F at 17 tons gross vehicle weight. Requirements for additional ammunition, armor kits and stowage increased gross operating weight to 20 tons and increased in-service cooling problems. Field operations have since demonstrated the need to provide for an improved cooling system design for the upweighted vehicle. The original liquid cooled system incorporated water-to-oil engine and transmission oil coolers in series with the engine radiator. The improved design separates engine and transmission heat rejection by incorporation of air-to-oil transmission cooler behind the radiator (cooling air flows in series first through the radiator, then through the transmission air-to-oil cooler). By this means reductions of engine coolant and engine oil temperature of 14F resulted while the transmission oil temperature was reduced by 39F. These gains were made over the best previous cooling condition in converter operation without increasing fan speed. The improved cooling system allowed for increased cooling capacity so that the 20 ton upweighted version of the vehicle could be cooled to the limit of track slip without exceeding allowable critical temperature limits.

The principle of using a large area low restriction air-to-oil cooler for transmission oil cooling can be applied to other liquid cooled military heavy duty vehicles to make major gains in vehicle cooling capacity possible.

Design considerations for this improved cooling system, laboratory testing at US Army Tank-Automotive Research and Development Command in Warren, Michigan and field testing at US Army Yuma Proving Ground in Yuma, Arizona are reported.