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Fig
.
4·39.
O
verd
riv
e
in
f
un
ction
The oil is drawn thr·ough the pre-filt.er by the plunger
pump and is conveyed undeT pressure through the
fine fi·lter. From here the oil fl.ows fUlrther through the
hydroulic cylinders to the relief and controi valves.
The controi va.lve
-
i s
dose-
d and the
I'
a rge
p-
iston of
the
r,
e lief va'lve is in its
lowe'
r position. This off-I'oads
the Slprings so that on.ly a low pressure is required
to press down the small pist.on of the r8llief
valve.
Oil then flows past the small piston out
in~o
the
channel to the
malinshaf.t.
When the
ov,
e rdrive is engaged, the controi
v,
a lve is
displa·ced and oi,1 flows through the oilway and
operates the
I
I'arge piston of the relief
valv-
e . This is
then moved upwards and causes
:
t he springs to ten-
sion. The more the springs tension the greater the
force ,is requi'red to press down the small piston, this
causing the hydraulic pressure to rise. The pistons are
ther·eby displaced in the hy,draulic cylinders, the c1utch
sliding member is puHed forwards and contact made
with the brake ring.
Wi·
t h disengagement of the overdrive, the
conn,
e c-
ti-on between channels
12
and
2
is c1osed.
Inst·
e ad,
th'
e
connection between channel 2 and the sump is opened.
This permits oill under the large piston of the relief
valve to flow ourt into the sump, the pressure in the
system drops and
dir,
e d drive lis engaged. Beaause of
the orihce nozzle in the 'channei and owing to a suit-
abl-
e balanci-ng of the spring force, a certain time
passes for the piston of rthe relief valve to move from
one outer posi"fJion to the other. This time
is
'
s
o
a,dapt-
ed that a smooth
engag'
e ment occurs without any
slipping of gears.
Oil passing the small piston of the ,reHef va,lve is
conveyed throug'h the channel and a drining in the
mainshaft to the uni -di'rectional c1utch and the needle
bearing shaft.
The'reaM-
e r the oil is aaught up by a
plate and I,ead via the planet gea-r back to the gear-
box housing, see Fig.
4-40.
Fig.
4·40.
Lubricating system
VOLVO
103174
4 : 15
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