Hyundai HL955 Manual page 354

2) 2) OPERATION OPERATION
The pump is a variable displacement piston pump. This pump has a maximum delivery pressure of
250 kgf/cm 2 . The axial piston type pump is used to supply oil flow to the cut off valve. The oil is
pressurized by the movement of rotary group in the pump.
When the engine is in operation, the drive shaft (1) is driven by the gears in the engine with rotary
group. There are nine piston assemblies (2) in rotary group.
Each piston inside cylinder (5) is held against swashplate (3) by piston shoe (4). Swashplate can
be any angle between the maximum angle and the neutral angle. The angle of swashplate
determines the amount of oil that is pushed out of each cylinder.
The neutral angle is perpendicular with drive shaft (1). When swashplate(3) is at the neutral angle,
pistons (2) do not move in and out of rotating cylinder. Therefore, no oil is drawn into the pump and
no oil is pushed out of the pump. The pump has zero displacement and zero flow.
When swashplate (3) is at the maximum angle, pistons (2) move in and out of cylinder. The
movement of the pistons allows the maximum amount of oil to be drawn into the cylinder. The
pump will produce the maximum displacement.
The swashplate (3) angle is controlled by command current signal to control valve solenoid (6). The
pump output pressure level can be set by the solenoid current. When the solenoid current signal
drops toward a zero value, the pump output pressure level is the maximum.
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FAN SYSTEM OPERATION FAN SYSTEM OPERATION
When the brake system pressure is below minimum pressure (125±5 bar), it has the high priority
than the fan system. Pump flow to the fan motor is blocked while brake system is charged.
However, The fan system has controlled pump when the brake system pressure is charged.
The fan speed solenoid valve (6) controls the pressure (fan speed) of pump when the brake
system is fully charged.
The fan speed solenoid valve (6) is a proportional solenoid. As current to the fan speed solenoid
increases, pump output pressure decreased, therefore, the fan motor rotates slower.
When the current of the fan speed solenoid valve (6) is reduced, the output pressure is increased.
The pump will be stroked and the pump will send maximum flow to the fan motor, thus, the fan
motor is turning faster.
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