Brake Power Master Cylinder. Doosan G33P-5 Plus

Brake Power Master Cylinder

Vehicle System 33 System Operation

Fig 4: Detail - Boost Not Applied (2 -> 6)

The flow divider provides continual flow of 0.8 GPM through the brake spool to “P” port (4) of power master cylinder. When the brake pedal is not pushed (neutral position), the fluid goes through the flow passage (2) between the master piston (1) and servo piston (6), flow passage (5) and chamber (8), then returns to tank, as shown in Fig 1.

When the brake pedal is pushed, the master piston (1) advances toward the servo piston (6). Oil flowing through oil passage (2) is restricted and increases pressure in chamber (3) which pushes the servo piston more to the right. The master and servo pistons continue to move independently in reaction to the flow and pressure changes until a balance is reached where the force in chamber (3) equals the force working against servo piston in chamber (10) plus the reaction force of spring (15) and flow passage (2) is closed (ref:

Fig 3 & Fig 4). Pressure then builds up to assist in brake application. The operator feels the feed-back force as pressure increases in chamber (3).

When the brake pedal is released, return spring (15) forces master piston (1) and a servo piston (6) to return to the initial position (or neutral position). As these pistons return, displaced oil within chamber (10) is replenished through check valve (11) from reservoir

(14). When the pistons have moved past the replenishing orifice (9), pressure in chamber (10) drops to zero and oil from reservoir (14) can now pass through the orifice.

Vehicle System 34

Relief valve (7) is built into the power master cylinder to prevent exceeding 40 bar (580 PSI) pressure within chamber (3). As pressure builds, the sleeve of the relief valve shifts and compresses the spring. This opens boost chamber (3) to drain chamber (8) preventing over-pressurizing the system. This limits excessive reaction force of the brake pedal.

In case of accidental engine shut down the system becomes mechanically operated. With no hydraulic boost the result is greater brake pedal force is required to stop the truck.

System Operation