Komatsu 830E-AC, Shop Manual

Page: 672 / 1085

L4-8 Steering Circuit L04048
Steering Left
(Refer to Figure 4-4):
When the operator turns the steering wheel “left”, the
steering control unit valve is opened to allow oil com-
ing in port P to pass to the gerotor section of the con-
trol unit to turn the rotor. Oil in the other side of the
gerotor flows through other passages in the control
unit valve and out steering control unit port L. This oil
enters port L of the flow amplifier assembly and goes
to a closed area B in the directional valve. As pres-
sure in this area builds, it also passes into the spool
through orifice C to the spring area on the end of the
directional valve. The pressure then moves the spool
compressing the springs on the opposite end. This
movement allows the oil entering area B to pass
through the directional valve to area D of the ampli-
fier valve through sleeve E holes to a passage
between sleeve E and valve F through hole G in
sleeve E where it initially is blocked by the valve
body. As pressure builds up in this area, oil also
flows from area D around the OD sleeve E around
pin H through orifice J to build pressure on the end of
the amplifier valve and opens hole G only enough to
allow the flow of oil coming from the steering control
unit to pass to the control area of the directional
valve. At the same time, the movement of sleeve E
opened the holes near the spring end to allow the oil
from the priority valve to flow into the center of sleeve
E. This oil now inside sleeve E pushes valve F
against its spring to give the oil access to a series of
holes K that are in the same plane as hole G. The
passage of oil through holes K past the valve body is
metered by holes K being opened the same propor-
tion as is hole G. The number of holes K (9) in sleeve E determine the
amount of additional oil that is added to the steering
control unit oil passing through hole G. This com-
bined oil going to the center area Q of the directional
valve passes out port CL of the flow amplifier assem-
bly and travels to the steering cylinders to steer the
front wheels to the left. As the cylinders move, oil is
forced to return out the opposite ends, enter port CR
of the flow amplifier assembly, pass through the
directional valve to area M, passes through the return
check valve N, and exit port HT to the hydraulic res-
ervoir.
At the steering control unit, when the operator turned
the steering wheel, supply oil from port P was also
delivered through the control unit valve to port LS.
This oil enters the flow amplifier assembly through its
LS port and builds pressure in the spring area of the
priority valve. This additional force on the spring end
of the priority valve causes area A to open and allow
the necessary flow and pressure to pass through the
amplifier valve to operate the steering cylinders.
The flow amplifier assembly includes a relief valve in
the priority valve spring area that is used to control
maximum steering working pressure to 17 237 kPa
(2500 psi) even though supply pressure coming into
port HP is higher. When 17 237 kPa (2500 psi) is
obtained, the relief valve prevents the LS pressure
from going higher and thereby allows the priority
valve to compress the spring enough to close off
area A when 17 237 kPa (2500 psi) is present.