INTRODUCTION TO THE HMMWV - OD1615 - LESSON 3/TASK 1
easier to fit in the engine compartment and has eliminated the need for a
remote or frame mounted booster previously used on some applications.
The hydro-boost system consists of a booster assembly, accumulator, power
steering gear, steering pump and reservoir, filter, hydraulic lines, master
cylinder and the brake system.
The booster itself consists of an open
center spool valve and sleeve assembly, lever assembly, input rod assembly,
power piston and an output push rod. The booster assembly is mounted to the
vehicle in much the same manner as a normal vacuum booster. The pedal rod
is connected to the booster input rod end. The master cylinder is located
at the opposite end of the booster. The booster's output push rod fits into
the primary piston of the master cylinder. The power steering pump, which
is unmodified except for a larger reservoir and an additional return port
for the hydro-boost return line, supplies the hydraulic pressure to the
hydro-boost unit through external lines.
When the engine is running, the
fluid enters the unit through the pump port where the majority of the fluid
is directed to the gear port and then to the steering gear by an external
line.
The small quantity of power steering fluid that did not go to the
power steering gear circulates inside the hydro-boost unit and then returns
to the steering pump reservoir by an external line.
The hydro-boost unit includes a reserve brake system that makes available
two or three power assisted brake applications in the event that the flow of
fluid from the power steering pump is interrupted by a stopped engine,
broken belt, pump failure, ruptured hose, etc.
This system uses a gas
accumulator to store fluid under gas pressure.
During normal operation, the accumulator is charged by fluid from the pump
port. This fluid is taken from the pump port before it gets to the spool
valve. The charging fluid flow is controlled by the accumulator valve which
consists of a check ball, spacer, plunger and plunger seat. The check valve
allows fluid under greater pressure than that in the accumulator to go
through the valve and into the accumulator. Once past the check valve, the
fluid then travels by internal passage to the accumulator.
The fluid
pressure exerts force on the accumulator piston which then compresses the
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