PLATE 9D0951 - Caterpillar

Illustration 1 g03476230
Illustration 2 g03476288
The brake and fan drive system contains a fixed displacement gear pump. The brake system has priority over the fan drive system.The idler gear (3) meshes with the drive gear (1). The rotation of the two gears creates a partial vacuum. The partial vacuum is created at the pump inlet as the gear teeth separate and draw the oil from the hydraulic tank. Oil enters the pump into cavity (4). The turning of the two gears causes the low-pressure oil from cavity (4) to move around the inner pump housing to cavity (2). As the teeth mesh at the outlet port, the oil is forced out of the gear pump.
Illustration 3 g03583765
(5) Shuttle Valves (6) Relief valve (7) Pressure sensor (8) Valve for Brake charging (9) Screen (10) Priority Valve (11) Brake and Fan Pump (12) Line to Tank (13) Line to fan (14) Orifice (15) Check valve (16) Lines to AccumulatorsThe brake/fan gear pump supplies hydraulic oil to the fan/brake system. The oil first flows to the accumulator charging valve. The accumulator charging valve controls the flow of oil from the fan/brake pump to the brake accumulators. Pressure relief valve (6) limits the oil pressure that flows from the fan/brake pump to the brake circuit. A spool in the accumulator charging valve then moves in order to allow the hydraulic oil to flow to one accumulator or to both accumulators. The accumulator charging valve maintains the pressure in the accumulators (16) at a constant range while the engine is running.The flow of hydraulic oil from the brake accumulators (16) is blocked at the accumulator charging valve. When the brake pedal is pressed, the charging valve routes hydraulic oil to the rear service brakes and to the front service brakes. This action engages the service brakes. Pressure feedback is sensed by each spool in the brake control valve allowing the operator to feel the application of the service brakes. The pressure to the brake lines varies. As the brake pedals are depressed, the hydraulic oil pressure in the brake lines increases. Due to the spring below the bottom brake valve, the maximum pressure to the front brakes is lower than the maximum pressure to the rear brakes.In addition, the fan/brake pump supplies pilot oil to the hydraulic fan system. Any excess oil which is not required for these systems is diverted back to the hydraulic oil tank.ReferenceRefer to System Operation, UENR4585, "Accumulator Charging Valve" for more information on the accumulator charging valve.