Vehicle System System Operation 22
Hydraulic Control Valve
Control valve has specific section of lift and tilt.
Overflow valve and flow-priority valve could be
mounted on the side port of inlet.
Oil circuit is of parallel with neutral back-flow
function. When the spool is in the neutral position,
pump is in the free load condition.
When controlling two or more than two spools at the
same time, usually actuator with less load acts first
and the one with more load acts later for the sake of
load difference. Work the more-load spool first and
control the stroke of the less one to have
simultaneous action under different load.
Principle of Side Cover of Inlet Port
Side cover of inlet port is composed of main relief
valve to limit max pressure in circuit, flow-priority
valve to supply oil in priority to steering and PF relief
valve to limit pressure in priority. See the description
of principle of relief valve below is only a introduction
of flow-priority valve.
Flow-priority valve may classify the oil as pre-set
priority flow (PF flow) and maintain flow (MF flow).
PF is for steering, MF is for valve sections to control
the loading.
Oil from Port P goes from throttle hole, check valve,
PF throttling part inside of spool FD into PF port. If
oil from port P is increased, pressure difference will
be generated in front and back of throttle hole.
Because of the pressure difference on ends of FD
spool, the spool goes toward the part to shut the PF
throttle part. And then, pressure difference goes
down as well as PF flow is reduced. Therefore, the
flow set by throttle hole and spring is ensured.
1. When MF flow pressure is higher than PF flow
pressure (in loading)
When in loading, MF flow pressure increases,
overall pressure increase as well. At this time, flow
in priority is increasing since PF flow pressure is
lower than MF flow. Once flow in priority increases,
pressure difference of throttle increases too. And
throttle effect is generated on PF throttle parts and
flow keeps stable.
2. When MF flow pressure is lower than PF flow
pressure ( in steering)
When in steering, PF flow pressure increases. And
overall pressure increases too. Flow is increasing
too with one side of MF flow pressure goes down.
So, when flow by throttle hole goes down, the
pressure difference decreases as well and FD spool
moves to the part to shut the MF throttle to keep
flow go stable as well as the pressure difference of
throttle back and forward.
To Next Page
Loading...
