jcb JS 200 Series, Service Manual

Page: 408 / 531

90 - 3
Section E
Hydraulics
9803/6400
Section E
90 - 3
Issue 2*
Slew Motor
Operation (continued)
Relief Valve Working Principles
1 On starting
Due to the superstructure’s inertia there is a build-up of
pressure in the motor when it begins to slew. To prevent
damage, excess pressure is diverted between ports
A
and B via poppet valves 43 (part of cross-line relief
valve J ).
2 When the brake is applied (cushioning)
When the slew control valve is returned to neutral the oil
return path from the motor is closed. While the
superstructure is coming to a halt it is, in effect, ‘driving’
the motor as a pump. This results in a pressure build-up
at the outlet port (
A or B depending on slew direction).
This increased pressure opens poppet valve 43 , which
allows oil to flow via paths g and h , opening check valve
29
and relieving the pressure into cavity
C
.
At the same time, oil flows between the two ports via the
cross-line relief valve
J , which has already been partially
opened by poppet valve 43 .
The result is a 2-stage relief action which momentarily
delays the pressure build-up as the superstructure
comes to a halt. This reduces the shocks arising due to
sudden braking.
3 Anti-Pendulum Feature
While the superstructure is coming to a halt, as
described in
2 , it drives the motor as a pump. The initial
result is a braking effect on the superstructure. However,
the resulting pressure build-up in port
A (or B , depending
on direction) tends to cause the superstructure to
‘bounce back’ a little. The process repeats itself to create
what is known as a ‘pendulum effect’.
To prevent this happening, check valves 50 and flow
control valves 48 work together to divert oil pressure
between ports A and B until the superstructure has come
to a halt.
Reduction Gear Structure and Working
Principles
(illustration reference page 83 - 2)
Power transmitted by the hydraulic motor output shaft is
transmitted to second sun gear
77 via first sun gear 66 ,
planetary gear 69 and holder 65 . Power is then transmitted to
output shaft 53 via second sun gear 77 , planetary gear 72
and holder 76 . The output shaft is constructed with an
integral pinion and is supported in gear case 58 by bearings
57 and 62 .
Due to the severe conditions under which the output shaft
operates, an oil seal
61 is provided in the centre of gear case
58 to protect the bearings from metal waste worn from the
gears. The bearing in chamber A is lubricated with gear oil
and the bearing in chamber B with grease.
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