DAF CF65, CF75, CF85 Series . Manual — part 959

©

200423

2-1

General

STEERING BOX

ΧΦ65/75/85 series

7

3

2. GENERAL

2.1 OVERVIEW DRAWING, STEERING BOX

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4 5

6 7

8

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12

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1.

Attachment pin, torsion bar

2.

Input shaft

3.

Pressure-limiting valve

4.

Cover

5.

Torsion bar

6.

Control valve

7.

Bushing

8.

Attachment pin, torsion bar

9.

Wheel deflection limiting valve

10.

Ball nut

11.

Sector shaft

12.

Worm shaft

13.

Piston

14.

Wheel deflection limiting valve

15.

Housing

16.

Adjusting bolt, wheel deflection limiting

valves

STEERING BOX

2-2

©

200423

General

3

ΧΦ65/75/85 series

7

2.2 OPERATION OF THE STEERING BOX

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12

4

2

7

7 12

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2

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©

200423

2-3

General

STEERING BOX

ΧΦ65/75/85 series

7

3

Hydraulic power steering
The oil flow in the steering box is controlled by the

control valve (6).

The control valve (6) consists of a bushing (7),

which is attached to the input shaft (2) and the

space in the worm shaft (12).

On the outside, the bushing (7) has a number of

recesses. The delivery line and the return line

and the channels leading to the cylinder halves

end in the chamber of the worm shaft (12). The

delivery line and the return line can be connected

to the channels leading to the cylinder halves

through the recesses of the bushing (7).

If the bushing (7) is turned in relation to the space

in the worm shaft (12), one cylinder half connects

to the delivery line and the other to the return line.

If the input shaft (2) is turned the other way, the

bushing (7) will switch the delivery line and return

line connections to the cylinder halves.

Because the control valve (6) increases the oil

flow to one side of the piston during steering and

connects the other side of the piston to the return

line, the oil can no longer circulate through the

steering box. As a result, pressure builds up on

one side of the piston and the piston moves.

If no steering takes place, the control valve (6) is

in its neutral position. In the neutral position the oil

flow to the left-hand and the right-hand side of the

piston is such that the forces exerted on the

piston by the oil are equal. Therefore, the piston

will not move. This is called the "hydraulic central

position" of the steering box. The oil pressure in

this situation is called the circulation pressure.

The neutral position of the steering box is factory-

set and cannot be changed.

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STEERING BOX

2-4

©

200423

General

3

ΧΦ65/75/85 series

7

A torsion bar (5) is fitted between the input

shaft (2) and the worm shaft (12) and connected

to the input shaft (2) and the worm shaft (12)

using pins (1) and (8).

While steering, the input shaft (2) will turn in

relation to the worm shaft (12), resulting in a

twisting movement of the torsion bar (5). The

torsion bar (5) ensures that when no torque is

exerted at the input shaft (and steering no longer

takes place), the input shaft (2) is returned to its

neutral position in relation to the worm shaft (12).

As a result, the control valve (6) also returns to

the neutral position and the hydraulic power

steering is deactivated.

Pressure limiting
The pressure-limiting valve (3) protects the

system from excessive system pressures. If the

preset valve pressure is reached, the valve opens

and connects the delivery line to the return line.

Bleeding
The steering box is auto-bleeding.

At circulation pressure, the steering box auto-

bleeds. At a higher system pressure, the bleeding

system is closed.

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6 7

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11

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