Hino 600, Workshop Manual, Page: 251 / 451

SERVICE BRAKE (HYDRAULIC BRAKE) BR02–7
PRINCIPLE OF OPERATION
EN1680102C100001
1. HYDRO-MAX BOOSTER
During normal system operation, fluid flow from a hydraulic
power source (the power steering pump) enters the inlet port of
the Hydro-Max booster, flows through the power piston, around
the throttle valve and through the flow switch, exiting through
the outlet port.
Force applied to the brake pedal by the vehicle operator is multi-
plied by the lever ratio of the pedal mechanism to move the pedal
rod of the booster. This movement closes the throttle valve
which restricts flow. This restriction of flow, which results in a
pressure increase acting on the power piston, applies an ampli-
fied force to the master cylinder primary piston. A reaction pis-
ton, inside the power piston subassembly, provides the driver
"pedal feel" during an application of the brake pedal.
Fluid flow through the flow switch opens the backup pump elec-
trical circuit during normal operation. A separate check valve in
the backup pump prevents back-flow through the pump during
normal power applications. In the event normal flow from the
power source is interrupted, the backup pump provides the
power at a reduced rate for stopping. Upon flow interruption, the
Integral flow switch closes, energizing a relay, providing electri-
cal power to the backup pump.
During backup operation, the pump re-circulates fluid within the
booster assembly with pressure built on demand via the throttle
valve. Fluid is retained within the booster by the inlet port check
valve.
2. MASTER CYLINDER
The primary circuit is separated from the secondary hydraulic
circuit. Hydraulic leakage in one circuit does not affect the func-
tion of the other circuit.
A differential pressure switch is available. It illuminates a light on
the dash panel to warn when there is a pressure differential
between the primary and secondary brake circuits caused by a
leak in one circuit. This may occur when one circuit leaks or is
improperly bled.