3 - 2
Brake Valve
During Travel - Brake Released
During travel, pressurised oil is fed into port A to open valve
127 and supply oil via port C to traction motor M. The
pressurised oil also enters chamber b through drilling a of
spool 123. The pressure build-up in chamber b causes spool
123 to move to the left to connect motor return port D to
port B.
The result is unrestricted oil flow and, therefore, rotation of
the motor. The movement of spool 123 also allows
pressurised oil to flow through port P into piston 112 of the
parking brake, overcoming the parking brake spring to
release the brake pressure.
Travel Stopped - Brake Activated
When travel is de-selected, there is no pressure at port A.
Spool 123 is no longer under the influence of pressurised oil
(as described above) and returns to its neutral position under
the influence of the two springs 128. This spool position
completely shuts off ports A and B from the motor feed and
return ports C and D.
The inertia of motor M immediately following de-selection of
travel causes a build-up of pressurised oil in port D. This
pressurised oil passes through the drilling of valve 201B into
chamber f and thence chamber g. The pressure moves
piston 213 up to force oil into chamber h. The pressure
build-up in port D opens valve 201B to allow the oil to flow
from port D to port C to prevent cavitation.
When piston 213 reaches the end of its pressure induced
stroke, the pressure in chamber f and g increases and the
valve 201B closes again, allowing a further increase in
pressure in port D. This causes valve 201A to open, passing
the oil in port D (at a higher pressure than that of the
machine main relief valve) into port C. The pressure in port D
is thereby controlled in two steps to provide smooth braking
to a standstill.
Section F Transmission
9803/6410
Section F
3 - 2
Issue 1
Operation
JS01630
JS01640
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