Iveco EuroCargo (12 to 26 t). Manual — part 162

77844

Description

The ball-circulation control hydraulic power steering is
essentially composed of a case in which manual steering
mechanism, an hydraulic cylinder controlled by a rotating
distributor valve, and hydraulic steering and safety limiting
valves are housed.

The rotary motion impressed to steering wheel is transmitted
from inlet shaft (7) to worm screw (3), through the torsion bar
(5).

The worm screw (3) in turn, being connected by means of a
set of balls (9) to the rack piston (12), transforms the rotary
motion into an axial motion of this latter one.

The piston rack toothing (12) meshes into the toothed-sector
shaft toothing and impresses a rotary motion thereto. The
steering control arm fixed on this shaft transmits the motion
to the wheel steering tie-rods.

This only-mechanical steering movement is servoassisted by
the pressurised oil supplied to an engine-actuated blade pump.

If when steering the wheels are subjected to violent impacts,
the force created by the same ones is transmitted through
outlet shaft (11) to rack piston (12) and from it to worm screw
(3). The internal hydraulic power steering system makes the
rotary distributor valve (6) send highly pressurised oil into the
cylinder chamber where such pressure can fight and absorb
the given impact force. In this way no recoils are generated on
the steering wheel.

The hydraulic power steering is equipped with an automatic
air drain valve.

1. Hydraulic steering limiting adjustment screw — 2. Hydraulic right steering limiting adjustment screw — 3. Worm screw —

4. Hydraulic left steering limiting adjustment screw — 5. Torsion bar — 6. Rotating distributor valve — 7. Entry shaft — 8. Cover —

9. Balls — 10. Hydraulic power steering case — 11. Outlet shaft — 12. Rack piston.

Figure 18

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The rotary distributor valve (4) is keyed-in on the torsion bar
(6) connecting inlet shaft (5) to worm screw (7); under
rectilinear running conditions, the valve (4) keeps open the
communication between incoming oil canalisation from blade
pump (2) and oil tank discharge (3) one.

1. Flow rate limiting valve - 2. Blade oil pump - 3. Oil tank - 4. Rotary distributor valve - 5. Inlet shaft - 6. Torsion bar -

7. Worm screw - 8. Outlet shaft - 9. Rack piston.

Figure 19

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77846

If when rotating the steering wheel the transmitted torque is
lower that the steering wheels resisting torque, torsion bar (7)
in its elastic area is subjected to a distortion, so that the rotary
distributor (4) integral therewith rotates with respect to valve
body (5), passing from neutral condition to operating
condition. Consequently, by closing the discharge canalisation
and opening the control one, the pressurised oil enters the
cylinder chamber affected by steering, generating the axial
displacement of the rack piston (9).

1. Flow rate limiting valve - 2. Blade oil pump - 3. Oil tank - 4. Rotary distributor vale - 5. Valve body - 6. Inlet shaft -

7. Torsion bar - 8. Hydraulic limiting valve - 9. Rack piston.

This hydraulic servoassistance action is kept till the hydraulic
steering limiting valve (8) intervenes or the action on the
steering wheel ceases that generated the torsion bar (7)
distortion.
In this case, the rotary distributor (4) will be placed again in its
neutral condition.
If the hydraulic servoassistance lacks, it is always possible to
steer even if with a greater effort on the steering wheel.

Figure 20

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1. Flow rate limiting valve - 2. Blade oil pump - 3. Oil tank - 4. Rotary distributor valve - 5. Valve body - 6. Inlet shaft -

7. Torsion bar - 8. Hydraulic limiting valve - 9. Rack piston.

Figure 21

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Base - February 2003