3304 & 3306 – Hydraulic Starting System

1. Reservoir. 2. Hand pump. 3. Pressure gauge. 4. Hydraulic starting motor. 5. Starter control valve. 6. Hydraulic pump (driven by engine timing gears). 7. Unloading valve. 8. Filter. 9. Accumulator.

The hydraulic starting motor (4) is used to turn the engine flywheel fast enough to get the engine started. When the engine is running, the hydraulic pump (6) pushes oil through the filter (8) into the accumulator (9). The accumulator (9) is a thick wall cylinder. It has a piston which is free to move axially in the cylinder. A charge of nitrogen gas (N2) is sealed in one end of the cylinder by the piston. The other end of the cylinder is connected to the hydraulic pump (6) and the hydraulic starting motor (4). The oil from the hydraulic pump (6) pushes on the piston which puts more compression on the nitrogen gas (N2) in the cylinder. When the oil pressure gets to 3000 psi (20 700 kPa), the accumulator (9) has a full charge. At this point the piston is approximately in the middle of the cylinder.

The unloading valve (7) feels the pressure in the accumulator (9). When the pressure is 3000 psi (20 700 kPa) the unloading valve (7) sends the hydraulic pump (6) output back to the reservoir (1). At the same time it stops the flow of oil from the accumulator (9) back to hydraulic pump (6). At this time there is 3000 psi (20 700 kPa) pressure on the oil in the accumulator (9), in the line to the unloading valve (7), in the lines to the hand pump (2) and to the hydraulic starting motor (4).

Before starting the engine, the pressure on the pressure gauge (3) should be 3000 psi (20 700 kPa). When the starter control valve (5) is activated, the oil is pushed from the accumulator (9) by the nitrogen gas (N2). The oil flow is through the hydraulic starting motor (4), where the energy from the compression of the fluid is changed to mechanical energy for turning the engine flywheel.

Hydraulic Starting Motor

1. Rotor. 2. Piston. 3. Thrust bearing. 4. Starter pinion. A. Oil inlet. B. Oil outlet.

The hydraulic starting motor is an axial piston hydraulic motor. The lever for the starter control valve pushes the starter pinion (4) into engagement with the engine flywheel at the same time it opens the way for high pressure oil to get into the hydraulic starting motor.

When the high pressure oil goes into the hydraulic starting motor, it goes behind a series of pistons (2) in a rotor (1). The rotor (1) is a cylinder which is connected by splines to the drive shaft for the starter pinion (4). When the pistons (2) feel the force of the oil they move until they are against the thrust bearing (3). The thrust bearing (3) is at an angle to the axis of the rotor (1). This makes the pistons (2) slide around the thrust bearing (3). As they slide, they turn the rotor (1) which connects through the drive shaft and starter pinion (4) to the engine flywheel. The pressure of the oil makes the rotor (1) turn very fast. This turns the engine flywheel fast enough for quick starting.

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