TM-9-2815-220-34 Direct Support Manual for AVDS-1790-2C and AVDS-1790-2D Engines Download

, -�- TM 9-2815-220-34 1-17. Manifold Air Induction and Heater System a. Tbosupercharger Assemblies. Exhaust gas driven turbosupercharger assemblies (figs. 1-1 and 1-2), one for each bank of cylinders, are mounted on each side of the engine, at the rear. The tur- bosuperchargers increase the pressure of the in- take air thereby delivering a higher density air to the cylinders as compared with a nonsupercharged engine. This higher density air, with a proper fuel flow, increases engine power. b. Intctke Manifold Heater (g. 1-12). (1) The intake manifold (figs. 1-1 and 1-2), which distributes induction air to each bank of cylinders, is equipped  th an electlically operated flame type intake manifold heater. The heater is provided as an aid for cold weather starting and cold weather operations. Operation of the heater switch (in the vehicle operator's compartment) energizes the manifold heater fuel solenoid valve ' the heater ignition unit, and spark plug for each heater simultaneously. Fuel is hand pumped through the manifold heater fuel filter and fuel solenoid valve and sprayed into the intake man- ifold. The fuel is ignited by the spark plug and burns in the intake manifold as the engine is cranking, and the flame heats the incoming air. This flame-heated air and the products of combus- tion are fed directly into the cylinders \vith little heat loss. This results in an immediate engine re- spose, and assures complete combustion at low engine rpm and at no-load operating conditions with low ambient temperature. (2) The manifold heater fuel inlet solenoid valve prevents fuel pumped by the fuel pump as- sembly from entering the air intake manifold hea- ter unless the heater system is energized. A man- ifold heater fuel return check valve and solenoid valve are located at the rear of the engine. The solenoid valve is also energized (opened) when the ignition unit and heate1· spark plugs are energized to permit excess fuel to be retued to the fuel I tanks. The main fuel backOow valve prevents back now of the fuel when the purge pump in the driver's compartment is actuated. 1-18. Exhaust System and Turbosuper- charger a. The exhaust system consists of four manifolds, one for each group of three adjacent cylinders. The two exhaust manifolds on each cylinder bank are connected to the turbosupercharger on their re- spective side of the engine. b. Exhaust gases from each side of the engine enter a turbosupercharger and are forced around a turbine housing, radially inward, and through a 1-18 Change 3 nozzle ring toward the turbine wheel. The exhaust gases drive the turbine wheel, which in turn drives the compressor wheel since both wheels are on a common shaft. Intake manifold air enters at the center of the compressor wheel and flows radially outward through a diffuser section into the com- pressor housing. The air at increased velocity then leaves through a tangential outlet on the outside of the compressor housing and enters the intake manifold. c. The exhaust gases are expelled from the tur- bosuper�lrnrgers into the vehicle exhaust system. 1-19. Cooling System NOTE The key numbers shown below n paren- B I heses r er to fig. 1-8. a. Fans. The top of the engine is shrouded to house two cooling fans (48 and 40) which draw cool air from the underside of the engine, through the cylinder fins, and discharge the hot air ve1·tica1ly from the top shroud. The fans are attached to adapters (39) and arc mounted on shafts which are driven through a fan drive clutch assembly (38). The rear fan clutch is dliven by the rear fan drive shaft (34), fan drive bevel gearshaft (33), and fan dl'i ven gearshaft (35). The front fan clutch is driven by the front fan drive shaft (32) and another fan driven gearshaft (35). b. Fan Drive and Clutch (fig. 1-13). The fan clutch is oil cooled. The fan clutch drive and driven disks are loaded by the centrifugal action of clutch balls and springs housed in the clutch assembly. The balls and spl'ings are in the driven member and apply upward force to the clutch disks. The clutch oil enters the fan drive vertical shaft from the fan drive housing through an annular groove in the shaft. The oil flows thro.ugh a central hole in the shaft to a distributor where it is dispersed to the ball bearings and to the clutch disks. The oil moves between the clutch disks by centrifugal action and drains back through the fan drive housing into the engine oil pan. c. Engine a+d Transmission Oil Coolers (fig. 1-1). All transmission and engine oil cooling is ac- complished by exteal oil coolers. The oil coolers are located on the sides of the engine above the cylinders. Air is drawn through the oil coolers by the cooling fans. A thermostatic control valve in each oil cooler controls the temperature of the oil from the cooler by permitting cold oil to bypass the coolers. This valve also permits oil to bypass the cooler in the event that the cooler becomes clogged.