7
SECTION 41 − STEERING − CHAPTER 1
603.54.471.00 − 11 − 2004
d
D−D F−F
e
f
7884
17
17
15
17
15
15
21
16
9
4
Left−hand steering control
(B, L−ht, fig. 3)
By turning the steering wheel in an anticlockwise direction,
the movement of the parts is inverted, the delivery grooves
(17, sect. E−E, fig. 2) direct the oil to the ducts (20) and con-
trol the left−hand turning action.
Emergency hydraulic control
(C, Er−ht, El−ht, fig. 3)
In the event of feed faults, steering is still possible by turning
the steering wheel. The valve (5) remains in the same posi-
tion as with normal control and the rotor works in the same
way as a hand pump, directing the oil to the control circuit.
The non−return valve (4) opens and cuts off the feed pump,
allowing the oil to flow directly from the reservoir to the rotor.
The valve (23) remains closed in order to prevent oil leaks
from faulty connecting pipes between the hydraulic pump
and the hydrostatic steering unit.
Cylinder safety valve and backflow valve (see, fig. 3)
The safety valves (33), when open, discharge the pressure
created by the piston (H) on one of the cylinder chambers
as a result of the strong external stress on the wheels. At
the same time, the lack of pressure in the opposite cham-
ber is compensated by the flow of oil from the open back-
flow valve (34). Pressure on one of the cylinder chambers
caused by weak external stress, insufficient to open the cy-
linder safety valve, is discharged by means of normal con-
trol valve seepage, whereas the lack of pressure in the op-
posite chamber is compensated by the backflow valve
(34), as illustrated in fig. 3. These valves, as well as elimina-
ting continuous steering corrections, prevent vibrations on
front wheels (shimmy), hydraulic circuit failure and steering
linkage distortion.
Hydrostatic steering operation circuit sectional view (*see fig. 2)
A. Neutral position operation diagram.
B. Right−hand turn (R−ht) and left−hand turn (L−ht) operation
diagram.
C. Emergency right−hand turn (Er−ht) and emergency left−
hand turn (El−ht) operation diagram.
d. Operation diagram for sections D−D and E−E in neutral
conditions*.
D. DANFOSS OSPC control valve.
e,f. Operation diagrams for sections D−D and E−E in two suc-
cessive right−hand turn phases*.
F. Filter.
H. Control cylinder.
M. Pump delivery.
N. Backflow valves (34) operation diagram with control valve
(D) in neutral and cylinder (H) piston under external stress
(indicated by the black arrow).
P. Pump.
R. Flow control.
S. Discharge to gearbox.
V. Steering wheel.
Z. Resonance attenuator filter.
4. Non−return valve.
5. Rotating valve.
6. Valve seat sleeve (5).
9. Rotor.
13 and 14.Oil flow ducts in the neutral position.
15. Delivery grooves (no. 6) to the compartments on the rotor in
the suction phase.
16. Ducts (n.12) alternately connecting with the grooves (15
and 17).
17. Delivery grooves (n.6) to the cylinder connecting with the
compartments on the rotor in the delivery phase and the
ducts (18 and 20)*.
19. Discharge grooves (n.6) to the cylinder connecting with the
ducts (18 and 20)*.
21. Ducts connecting the holes (16) with the compartments on
the rotor in suction or delivery phases.
23. Non−return valve.
24. Pressure relief valve (setting: page 1).
26. Left−hand cylinder chamber connecting duct.
27. Right−hand cylinder chamber connecting duct.
33. Cylinder safety valve (setting: page 1).
34. Backflow valve.
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